Effects of systemically and intrastriatally injected haloperidol and apomorphine on grooming, feeding and locomotion in the rat

The effects of haloperidol and apomorphine on unconditioned behaviour of rats were tested in an open field. Systemically injected, the dopamine-antagonist haloperidol (0.01-0.3 mg/kg i.p.) decreased feeding and locomotion, but the average bout-length of grooming was increased at higher doses. Intrastriatally injected haloperidol (2.5 μg/0.5 μl) markedly increased grooming and to a lesser extent feeding. Locomotion remained unaffected. Thus, the sedative effects of peripherally administered haloperidol on locomotion and feeding are not mediated by dopamine in the antero-dorsal striatum. It is suggested that under haloperidol the behaviour of the animals is preferentially guided by exteroceptive stimuli, e.g. they show feeding and grooming while spontaneous behaviours which under control conditions may compete with feeding and grooming are suppressed. The dopamine-agonist apomorphine (0.05-2.0 mg/kg s.c.), systemically injected, suppressed grooming, feeding and locomotion. Intrastriatally injected apomorphine (5 μg/0.5 μl) only inhibited grooming. Thus, the inhibitory effects of peripherally administered apomorphine on feeding and locomotion are not mediated by dopamine at this site of the striatum. The inhibition of grooming is opposite to the effect of haloperidol and may indicate that dopamine in the antero-dorsal striatum is at least partly involved in a direct control of grooming.