Neuropeptide deficits in schizophrenia vs. Alzheimer's disease cerebral cortex

ORIGINAL ARTICLES i

Neuropeptide Deficits in Schizophrenia Alzheimer's Disease Cerebral Cortex

VS.

Steven M. Gabriel, Michael Davidson, Vahram Haroutunian, Peter Powchik,

Linda M. Bierer, Dushyant P. Purohit, Daniel P. Perl, and Kenneth L. Davis

Neuropeptide concentrations were determined in the postmortem cerebral cortex from 19 cognitive-impaired schizophrenics, 4 normal elderly subjects, 4 multi-infarct dementia (MID) cases, and 13 Alzheimer's disease (AD) patients. Only AD patients met criteria for AD. The normal elderly and MID cases were combined into one control group. Somatostatin concentrations were reduced in both schizophrenia and AD. Neuropeptide Y concentrations were reduced only in schizophrenia, and corticotropin-releasing hormone concentrations were primarily reduced in AD. Concentrations of vasoactive intestinal polypeptide and cholecystokinin also were reduced in schizophrenia, although not as profoundly as somatostatin or neuropeptide Y. In AD, cholecystokinin and vasoactive intestinal peptide were unchanged. Neuropeptide deficits in schizophrenics were more pronounced in the temporal and frontal lobes than in the occipital lobe. The mechanisms underlying these deficits in schizophrenia and AD are likely distinct. In schizophrenia, a common neural element, perhaps the cerebral cortical gaba-aminobutyric acid (GABA)-containing neuron, may underlie these deficits.

Key Words: Schizophrenia, Alzheimer's disease, somatostatin, neuropeptide Y, vasoactive intestinal polypeptide, corticotropin-releasing hormone, cholecystokinin, gamma aminobutyric acid

B I O L PSYCHIATRY 1996;39:82-91

Introduction

The identification of behaviorally active neuropeptides has naturally sparked interest in their role in brain disorders. Neurodegenerative diseases of aging that are characterized by well-defined end point diagnostic criteria, like Alzhei- mer's disease (AD), have received the most attention. In

From the Departments of Psychiatry, Mount Sinai School of Medicine, New York, New York, and Bronx Veterans Affairs' Medical Center, Bronx, New York.

Address reprint requests to Steven M. Gabriel, Ph.D., Department of Psychiatry, Bronx Veterans" Affairs Medical Center, 130 West Kingsbridge Road, Bronx, NY 10468.

Received April 6, 1994; revised October 14, 1994.

addition to the loss of cholinergic projection neurons (Perry et al 1978; White et al 1977), neuropeptide- containing neurons appear affected in AD. This is reflected in a pronounced decline in somatostatin and corticotropin-releasing hormone concentrations, among others (Davies et al 1980; De Souza et al 1986; Bissette et al 1985; Arai et al 1984; Beal et al 1986b; Crystal and Davies 1982). The postmortem investigation of neuropeptides in schizophrenia must additionally contend with an institutionalized population expressing life long heteroge- neous symptoms. Nevertheless, cerebral cortical concentrations of somatostatin are reduced in schizophrenics as in AD (Nemeroff et al 1983; Roberts et al 1983). The

© 1996 Society of Biological Psychiatry 0006-3223/96/$15.00 SSDI 0006-3223(95)00066-P

Peptides in Schizophrenia vs. AD BIOL PSYCHIATRY 83 1996;39:82-91

Table 1. Demographic Characteristics of the Subject Groups

A g e (years; PMI Gender CDR

Group n mean 4- sd) (mean -+ sd) (M/F) (mean 4- sd)

Elderly control 8 82.6 4- 9.1 361 4- 139 2/7 0.94 4- 1.49

Alzhe imer ' s 13 71.0 - 9,2 438 4- 258 10/3 4.45 4- 0.69

disease

Schizophrenia a 19 75.8 4- 12.7 1778 4- 347 10/9 2.16 + 1.25

~AI1 schizophrenics had prolonged exposure to neuroleptic medication during chronic institutionalization; 8 of these patients were not treated with neuroleptics at least 6 months prior to death. There was no difference between neuroleptic (n = 11) and off-neuroleptic groups (n = 8) for any of the five neuropeptides (all p values > 0.12).

