Increased schedule-induced polydipsia in the rat following subchronic treatment with MK-801.

Primary polydipsia, defined as excessive fluid intake not explained by medical causes, has been reported to occur in over 20% of chronically ill psychiatric inpatients and is especially common in schizophrenic populations. We tested the hypothesis that in an animal model of schizophrenia-like symptoms (subchronic injections of MK-801, 0.5 mg/kg twice daily for 7 days) an increase in the acquisition of schedule-induced polydipsia (SIP) will occur. Young adult, male rats acquired SIP when food-restricted and placed on a non-contingent fixed-time 1-min food schedule. In comparison with saline-treated control animals, subchronic MK-801 treatment significantly increased SIP. These findings suggest an animal model of polydipsia associated with schizophrenia in humans.