Upregulation of CB1 receptors and agonist-stimulated [35S]GTPgammaS binding in the prefrontal cortex of depressed suicide victims.

Endogenous and exogenous cannabinoids (CBs) acting through the CB(1) receptors have been implicated in the regulation of several behavioral and neuroendocrine functions. Modulation of endocannabinoidergic system by ethanol in mouse brain, and the association of suicide and mood disorders with alcoholism suggest possible involvement of the cannabinoidergic system in the pathophysiology of depression and suicide. Therefore, the present study was undertaken to examine the levels of CB(1) receptors and mediated signaling in the dorsolateral prefrontal cortex (DLPFC) of subjects with major depression who had died by suicides (depressed suicides, DS). [(3)H]CP-55,940 and CB(1) receptor-stimulated [(35)S]GTPgammaS binding sites were analyzed in membranes obtained from DLPFC of DS (10) and matched normal controls (10). Upregulation (24%, P<0.0001) of CB(1) receptor density (B(max)) was observed in DS (644.6+/-48.8 fmol/mg protein) compared with matched controls (493.3+/-52.7 fmol/mg protein). However, there was no significant alteration in the affinity of receptor (DS; 1.14+/-0.08 vs control; 1.12+/-0.10 nM). Higher density of CB(1) receptors in DS (38%, P<0.001) was also demonstrated by Western blot analysis. The CB(1) receptor-stimulated [(35)S]GTPgammaS binding was significantly greater (45%, P<0.001) in the DLPFC of DS compared with matched controls. The observed upregulation of CB(1) receptors with concomitant increase in the CB(1) receptor-mediated [(35)S]GTPgammaS binding suggests a role for enhanced cannabinoidergic signaling in the prefrontal cortex of DS. The cannabinoidergic system may be a novel therapeutic target in the treatment of depression and/or suicidal behavior.

Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims.

Suicide and depression are associated with reduced serotonergic neurotransmission. In suicides, there is a reduction in serotonin transporter (SERT) sites and an increase in postsynaptic 5-HT(1A) receptors in localized regions of the prefrontal cortex. In depression, there is a diffuse decrease in SERT binding throughout the dorsoventral extent of the prefrontal cortex. Serotonergic innervation of the prefrontal cortex arises predominantly from neurons in the brainstem dorsal raphe nucleus (DRN). We, therefore, examined postmortem SERT binding and mRNA expression, as well as 5-HT(1A) autoreceptor binding in the DRN of 10 matched pairs of controls and depressed suicide victims. The concentration of SERT sites, SERT mRNA, and 5-HT(1A) binding was not different between controls and suicides (p >.05). In the DRN of suicides, the volume of tissue defined by 5-HT(1A) binding was 40% smaller than controls. An index of the total number of 5-HT(1A) receptors (receptor binding x volume of receptor distribution) was 43.3% lower in the DRN of suicides, compared with controls. The suicide group had 54% fewer DRN neurons expressing SERT mRNA compared with controls. In the serotonin neurons that expressed the SERT gene, expression per neuron was greater in suicides. Less total 5-HT(1A) and SERT binding is consistent with results of in vivo studies in depression. Less feedback inhibition of serotonin DRN firing via 5-HT(1A) autoreceptors and enhancement of serotonin action due to less uptake of serotonin, is consistent with compensatory changes in response to hypofunction in depressed suicides.

In vitro autoradiography of serotonin 5-HT(2A/2C) receptor-activated G protein: guanosine-5'-(gamma-[(35)S]thio)triphosphate binding in rat brain.

Agonist activation of G protein-coupled receptors induces an increase in the binding of guanosine 5'-(gamma-[(35)S]thio)triphosphate ([(35)S]GTPgammaS); this increase in binding has been used as a tool to investigate receptor interaction with the heterotrimer guanine nucleotide-binding regulatory protein (G protein). The present study uses agonist-stimulated [(35)S]GTPgammaS binding to characterize serotonin 5-HT(2A/2C) receptors in rat brain membrane fractions and demonstrate the anatomical localization of the receptors by in vitro autoradiography on slide-mounted sections. The stimulatory effect of the agonist [1-(2,5-dimethoxy-4-iodophenyl)]-2 aminopropane (DOI) is compared to that of serotonin (5-HT). Autoradiography revealed a similar localization of DOI- and 5-HT-stimulated binding of [(35)S]GTPgammaS in distinct areas of prefrontal and parietal cortex, consistent with previously reported 5-HT(2A) receptor distribution. Specific binding was demonstrated in the frontal and parietal cortex, medial prefrontal, and cingular and orbital-insular areas as well as in the hippocampal formation, septal areas, the nucleus accumbens, and the choroid plexus. MDL 100105, a specific 5-HT(2A) antagonist, and ketanserin, an antagonist of 5-HT(2A/2C) receptors, blocked DOI stimulation in all labeled areas, whereas 5-HT stimulation was only partially blocked (70-80%). A small but significant inhibition was observed with the specific antagonist of 5-HT(2C/2B), SB 206553. This autoradiographic technique provides a useful tool for measuring in situ changes in specific receptor-Gq protein coupling in anatomically discrete brain regions, under physiological and pathological conditions.

A serotonin transporter gene promoter polymorphism (5-HTTLPR) and prefrontal cortical binding in major depression and suicide.

BACKGROUND: Major depression and suicide are associated with fewer serotonin transporter (5-HTT) sites. The 5'-flanking promoter region of the 5-HTT gene has a biallelic insertion/deletion (5-HTTLPR). We assayed prefrontal cortical (PFC) 5-HTT binding in major depression and suicide and examine the relationship to the 5-HTTLPR allele. METHODS: Postmortem brain samples from 220 individuals were genotyped for the 5-HTTLPR polymorphism. Binding of 5-HTT was assayed by quantitative autoradiography in the PFC of a subset of subjects (n = 159). Clinical information, including DSM-III-R Axis I diagnoses, was obtained by psychological autopsy and medical chart review. RESULTS: Binding to 5-HTT was lower in the ventral PFC of suicides compared with nonsuicides and was lower throughout the PFC of subjects with a history of major depression. The 5-HTTLPR genotype was associated with major depression but not with suicide or 5-HTT binding. CONCLUSIONS: A diffuse reduction of 5-HTT binding in the PFC of individuals with major depression may reflect a widespread impairment of serotonergic function consistent with the range of psychopathologic features in major depression. The localized reduction in 5-HTT binding in the ventral PFC of suicides may reflect reduced serotonin input to that brain region, underlying the predisposition to act on suicidal thoughts. The 5-HTTLPR genotype was not related to the level of 5-HTT binding and does not explain why 5-HTT binding is lower in major depression or suicide. Arch Gen Psychiatry. 2000;57:729-738