localization of cholecystokinin within dopamine neurons and its pharmacological interactions with dopamine suggests a role for this neuropeptide in schizophrenia (Nair et al 1985). Indeed, cholecystokinin deficits have been noted in schizophrenic brains and cerebral spinal fluid (Roberts et al 1983; Lieberman and Koreen 1993) while cholecystokinin analogues have been tested for the amelioration of schizophrenic symptoms (Lieberman and Koreen 1993). Other behaviorally active peptides, such as neuropeptide Y and vasoactive intestinal polypeptide, have been studied in postmortem schizophrenic brains as well (Widerlov et al 1988; Zech et al 1986; Roberts et al 1983).

The nature of the association between peptidergic abnormalities and neural function is far from elucidated. Beyond the demonstration of behavioral effects of peptides in animal models that imply a role in clinical conditions, neuropeptides have proven useful as markers of neuronal populations and their activity. In degenerative brain disorders, changes in postmortem tissue concentrations of some neurochemicals appear to reflect cell loss (Davies et al 1990; Chan Palay 1987). Yet many studies in patients with AD suggest that cortical neurons are not simply lost, but are dystrophic (Nakamura and Vincent 1986; Chan Palay et al 1985; Kelley and Kowall 1989; Unger and Lange 1992). In these neurons, abnormal neuropeptide concentrations could derive from alterations in expression or activity. For schizophrenia, similar decreases in neurochemicals may reflect expression, cell loss, or synaptic alterations at any time during the life span, as well as altered distribution of neurons during development (Carpenter et al 1993).

We have begun the antemortem characterization of a large population of chronically institutionalized elderly schizophrenics. This first antemortem examination of neuropeptide concentrations in this group consists largely of schizophrenics exhibiting global cognitive impairment. Cognitive impairment is a common finding in elderly schizophrenics and recent evidence suggests that it does not simply reflect the additional insult of a degenerative illness, like AD (Powchik et al 1993; Purohit et al 1993; Arnold et al 1993). The present study measured five

neuropeptide immunoreactivities in the frontal and temporal lobes, which have been implicated in schizophrenia (Carpenter et al 1993), and in the occipital lobe, which is not usually implicated. It was hypothesized that peptide abnormalities would be most pronounced in the frontal and temporal lobe tissues of schizophrenics. It was further hypothesized that at least some of the peptidergic abnormalities will be illness-specific. Therefore, the schizophrenic patients were compared not only to elderly subjects but also to a group of patients with AD who share the common symptom of cognitive impairment.

Materials and Methods

Brain bank tissues were obtained from the Departments of Psychiatry at the Mount Sinai and the Bronx Veterans' Affairs Hospitals. The schizophrenics were chronic inpa- tients, while the elderly control group and patients with AD were nursing home residents. Patients were classified as schizophrenics if the presence of schizophrenic symptoms could be documented before age 40, the medical records contained specific examples of the psychotic symptoms and evidence of at least 10 years of psychiatric hospitalization with a diagnosis of schizophrenia, the Diagnostic and Statistical Manual of Mental Disorders, 3rd ed., revised, (DSMIII-R) diagnosis of schizophrenia was agreed upon by two experienced clinicians, and the tissue did not meet criteria for AD or any other known degenerative disorder. This assessment was based on retrospective chart review conducted within several weeks of death as described previously (Powchik et al 1993). All patients with AD met criteria for AD (Khachaturian 1985; Mirra et al 1991). The elderly control group consisted of normal subjects (n = 4) and patients with multi-infarct dementia (MID) (n = 4). The normal subjects had no chart review evidence of dementia, neuropathologic signs, or psychiatric illness, while the patients with MID had chart review evidence plus neuropathologic findings of cerebro- vascular disease and multiple infarcts sufficient to account for a dementia. Schizophrenic and AD subjects were assessed for the severity of cognitive impairment using the

