Ž .European Journal of Pharmacology 405 2000 341–349www.elsevier.nlrlocaterejphar

Psychoneurendocrinology: a science of the past or anew pathway for the future?

Francesca Brambilla)

Dipartimento di Scienze Neuropsichiche, Istituto Scientifico Ospedale S. Raffaele, Via Prinetti 29, 201279 Milan, Italy

Accepted 28 June 2000

Abstract

Psychoneuroendocrinology is a branch of neuroscience that developed in the beginning of the last century, which investigates thepossibility of a cause–effect link between endocrinopathies and mental disorders — with these studies ending in negative results.Psychoneuroendocrinology was then used as a methodological approach for the investigation of neurotransmitter function, on the basis ofthe observation that neurotransmitters regulate neurohormone and peripheral hormone secretions. Data were obtained for hypothalamicnoradrenergic, serotoninergic, dopaminergic, gabaergic and acetylcholinergic functions, which could not be automatically extended tohigher brain centers whose impairments might be etiopathogenetically involved in the development of mental disorders. Future studiesshould focus on new methodological approaches to brain biochemistry, on investigation of genetic, molecular biology, brain imaging,psychoneuroimmunoendocrinology, neuropeptide and neurosteroid secretion in relation to brain endocrine function in mental diseases.q 2000 Elsevier Science B.V. All rights reserved.

Keywords: Psychoneuroendocrinology; Psychoneuroimmunoendocrinology; Genetic; Molecular biology

1. Introduction

1.1. The history of psychoneuroendocrinology

Ž .The history of Psychoneuroendocrinology PNE hasancient roots, going back to the beginning of the centurywhen clinicians and researchers looked for a possible linkbetween disorders of brain biochemical functions and nor-mal or pathological mentation. This was done in the hopeto find a solid organic background for the development ofmental disorders and for their pharmacological treatments.

In a first approach, a cause–effect link between periph-eral well-defined endocrinopathies and similar nosographi-cally well-defined psychopathologies was looked for. Thiswas done on the basis of occasional observations that thedevelopment of hormonal disorders was often followed bythe appearance of more or less evident changes of cogni-tion, mood and behavior. Anecdotal data were reported,where it was actually shown that in single cases variousmental diseases, mostly schizophrenia and depression, ap-peared after the development of endocrinopathies and dis-appeared after their therapeutic correction. What was in-

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triguing was the fact that different endocrine imbalanceswere accompanied by the same types of psychopathologiesand, vice versa, that the same endocrine imbalance wasaccompanied by different types of psychopathologies. Novalid explanations were given for the phenomenonŽChatelanat, 1978; Brambilla et al., 1978; Fava et al.,

.1987 .These studies took place in the first decades of the

century, and led nowhere since the erratic, inconsistent andnot mandatory correlates were only anecdotal and possiblyjust artifactual. It was only suggested that the metabolicalterations could be one among multiple precipitating fac-tors, acting in predisposed individuals as a stressing ele-ment to disclose a full-blown mental disease, or to modu-late its symptomatological aspects and its course.

It was proposed, next, that psychoneuroendocrinologycould be used as a methodological approach for the studyof brain biochemistry. This was the time of the famousAwindow on the brainB proposed in the 1960s by EdwardSachar, one of the founders of psychoneuroendocrinology,in the tentative to find noninvasive, nontraumatic methodsof approach to the study of brain biochemical function inrelation to the development and characterization of normal

Ž .and pathological mentation in humans Sachar, 1976 . The

0014-2999r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0014-2999 00 00564-1

( )F. BrambillarEuropean Journal of Pharmacology 405 2000 341–349342

hypothesis was not inappropriate, since researches in ex-perimental animals were consistently demonstrating thatthe secretions of peripheral hormones are under the directmodulation of the hypothalamic releasing–inhibiting hor-mones, which in turn are stimulated or inhibited by cen-trally produced and secreted neurotransmitters and neu-ropeptides. Therefore, the study of the secretions of pe-ripheral hormones could give information on the functionalstatus of neurotransmitters–neuropeptides in the wholebrain or in specific brain areas. When the neuroendocrineresearch was implemented by stimulatory–inhibitory tests,which used psychopharmacological drugs acting on thesecretion of specific central neurotransmitters or on theirpre–postsynaptic receptors to induce well-defined hor-monal responses, the dream of the Awindow on the brainBseemed to have come true.

The mass of data obtained was enormous and extremelyimportant. Alterations of functions of the hypothalamo-pituitary–adrenal axis, of the hypothalamo-pituitary–thyroid axis, of the hypothalamo-pituitary–gonadal axis, ofthe secretion of growth hormone, of prolactin, of endoge-nous opioids and of various neuropeptides were reportedand considered specific for one or another psychopathol-ogy, even being considered as mandatory markers for thediagnosis of a disease and necessary for its nosographical

Ždefinition Shah and Donald, 1984; Brown et al., 1984;Halbreich, 1987; Schatzberg and Nemeroff, 1988; Hols-boer, 1989; De Souza and Nemeroff, 1990; Musselman

.and Nemeroff, 1996 .Typical is the story of the hypothalamo-pituitary–

Ž .adrenal function in Major Depressive Disorders MDD . Aplethora of data were reported, indicating that MDD wereaccompanied by hyperfunction of the hypothalamo-pitui-tary–adrenal system, with a disruption of the normal feed-back and feedthrough mechanisms occurring not only dur-ing the symptomatologically active phases of the diseasebut sometimes also during the phases of remission, in thelast cases representing an unfavourable factor for the re-sponses to therapies and the prognosis of the diseaseŽ .Holsboer, 1989 . As mentioned before, each endocrineimbalance was considered as a signal of specific neuro-transmitter alterations, able to indicate what type of brainbiochemical impairment was responsible on the one sidefor the endocrine alteration and on the other for thepsychopathology. Just to make an example, the hypotha-lamo-pituitary–adrenal hypersecretion so frequently occur-ring in MDD was considered as expression of noradrener-gic or acetylcholinergic hyperfunctions or of serotoniner-gic hypofunction in the hypothalamus and possibly inhigher brain centers, since both noradrenaline and acetyl-choline are physiological stimulators of the hypothalamo-

Žpituitary–adrenal axis and serotonin inhibits it Muller et.al., 1977 . In other words, the pathogenesis of MDD was

considered to be linked to noradrenaline or acetylcholinehyperfunctions or to serotonin hypofunction, occurring notonly in the hypothalamus but possibly also in higher brain

areas more specifically involved in the regulation of affec-Ž .tivity Holsboer, 1989 .

