86 (2006) 45–53www.elsevier.com/locate/schres

Schizophrenia Research

Evidence that brain tissue volumes are associated with HVAreactivity to metabolic stress in schizophrenia

Machteld Marcelis a,⁎, John Suckling b, Paul Hofman c, Peter Woodruff d,Ed Bullmore e, Jim van Os a,f

a Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University,PO Box 616 (VIJV1), 6200 MD Maastricht, The Netherlands

b Brain Mapping Unit, Department of Psychiatry, University of Cambridge, Addenbrooke's Hospital, Cambridge, UKc Department of Radiology, University Hospital Maastricht, Maastricht, The Netherlands

d Department of Psychiatry, Sheffield Cognition and Neuroimaging Laboratory, Academic Clinical Psychiatry, University of Sheffield,The Longley Centre, Norwood Grange Drive, Sheffield, S5 7JT, UK

e Department of Psychiatry, University of Cambridge, UKf Division of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK

Received 27 July 2005; received in revised form 1 May 2006; accepted 2 May 2006Available online 27 June 2006

Abstract

Background: Although liability to psychosis is thought to have its origins in cerebral alterations, expressed as cerebral grey andwhite matter loss, less is known about the degree to which such vulnerabilities impact on functional parameters, in particular alteredstress reactivity. Breier et al. [Breier, A., Davis, O.R., Buchanan, R.W., Moricle, L.A., Munson, R.C., 1993b. Effects of metabolicperturbation on plasma homovanillic acid in schizophrenia. Relationship to prefrontal cortex volume. Arch. Gen. Psychiatry 50(7),541–550] reported that lower prefrontal cortex volume was associated with altered metabolic stress response, but this finding hasnever been replicated.Methods: Thirty-one patients with psychosis underwent structural magnetic resonance imaging scanning and a metabolic stressparadigm (glucoprivic 2-deoxyglucose (2DG) condition versus placebo condition) that yielded information on plasmahomovanillic acid (HVA) reactivity. Total cerebral tissue volumes were derived from automated segmentation procedures.Associations between metabolic stress and tissue volumes (as well as their interactions) on the one hand, and plasma HVA level onthe other, were investigated using multilevel random regression techniques.Results: Analysis revealed a significant increase in plasma HVA over time in the 2DG condition. The increase in HVA in the stresscondition was stronger in patients with lower grey and white matter volumes. There was no significant interaction betweenmetabolic stress and CSF volume.Conclusion: Lower grey and white matter volumes in schizophrenia are associated with a dysregulated dopaminergic/noradrenergicmediated stress response. These findings may support the hypothesis that alterations in cortico-subcortical connections affectpsychosis susceptibility through an altered stress response.© 2006 Elsevier B.V. All rights reserved.

Keywords: Schizophrenia; Brain alteration; Magnetic resonance imaging; Metabolic stress; Homovanillic acid; Dopamine

⁎ Corresponding author. Tel.: +31 43 3688679/666; fax: +31 43 3688689.E-mail address: m.marcelis@sp.unimaas.nl (M. Marcelis).

0920-9964/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.schres.2006.05.001

46 M. Marcelis et al. / Schizophrenia Research 86 (2006) 45–53

1. Introduction

The liability to schizophrenia is thought to have itsorigins in cerebral alterations, expressed as structuralabnormalities such as reductions in total brain volume,and grey and white matter volume (Wright et al., 2000).However, very little is known about how suchvulnerabilities impact on functional measures, in partic-ular the response to stress.

The altered stress response in schizophrenia isthought to be associated with the process of dopaminesensitization, referring to hyperresponsiveness of DAneurons to environmental stimuli, in which exposure toeven moderate levels of stress are associated with anexcessive DA response (Davis et al., 1991; Glenthoj,1995; Laruelle, 2000; Laruelle and Abi-Dargham,1999). In schizophrenia, a dysregulated, hyperdopami-nergic state may lead to stimulus-independent release ofdopamine and to aberrant assignment of salience toexperiences, which may serve as a framework for theemergence of psychotic symptoms (Kapur, 2003).