84 BIOL PSYCHIATRY S.M. Gabriel et al 1996;39:82-91

Table 2. Parameters for the Five Radioimmunoassays"

Coefficients of variation (%)

Sensitivity EDso (pg/ Assay (pg/Tube) Tube) Intraassay Interassay

Somatostatin b 0.8 9.9 5 19 Neuropeptide yc 15 160 6 22 CRH a'g 1.0 11.8 3 11 VIW 'g 0.4 4.3 3 19 Cholecystokinin fg 3.9 101.7 3 19

"For all assays: (l) = code, lot; (2) = final titer; (3) = relevant % cross-reactivities; <0.01% unless otherwise noted.

b(1) SSRb#4, 3-7-83; (2) 1:100,000; (3) 100% for somatostatin~l_t4~ and somatostatin(l_285.

c(1) NPY#I, 11-14-85; (2) 1:30,000; (3) 0% for pancreatic polypeptide with Dupont NEX-222 radiolabel.

a(l) 8561N, 006803-5; (2) 1:144,000; (3) 100% to human CRH, 0.01% to frog sauvagine.

"(1) 716lN, 020944-6; (2) 1:450,000; (3) 100% to human VIP, 100% to VIP(lo 285.

I(1) 7181N, 027249-1; (2) 1:27,000; (3) 100% for nonsulfated cholecystokinin(26-33), ch°lecyst°kinin~t 335, cerulein, gastrin, and big gastrin; 78% for sulfated cholecystokinin(26_33 ), 63% for cholecystokinin(27_335, 14% for cholecystokinin~3o_33 ) and human pancreatic polypeptide.

gAssays were performed in polypropylene tubes (#57.512, Sarsdedt) in 0.1M sodium phosphate pH 7.4, with 100mM NaCI, 10mM EDTA, 0.1% bovine serum albumin, 0.02% sodium azide, and 0.1% Triton X-100. Tracer addition (2500 cpm) was delayed 72 hours after incubation at 4°C. Separation was achieved 24 hours thereafter with goat anti-rabbit "t-globulin (1:80 final, Linco Research, St. Louis, MO) diluted in 5% polyethylene glycol.

Clinical Dementia Rating Scale (CDR) (Hughes et al 1982). Table 1 describes the demographic and clinical characteristics of the subjects. The CDR scores indicate that the schizophrenic group was cognitive-impaired, although with a much greater range than the patients with AD. The patients with AD all were severely demented, which would be expected at the end stage of this illness. The age at death for the elderly control group was nominally greater, the postmortem interval (PMI) between the groups was significantly different (p < 0.001, df =

2,38, F = 8.6) as was the gender distribution between groups (p < 0.02, df = 2,37, F = 4.51). Therefore, these three covariables were included in all model testing (analysis of variance for repeated measures) and within region multiple comparison (Tukey, p < 0.05) procedures.

The six left hemispheric gyri surveyed were limited to within gyms Brodmann areas, as defined using anatomical maps. They were the superior frontal gyms corresponding to Brodmann 8 (F8), the cingulate gyms corresponding to the combination of Brodmann 24 and Brodmann 32 (F24), the inferior frontal gyms corresponding to Brodmann 44 (F44), the superior temporal gyms corresponding to Brod- mann 22 (T22), the parahippocampal gyms corresponding to Brodmann 36 (T36), and the superior parietal gyms corresponding to occipital Brodmann 17 (O17). In these dissections, no more than a I mm white matter border was included and no visible infarcts were included. The right hemisphere is used for neuropathological examination and

