Long-term behavioral and biochemical effects of 6-hydroxydopamine injections in rat caudate-putamen

Unilateral injections of 6-hydroxydopamine into the rat striatum result in amphetamine-induced circling behavior. This rotational behavior was associated with an almost complete disappearance of desmethylimipramine-insensitive [3H]mazindol binding sites--which represent dopamine uptake sites-in the ipsilateral caudate-putamen (CPu), the substantia nigra pars compacta (SNpc), and in the ventral tegmental area (VTA). There were significant increases in [3H]spiperone-labeled dopamine (DA) D2 receptors in specific subdivisions of the ipsilateral CPu, with the dorsolateral (DL) and ventrolateral (VL) regions showing significant increases in DA D2 receptors. There were nonsignificant increases in the dorsomedial (DM) aspects of the ipsilateral CPu whereas there were no changes in the ventromedial (VM) aspects of that structure. In contrast, there were no significant changes in [3H]SCH 23390-labeled DA D1 receptors in any of the subdivisions of the CPu ipsilateral to the 6-OHDA-induced lesions. These results provide evidence that intrastriatal injections of 6-OHDA result in biochemical changes in rat brain which are almost identical to those observed after 6-OHDA-induced lesions of the substantia nigra. These long-term biochemical effects caused by intrastriatal 6-OHDA injections provide further support for the idea that the nigral DA cell loss observed in the brains of parkinsonian patients could be secondary to retrograde changes due to oxyradicals generated during the metabolism of catecholamines within the caudate-putamen.