An experimental paradigm to examine perturbationon dopamine function following stress exposureinvolves glucose deprivation by intravenous infusionof 2-deoxyglucose (2DG) (Breier, 1989; Breier et al.,1992b; Mitropoulou et al., 2004). The glucose-analog2DG causes glucoprivation by competing with glucose-6-phospate during the early stage of glycolysis andinhibits intracellular glucose utilization. As glucose isthe primary energy source for the central nervoussystem, disruption of glucose metabolism is a potentCNS stressor. This metabolic stress paradigm has beenfound to produce robust activation of the hypothalamic–pituitary–adrenal (HPA) axis, as well as elevations ofepinephrine and of behavioral (stress/anxiety) andphysiologic (heart rate/blood pressure) measures (Breieret al., 1992b; Elman et al., 1999). Moreover, it stronglyaffects central and peripheral dopamine function, as wellas the plasma levels of homovanillic acid (HVA), abreakdown product of dopamine as well as noradren-aline. Plasma HVA, although largely derived from theperiphery, is thought to reflect, at least partly, the centraldopamine response to stress (Breier, 1989; Breier et al.,1993b).

Measuring plasma HVA repetitively duringmetabolicstress, Breier et al. (1993b) not only found that patientswith schizophrenia had significantly greater 2DG-induced plasmaHVA elevations as compared to controls,but also that these elevations in HVA levels wereassociated with lower prefrontal cortex volumes. In arecent study using the same paradigm, this finding ofaltered stress response in schizophrenia was replicated,

with patients showing an increased dopamine (DA)/noradrenaline (NA) response compared to controls(Marcelis et al., 2004). The aim of the present inves-tigation was to independently replicate the earlierfindings of a relationship between brain tissue and theHVA response to metabolic stress (Breier et al., 1993b),but now in a much larger sample.

We hypothesized that functional cerebral vulnerabil-ity, conceptualized in terms of heightened DA/NAresponsivity during 2DG perturbation is associated withchanges in brain structure in psychosis. Increasingevidence indicates that temporolimbic–prefrontal dys-function in schizophrenia is associated with enhancedsubcortical dopamine release (Heinz et al., 2003).Alterations in the capacity of a stress buffering system,such as prefrontal dopaminergic function, may resultfrom aberrant development of cortical cytoarchitecture(Weinberger and Lipka, 1995). During mild stress,dopamine release and metabolism is preferentiallyincreased in the mesocortical system, compared to themesolimbic and nigrostriatal systems. This increase inprefrontal dopamine following mild stress is thought toinhibit subcortical dopamine transmission, therebyproviding protection against positive symptoms (Deutchet al., 1990; Vermetten and Bremner, 2002). Byimpacting negatively on mesocortical dopamine func-tion, reduced cortical volume in schizophrenia may thusaffect the stress-buffering system and lead to increasesin subcortical dopamine activity following even mildstressors (Laruelle, 2000).

Dysfunctional connections between the cortex andthe midbrain may be reflected by white matterreduction. We tested whether reduced cerebral greyand white matter is associated with an increased DA/NA-mediated stress response following 2DG-adminis-tration in patients with psychosis.

2. Methods

2.1. Study sample

The patient sample is part of the MaastrichtPsychosis Study (Marcelis et al., 2003a,b, 2004). MRIand HVA data were available for 31 out of 50 patientswith psychosis.

Patients between 16 and 55 years with a life-timehistory of psychosis according to the RDC criteria(Spitzer et al., 1978), who were not currently in need ofin-patient treatment, intensive case management homecare, or case management crisis intervention, wererecruited at the community mental health center inMaastricht, the Netherlands.

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Other inclusion criteria included being in goodhealth, as determined by a physical examination,electrocardiography, and routine laboratory investiga-tions. Individuals with a history of severe head trauma,neurological disorders, and/or other medical disordersthat might have significantly affected brain function orstructure were excluded, as well as individuals who usedalcohol in excess of five standard units per day or illicitdrugs on a weekly basis.