was not processed for neurochemistry. Samples were processed blind with respect to diagnosis. Individual samples were heat-extracted in 0.1N HC1 (Gabriel et al 1993). This method is suitable for the extraction of cholecystokinin (data not shown). All measures were obtained from a single supernatant extract using the radioimmunoassays described in Table 2. Data were nor- malized relative to total protein, as determined in the acid-insoluble extraction precipitate plus residual extract (Lowry et al 1951). Somatostatin-like immunoreactivity (somatostatin) and neuropeptide-Y-like immunoreactivity (neuropeptide Y) were determined as described previously (Gabriel et al 1993). Tissue concentrations of corticotropin releasing hormone-like immunoreactivity (CRH), vasoactive intestinal polypeptide-like immunoreactivity (VIP), and nonsulfated cholecystokinin octapeptide-like immunoreactivity (cholecystokinin) were determined using re- agents from Peninsula (Belmont, CA) after within-labora- tory standardization.

Figure 1. Cerebral cortical concentrations of somatostatin from elderly control subjects, schizophrenics, and patients with AD. Significant effects were found for diagnostic group (p < 0.00001, df = 2,33, F = 19.75), region (p < 0.00001, df = 5,180, F = 33.26), and the diagnostic group by region interaction (p < 0.0002, df = 10,180, F = 4.33). aln the elderly control group concentrations of somatostatin in the three highest (F44 and temporal lobe) regions were different from both F8 and O17. For AD patients, T36 was greater than any other region. Significant decreases in somatostatin concentrations within an individual region were observed in AD vs. the elderly control group for F24 (47%), F44 (47%), T22 (40%), and T36 (25%), and for schizophrenia vs. the elderly control group for F24 (45%), F44 (51%), T22 (66%), and T36 (51%). When MID cases were excluded from this analysis, the difference between AD cases and the elderly control group in T22 was not significant. All individual group comparisons are p < 0.05.

I I CONTROL ~ 1 A!_ZHEIMER'S

._~ 6 ~ SCHIZOPHRENIA

==5 E

~ 4 Z

F8 F24 F44 T22 T36 O 17

BRODMANN REGION a

Peptides in Schizophrenia vs. AD B1OL PSYCHIATRY 85 1996;39:82-91

.~ 100 [ ~ CONTROL ALZHEIMER'S

I SCHIZOPHRENIA

8o

I

a

~ 20 Z

F8 F24 F44 T22 T36 O17

B R O D M A N N REGION a

Figure 2. Cerebral cortical concentrations of neuropeptide Y from elderly control subjects, schizophrenics, and patients with AD. Significant effects were found for diagnostic group (p < 0.00001, df = 2,32, F = 17.31), region (p < 0.00001, df = 5,175, F --- 95.04), and the diagnostic group by region interaction (p < 0.00001, df = 10,175, F = 6.05). aWithin each diagnostic group, neuropeptide Y concentrations in F8 and O17 were significantly lower than the other four regions (other frontal and all temporal). Within-region significant decreases in neuropeptide Y concentrations in schizophrenia patients vs. the elderly control group were found for F24 (39%) and T22 (40%). All individual group comparisons are p < 0.05.

Results

Figures 1-5 present the neuropeptides for six Brodmann regions ordered from left to right by frontal, temporal and occipital regions. Analysis of variance failed to reveal any difference between the normal elderly and MID patient groups (somatostatin, p > 0.97, df = 1,6, F = 2.51; neuropeptide Y, p > 0.58, df = 1,6, F = 0.33; cholecystokinin, p > 0.94, df = 1,6, F = 0.006; VIP, p > 0.88, df = 1,6, F = 0.05; CRH, p > 0.07, df = 1,6, F = 4.51). Therefore, these two subject groups were combined as one elderly control group for the analyses shown in Figures 1-5. For these data, additional analyses in which the MID cases were excluded (i.e., the elderly control group included only four normal elderly cases) did not significantly alter the main effects or the within-region diagnostic group differences (data not shown).