The same deductions were proposed for the other psy-chopathologies and neuroendocrine dysfunctions, whichsometimes concurred in the suggestion of a specific neuro-transmitter pathology, and sometimes were discordant. Wecould mention the blunted thyroxine-releasing-hormoneresponses to thyrotropin-releasing hormone stimulation,the impaired prolactin and cortisol responses to serotonin-ergic probes, the altered growth hormone responses tonoradrenaline, dopamine, serotonin, acethylcholine and g-

Ž .aminobutyric acid GABA stimulations, all of which wereobserved in MDD, schizophrenia, anxiety disorders, eating

Ždisorders, personality disorders, and so on Brown et al.,1984; Checkley and Arendt, 1984; Pandey et al., 1984;

.Loosen, 1987; Nash and Meltzer, 1991; Brambilla, 1999 .In the meantime, the study of circadian rhythms of

hormonal secretions were offering a deeper insight in thebrain biochemistry. Circadian rhythms of hormonal secre-tions are regulated by AclocksB located in the hypothala-mus but also in higher brain areas. All the neuroendocrinedata that were obtained in basal or pharmacologicallystimulated–inhibited conditions pointed to neurotrans-mitter functions only in the hypothalamus, while the studyof the circadian rhythms of hormonal secretions referredalso to suprahypothalamic areas. These researches revealedimpairments in circadian rhythmicity with advanced ordelayed phases or with total disorganization occurring invarious psychopathologies, as expression of hypothala-

Žmic–suprahypothalamic alterations Wehr and Goodwin,.1983; Monteleone et al., 1999 .

At this point, the interpretation of the mass of data thatwere sometimes concordant and sometimes discordant intheir immediate meaning, pointing to one or another typeof biochemical brain pathology for each mental illness,became a real problem. Doubts started to rise on theconsistency and validity of this diagnostic and prognosticapproach. Psychoneuroendocrinology did not seem to offerthe biochemical AtargetB for each psychopathology, but,rather, made the history of etiopathogenesis, nosography,prognosis and therapeutic choices of mental disorders soconfused and intriguing that authoritative researchers sug-gested to abandon it, the observed hormonal pathologiesbeing defined as aspecific, casual, nonvalidable, and, inall, insignificant and meaningless for the understanding ofthe etiopathogenesis of mental disorders.

What had happened? It was evident from most of thereports that none of the hormonal alterations were consis-tently present in each patient suffering from any one of themental disorders. Rather, they generally occurred in arelatively small percentage of subjects, without apparentmain symptomatological and demographic differences be-ing demonstrable between patients who did and those whodid not had the endocrine imbalance. It could also beobserved that within the same mental disease, one group ofpatients had one neuroendocrine alteration, while another

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group of apparently similar patients could have exactly theopposite impairment or even absolutely normal hormonalsecretions. Moreover, the same neuroendocrine disorderwas observed in more than one totally different psy-chopathology and sometimes even in physical diseases thatwere not accompanied by concomitantly impaired menta-tion. Pharmacological manipulations revealed very contro-versial responses related to the same neurotransmitter func-tion, with hyperresponses of one hormone and hypore-sponses of another to the same probe. Finally, most of thebiochemical impairments were present during the symp-tomatologically active phases of the diseases to disappearduring their remission, which suggested that they could bethe consequence and not the cause of mental illnesses.

Even taking into account all these drawbacks, are wereally convinced that the hormonal alterations observed areunspecific, casual, nonvalidable, and especially meaning-less? Or, as often happens in the history of science, havewe used psychoneuroendocrinology inappropriately, andbecause of that, obtained results that we do not know howto interpret and, even less, how to use?

1.2. Critical reÕision of past psychoneuroendocrine re-searches

If we make a critical review of all the data reported inthe literature, it is clear that psychoneuroendocrinology hasused an array of static and dynamic neuroendocrine tests,which encompass the entire function of the hypothalamo-pituitary–peripheral glands including all basal hormonalsecretions, their responses to pharmacological stimula-tions–inhibitions, and the sensitivity of their pre–post-synaptic receptors. But looking at the meaning of thesedata, it is evident that they refer mostly to the function ofthe hypothalamus, and that alterations of higher braincenters possibly involved in the etiopathogenesis of mentaldisorders can only be inferentially proposed. Unfortu-nately, inferential hypotheses are not sufficient nor suffi-ciently validable, and could be a first source of confusionin the interpretation of the meaning of the data obtained,leading to hazardous theories. In other words, the psy-choneuroendocrine tests can be used, always rememberingthat they give validable information only on the functionof the hypothalamus, and not of higher brain areas whoseimpairments are possibly etiopathogenetically responsiblefor the development of mental disorders. Even with thispoint in mind, however, it is worth to suggest that thebiochemical alterations occurring in suprahypothalamic ar-eas must influence the hypothalamic function because ofthe projections existing between the various brain nuclei,and therefore it cannot be excluded that the hypothalamicimpairments reflect those of higher brain centers.