The study was approved by the local medical ethicscommittee, and all the subjects gave written informedconsent in accordance with the committee's guidelines.

2.2. Clinical and diagnostic procedures

Patients were interviewed with the Life Chart (WHO,1992), BPRS (Lukoff et al., 1986; Overall and Gorham,1962), the PANNS (Kay et al., 1987, 1988) and wereadditionally screened for symptoms listed in the OCCPI(McGuffin et al., 1991). The computerised programOPCRIT (McGuffin et al., 1991) yielded the followingRDC-diagnoses: schizophrenia (n=25) and schizo-affective disorder (n=6). To determine life-time historyof alcohol and drug use, the Composite InternationalDiagnostic Interview (CIDI) (Smeets and Dingemans,1993) was administered. All current medications wererecorded.

2.3. Image acquisition and processing

2.3.1. Image acquisitionMRI scans were obtained at the Department of

Radiology, University Hospital Maastricht, The Nether-lands, with a Gyroscan NT T-I1 (Philips MedicalSystems) operating at 1.5 T. Three millimetre thickinterleaved two-dimensional dual-echo fast spin-echoimages (60 slices, 0.3 mm gap between slices) wereacquired and angled parallel to the clivus, covering theentire brain. Proton density (PD) weighted and T2-weighted images were acquired simultaneously (echotime (TE)1=20 ms, TE2=100 ms, TR=4000 ms, echotrain length: 6, total acquisition time: 10 min 12 s). Thematrix size and field of view was set at 256×205 and22 cm, respectively. The number of signal averageswas 1.

2.3.2. Image processingImage processing and computations were done on a

SUN Ultra10 (Sun MicroSystems Inc., Mountain View,CA, USA) workstation with the BAMM software (BrainActivation and Morphological Mapping, University ofCambridge, UK). Initially, a mask of parenchymal tissue

was generated from linear scale-space features derivedfrom the PD weighted images (Suckling et al., 1999a).Each voxel in the mask was then categorised in terms ofthe proportion occupied by grey matter, white matter,CSF or dura/blood vessels. This algorithm partitionedthe feature space formed by the two MR echoes (PD andT2-weighting), using a four-class modified fuzzyclustering scheme, and assigned continuous member-ship of each tissue class to every voxel (Suckling et al.,1999b). Axial non-uniformity of image contrast, due tothe reduction in sensitivity at the edges of thetransmitting/receiving coil, was corrected with a movingwindow scheme. Classifying data in this manner allowsfor changes in the distribution of voxels in feature space.For a detailed description, see Suckling et al. (1999b).Total cerebral tissue volumes were obtained bysumming over all proportions and multiplying byvoxel volume.

2.4. Metabolic stress paradigm (2-deoxy-glucoseprotocol)

A full description of this paradigm applied to a largersample can be found elsewhere (Marcelis et al., 2004).In brief, all subjects underwent double-blind adminis-tration of the glucose analog 2DG and placebo, inrandomized order. The 2DG doses were 50 mg/kgmixed in 100 ml of isotonic saline. Placebo was acomparable volume of isotonic saline (NaCl, 0.9%).Both conditions (2DG/placebo) were given within oneweek, with at least two days in between. Subjects had tofast from midnight prior to both test days and wereallowed to drink only water ad libitum. During the test,subjects rested supine in bed from 8:45 a.m. until 12:30p.m. At 8:45 a.m., an intravenous catheter was insertedin the antecubital fossa and kept patent with a slow dripof isotonic saline. At 9:50 a.m., two baseline venousblood samples were taken 10 min and 0 min prior toinfusion. At 0 min, 2DG or placebo was infused over aperiod of 20 min. Four more blood samples were takenat 60 min, 90 min, 120 min and 150 min after theinfusion was started.

