Effects of quinpirole on the behaviour shown by mice in the light-dark box and during social interactions

Abstract

Quinpirole (0.25, 0.5 and 1.0 mg/kg) was administered by intraperitoneal injection to pair-housed adult DBA/2 mice. Controls received injections of physiological saline. Effects on behaviour during 5 min social encounters with untreated partners were examined by ethological procedures, commencing at 30 min after injection. Behaviour was examined in an aversive and less aversive situation, an unfamiliar neutral cage and the home cage. Behavioural effects were then assessed in a two-compartment black and white test box. Quinpirole dose-dependently increased the frequency and duration of flight, including the specific element “retreat”. At 0.5 mg/kg, the element, “freeze”, was also increased during encounters in the neutral cage. Immobility (a flaccid sitting posture) and sniffing of the substrate were increased by quinpirole to a similar extent at all dose levels, while non-social activity and social investigation were reduced. The significance of the effects of quinpirole in the home cage and neutral cage were qualitatively similar; the only quantitative differences were a greater enhancement of the duration of immobility and the frequency of substrate sniffing in the home cage. In the light-dark box, quinpirole reduced the number of transitions between light and dark compartments and decreased line crossings and scans/unit time in the light compartment, although it increased the amount of time in the light compartment into which mice had been originally placed. The induction of immobility and decrease of several active behavioural responses may arise from a D 2 autoreceptor inhibition of locomotor activity. The dose-related enhancement of flight by quinpirole may represent a useful model of fear-related behaviour which differs from behavioural effects induced by anxiogenic benzodiazepine inverse agonists.