Inhibition of cerebral type 1 cannabinoid receptors is associated with impaired auditory mismatch negativity generation in the ketamine model of schizophrenia

RATIONALE: Preclinical and clinical research suggests that the endogenous cannabinoid system is involved in cognitive impairments related to schizophrenia. In particular, the deficient generation of mismatch negativity (MMN) indicating auditory sensory memory is a characteristic finding in schizophrenic patients. Experimental studies implicate deficient N-methyl-D: -aspartate (NMDA) receptor functioning in such abnormalities. OBJECTIVES: The primary aim of this study was to investigate the effects of the cannabinoid CB(1) receptor antagonist rimonabant on MMN deficits in the NMDA receptor antagonist model of schizophrenia by using ketamine. METHODS: Twenty-four healthy male subjects participated in a randomized, double-blind, placebo-controlled cross-over study with subanesthetic doses of intravenous ketamine. The MMNs to frequency and duration deviants were elicited within an auditory oddball paradigm and recorded by a 32-channel EEG. Psychopathology was assessed using the Psychotomimetic States Inventory. RESULTS: Twenty subjects completed both experimental sessions. Ketamine infusion had no significant effect on MMN amplitudes in both deviance conditions. In contrast to placebo, co-administration of rimonabant produced significant deficits in MMN amplitudes to duration deviants at electrode position Fz. CONCLUSIONS: The results point to the involvement of the endogenous cannabinoid system in auditory sensory memory as a cognitive key feature in schizophrenia. They particularly suggest that CB(1) receptor antagonism may impair cognitive performance by a disturbed interaction between endocannabinergic activity and glutamatergic neurotransmission implied in schizophrenia

Polygenic risk scores across the extended psychosis spectrum

As early detection of symptoms in the subclinical to clinical psychosis spectrum may improve health outcomes, knowing the probabilistic susceptibility of developing a disorder could guide mitigation measures and clinical intervention. In this context, polygenic risk scores (PRSs) quantifying the additive effects of multiple common genetic variants hold the potential to predict complex diseases and index severity gradients. PRSs for schizophrenia (SZ) and bipolar disorder (BD) were computed using Bayesian regression and continuous shrinkage priors based on the latest SZ and BD genome-wide association studies (Psychiatric Genomics Consortium, third release). Eight well-phenotyped groups (n = 1580; 56% males) were assessed: control (n = 305), lower (n = 117) and higher (n = 113) schizotypy (both groups of healthy individuals), at-risk for psychosis (n = 120), BD type-I (n = 359), BD type-II (n = 96), schizoaffective disorder (n = 86), and SZ groups (n = 384). PRS differences were investigated for binary traits and the quantitative Positive and Negative Syndrome Scale. Both BD-PRS and SZ-PRS significantly differentiated controls from at-risk and clinical groups (Nagelkerke's pseudo-R-2: 1.3-7.7%), except for BD type-II for SZ-PRS. Out of 28 pairwise comparisons for SZ-PRS and BD-PRS, 9 and 12, respectively, reached the Bonferroni-corrected significance. BD-PRS differed between control and at-risk groups, but not between at-risk and BD type-I groups. There was no difference between controls and schizotypy. SZ-PRSs, but not BD-PRSs, were positively associated with transdiagnostic symptomology. Overall, PRSs support the continuum model across the psychosis spectrum at the genomic level with possible irregularities for schizotypy. The at-risk state demands heightened clinical attention and research addressing symptom course specifiers. Continued efforts are needed to refine the diagnostic and prognostic accuracy of PRSs in mental healthcare