Blood was collected in tubes containing 0.5 ml ofan EDTA (40 mg/ml) and Na2S2O5 (20 mg/ml)solution. Plasma was obtained by centrifugation(15 min at 3000 rpm) in a refrigerated centrifuge(5 °C) and was then stored at −80 °C until assaying. A515 WATERS isocratic HPLC was used for assayingHVA, with a Symmetryshield RP18 25 cm column forthe separation of the compounds. Intra-assay variabilitywas 5% for HVA. Inter-assay variability was 9% forHVA.

Fig. 1. Effects of 2-deoxy-glucose and placebo on plasma HVA (ng/ml) in 31 patients with psychosis. Data points represent mean plasmaHVA levels. Time 1 and 2 reflect the two pre-infusion (baseline)occasions on which plasma HVAwas measured (i.e., 10 min and 0 minprior infusion). Times 3–6 reflect the four post-infusion samplingoccasions: respectively, 60 min, 90 min, 120 min, and 150 min post-infusion. The increase in HVA over time in the 2DG conditioncompared to the placebo condition was statistically significant(condition×timeB interaction term, Likelihood Ratio Statistic (LRS)=84.93, p<0.001).

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2.5. Statistical analyses

The data were analyzed with the STATA computerprogram, version 8 (StataCorp., 2001). The variable“condition” had two levels: the placebo condition(reference) and the 2DG condition. HVA was sampledon six occasions (time 1–6). Time points 1–6 weredivided into the variables timeA (time 1–2) and timeB(time 3–6) reflecting the two pre- and the four post-infusion measurement occasions. TimeB served as theindependent variable of interest, with timeA as covariateto control for baseline values. The mean HVA level ofthe two pre-infusion samples for each person and eachcondition was used to construct a baseline HVAvariable(HVA_base) (Marcelis et al., 2004).

To investigate the effect of global tissue volume onHVA during metabolic stress, multilevel linear regres-sion analyses (see below) were conducted with HVA asthe dependent variable and tissue volume, condition,timeB, as well as their interactions, as independentvariables. In addition, HVA-baseline, timeA, age, sexand total brain volume were added as covariates to adjustfor their a priori hypothesized confounding effects.

As the average measure of HVA is assumed to varyacross persons, two observations will be more similar ifthey are from the same person. Our design of repeatedmeasures within the same person therefore compro-mised statistical independence of the observations. Inorder to deal with this issue, multilevel randomregression models were fitted (Goldstein, 1987) withthe XTREG module in STATA. The β is the fixedregression coefficient of the predictor in the multilevelmodel and can be interpreted identically to the estimatein a unilevel regression analysis. Interaction terms wereevaluated by Likelihood Ratio test.

3. Results

3.1. Subjects and descriptives

The sample consisted of 15 men and 16 women. Themean age was 30.7 years (S.D.: 7.4) and mean age offirst psychotic symptoms was 22.1 years (S.D.: 5.8).The mean duration of illness was 8.6 years (S.D.: 5.7).Twenty-eight patients were receiving antipsychoticmedication (atypical: n=15; typical: n=13). Meancurrent dosage in terms of standard haloperidolequivalents was 4.99 (S.D.: 3.06). Of the 28 patients,12 patients also used a benzodiazepine, and 4 used anantidepressant.

Mean tissue volumes were, for grey matter:559.5 cm3 (SD: 64.0); for white matter: 545.4 cm3

(SD: 63.4); for CSF: 169.2 cm3 (SD: 32.0). Total cere-bral brain volume (grey+white+CSF volume) was1274.1 cm3 (SD: 127.2). Mean levels of HVA (ng/ml) atthe six measurement points during the stress andplacebo condition are presented in Fig. 1.

There was no evidence for an effect of antipsychoticmedication dosage (expressed as standard haloperidolequivalents) on brain tissue volume (β for grey matter:1.01, 95% CI: −3.19–5.21; β for white matter:−3.52,95% CI:−7.9–0.86; β for CSF: 2.5, 95% CI:−1.08–6.10).

