Nicotine-conditioned place preference, reversal learning and social interaction in MK-801-induced schizophrenia model: Effects of post-weaning enriched environment.

Abstract

Based on the clinical observations of severe cognitive deficits in schizophrenia patients and the relationship between environmental parameters and the severity of schizophrenia symptoms, the present study investigated these parameters in an dizocilpine (MK-801)-induced schizophrenia model in rats. In addition to, it evaluated whether a post-weaning enriched environment (EE) would affect the nicotine-induced conditioned place preference (CPP) and the motor and cognitive deficits caused by MK-801 treatment. Male Wistar rat pups were injected peritoneally with MK-801 (1 mg/kg) on a daily basis between the 6th and the 10th postnatal days (P) and were exposed to either an enriched or a standard cage from P21 until the end of the experiments. The rats were evaluated in open-field and three-chamber social interaction tests. Moreover, spatial and reversal learning was assessed by the Morris water maze (MWM). The animals were conditioned with 0.6 mg/kg nicotine and tested for CPP. Increased self-grooming, exploratory behaviour, potentiated nicotine-CPP and decreased social behaviours, delayed spatial learning and memory and impaired reversal learning in the water maze were observed in the MK-801 treatment group. Housing in an EE improved cognitive and behavioural deficits associated with postnatal MK-801 treatment. The results suggested that neonatal N-methyl-d-aspartate (NMDA) receptor hypofunction may cause susceptibility to these behaviours and indicated the importance of environmental conditions in the development of schizophrenia and probably other neuropsychiatric disorders.