Fluoxetine reduced polydipsia and bar pressing without reducing motor activity

Abstract

Fluoxetine (FLX) is a selective serotonin reuptake inhibitor which is used, among other, for the treatment of obsessive-compulsive disorder (OCD). FLX has been shown to decrease schedule- induced polydipsia, and is considered an animal model for obsessive-compulsive disorder. The aim of the present research was to verify whether FLX-induced reduction of polydipsia could be explained by a motor deficit caused by the drug. Polydipsia was induced in rats pressing a lever on a fixed interval 60s (F1 60) schedule of food reinforcement. Daily 32 min baseline sessions were conducted until stable polydipsic behavior was obtained in 16 subjects with daily water intake between 10 and 15 ml. subjects were then given either 5 mg/kg FLX (N=8) i.p. injections during 28 days, followed by 10 mg/kg FLX or vehicle injections during 21 days. During treatment experimental sessions were run once a week behavior observation was registered according to defined categories on the last baseline F1 session and the last FLX 5 mg and FLX 10 mg sessions. The following measures were taken: volume of water drunk, frequency of lever- pressing responses, and observed responses in the locomotion, rearing and sniffing categories. FLX reduced both polydipsia and F1 response rate at 10 mg/kg, but did not alter locomotion and rearing. Sniffing was significantly increased at both drug dosages. It was concluded that FLX affect on schedule induced polydipsia is independent of motor effects. The simultaneous reductions of induced drinking and response rate can be attributed either to the anti-compulsive action of FLX or to the reduction in the reinforcing value of food due to the anorexic effect of the drug. Whatever the interpretation, the results agree with the hypothesis that operant and induced behavior are controlled by the same variables and share a common nature.