The pattern of neuropeptide concentrations in these cognitive-impaired schizophrenics reveals a broad-based multiple peptide deficit syndrome. The decrements in somatostatin were most pronounced of the five neuropeptides and were decreased in all six of the regions evalu- ated. Pervasive, but not as pronounced, decrements in cholecystokinin and neuropeptide Y were also evident. Less dramatic were VIP concentrations, which were only lower within individual regions when compared to the AD

groups. The concentrations of CRH were different from controls in only one region examined: F24. This neuropeptide deficit pattern for schizophrenia contrasts with AD, which shows profound decrements in somatostatin and CRH across the six cortical regions examined, but little or no change in the three other neuropeptides: cholecystokinin, V1P, and neuropeptide Y. Therefore, somatostatin and neuropeptide Y concentrations show the largest schizophrenia vs. control effect sizes (1.7-2 in T20). While the group differences were large, the numbers of cases within the schizophrenic group was small (n = 19). Based on a power analysis, this number of cases is insufficient to obtain meaningful correlations with CDR.

Discussion

These present data demonstrate pervasive neuropeptide deficits in the postmortem cerebral cortex from elderly cognitively impaired schizophrenics. Immunoreactivities to somatostatin, neuropeptide Y, cholecystokinin, VIP, and CRH are all localized to a varying degree within cortical gamma-aminobutyric acid (GABA)-containing interneurons (Ong and Garey 1991; Dennison-Cavanagh et al 1993; Foley et al 1992; Rogers 1992). The magnitude of each peptide deficit in schizophrenia corresponds well with the relative localization of that peptide within these GABA-containing interneurons. Investigations of neuro-

Figure 3. Cerebral cortical concentrations of cholecystokinin from elderly control subjects, schizophrenics, and patients with AD. Significant effects were found for the diagnostic group (p < 0.002, df = 2,33, F = 7.32), region (p < 0.00001, df = 5,180, F = 36.01), and diagnostic group by region interaction (p < 0.02, df = 10,180, F = 2.11). aSignificant decreases in cholecystokinin concentrations in schizophrenia vs. the elderly control group were detected for F44 (29%), T22 (37%), and T36 (38%). All individual group comparisons are p < 0.05. The nominal individual differences between the AD vs. elderly control group were not significantly different within an individual region.

r - - I CONTROL I I ALZHEIMER'S

6 I SCHIZOPHRENIA

~ 4

0

F8 F24 F44 T22 T36 O17

BRODMANN REGION a


0.8 - - I CONTROL

0.7 ~ ALZHEIMER'S S C H I Z O P H R E N I A

.c_ 0,6

~ 0 . 5 E ~ o.4

I 0. .~ 0.3

0.2

0.1

F8 F24 F44 T22 T36 O17

BRODMANN REGION a

Figure 4. Cerebral cortical concentrations of VIP from elderly control subjects, schizophrenics, and patients with AD. Signifi- cant effects were found for the diagnostic group (p < 0.03, df = 2,33, F = 3.96) and region (p < 0.00001, df = 5,180, F = 76.77), but not the interaction between the group and region (p < 0.10, df = 10,180, F = 1.65). "Within each patient group, the VIP concentrations in F8 and O17 were significantly lower than the three temporal lobe regions. Although VIP concentrations were significantly lower within regions for schizophrenia vs. AD for T22 and T36, there were no significant differences between schizophrenia and the elderly control group for any region. All individual group comparisons are p < 0.05.

nal and synaptic populations in the cerebral cortex suggest the presence of neuropeptides in GABAergic cells in descending order of abundance as substance P, somatostatin, and neuropeptide Y, with VIP and cholecystokinin present in lesser abundance (Dennison-Cavanagh et al 1993; Foley et al 1992). The pattern of neuropeptide deficits, in the present study, does not fit the alternative explanation of a disorder of multiple neuropeptide-containing cortically projecting afferents. For example, if these deficits were due to a noradrenergic involvement, it would be expected that both neuropeptide Y and galanin would be altered (Gabriel et al 1994; Chan Palay et al 1990). The lack of VIP or galanin deficits likewise fits our previous observation that cholinergic neurons are not deficient in schizophrenia (Haroutunian et al 1993). Thus, these data suggest a defect in neuropeptide expressing, GABA-containing neurons in the cerebral cortex of schizophrenics. This hypothesis is supported by observations of deficits in small interneurons in the prefrontal and cingulate cortices of schizophrenics, and the likely result of this GABA-contalning interneuron loss: an increase in the numbers of GABA A receptors (Benes et al 1991, 1992).