A second point that must be taken into consideration isthat most of the psychoneuroendocrine studies had beenprogrammed on the hypothesis that each mental disorder is

based on a single neurotransmitter impairment, possiblyoccurring in the entire brain. Typical examples of thistheory are the hypotheses of an increased dopamine secre-tion in the whole brain, responsible for schizophrenia, thatof noradrenergic hypo- or hypersecretion and of acethyl-cholinegic hypersecretion for MDD and anxiety disorders,of serotoninergic hypofunction for MDD, of gabaergicalterations for anxiety disorders and of specific neuropep-

Žtide impairments for many diseases Siever, 1987; Jimer-son, 1987; Janowsky and Risch, 1987; Meltzer and Lowy,

.1987; Losonczy et al., 1987; Hommer et al., 1987 .Today,nobody would still support this theory, since in the mean-time it has been amply demonstrated that plasticity phe-nomena occur in the brain, leading to changes of multipleneurotransmitter–neuropeptide functions as a consequenceof the primary impairment of one of them. In other words,an array of biochemical alterations has been demonstratedto concomitantly occur in each psychopathology, some ofthem possibly representing reactive phenomena one toanother, but each of them concurring in the development,course and prognosis of each psychopathology. This wouldlead to complex peripheral hormonal responses to theadministration of centrally acting probes, whose results canseem contrasting one to another for various reasons. First,each probe may act simultaneously on multiple neurotrans-mitters or on different neurotransmitter receptors responsi-ble for the contrasting peripheral hormonal responses. Or,by acting contemporarily on different brain nuclei eachprobe may start cascades of events leading to multiplehormonal responses. The problem of the choice of phar-macological probes is extremely important, since unlesswe start to use probes extremely pure, acting only on oneneurotransmitter system in a specific bran area, we willhave always to confront the problem of the significance ofthe results of the tests applied.

A third point worth to remember is that most of thesubjects who come to the observation of clinicians andresearchers have previously been treated with psychotropicdrugs, which modify central neurotransmitter–neuropeptidefunctions and central–peripheral endocrine secretions andcapacity to respond to stimuli acting through neurotrans-mitter systems. Many of the psychoneuroendocrine impair-ments reported in the literature are not primary, but sec-ondary to psychopharmacological therapies. This does notautomatically exclude their importance in the pathogenesisof mental illnesses. In fact, a mental disorder is not aconstant pathology in regard to symptomatological andbiological aspects from its beginning to its end, but is acontinuous pathoplastic event with an alteration leading tobuffering situations, which in turn start cascades of events,all of them concurring in the modulation of the course ofthe diseases. When we investigate the biochemical bases ofmental disorders, it is very important to look for factorswhich can be etiopathogenetically involved in their devel-opment, but it is equally important to know the pathologi-cal factors which occur during the course of the diseases,

( )F. BrambillarEuropean Journal of Pharmacology 405 2000 341–349344

modulating or changing their symptomatological aspects,their capacity to respond to therapies and therefore theirprognosis. Thus, even to define biochemical pathologieswhich are secondary to psychopharmacological treatmentsis extremely important, as long as we are well aware thatthey are not primary but artificially induced by our thera-peutic interventions.

A fourth point must to be taken into consideration. Inthe hope to find the biochemical background of each majormental disorder, there has been an attempt to correlateneuroendocrine impairments to one or another psy-chopathology defined according to the Diagnostic andStatistical Manual of Mental Disorders, III or IV editionsŽDSM III or IV; American Psychiatric Association 1980

.and 1994 criteria, often with disappointing results. Maybe,this is where we have made another mistake. Possibly, theneuroendocrine alterations that we have found in mentallysick subjects do not refer to any nosographically well-de-fined Axis I mental disorder, like for instance MDD orschizophrenia, but to specific personality characteristicpresent in the patients, which might not necessarily be partof the predominant mental disorder. Personality character-istics and consequential behaviors are modulated by bio-chemical mechanisms, the neuroendocrine ones often be-ing mandatory for their development and their patterns. Atypical example is that of aggressiveness, which is nor-mally initiated and sustained by the secretion of testos-terone and possibly of other androgens, under the stimula-tory regulation of noradrenaline and the modulatory one of

Ž .serotonin Gerra et al., 1996; Finkelstein et al., 1997 .Normal, high or low levels of testosterone correlate withnormal, high or low levels of aggressiveness, which can bethe background for the development of pathological ag-gressiveness when the serotonin secretion is reduced andits modulatory activity is missing. Testosterone secretioninhibits serotonin secretion and stimulates the noradrener-gic ones, the latter being a stimulator of aggressiveness byitself. The reduced serotonin secretion and the increasednoradrenaline one might be the basis for the developmentof MDD or anxiety disorders in predisposed individuals. Inother words, a higher than normal or even a high–normaltestosterone secretion might be the basis on the one sidefor a increased aggressiveness and on the other for neuro-

Ž .transmitter s alterations, which can be mandatory for thedevelopment of an Axis I mental illness. The testosteronealteration, by itself, is only responsible for aggressiveness,but in that it modifies noradrenergic and serotoninergicfunctions it may concur to the development of majormental disorders in patients genetically or metabolicallypredisposed to them. It is obvious, therefore, that analteration of noradrenergic and serotoninergic functionsand of the related hormonal secretions observed in patientswith MDD or anxiety disorders might, occasionally, belinked to the presence of aggressiveness and its biologicalbackground. In this case, we will see in the patients thebiochemical changes which are related to aggressiveness

and which may not be present in any other MDD oranxiety disorders patient.

A fifth point pertains to the fact that many externalfactors can intervene in modulating brain biochemistry andthe related peripheral hormonal secretions. These includenutrition, drinking, sleep, exercise, concomitant physicalpathologies, changes of externalrinternal temperature, lifeevents, multiple drug consumption, and geographically orsocially-linked variations of biological circadian rhythms.Each one of these variables may interfere with the secre-tions of neurotransmitters–neuropeptides and therefore,obscure the biochemical characteristics of the mental disor-ders and their etiopathogenetic meaning. In the meantime,they may be among the AprimaryB factors responsible, inpredisposed individuals, for the pathogenesis of specific

Ž .psychopathologies. In this regard, Van Praag 1996 hassuggested an intriguing hypothesis for the pathogenesis ofMDD, linked to a genetic predisposition to affective disor-ders and to intrinsic liability of the hypothalamo-pituitary–adrenal axis with difficulties in coping with ex-ternal and internal stimulations. In these subjects, superim-posed activating stressful events may lead on the one sideto the development of specific hypothalamo-pituitary–adrenal-dependent psychopathological symptoms, includ-ing anxiety and worsening of the coping difficulties, andon the other to a hypothalamo-pituitary–adrenal stimula-tion, and as a consequence to a hypothalamo-pituitary–adrenal-dependent inhibition of central serotoninergicfunction, MDD being the final breakdown of the converg-ing biochemical and mental homeostatic capacities of theindividual. In this case, life events have been mandatoryfor the development of the disorder, obviously in geneti-cally predisposed individuals. The alterations of the hy-pothalamo-pituitary–adrenal axis of these patients may notoccur in others with better functioning biological andpsychological coping systems.