3.2. Association between global tissue volumes andHVA level changes during metabolic stress

There was a significant effect of condition on HVA(β=1.54, p<0.001). In addition, a significant condi-tion× timeB interaction was found (Likelihood RatioStatistic (LRS)=84.93, p<0.001), indicating an in-crease in HVA over time in the 2DG condition comparedto the placebo condition.

In Fig. 2A, HVA level differences between the stressand placebo condition at the six measurement pointsare depicted for three grey matter volume groups,suggestive of interaction. This hypothesis was exam-ined statistically by fitting a three-way interactionbetween grey matter volume, condition, and time B,which yielded a significant negative grey matter×con-dition× timeB interaction (β=−0.0036, p<0.021). Thisnegative interaction indicates that the increase in HVAin the stress condition was stronger in patients with

Fig. 2. These figures reflect the differences in mean plasma HVA levels(ng/ml) between the two conditions (i.e., 2DG and placebo condition),stratified by brain volume group. The lines in the figure in (A) indicatethree grey matter tertiles and the lines in the figure in (B) indicate threewhite matter tertiles: lowest volume group (open squares), middlevolume group (closed squares), and highest volume group (closedtriangle). Time 1 and time 2 reflect the two pre-infusion (baseline)sampling occasions (i.e., 10 min and 0 min prior infusion). Times 3–6reflect the four post-infusion measurement points at, respectively,60 min, 90 min, 120 min, and 150 min post-infusion.

49M. Marcelis et al. / Schizophrenia Research 86 (2006) 45–53

lower grey matter volume than in patients with highergrey matter volume. Adjustment for age, sex, totalbrain volume, and medication dosage did not affect theresults (β=−0.0041, p<0.005).

For white matter volume, a significant negative whitematter×condition× timeB interaction was found (β=−0.0032, p<0.046), indicating that the increase in HVAduring metabolic stress was stronger in patients withlower white matter volume than in patients with higherwhite matter volume. Adjustment for age, sex, totalbrain volume and medication dosage did not changeeffect size and associated significance level (β=−0.0031, p<0.039). Although the smallest increase in

HVA during stress was measured in the group with thehighest white matter volumes, plotting of HVA leveldifferences between 2DG and placebo conditions overtime separately for each tertile of white matter did notreveal a dose–response relationship (Fig. 2B).

For the measure of CSF volume, no significantCSF×condition× timeB interaction was apparent, al-though the direction of the effect was similar (β=−0.0008, p<0.80).

In order to examine whether the effect of grey mattervolume was independent of white matter volume andvice versa, both interaction terms were entered in theanalyses, which reduced both the effect size andstatistical significance of the interaction with greymatter volume, as well as of the interaction with whitematter volume (grey matter×condition× timeB: β=−0.0027, p<0.19; white matter×condition× timeB:β=−0.00149, p<0.47). This suggests that the effectsof grey and white matter volume on HVA reactivity arecorrelated.

4. Discussion

Total grey and white matter volume in patients withpsychotic disorder were negatively associated with HVAreactivity during metabolic stress, suggesting thatreduced grey and white matter volume lead to anenhanced DA/NA-mediated stress response. CSF wasnot significantly associated with HVA reactivity,suggesting that altered CSF volume does not affect theDA/NA-mediated stress response.

The metabolic stress paradigm has been usedpreviously in preclinical and clinical studies. Forexample, studies in rats and healthy volunteers haveshown a 2DG-induced increase in cerebral blood flow tomultiple cortical and subcortical regions (Breier et al.,1993a; Elman et al., 1999), as well as a 2DG-inducedincrease in striatal dopamine release using [11C] PET inhealthy subjects (Adler et al., 2000). The paradigm wasfirst applied to patients with schizophrenia by Breier etal. (Breier, 1989; Breier et al., 1993b), and their findingsof altered HVA reactivity in this patient group haverecently been replicated in a larger sample (Marcelis etal., 2004).