Immunoreactivity for somatostatin is most exclusively found within nonpyramidal cortical interneurons and is

largely not reported within cortical afferents (Hornung et al 1992; Rogers 1992; de Lima and Morrison 1989; Kaneko et al 1992). Although neuropeptide Y appears to be contained exclusively within interneurons that are also somatostatin-immunoreactive, neuropeptide Y is also contained within cholinergic and noradrenergic afferents (Chronwall et al 1984; Chan Palay 1987; Kowall and Beal 1988; Dennison-Cavanagh et al 1993; Foley et al 1992; Rogers 1992; Chan Palay et al 1990). As a result, neuropeptide Y deficits are less pronounced in schizophrenics in the present study. The less pronounced deficits in cholecystokinin and VIP immunoreactivities in schizophrenics may likewise be due to their additional presence within subcortical afferents and intracortical neurons associated with the cerebral vasculature (Eckenstein and Baughman 1984; Uddman and Edvinsson 1989; Senut et al 1989; Ong and Garey 1991; Nair et al 1985; Seroogy et al 1989). Corticotropin-releasing hormone, which was unchanged in all but one brain region of schizophrenics, is expressed in low concentrations within a small population of GABA-containing interneurons (Rogers 1992). The one region that did exhibit a decline in CRH immunoreactivity in schizophrenia was the cingulate cortex. This brain area has been implicated as showing pronounced abnormalities in interneuron populations in schizophrenia and possible involvement in the negative symptoms of this disease (Benes et al 1991).

Figure 5. Cerebral cortical concentrations of CRH from elderly control subjects, schizophrenics, and patients with AD. Signifi- cant effects were found for the diagnostic group (p < 0.001, df = 2,33, F = 8.46), region (p < 0.00001, df = 5,180, F = 16.7), and the group by region interaction (p < 0.00001, df = 10,180, F = 5.52). CRH concentrations were significantly lower for AD vs. the elderly control group in F8 (46%), F24 (57%), T44 (59%), T22 (54%), and T36 (45%). CRH concentrations were significantly lower for schizophrenia vs. the elderly control group in F24 (24%). All individual group comparisons are p < 0.05.

0.35

CONTROL 0.30 ~ ALZHEIMER'S

~ SCHIZOPHRENIA r -

0,25 e~

E 0.20

3- 0.15 n~

o.10

0.05

F8 F24 F44 "22 T36 O17

BRODMANN REGION a


The inclusion of AD cases as a disease control group for schizophrenia proved useful. Although antemortem cognitive measures have only recently been performed on elderly schizophrenic patients, they share with AD patients a profound cognitive impairment. We and others have demonstrated that brain tissue from schizophrenics, on the whole, does not display the usual neurohistological markers known to correlate with common forms of dementia: plaques, tangles, Lewy bodies, infarcts, and ALZ-50 immunostaining (Purohit et al 1993; Powchik et al 1993; Arnold et al 1993). In AD, the loss of acetylcholine- containing neurons most clearly relates to cognitive decline (Perry et al 1978). The profound decrease in cortical cholinergic activity markers that is the hallmark of AD is not present in cerebral cortical tissues of cognitive-impaired schizophrenics (Haroutunian et al 1993). Despite the exclusion of schizophrenic cases with AD-like changes, the schizophrenic group in the present study exhibited cognitive impairment.