The sixth point refers to the very intriguing observation,mentioned before, that the same neurotransmitter–neuropeptide impairment can occur in psychopathologieswhich are pathogenetically and symptomatologically com-pletely different. Just to make some examples, serotonindeficiency and noradrenaline and corticotropin-releasing-hormone hypersecretions can occur in MDD, but also inGeneralized Anxiety, in Obsessive–Compulsive Disorder,in Panic Disorders, in Posttraumatic Stress Disorders, inEating Disorders and possibly in other psychopathologiesŽSchatzberg and Nemeroff, 1988; Lynn-Brown and Van

.Praag, 1991 . How can the same impairment be at thebasis of different mental illnesses? It may be that a neu-roendocrine pathology which is constantly or at least veryfrequently present in totally different mental disordersmight not be the primary cause or the correlate of any oneof these disorders, but the cause or the correlate of aspecific symptomatology common to each of the patholo-gies, which, because of that, share the same hormonalabnormalities as expression of a common brain alteration.

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This does not mean that the neuroendocrine impairmentsare only an expression of symptomatic phenomena that aremarginally related to the nosography and etiopathogenesisof mental disorders, but that they could be the expressionof symptoms which are actually part of any one of them.Another possible explanation is that a specific brain bio-chemical impairment expressed peripherally by a hormonalalteration and clinically revealed by a symptom or a groupof symptoms that can appear in different mental disorders,may be in one case the starting point for a cascade ofbiochemical events etiopathogenetically leading to onepsychopathology and in the meantime be only temporarilyinvolved in the modulation of the course of other psy-chopathologies. As an example, thyroid dysfunctions canbe only a precipitating factor for the development of MDDin genetically predisposed individuals, through the effectsof thyroid hormones on noradrenaline, dopamine, and sero-tonin systems. In the meantime, the thyroid-linkedmonoamine alterations can worsen characteristics, whichare normally modulated by the hypothalamo-pituitary–thyroid system like anxiety, leading to a full-blown anxietydisorder. The same could be suggested for other personal-ity characteristics, which are normally modulated by thehypothalamo-pituitary–thyroid axis, like pathological ag-gressiveness, impulsiveness or sensation seeking.

All these aspects of psychoneuroendocrinology must betaken into account to explain the apparently contradictingresults of this branch of investigation, and to validate itsmeaning and usefulness. All the data reported in theliterature should be revisited with these criticisms in mind,thus making it possible to offer a real AmirrorB of brainfunctions and dysfunctions.

2. The future of psychoneuroendocrinology

Where do we go from here?Studies in experimental animals are steadily opening

new pathways of research and day by day clarifying themechanisms of brain functions in normal and abnormalsituations. Studies in humans lag far behind due to ethicalreasons, methodological difficulties, lack of compliance,and, as mentioned above, interferences of an array ofexternal–internal factors that can be carefully avoided inanimals but not always in humans. All these drawbacksmake studies of human brain function still extremely diffi-cult, and the search for acceptable, non-invasive methodsof investigation mandatory. In this regard, psychoneuroen-docrinology can still be an important branch of investiga-tion, as long as it takes new innovative steps, indispensableto validate its meaning and its significance.

2.1. Methodological proposals

A first point, which should be taken into consideration,is the fact that psychoneuroendocrinology has always used

pharmacological probes to stimulate or inhibit neurotrans-mitter, neuropeptide, neurohormone secretions and theirreceptor sensitivities to investigate the brain capacity toconfront the everyday life or new events. Even though thistype of investigation has a rationale, in that the drugs usedwere as much as possible specific modulators of eachbiochemical brain activity, they have always been adminis-tered without real knowledge of how much drug shouldhave been used to define the state of function of each brainsystem in a physiological situation. Most of the time, wehave probably used stimuli that were pharmacologicalrather than physiological, and, in all, probably too massiveresulting in responses which could hardly mimic the nor-mal brain activity. This might have obscured the realcapacity of the brain biochemical system to adapt to everyday situations. Difficulty in coping with external and inter-nal stimuli seems to be one of the core symptoms of most,if not all, psychopathologies. We are not even talkingabout coping with severe life events, but with the changesthat occur during everyday life and require modest mecha-nisms of adaptation. The dynamic tests we have used up tonow to study the coping capacities of mentally sick pa-tients can certainly reveal severe pathologies of the varioussystems that are involved in adaptation, but not the minorones that might not be clinically evident but are certainlyof great importance for the brain’s homeostatic mecha-nisms and for the patient’s social life.

At this point, we should investigate the brain regulatorysystem by using stimuli that would mimic everyday situa-

Žtions, using on the one hand physical stimulations e.g.,feeding, drinking, adaptation to high and low temperature,

.exercise, sleeping and on the other, mental situationsŽe.g., execution of mental tests, of work, of study, of

.public speeches, etc. . This type of investigation mightreveal specific biochemical alterations of the adaptationsystems, including the secretory tonus of classical neuro-transmitters, neuropeptides, neurohormones and peripheralhormones, whose impairments might underlie the copingdifficulties of the subjects and might be the basis forsubsequent psychopathological features.

A second point worthy to be taken into consideration isthe fact that any single psychoneuroendocrine test can givecontradictory responses, resulting in the contemporaneoussuggestion of hyperactivity and hypoactivity of a neuro-transmitter system according to the type of neuroendocrineaxis used as a mirror of the brain situation. This may bedue to the fact that a pharmacological probe can act indifferent brain areas in which the same neurotransmitterevokes different secretory cascades, which are modulatedin turn by multiple neurotransmittersrneuropeptides withensuing apparent conflicting peripheral results. Alterna-tively, it may be due to the fact that a probe used toinvestigate a specific neurotransmitter function can act ondifferent receptors each of which has different peripheraleffects, and therefore induces apparently opposite down-stream responses.

