Abnormalities in L-glutamic acid (glutamate) and GABA signal transmission have been postulated to play a role in depression, but little is known about the underlying molecular determinants and neural mechanisms. Microarray analysis of specific areas of cerebral cortex from individuals who had suffered from major depressive disorder demonstrated significant down-regulation of SLC1A2 and SLC1A3, two key members of the glutamate͞neutral amino acid transporter protein family, SLC1. Similarly, expression of L-glutamate-ammonia ligase, the enzyme that converts glutamate to nontoxic glutamine was significantly decreased. Together, these changes could elevate levels of extracellular glutamate considerably, which is potentially neurotoxic and can affect the efficiency of glutamate signaling. The astroglial distribution of the two glutamate transporters and L-glutamate-ammonia ligase strongly links glia to the pathophysiology of depression and challenges the conventional notion that depression is solely a neuronal disorder. The same cortical areas displayed concomitant up-regulation of several glutamate and GABA A receptor subunits, of which GABA A␣1 and GABAA␤3 showed selectivity for individuals who had died by suicide, indicating their potential utility as biomarkers of suicidality. These findings point to previously undiscovered molecular underpinnings of the pathophysiology of major depression and offer potentially new pharmacological targets for treating depression.bipolar disorder ͉ GABAA receptors ͉ glutamate transporters ͉ major depression ͉ suicide C linical depression, the phenotypic hallmark of the two leading mood disorders [major depressive disorder (MDD) and bipolar affective disorder (BPD)], is the most common psychiatric illness. It affects Ϸ121 million people worldwide, with 10-20% of women and 5-12% of men estimated to experience a depressive episode in any 1-year period, and with evidence of suicidality in 15% of those affected (ref.

Posttranslational processing of proproteins and prohormones is an essential step in the formation of bioactive peptides, which is of particular importance in the nervous system. Following a long search for the enzymes responsible for protein precursor cleavage, a family of Kexin/subtilisin-like convertases known as PC1, PC2, and furin have recently been characterized in mammalian species. Their presence in endocrine and neuroendocrine tissues has been demonstrated. This study examines the mRNA distribution of these convertases in the rat CNS and compares their expression with the previously characterized processing enzymes carboxypeptidase E (CPE) and peptidylglycine alpha-amidating monooxygenase (PAM) using in situ hybridization histochemistry. Furin mRNA was ubiquitously distributed and detected both in neurons and non-neuronal tissue throughout the brain with a higher abundance in ependyma, the circumventricular organs, the islands of Calleja, hippocampus, and allocortex. The cellular localization of PC1 and PC2 was exclusively neuronal with highest concentrations in known neuropeptide-rich brain regions. In general, PC2 was more widely expressed than PC1 in the CNS, although many regional variations were detected. The identification of specific combinations of convertase expression together with CPE and PAM expression in neuropeptide-rich brain regions suggests that specific enzymatic pathways are involved in neuropeptide precursor processing, and that these specific combinations are responsible for region-specific differences of posttranslational processing.

The opioid peptide dynorphin is widely distributed in neuronal tissue of rats. By immunocytochemical methods, it was shown previously that dynorphin-like immunoreactivity is present in the posterior pituitary and the cells of the hypothalamic neurosecretory magnocellular nuclei which also are responsible for the synthesis of oxytocin, vasopressin, and their neurophysins. By using an affinity-purified antiserum to the non-enkephalin part of the dynorphin molecule it has now been demonstrated that dynorphin and vasopressin occur in the same hypothalamic cells of rats, whereas dynorphin and oxytocin occur in separate cells. Homozygous Brattleboro rats (deficient in vasopressin) have magnocellular neurons that contain dynorphin separate from oxytocin. Thus dynorphin and vasopressin, although they occur in the same cells, appear to be under separate genetic control and presumably arise from different precursors.

Using in situ hybridization techniques, the expression of 5-HT1A receptor mRNA was measured within the hippocampal formation after bilateral adrenalectomy (ADX). After 24 hr ADX, 5-HT1A receptor mRNA expression was significantly increased in all hippocampal subfields in ADX animals relative to sham-operated controls (SHAM). The magnitude of the increase was most pronounced within CA2 (127%) and CA3/4 (94%)-subfields of dorsal hippocampus, intermediate in the dentate gyrus (73%), and least within CA1 (60%). Administration of exogenous corticosterone (CORT) at the time of ADX maintained the level of 5-HT1A receptor mRNA expression within the range of SHAM animals. In vitro receptor autoradiographic analysis of 5-HT1A receptors in adjacent sections from the same animals indicated a simultaneous increase in 5-HT1A binding throughout the hippocampus in response to ADX. 5-HT1A binding increased to a similar extent (approximately 30%) in CA subfields and dentate gyrus but remained within SHAM levels in CORT-replaced animals. 5-HT1A receptor mRNA levels were also increased in hippocampal subregions of 1 week ADX animals relative to SHAM animals. Within both CA1 and CA2 subfields, the increments were approximately double those observed after 1 d ADX. 5-HT1A receptor binding was increased in every hippocampal subfield to a similar extent as that observed after 1 d ADX. Increases in both 5-HT1A receptor mRNA expression and 5-HT1A receptor binding were preventable by administration of exogenous CORT at the time of ADX. Hippocampal 5-HT1C receptor mRNA and D1 receptor mRNA expression were not significantly altered by either acute or chronic ADX treatment. These data indicate that adrenal steroids may selectively regulate hippocampal 5-HT1A receptors at the level of 5-HT1A receptor mRNA expression.

The present study examines the relative levels of vasopressin (AVP) mRNA within the paraventricular (PVN), supraoptic (SON), and suprachiasmatic (SCN) nuclei of the rat hypothalamus, and details the rates at which these levels change over the course of a 6 d salt-loading regimen. The quantitation of vasopressin mRNA was achieved by using three different procedures: (1) cell-free translation in rabbit reticulocyte lysate or (2) Northern analysis of poly(A)RNAs isolated from micro-punch dissected SON, PVN, and SCN, and (3) in situ hybridization histochemistry. The former involved the quantitative immunoprecipitation of the neurophysin precursors containing arginine8-vasopressin (AVP) or oxytocin, and the latter two techniques employed a radiolabeled synthetic oligodeoxynucleotide complementary to the 3' region of the AVP mRNA. Both the cell-free studies and the Northern gel analyses detected a sevenfold increase of AVP mRNA in the SON, a fivefold increase in the PVN, and no significant change in the SCN following 6 d of salt-loading. After the initiation of salt-drinking, these increases were shown to occur between 24 and 48 hr in the SON and between 48 and 72 hr in the PVN. The in situ hybridization studies revealed the anatomically correct hybridization of either 32P- or 3H-labeled AVP oligonucleotide to magnocellular perikarya within both the SON and PVN. Autoradiographic grains could be shown to be confined to the cytoplasm of these cells, and could be co-localized with immunoreactivity directed against the carboxy terminus of the AVP percursor. Comparison of x-ray level autoradiograms of control and 6 day salt-loaded SON revealed up to a sevenfold increase in specific signal in the salt-loaded sections. It is concluded that the response of AVP mRNA to osmotic stimuli in the three hypothalamic nuclei is heterogeneous, and that this heterogeneity can be explained by separating AVP neurons into two systems: one responsible for eliciting the antidiuretic actions of AVP via plasma AVP levels, and the other involved in CNS activities not directly involved with antidiuresis.