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It has been hypothesized that a deficit in serotonin may be a crucial determinant in the pathophysiology of major depression. Serotonin-1A receptors are located on serotonin cell bodies in the midbrain dorsal raphe (DR) nucleus, and the activation of these receptors inhibits the firing of serotonin neurons and diminishes the release of this neurotransmitter in the prefrontal cortex. Repeated treatment with some antidepressant medications desensitizes serotonin-1A receptors in the rat midbrain. The present study determined whether the binding of [, an agonist at serotonin-1A receptors, is altered in the midbrain of suicide victims with major depression. Radiolabeling of the serotonin-1A receptor in the DR varied significantly along the rostral-to-caudal extent of the human midbrain. The binding of [ 3 H]8-OH-DPAT to serotonin-1A receptors was increased significantly in the midbrain DR of suicide victims with major depression as compared with psychiatrically normal control subjects. In suicide victims with major depression, the increase in the binding of [ 3 H]8-OH-DPAT to serotonin-1A receptors was detected in the entire DR and specifically localized to the dorsal and ventrolateral subnuclei. Enhanced radioligand binding of an agonist to inhibitory serotonin-1A autoreceptors in the human DR provides pharmacological evidence to support the hypothesis of diminished activity of serotonin neurons in suicide victims with major depression.

The norepinephrine transporter (NET) is a membrane protein responsible for termination of the action of synaptic norepinephrine and is a site of action of many drugs used to treat major depression. The present study determined whether the binding of [ 3 H]nisoxetine to the NET is altered in the locus coeruleus (LC) in major depression, using brain tissue collected postmortem from subjects diagnosed with major depression and from age-matched normal control subjects. Thirteen of the 15 major depressive subjects studied died by suicide. The distribution of [ 3 H]nisoxetine binding along the rostro-caudal axis of the nucleus was uneven and was paralleled by a similar uneven distribution of neuromelanin-containing cells in both major depressives and psychiatrically normal control subjects. The binding of [ 3 H]nisoxetine to NETs in the midcaudal portion of the LC from major depressive subjects was significantly lower than that from age-matched, normal control subjects. The binding of [ 3 H]nisoxetine to NETs in other regions of the LC was similar in major depressives and control subjects. In contrast to reductions in binding to NETs, there were no significant differences in the number of noradrenergic cells at any particular level of the LC between major depressives and normal control subjects. The decreased binding of [ 3 H]nisoxetine to NETs in the LC in major depression may reflect a compensatory downregulation of this transporter protein in response to an insufficient availability of its substrate (norepinephrine) at the synapse.

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Serotonin1A (5-HT1A) and serotonin2A (5-HT2A) receptors in the brain have been implicated in the pathophysiology of suicide. Brain samples were collected at autopsy from suicide victims with a current episode of major depression and matched comparison subjects who died of natural or accidental causes. Retrospective psychiatric assessments were collected from knowledgeable informants for all suicide victims and most of the comparison subjects. Psychiatric diagnoses were determined according to DSM-III-R criteria. Any subjects with current psychoactive substance use disorders were excluded. Quantitative receptor autoradiography was used in serial sections of the right prefrontal cortex (area 10) and hippocampus to measure the binding of [3H]8-hydroxy-2-(di-n-propyl)-aminotetralin ([3H]8-OH-DPAT) to 5-HT1A receptors and [3H]ketanserin to 5-HT2A receptors. Analysis of covariance was used to compare control subjects and suicide victims with major depression. The age of subjects, the time from death to freezing the tissue (postmortem interval), and the storage time of tissues in the freezer were used as covariates in the analyses. There were no significant differences between suicide victims with major depression and comparison subjects in 5-HT1A or 5-HT2A receptors in area 10 of the right prefrontal cortex or the hippocampus. The current results suggest that the number of 5-HT1A and 5-HT2A receptors in the right prefrontal cortex (area 10) or hippocampus are not different in suicide victims with major depression.

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