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To differentiate between these possibilities and recog-nize the real significance of the responses obtained, weshould use, contemporaneously or subsequently, multiplepsychoneuroendocrine tests that could differentiate be-

Ž .tween the brain areas on which the probe s is acting andbetween the responses of various receptors for each neuro-transmitter and neuropeptide. This approach may seem tomake the investigations too complicated and not accept-able to the patients, but this is not necessarily so. In fact, asingle test can include a probe stimulating one receptorand another inhibiting another receptor, or one stimulatingthe secretion of a neurotransmitter and another stimulatinganother neurotransmitter, or one acting on a neurotrans-mitter and another blocking the effects of a modulatoryneuropeptide, or one acting on one type of receptors andthe other on another receptor for the same neurotrans-mitter. Such combinations have already been used withexcellent results. Just as an example, the combination ofthe dexamethasone or the metopyrone suppression testswith the corticotropin-releasing hormone stimulation testhas greatly clarified the type and magnitude of the secre-tory alterations of the hypothalamo-pituitary–adrenal axisin MDD, in anxiety disorders, in Eating Disorders, alcohol

Žaddiction, and normal or pathological aging Van.Bardeleben et al., 1988 . The combination of the tests has

Ž .been especially helpful in pointing out the level s , andtherefore the brain area, where the impairments take placeand, as a consequence, the possible etiopathogenetical roleof the hypothalamo-pituitary–adrenal dysfunctions in thedevelopment of the above mentioned disorders.

2.2. Molecular biology studies

So far, psychoneuroendocrinology has directed its atten-tion to the investigation of the first and second steps of thebiological activities of the brain, including the secretionof neurotransmitters–neuropeptides–neurohormones–peri-pheral hormones and the sensitivity of their pre- or postsy-naptic receptors. Very little has been done to study thepossible importance of alterations of neuronal membrane,or of second messenger production and function and, ingeneral, on the cascade of events that precede the secretionof neurotransmitters, neuropeptides and hormones, or fol-low the stimulation–inhibition of their receptors.

Today, molecular biology in experimental animals hasfurnished data vital for the knowledge of the cellularactivities involved in normal and pathological physical andbrain life. Not much is known in humans, however, regard-ing the reciprocal influences of extra- and intracellularcomponents and activities of neurons and endocrine cellsfor the development of mental disorders.

Some work in this regard has been done in experimentaltransgenic animals, in whom genetic deoxy-ribonucleicacid-linked alterations of specific hormonal functions haveresulted in significant brain alterations and consequent

Ž .behavioral changes Marchetti et al., 1997 . This suggests

that similar spontaneously occurring alterations in humansmay lead to specific psychopathologies. Obviously, thestudy of neuronal molecular biology in living humansseems to be impossible. However, it has been suggested,and sometimes demonstrated, that some peripheral cellfunctions mimic the neuronal ones. For instance, periph-eral blood mononuclear cells have been observed to se-crete neurotransmitters and neurohormones and to possesstheir specific receptors similarly to what occurs in thehypothalamus. Platelets have been reported to display pre-and postsynapyic receptors for some neurotransmitters act-ing like those of central neurons. It has never been prop-erly investigated in experimental animals, and much less inhumans whether or not central and peripheral neurons havesimilar intra- and extracellular components and functions.This field should be developed to offer new possibilities ofunderstanding the mechanism of central neuronal functionsin regard to psychoneuroendocrinology.

2.3. Psychoneuroimmunoandocrinology

In the last two decades, numerous investigations haverevealed that the immune and the neuroendocrine functionsamply interrelate in regulating the mechanisms of adapta-tion to internal and external stimuli. More recently, the

Ž .central nervous system CNS has been observed to be partof a triangle that includes the neuroendocrine and theimmune system, each of which maintains a strict control ofthe function of the others. Most of the work that has beendone, however, regards the effects of the CNS on theimmune and the endocrine system and much less on thecontrary. In particular, the effects exerted by the immunesystem on the hypothalamus and suprahypothalamic cen-ters are still poorly understood.

Some data obtained in experimental animals suggestthat concomitant immune and neuroendocrine dysfunctionsoccurring during the pre- or postnatal life can result inanatomical alterations in the CNS with ensuing behavioralimpairments. In humans, pre- or immediately postnatalimmune alterations have been suggested to alter braindevelopment and functions specifically leading to

Ž .schizophrenia Waksman, 1990; Ader et al., 1991 . Dataon the development of other psychopathologies are lackingand worth of further investigations.

In experimental animals, many studies have been doneon the effects of pro- and anti-inflammatory cytokines onbehavior, ranging from modulation of hunger, satiety,drinking, sleeping, sexual activity, socialization, ex-

Ž .ploratory behavior and avoidance Ader et al., 1991 . Forhumans, very few studies of the effects of cytokine onmentation and on behavior have been reported. However,alterations of cytokine secretion occurring in parallel withmultiple hormonal impairments have been found in affec-tive disorders, anxiety disorders, and in schizophreniaŽWaksman, 1990; Muller and Ackenheil, 1998; Maes and

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.Van West, 1999 , suggesting that they are possibly in-volved in the modulation of mental disorders.

2.4. Psychoneuroendocrinology of personality character-istics

As mentioned above, the study of the effects thatneuroendocrine secretions exert on the development ofpersonality characteristics in so-called normal subjects ismandatory to understand the modulatory importance ofphysiological hormonal fluctuations along a wide range ofnormal values, as the basis and core of possible subsequentpsychopathologies. This type of study should define thebackground for the development of apparently minor per-sonality variations, on the one side, and of feedbackbiochemical impairments, on the other, the two compo-nents possibly leading toward mental disorders. In otherwords, it should first be defined which psychologicalaspect is modulated by which hormonal secretion, startingfrom the wide range of hormonal and psychological varia-tions in normal individuals, and then proceed to investigatetheir influences on the etiopathogenesis of mental disor-ders. Earlier, we have mentioned the example of testos-terone modulation of aggressiveness. Most of the studies inthe literature deal with highly pathological aggressiveness,or with other personality disorders and their possible bio-logical background, but still too little is known about thenormal fluctuations of personality characteristics in everyday life and their relation to every day brain biochemicalchanges of function. This investigation should be extendedto each personality characteristic of AnormalB individuals,since each one of them can represent, even when mini-mally impaired, one of the basis or, at least, a veryimportant component of successive psychopathologies.This type of study should be of importance in the field ofprevention of mental disorders and in that of pharmaco-logical correction of minor personological changes beforethey reach clinically significant levels.

