Schizophrenia

The Science of Mental Health

Steven E. Hyman

• Publisher: Routledge
• Year: 2001
• eBook ISBN: 9781136761324
• Topic: Psychology
• Subtopic: Mental Health in Psychology
• Index: Psychology

First published in 2002. Routledge is an imprint of Taylor & Francis, an informa company.

Lamina-Specific Alterations in the Dopamine Innervation of the Prefrontal Cortex in Schizophrenic Subjects

Mayada Akil, M.D., Joseph N. Pierri, M.S., M.D., Richard E. Whitehead, B.S., Christine L. Edgar, B.S., Carrie Mohila, B.S., Allan R. Sampson, Ph.D., and David A. Lewis, M.D.

Objective: Abnormalities in dopamine neurotransmission in the prefrontal cortex have been implicated in the pathophysiology of schizophrenia. However, the integrity of the dopamine projections to the prefrontal cortex in this disorder has not been directly examined. Method: The authors employed immunocytochemical methods and antibodies against tyrosine hydroxylase, the rate-limiting enzyme in dopamine biosynthesis, and the dopamine membrane transporter to examine dopamine axons in the dorsomedial prefrontal cortex (area 9) from 16 pairs of schizophrenic and matched control subjects. Results: Compared to the control subjects, the total length of tyrosine hydroxylase-immunoreactive axons was unchanged in the superficial and middle layers of the schizophrenic subjects but was reduced by an average of 33.6% in layer 6. The total length of tyrosine hydroxylase-positive axons in layer 6 was decreased in 13 of the schizophrenic subjects compared to their control subjects. Axons immunoreactive for the dopamine membrane transporter showed a similar pattern of change. In contrast, axons labeled for the serotonin transporter did not differ between schizophrenic and control subjects in any layer examined. In addition, the density of tyrosine hydroxylase-containing axons did not differ between monkeys chronically treated with haloperidol and matched control animals. Conclusions: These findings reveal that schizophrenia is associated with an altered dopamine innervation of prefrontal cortex area 9 that is lamina- and neurotransmitter-specific and that does not appear to be a consequence of pharmacological treatment. Together, these data provide direct evidence for a disturbance in dopamine neurotransmission in the prefrontal cortex of schizophrenic subjects.

(Am J Psychiatry 1999; 156:1580–1589)

In its original formulation, the dopamine hypothesis of schizophrenia posited that the psychotic symptoms of this disorder were due to a hyperdopaminergic state (1,2). This hypothesis has undergone substantial revisions as a result of recent advances in our understanding of the complexity of dopamine systems and of the pathophysiology of schizophrenia. For example, perturbations of the dopamine system in schizophrenia have been suggested to be in opposite directions in different brain regions (3), such that a hyperdopaminergic srate in subcortical structures coexists with a deficit in dopamine neurotransmission in the prefrontal cortex. The former has been proposed to account for the psychotic symptoms, and the latter has been proposed to contribute to the cognitive deficits and negative symptoms, that are characteristic of schizophrenia (4,5).

The normal function of the prefrontal cortex clearly depends on an intact dopamine innervation (6,7,8), and several lines of evidence suggest that the dopamine innervation of the prefrontal cortex may be abnormal in schizophrenia. For example, schizophrenic subjects have been shown to have altered levels of expression of rhe mRNAs for some classes of dopamine receptors in the prefrontal cortex (9,10). In addition, drug-naive schizophrenic subjects were reported to exhibit a decreased density of dopamine D₁-like receptors in the prefrontal cortex, and the density of receptors was directly associated with performance on a cognitive task, the Wisconsin Card Sorting Test (11), that is dependent on the function of the prefrontal cortex. This notion of a hypodopaminergic state in the prefrontal cortex of schizophrenic subjects is also supported by the observation that dopamine agonists increase prefrontal cortex blood flow and that these metabolic changes are associated with improved performance on the Wisconsin Card Sorting Test (12,13). Finally, chronic administration of phencyclidine, which mimics some symptoms of schizophrenia in humans, produces cognitive deficits and hypofunction of prefrontal cortex dopamine in monkeys (14). However, despite the substantial interest in the role of prefrontal cortex dopamine in the pathophysiology of schizophrenia, the integrity of dopamine afferents from the mesencephalon to the prefrontal cortex has not previously been examined in schizophrenic subjects.

