Behavioural effects mediated by unilateral nigral dopamine receptor stimulation in the rat

Unilateral intranigral injections of dopamine in conscious rats pretreated with nialamide resulted in either ipsiversive or contraversive rotation depending upon the site of injection. Injection of dopamine (50 micrograms) into the zona compacta of the substantia nigra induced weak ipsiversive or mixed ipsiversive and contraversive rotation. Injection of dopamine (12.5-50.0 micrograms) into zona reticulata of substantia nigra induced only contraversive circling. Destruction of the ipsilateral medial forebrain bundle (MFB) using 6-hydroxydopamine (6-OHDA) abolished ipsiversive circling but enhanced contraversive circling produced by dopamine or apomorphine. The combination of a unilateral 6-OHDA lesion of MFB with a kainic acid or electrolesion of the ipsilateral strio-nigral and pallido-nigral pathways reduced contraversive circling to intranigral apomorphine (10 micrograms). Ipsiversive circling produced following intranigral injection of dopamine is dependent upon the integrity of ascending dopamine neurones. Contraversive rotation is independent of ascending dopamine pathways but is reliant upon afferent input to the substantia nigra from the striatum and/or globus pallidus.