The association between grey matter volume andHVA reactivity to metabolic stress is consistent with aprior report on the relationship between decreased greymatter volume in the prefrontal cortex and excessiveHVA release in patients with schizophrenia, measuredduring similar stress conditions (Breier et al., 1993b). Ina sample of three times as many patients, and for the firsttime since the publication of Breier more than 10 years

50 M. Marcelis et al. / Schizophrenia Research 86 (2006) 45–53

ago, these findings have now been independentlyreplicated by the present study, in that reduced cerebralgrey matter alterations were associated with increasedplasma HVA levels during 2DG administration. Al-though subregions of grey matter such as the prefrontalcortex were not examined, the present investigationextends the earlier findings (Breier et al., 1993b) byinvestigating not only grey matter in relation to thestress measure, but also white matter and CSF.

White matter provides the physiological basis forcortico-cortical and subcortico-cortical connectionsand there is accumulating evidence for abnormalconnectivity in schizophrenia (Friston and Frith, 1995;Hubl et al., 2004). Recent investigations into theorganization of cerebral white matter are indicative ofdeficient intra- and interhemispheric connectivity inpatients with schizophrenia (Burns et al., 2003;Hulshoff Pol et al., 2004; Kubicki et al., 2003; Zhouet al., 2003). The present results showed thatdecreased white matter volume was associated withan enhanced DA/NA mediated stress response,although the evidence was less strong than for greymatter and might plausibly be attributed to thecorrelation between grey and white matter. Despitethe lack of clarity concerning the exact relationshipbetween grey and white matter, reductions in thesetissue volumes were associated with excessive DA/NArelease following metabolic stress.

Reduced grey matter may reflect widespread (in-cluding prefrontal) cortical volume loss. White matterreduction may indicate impairments in the connectionsbetween the (prefrontal) cortex and subcortical struc-tures. The present findings may fit the model postulatingthat stress-induced increases in mesocortical prefrontaldopamine activity are involved in regulating subcorticaldopamine activity, by exerting an inhibitory influenceon striatal dopamine. Indeed, reduced grey mattervolume in schizophrenia may impact on corticaldopamine function and diminish its “brake” functionon the striatal dopamine system, resulting in excessiverelease of striatal dopamine following even mild stress(Laruelle, 2000). The aberrant stress regulation systemin schizophrenia may be the consequence of primarydeficits of the prefrontal cortex, but could be the resultof abnormal inputs due to alterations in other regionssuch as mesotemporal structures, which are often foundto be affected in schizophrenia (Breier et al., 1992a;Heinz et al., 2003).

Thus, grey and white matter deficits may mediate thealtered HVA response to stress, assuming that theseglobal tissue alterations reflect dysfunctional cortico-subcortical circuitry (i.e., dysinhibition of striatal

dopamine release by loss of cortical control). Thismechanism is thought to be more pronounced duringperturbing than during resting conditions (Breier et al.,1993b).

However, as the present study yielded only indirectevidence by examining global tissue volumes inrelation to the DA/NA mediated stress response, thishypothesized dysfunctional neurocircuit involved instress regulation needs to be more directly tested usingtechniques such as positron emission tomography(PET) and single photon emission tomography(SPECT). Dopamine receptor imaging studies havealready produced direct evidence for a cortical originof the upregulated striatal dopamine function inschizophrenia (Kapur and Lecrubier, 2003). Whetherthe hypothesized DA dysregulation is reflective of astate, of a trait, or the combination of trait/state alsowarrants further investigation. Recent evidence sug-gests that both components are involved: a statecomponent associated with psychotic exacerbationsand a trait component present in remitted patients andin schizophrenia spectrum disorder (Abi-Dargham etal., 2004).

CSF volume, in contrast to grey and white mattervolume, was not associated with altered HVA reactivity.This suggests that altered CSF volume is not part of thesame neurobiological substrate that leads to an enhancedcentral stress response.

