Baclofen-induced modification of conditioned discriminative avoidance behaviour and contraversive turning in the rat.

The effects of baclofen, a gamma-aminobutyric acid derivative, on conditioned avoidance behaviour and on the turning produced by unilateral 6-OHDA lesions of the s. nigra were investigated in rats. The small impairment of conditioned avoidance behaviour induced by baclofen (1-4 mg/kg i.p.) was potentiated by combination with benztropine, an anticholinergic agent. Moreover, baclofen reversed the suppression of avoidance responses and the inhibition of turning induced by physostigmine, suggesting an interaction of baclofen with cholinergic transmission processes at the nigrostriatal level. After alpha-methyltyrosine, baclofen like haloperidol, produced a marked increase in avoidance response failures suggesting an additional inhibitory effect of the compound on dopaminergic transmission. The pattern of results indicates that baclofen affects the feedback-loop regulation processes in the nigrostriatal area of the brain.