This results in one common known substrate, somatostatin, being diminished in both disease populations. This neuropeptide has been shown to be decreased in the brain tissues and cerebral spinal fluid of patients with neurologic disease, including schizophrenia, and may therefore be a generalized marker for many brain disorders associated with cognitive impairment (Alhainen et al 1991; Reinikainen et al 1990; Beal et al 1985; Tamminga et al 1987). In the present small patient populations, no significant correlations were found between somatostatin and CDR in schizophrenics or in the maximally impaired AD group (data not shown). A definitive answer must await the study of a large patient cohort displaying the full range in the CDR scale. At present, it is not clear whether the somatostatin deficits in schizophrenia and AD are related to each other, or to cognition in general. They may reflect changes in separate neuronal populations. This is supported by the discordant reductions in neuropeptide Y concentrations in AD and schizophrenia. Concentrations of neuropeptide Y in patients with AD and the elderly control group were virtually identical in all six cerebral cortical regions, as we have reported previously in a separate experiment (Gabriel et al 1993).

The pattern of distribution and colocalization for somatostatin and neuropeptide Y is the most extensively studied of the neuropeptides presented here. The present study did not find significant correlations between neuropeptide Y and somatostatin concentrations in any region (data not shown). This is not unexpected because neuropeptide Y is contained within a larger set of somatostatin-containing neurons (Chronwall et al 1984; Chan Palay 1987), and as well as cortically projecting afferents (Chan Palay et al 1990). However, the majority of these intrinsic somatostatin plus neuropeptide Y-containing neurons in the cerebral

cortex also exhibit nicotinamide-adenine dinucleotide phosphate (NADPH)-diaphorase activity (Unger and Lange 1992; Vincent et al 1983). The NADPH diaphorase enzyme is identical to nitric oxide synthase (Hope et al 1991), and appears to be associated with neurons resistant to degeneration (Hyman et al 1992; Ferrante et al 1985; Unger and Lange 1992). A large subpopulation of somatostatin-containing neurons that are neither neuropeptide Y or NADPH staining may be diminished in AD (Gaspar et al 1989). The present data suggest that the somatostatin- containing neurons affected in AD do not express neuropeptide Y, while in schizophrenia additional neurons, perhaps expressing both somatostatin and neuropeptide Y, may be involved. A recent report suggests that NADPH- staining neurons show an altered distribution in the postmortem cerebral cortex of schizophrenics (Akbarian et al 1993). This would indicate that disturbed neuronal development may contribute to schizophrenia. Therefore, neurons containing somatostatin, neuropeptide Y, and, perhaps, nitric oxide synthase may represent a subpopulation of neurons not lost but abnormally distributed in schizophrenia. The involvement of this unique class of neurons in schizophrenia would suggest new sites for pharmacological intervention.

The inclusion of both normal elderly and patients with MID in the elderly control group is a necessary compro- mise that reflects the great difficulty in obtaining normal subjects for postmortem studies. However, no neuropeptide measure was significantly different between the two groups that constituted the elderly control group. Further- more, the exclusion of the MID cases did not change the results of the overall analysis, despite reducing the control group by one-half. Previously, cerebral spinal fluid concentrations of somatostatin were found to be reduced in patients with MID compared to controls (Beal et al 1986a). Similar reductions in tissue concentrations of neuropeptides in this patient population have not been reported. Several points argue against the contribution to the data of such phenomena as gender, age, and postmortem interval (PMI) differences, tissue shrinkage, or inappropriate control or patient populations. Studies that simulate autopsy conditions suggest that neuropeptide concentrations are stable over the range of PMI for the present study (Beal et al 1986c; Emson et al 1981). There were no global or generalized reductions in the concentrations of all peptides in the schizophrenic group, which might be expected owing to the longer PMI. For example, CRH was largely unchanged in schizophrenics relative to the elderly control group, despite pronounced reductions in CRH in patients with AD in this and previous studies (Bissette et al 1985; De Souza et al 1986). A sixth neuropeptide measured in these same extracts, human galanin-like immunoreactivity, was unchanged in schizophrenics compared to controls


(Gabriel et al 1994), although this contrasts with recent report (Frederiksen et al 1991).