We and others have previously described the dopamine innervation of the primate prefrontal cortex by using immunocytochemical methods and antibodies directed against dopamine, the dopamine membrane transporter, or tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis (15,16,17,18,19). In both monkeys and humans, dopamine afferents innervate all regions of the prefrontal cortex, with labeled axons being particularly dense in the dorsomedial region, area 9. In the present study, we used a similar approach to evaluate the relative density and laminar distribution of dopamine axons in postmortem specimens of area 9 from matched pairs of schizophrenic and normal control subjects.

METHOD

Human Tissue Specimens

Postmortem tissue specimens from 32 human brains were obtained during autopsies conducted at the Allegheny County Coroner’s Office. Written informed consent for brain donation and diagnostic interviews was obtained from the next of kin. These procedures were approved by the University of Pittsburgh’s Institutional Review Board for Biomedical Research.

Neuropathological examination revealed abnormalities in four subjects. In three (subjects 207. 213, and 313), occasional neuritic plaques were identified in the neocortex. However, the density of the plaques was insufficient to meet the diagnostic criteria for Alzheimer’s disease, and none of the subjects had a clinical history of dementia. The cause of death involved brain damage in two subjects (subject 207: subdural hematoma in the left parietal region; subject 517: vascular malformation and hemorrhage confined to the right temporal lobe), but no neuropathological abnormalities were detected in either subject in the region of interest for this study.

Consensus DSM-III-R diagnoses were made by an independent panel of experienced clinicians, who used information obtained from clinical records and structured interviews with one or more surviving relatives of each subject (20). Sixteen of the subjects had a diagnosis of schizophrenia or schizoaffective disorder (table 1). One of the schizophrenic subjects (subject 234) had never been medicated; three (subjects 537, 621, and 207) had nor taken neuroleptics for 10 months, 8 years, and 10 years, respectively, before death; and another subject (subject 185) was known to have been noncompliant with prescribed medications. The absence of medication in these subjects was confirmed by toxicology screens conducted on all subjects at the time of death. Two schizophrenic subjects (subjects 428 and 517) were being treated with rhe atypical antipsychotic agent clozapine at the rime of death, and the remaining nine schizophrenic-subjects were receiving typical neuroleptics.

As shown in table 1, each schizophrenic subject was matched to one control subject for gender (the ratio of men to women was 10:6 in both groups) and race (with the exception of pair 16). Subjects were also matched as closely as possible for age and postmortem interval. The schizophrenic and control subjects did not differ in mean age (53.8 years, SD=9.4. and 54.6 years, SD=9.2, respectively) or postmortem interval (9.4 hours, SD=3.9, and 9.2 hours, SD=4.7, respectively). One control subject (subject 245) had a history of alcohol dependence. The remaining 15 control subjects had no known neurological, psychiatric, or substance abuse histories.

Tissue Preparation and Immunocytochemical Procedures

The left frontal lobe of each brain was cut into 1.0-cm-rhick coronal blocks. Blocks were immersed in cold 4% paraformaldehyde in phosphate buffer for 48 hours and then stored in a cryo-protectant at −30°C (20). Mean tissue storage time in cryopro-tectant did not significantly differ between schizophrenic (.51.0 months, SD=21.9) and control (43.4 months, SD=28.9) subjects. In addition, previous studies have demonstrated that tissue storage under these conditions does not alter immunorcactivity for the antigens examined in this study (21). Blocks were sectioned coronali)-at 40 pm, and every 10th section was stained for Nissl substance with thionin. These sections were used to identify the location of area 9 on the superior frontal gyrus through use of the cytoarchi-tectonic criteria (20).

Floating tissue sections were processed for tyrosine hydroxylase or serotonin transporter immunoreactivity by using the avidin-biotin procedure and the Vectastain ABC Elite kit (Vector Laboratories, Budingame, Calif.), as previously described (22), or for dopamine membrane transporter immunoreactivity by using a modification of the biotin amplification procedure (23). Tissue sections from each matched pair of schizophrenic and control subjects were always processed together. All slides were coded to conceal the subject number and diagnosis. The following antibodies were used in this srudy. 1) An affinity-purified sheep IgGl antibody (supplied by Dr. J. Haycock, Louisiana State University, New Orleans), raised against tyrosine hydroxylase purified from rat pheochromocytoma (24), was used at a concentration of 0.7 µg/ml. 2) A rat antibody (Chemicon, Temecula, Calif.), raised against a fusion protein containing the N-terminus of the human dopamine membrane transporter protein (25), was used at a dilution of 1:2,000. 3) A rabbit antibody, raised against a fusion protein containing the carboxy-terminus of the human serotonin transp...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Introduction
• Overview
• Epidemiology
• Genetics
• Natural History
• Brain Development
• Neurobiology of Disease
• Treatment
• Acknowledgments