2.5. Genetic studies

In the past decade, studies of the genetic background ofmental disorders have been flourishing, being especiallycentered on the research of specific impairments of secre-tion of the main neurotransmitters and of their receptorsensitivity. Very scarce or no data are reported regardingthe genetic regulation of neurohormones and neuropeptidesboth in normal and pathological mentation. This type ofinvestigation should be developed, since it is well knownthat neurohormones and neuropeptides intervene in thedevelopment of mental disorders, possibly not only byacting as modulators of neurotransmitter functions but alsoas neurotransmitters by themselves, acting on their specificreceptors. Genetically conditioned alterations of thephysiological functions of neurohormones may be at thebasis of the incapacity to adapt to internal and external

events. This has been proposed to occur for the hypotha-lamo-pituitary–adrenal function in MDD by Van PraagŽ .1996 , as mentioned above, but it could be present in anyother brain hormonal function, being responsible not onlyfor specific endocrinopathies but also for psychopatholo-gies.

2.6. Brain imaging

Researches using brain imaging techniques for the in-vestigation of anatomical aspects and functions of wholebrain and of specific brain nuclei are steadily growing,leading to a better understanding of CNS development andits physiological activity, and of the connections betweenvarious brain areas. Recently, these techniques have beenapplied to the studies of psychopathologies, in the hope tobetter clarify their brain pathological aspects. Electricalactivities, blood flow and few data on distribution andfunction of neurotransmitter secretion and their receptoractivities have been reported. But, again, no data exist onthe secretion of neurohormones, neuropeptides and neuros-teroids, and on their receptor functions.

2.7. Hormonal therapies

A psychoneuroendocrine field that should be developedfurther is that of hormonal or antihormonal therapies, assingle or multidrug treatments of psychopathologies. Therational for this therapeutic approach is based, on onehand, on the observation that multiple hormonal impair-ments occur during mental disorders, and, on the other,that hormones may act as neurotransmitters or as modula-tors of neurotransmitter functions in the CNS — in bothcases, being possibly involved in the pathogenesis of men-tal disorders.

In the past, hormonal therapies have been used as singletreatments of mental disorder with very poor results. Thiswas due to the scarce and approximate knowledge of thebiochemical background of psychopathologies, the effectsof hormones on CNS activity, and also to the lack of purehormonal preparations. Recently, hormonal therapies havebeen tried again, but most of the therapeutic trials were notblind and controlled by placebo, and therefore their valid-ity are still questionable.

Estrogens, androgens and thyroid hormones have beenused in MDD in conjunction with classical psychotropicdrugs to increase the receptor sensitivity of neurotrans-mitters, and therefore to potentiate the effects of antide-

Žpressants Kleiber et al., 1979; Oppenheim, 1983; Halbre-.ich, 1996; Aronson et al., 1996; Callahan et al., 1997 .

Glucocorticoids, antiglucocorticoids, endogenous opioidsand anti-opioids, gonadal hormones, antigonadotropindrugs have been used in MDD, and colecystokinin, en-dogenous opioids and anti-opioids have been used inschizophrenia and in autism, with uncertain resultsŽCrammer, 1986; Murphy et al., 1991; Wolkowitz et al.,

.1993 . This field, however, is worth further investigation

( )F. BrambillarEuropean Journal of Pharmacology 405 2000 341–349348

Ž .with protocols that should take into consideration: i thespecific neurohormone, neuropeptide, neurosteroid alter-ations of each type of mental pathology taken into consid-

Ž .eration, and ii the effects that hormones can exert notonly at the level of neurotransmitter secretions and recep-tor sensitivities but also on second-messenger function andintracellular component in general. The correction of aneurohormonal impairment can be mandatory for the prog-nosis of mental disorders, since it has already been amplydemonstrated that the persistence of hormonal impairmentsin the course of mental disorders is an unfavourable prog-nostic parameter.

2.8. Neuropeptide and neurosteroid secretions

The actions exerted by neuropeptides and neurosteroidson CNS have been amply investigated in experimentalanimals, but are still poorly confirmed in humans.

It is well known that in experimental animals, neu-ropeptide and neurosteroids are secreted by the CNS andact in some cases and some areas by stimulating andinhibiting their specific receptors, and in other cases andother areas by modulating secretion and receptor sensitiv-ity of classical neurotransmitters. This has been hardlycontrolled in humans, because of ethical reasons, poorfeasibility, lack of compliance, lack of appropriate method-ologies, and so on. However, it is extremely important toextend the animal studies to humans since neuropeptidesand neurosteroids modulate cognition, affectivity and be-havior in experimental animals and they might do the samein men. The effects of corticotropin-releasing hormone onmood, anxiety and psychological coping with stressŽ .Holsboer, 1989 , of vasopressin and oxytocin on learning

Ž .and memory De Wied, 1990 , of neurosteroids on anxietyŽ .and depression Rupprecht and Holsboer, 1999a,b , are

well known for animals but not fully demonstrated inhumans.

3. Conclusions

Psychoneuroendocrinology — or better yet, psychoneu-roimmunoendocrinology — has been demonstrated in thepast to be a good type of approach for the knowledge ofnormal and pathological brain function, and should not beabandoned in the future. Obviously, it cannot be usedtoday in the same way that it has been used in the past,since, as mentioned above, the methodological approachesadopted up to now have given already the maximum ofpossible responses and we will go nowhere by using thesame techniques over and over again in the future. Weneed to develop new methodologies to open new pathwaysbut, mostly, to bring psychoneuroendocrine investigationsin the context of multiple brain biological researches. Theimpaired secretion of one single neurohormone or neu-ropeptide, taken as an isolated phenomenon, will be

severely pressed to offer a complete pathogenetic hypothe-sis for the development of a mental disorder but can bemandatory in the context of a complex pathoplastic situa-tion, where neurotransmitters, neuropeptides, neuros-teroids, neurohormones and immune components all inter-play in a game of reciprocal stimulation–inhibition phe-nomena resulting in final breakdowns of brain physio-logical functions.