The present report confirms previous observations of postmortem cerebral cortical deficits in somatostatin and CRH concentrations in AD and multiple neuropeptides in schizophrenia (Bissette et al 1985; De Souza et al 1986; Davies et al 1980; Roberts et al 1983; Nemeroff et al 1983; Frederiksen et al 1991). The present findings are bolstered by the measurement of five neuropeptides in a single acidic tissue extract, which permits more direct comparison between neuropeptides while reducing interpatient and interbatch variation. These data are not without differences with previous work. This is most notable regarding the variable of effects of neuropeptide Y in AD (Gaspar et al 1989; Allen et al 1984; Dawbarn et al 1986; Nakamura and Vincent 1986; Chan Palay et al 1985; Beal et al 1986b; Gabriel et al 1993). It is uncertain why such differences exist, although this may reflect differences between late- and early-onset AD and cohort size (Beal et al 1988; Mann et al 1984). A more extensive report of the temporal pole and subcortical regions including hippocampus and amygdala found no changes in somatostatin or neuropeptide Y in schizophrenia (Beal et al 1987). Although cerebrospinal fluid concentrations of neuropeptide Y have been reported to be unchanged in schizophrenics (see Lieberman and Koreen 1993, for review), two studies that report a restricted number of cortical regions suggest that neuropeptide Y is reduced in the temporal cortex (Frederiksen et al 1991; Widerlov et al 1988). In most studies, VIP has not been found to be reduced in AD (Ferrier et al 1983; Rossor et al 1980), although one study found decreases in insular and angulate cortex (Arai et al 1984), regions not studied here. In schizophrenics, VIP has been found to be unchanged in the cerebral cortex but increased in the amygdala, particularly in patients with negative symptoms (Roberts et al 1983; Zech et al 1986). Cholecystokinin concentrations have been largely but not unanimously unchanged in patients with AD (Rossor et al 1981; Perry et al 1981; Ferrier et al 1983; Mazurek and Beal 1991), and, not without exceptions, decreased in schizophrenics (Perry et al 1981; Roberts et al 1983; Nair et al 1985).

Our finding of multiple neuropeptide deficits in schizophrenia implicates dysfunction of cortical interneurons, probably GABAergic. Considerable evidence suggests that the frontal and temporal cortex are key structures affected in schizophrenia (Carpenter et al 1993). The temporal lobe of our elderly control group contained the highest concentrations of somatostatin and neuropeptide Y, while these same peptides displayed the most pronounced reductions in the temporal cortex. Of the neuropeptide deficits associated with schizophrenia, only cholecystokinin was significantly decreased in occipital cortex of schizophrenics. Because of the close association of cholecystokinin with dopamine (Nair et al 1985), this generalized deficit may be related to chronic neuroleptic treatment. Long-term neuroleptic exposure has been shown to change neuropeptide expression in animals (Perez-Oso et al 1990; Miyake et al 1990). Although the length of time off of neuroleptics was brief, this study (see Table 1) and others suggest that neuroleptics are not the likely cause of postmortem changes in schizophrenia (Benes et al 1992; Frederiksen et al 1991). Although the deficits in these peptides largely correspond to their colocalization within cortical GABAergic neurons, the data could, as an alternative, implicate a specific subset of GABA and somatostatin-containing neurons. At present it is not clear whether these peptidergic subsets vary accord- ing to state, as is the case with neuroendocrine neurons (Sawchenko et al 1984). Besides cognitive impairment, possible state changes in schizophrenics that could be reflected in differences in peptide expression include specific symptoms, social deprivation, and isolation due to chronic institutionalization and neuroleptic drug history. This initial schizophrenic cohort was too small to associate neuropeptide changes conclusively with any disease pa- rameter, but provide a basis for future investigations on larger antemortem assessed patient cohorts.

The authors acknowledge the excellent technical assistance of Mrs. Debra Lazarus and Mrs. Nancy Ruiz.

This work was supported by federal grants VA5118 and MH46436 (MD), and AG02219, AG05138, MH45212, and VA4125 (KLD).

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Neuropeptide deficits in schizophrenia vs. Alzheimer's disease cerebral cortex