Pharmacological evidence for dopaminergic pallido-striatal interaction

In rats the contents in dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) of neostriatum (nucleus caudatoputamen, NCP) and paleostriatum (globus pallidus, GP) were measured after transection of the capsula interna (CI) or after injection of 6-hydroxydopamine (6-OHDA; 20 microgram/2 microliter) into the GP of one side. The circling behaviour of the lesioned animals following apomorphine was also studied. 6-OHDA as well as transection decreased the contents in DA and DOPAC in NCP and GP significantly. Following both treatments DA levels in neostriatum were lowest. Nigro-neostriatal pathway lesioned animals (transected or injected with 6-OHDA 16 microgram/2 microliter into substantia nigra, SN) rotated towards the side of lesion after apomorphine (5 mg/kg IP), whereas GP lesioned animals rotated towards the intact side. In animals with both GP and SN lesions at one side turnings of similar intensity towards both sides were seen. In intact rats DA injections (200 microgram/2 microliter) into SN or NCP exhibited contralateral, injections into GP exhibited ipsilateral rotations. The results strengthen the hypothesis on the participation of GP in the regulation of neostriatal content of DA and shows the interaction of the hypothetical dopaminergic pallido-striatal pathway with nigro-neostriatal pathways.