The discovery of the temporal position — primary orsecondary — of neurohormonal impairments in this patho-logical game may be of importance from an etiopatho-genetic point of view. But equally important is the knowl-edge of the effects on perpetuation of a mental diseaseexerted by neurohormonal dysfunctions, regardless ofwhether or not they are the primum movens of the psy-chopathology. It is well known, for instance, that a persis-tent hyperfunction of the hypothalamo-pituitary–adrenalsystem seems to be pathogenetically mandatory for thepersistence of MDD, its resistance to any therapy, and itstendency to relapse. Today, this is leading towards thesearch for therapeutic interventions centered on the inhibi-tion of corticotropin-releasing hormone, which seems to bepromising. But very little is known about all the otherneuropeptides and neurohormones.

At this point, we must have the courage to look over allour old data, file away some of them to revisit later someresearches and hypotheses under new perspectives, and, inthe meantime, proceed along totally different pathways, aswe have done so successfully in the past. In our lives wehave seen the birth and the abandonment of many scien-tific branches of research, and many hypotheses. And aftera period of rejection, many of them have been taken upunder different perspectives and with different method-ological approaches, resulting in the discovery of impor-tant aspects of animal and human lives.

The future is in front of us.

References

Ader, R., Felten, D.L., Cohen, N., 1991. Psychoneuroimmunology. Aca-demic Press, San Diego, USA.

American Psychiatric Association, 1994. Diagnostic and Statistical Man-Ž .ual for Mental Disorders. 4th edition III and IV editions American

Psychiatric Press, Washington, DC, 1994.Aronson, R., Offman, H.J., Joffe, R.T., Naylor, C.D., 1996. Triiodothyro-

nine augmentation in the treatment of refractory depression: a meta-analysis. Arch. Gen. Psychiatry 53, 842–848.

Brambilla, F., Bridges, P.K., Endroczi, E., Heuser, G., 1978. PerspectiveIn Psychochobiology. Akademiai Kiado Press, Budapest Hungary.

Brambilla, F., 1999. Neurohormonal alterations in eating disorders andobsessive compulsive disorders: a common biological basis? In: Bel-

Ž .lodi, L., Brambilla, F. Eds. , Eating Disorders and Obsessive Com-pulsive Disorder: An Etiopathogenetic Link? Centro Scientifico ed.,Torino, Italy, pp. 77–98.

Brown, G.M., Koslow, S.H., Reichlin, S., 1984. Neuroendocrinology andPsychiatric Disorder. Raven Press, New York, USA.

Callahan, A.M., Frye, M.A., Marangell, L.B., George, M.S., Ketter, T.A.,L’Herrou, T., Post, R.M., 1997. Comparative antidepressant effects ofintravenous and intrathecal thyrotropin-releasing hormone: confound-

( )F. BrambillarEuropean Journal of Pharmacology 405 2000 341–349 349

ing effects of tolerance and implications for therapeutics. Biol. Psy-chiatry 41, 264–272.

Chatelanat, P., 1978. Troubles mentaux symptomatiques d’affectionsmedicales. Schweiz. Rundsch. Med. 67, 518–526.´

Checkley, S., Arendt, J., 1984. Pharmacoendocrine studies of G.H., PRL,and melatonin in patients with affective illness. In: Koslow, G.M.,

Ž .Reichlin, S.H. Eds. , Neuroendocrinology and Psychiatric Disorder.Raven Press, New York, pp. 165–190.

Crammer, J.L., 1986. Premenstrual depression, cortisol and estradioltreatment. Psychol. Med. 16, 451–455.

De Souza, E., Nemeroff, C.B., 1990. Corticotropin-releasing factor: basicand clinical studies of a neuropeptide. CRC Press, Boca Raton, USA.

De Wied, D., 1990. Neuropeptides — Basics and Perspectives. Elsevier,Amsterdam.

Finkelstein, J.W., Susman, E.J., Chinchilli, W.M., Kunselman, S.J.,D’Arcangelo, M.R., Schwab, J., Demers, L.M., Liben, L.S., Looking-bill, G., Kulin, H.E., 1997. Estrogens and testosterone increasesself-reported aggressive behaviors in hypogonadal adolescents. J.Clin. Endocrinol. Metab. 82, 2433–2438.

Fava, G.A., Sonino, N., Morphy, M.A., 1987. Major depression associ-ated with endocrine disease. Psychiatr. Dev. 4, 321–348.

Gerra, G., Avanzini, P., Zaimovic, A., Fertonani, G., Caccavari, R.,Delsignore, R., Gardini, F., Talarico, E., Lecchini, R., Maestri, D.,Brambilla, F., 1996. Neurotransmitter and endocrine modulation ofaggressive behavior and its components in normal humans. Behav.Brain Res. 81, 19–24.

Halbreich, U., 1987. Hormones and Depression. Raven Press, New York,USA.

Halbreich, U., 1996. Role of estrogens in depression of menopausalwomen. Proc. X World Congr. Psychiatr. pp. S1121–S1122.

Holsboer, F., 1989. Psychiatric implications of altered limbic–hypo-thalamic–pituitary–adrenocortical activity. Eur. Arch. Psychiatr. Neu-rol. Sci. 238, 302–322.

Hommer, D.W., Skolnick, P., Paul, S.M., 1987. The benzodiazepinergabaŽ .receptor complex and anxiety. In: Meltzer, H.Y. Ed. , Psychophar-

macology: The Third Generation of Progress. Raven Press, NewYork, pp. 977–984.

Janowsky, D.S., Risch, S.C., 1987. Role of acetylcholine mechanisms inŽ .the affective disorders. In: Meltzer, H.Y. Ed. , Psychopharmacology:

The Third Generation of Progress. Raven Press, New York, pp.527–534.

