Cannabinoid/anandamide system and schizophrenia: is there evidence for association?

Cognitive impairments during psychotic episodes are assumed to be caused not only by one single putative classical neurotransmitter dysfunction but also to be due to an impaired equilibrium of the interaction between different neurobiological generators of cognitive processes. Here, the perceptual abnormalities induced by psychotogenic agents play a major role as tools for understanding model psychoses. The recently discovered cannabinoid receptor system with its endogenous ligand anandamide can be regarded as an extremely relevant regulation system, a dysfunctionality of which may explain at least one subtype of endogenous psychoses. The present paper discusses the possible associations between the endogenous anandamide/cannabinoid system and schizophrenic psychoses. Neuropsychological experiments with the 3-D inversion paradigm were performed in healthy volunteers intoxicated with delta9-Tetrahydrocannabinol (delta9-THC). The 3-D inversion paradigm represents a visual illusion of binocular depth perception. Such an inversion occurs in many cases, especially when objects with a higher degree of familiarity (e.g. photographs of faces) are displayed. It is assumed that cognitive factors override the binocular disparity cues of stereopsis. We tested the hypothesis that, during psychotic and related prepsychotic states, the human CNS is unable to correct implausible perceptual hypotheses. Our study provides evidence of strong similarities between data acquired from patients, suffering from productive schizophrenic psychoses and delta9-THC-intoxicated healthy volunteers, as concerns disturbances in the internal regulation of perceptual processes.