Differential impact of heavy cannabis use on sensory gating in schizophrenic patients and otherwise healthy controls.

Cannabis abuse may precipitate the onset of schizophrenia and a dysfunction of the endocannabinoid system may be involved in the pathology of schizophrenia. Nevertheless, only few studies have addressed the neurobiological consequences of cannabis abuse for the development and course of schizophrenia. We measured the long-term effect of chronic cannabis abuse on the inhibitory function of the brain by the auditory P50 sensory gating in schizophrenic (n=15) and otherwise healthy chronic cannabis abusers (i.e. cannabis controls; n=11) and compared it to that of schizophrenic patients (n=12) and healthy controls (n=18) without cannabis or other drug abuse. All study subjects had to be abstinent from cannabis for at least 28 days. The main finding of our study was a P50 sensory gating deficit in cannabis controls that was correlated with the number of years with daily consumption (r=0.81; p=0.003). In contrast, we found no differences in P50 sensory gating between schizophrenic cannabis-abusers and non-abusers or healthy controls and no correlation with the number of years with daily consumption in those groups. To our knowledge this is the first study comparing the influence of chronic cannabis abuse in schizophrenic and otherwise healthy abusers on the inhibitory function of the brain. Our data provide some evidence that chronic cannabis abuse may affect sensory cortical circuits even after prolonged abstinence and they point to a possible differential effect in schizophrenic and otherwise healthy users.