Jimerson, D.C., 1987. Role of dopamine mechanisms in the affectiveŽ .disorders. In: Meltzer, H.Y. Ed. , Psychopharmacology: The Third

Generation of Progress. Raven Press, New York, pp. 505–512.Kleiber, E.L., Broverman, D.M., Vogel, W., Kobayashi, Y., 1979. Estro-

gen therapy for severe persistent depression in women. Arch. Gen.Psychiatry 36, 550–554.

Loosen, P.T., 1987. Thyroid hormones and affective state. In: Halbreich,Ž .U. Ed. , Hormones and Depression. Raven Press, New York, pp.

357–383.Losonczy, M.F., Davidson, M., Davis, K.L., 1987. The dopamine hypoth-

Ž .esis of schizophrenia. In: Meltzer, H.Y. Ed. , Psychopharmacology:The Third Generation of Progress. Raven Press, New York, pp.715–726.

Lynn-Brown, S., Van Praag, H., 1991. The Role of Serotonin In Psychi-atric Disorders. BrunnerrMazel, New York, USA.

Maes, M., Van West, D., 1999. Cytokine production in anorexia nervosaand obsessive compulsive disorder: a review. In: Bellodi, L., Bram-

Ž .billa, F. Eds. , Eating Disorders and Obsessive Compulsive Disorder:An Etiopathogenetic Link? Centro Scientifico ed., Torino, Italy, pp.111–124.

Marchetti, B., Morale, M.C., Gallo, F., 1997. Neurochemical, immuno-

logical and pharmacological assessments in a transgenic mouse modelof the endocrine changes in depression. Aging Clin. Exp. Res. 4,

Ž .26–27, suppl. .Meltzer, H.Y., Lowy, M.T., 1987. The serotonin hypothesis of depres-

Ž .sion. In: Meltzer, H.Y. Ed. , Psychopharmacology: The Third Gener-ation of Progress. Raven Press, New York, pp. 513–526.

Monteleone, P., Catapano, F., Tortorella, A., Maj, M., 1999. Hormonalcircadian rhythms in patients with eating disorders and in patientswith obsessive–compulsive disorder. In: Bellodi, L., Brambilla, F.Ž .Eds. , Eating Disorders and Obsessive Compulsive Disorder: AnEtiopathogenetic Link? Centro Scientifico ed., Torino, Italy, pp.99–110.

Muller, E.E., Nistico, G., Scapagnini, U., 1977. Neurotransmitters and`Anterior Pituitary Function. Academic Press, New York, USA.

Muller, N., Ackenheil, M., 1998. Psychoneuroimmunology and the cy-tokine action in the CNS: implications for psychiatric disorders. Prog.Neuropsychopharmacol. Biol. Psychiatry 22, 1–33.

Murphy, B.E.P., Dhar, V., Ghadirian, A.M., Chouinard, G., Keller, R.,1991. Response to steroid suppression in major depression resistant toantidepressant therapy. J. Clin. Psychopharmacol. 11, 121–126.

Musselman, D.L., Nemeroff, C.B., 1996. Depression and endocrine disor-ders: focus on the thyroid and adrenal system. Br. J. Psychiatry 168,123–128.

Nash, J.F., Meltzer, H.Y., 1991. Neurendocrine studies in psychiatricŽ .disorders. In: Lynn Brown, S., Van Praag, H.M. Eds. , The Role of

Serotonin in Psychiatric Disorders. BrunnerrMazel, New York, pp.57–90.

Oppenheim, G., 1983. Estrogen in the treatment of depression: neu-ropharmacological mechanisms. Biol. Psychiatry 17, 721–725.

Pandey, G.N., Ali, S.I., Casper, R., Davis, J.M., 1984. NeuroendocrineŽ .studies in schizophrenia. In: Shah, N.S., Donald, G.D. Eds. , Psy-

choneuroendocrine Dysfunction. Plenum, New York, pp. 503–548.Rupprecht, R., Holsboer, F., 1999a. Neuroactive steroids: mechanisms of

action and neuropharmacological perspectives. Trends Neurosci. 22,410–416.

Rupprecht, R., Holsboer, F., 1999b. Neuropsychopharmacological proper-ties of neuroactivesteroids. Steroids 64, 83–91.

Sachar, E., 1976. Hormones, Behavior And Psychopathology. RavenPress, New York, USA.

Schatzberg, A.F., Nemeroff, C., 1988. The Hypothalamic–Pitutary–Adrenal Axis: Physiology, Pathophysiology, and Psychiatric Implica-tions. Raven Press, New York USA.

Shah, N.S., Donald, A.G., 1984. Psychoneuroendocrine Dysfunction.Plenum, New York, USA.

Siever, L.J., 1987. Role of noradrenergic mechanisms in the etiology ofŽ .the affective disorders. In: Meltzer, H.Y. Ed. , Psychopharmacology:

The Third Generation of Progress. Raven Press, New York, pp.493–504.

Van Bardeleben, V., Stalla, G.K., Muller, O.A., Holsboer, F., 1988.Blunting of ACTH response to human CRH in depressed patients isavoided by metyrapone pretreatment. Biol. Psychiatry 24, 782–786.

Van Praag, H.M., 1996. Serotonin-related, anxietyraggression-driven,stressor-precipitated depression. A psychobiology hypothesis. Eur.Psychiatry 11, 57–67.

Waksman, B.H., 1990. Immunological Mechanisms in Neurologic andPsychiatric Disease. Raven Press, New York, USA.

Wehr, T.A., Goodwin, F.K., 1983. Biological rhythms in manic–depres-Ž .sive illness. In: Wehr, T.A., Goodwin, F.K. Eds. , Circadian Rhythms

In Psychiatry. Boxwood Press, Pacific Grove, CA, USA, pp. 129–184.Wolkowitz, O., Resuss, V.I., Manfredi, E., Ingbar, J., Brizendine, L.,

Weingartner, H., 1993. Ketokonazole administration in hypercorti-solemic depression. Am. J. Psychiatry 150, 810–812.