4.1. Methodological considerations

Much of the plasma HVA originates from central andperipheral noradrenaline (NA) systems. Even underfasting conditions, around 75% of plasma HVA derivesfrom NA neuronal metabolism (Kopin et al., 1988).Nevertheless, plasma HVA changes also reflects centraldopamine (DA) activity (Amin et al., 1992), or can atleast be regarded as a central response to stress (Marceliset al., 2004).

Global tissue volumes, and not specific brain areas,were investigated in relation to stress reactivity. In ameta-analysis, decreases in grey matter of around 2%and in white matter of around 1% have been found inpatients versus controls (Wright et al., 2000). Althoughthese grey and white matter changes are not equallydistributed but are more pronounced in certain areasthan in others, they are not specific to any particularbrain area, and findings regarding sub-areas of the brainare not as consistent as the findings regarding globalgrey and white matter changes. Thus, changes in globaltissue volumes are among the most robust in theliterature and are arguably most suitable in the search for

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associations between brain measures and clinicalvariables.

A possible shortcoming of the current study is theabsence of a control group which precludes definiteconclusions as regards the relevance of the findings forschizophrenia. However, investigating the functionalcorrelate of a structural brain abnormality is relevantand biologically plausible in a population that is knownto exhibit the abnormality in question (i.e., individualswith schizophrenia). This was our rationale forexamining the association between tissue volumes andstress-induced plasma HVA in patients only, similar tothe approach used in a previous report on theassociation between prefrontal cortex volume and2DG-induced HVA increase in patients with schizo-phrenia (Breier et al., 1993b). Moreover, the presentfindings have face validity, in that they replicate andsupport findings and hypotheses previously described inthe literature (Breier et al., 1993b; Kapur and Lecrubier,2003).

Almost all patients were taking an antipsychoticmedication that influences dopamine levels. However,patients with schizophrenia have a much stronger HVAincrease than controls during 2-DG exposure, indicatingthat (chronic) antipsychotic treatment does not precludestress-induced increases in dopamine function (Breier etal., 1993b; Marcelis et al., 2004). Moreover, antipsy-chotic medicated and non-medicated patients do notshow differences in HVA reactivity during metabolicstress (Breier et al., 1993b). Acute and chronicbenzodiazepine treatment has been found to diminishthe effect of stress-induced activation of the mesocor-tical DA system (Hegarty and Vogel, 1995). Ifbenzodiazepine use could have introduced a bias inthe present results, this would presumably have led to anunderestimation of the strength of the associationbetween tissue volume and HVA reactivity, as the latterwould have been stronger in the absence of benzodiaz-epine use.

It has recently been suggested that antipsychoticmedication may affect brain morphology (Dazzan etal., 2005; Lieberman et al., 2005). In the present study,we were not able to correct for lifetime medicationdose, but (1) adjustment for current antipsychoticdosage did not affect the strength nor the significanceof the three-way interaction term in the main analyses,and (2) there was no evidence of any direct effect ofcurrent dosage on the three types of brain tissuevolume. These findings make it unlikely that the dose–response association between tissue volume and stress-induced HVA increase can be fully explained by theeffects of antipsychotic medication.

4.2. Conclusion

This investigation explored whether changes in brainstructure in schizophrenia may affect central nervoussystem functioning through a dysregulated dopaminer-gic stress response. The robust measures of grey andwhite matter volume, but not CSF volume, werenegatively associated with the central stress response.The findings support the hypothesis that compromisedneurocircuits, in terms of dysfunctional cortico-subcor-tical connections, may provide the anatomical basis forstress-induced increases in striatal dopamine, whichmay consequently affect psychosis susceptibility. Neu-roreceptor imaging techniques, such as PETand SPECT,which can be used to more directly assess regionalcerebral dopamine concentrations and fluctuationstherein provide the tools to further test this hypotheticalpathway mediating the central stress response.

Acknowledgements

This study was supported by the Dutch Brain Societyand the Dutch Prevention Fund.

We thank Truda Driesen for her assistance in datacollection.

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