STRIATAL RESPONSES TO DECORTICATION .1. DOPAMINERGIC AND ASTROCYTIC ACTIVITIES

Unilateral ablation of the frontal cortex induced 30%-50% decrease of dopamine (DA) concentration in the ipsilateral striatum at 10 and 27 days after lesioning. There were increased ratios of dihydroxyphenylacetic acid (DOPAC): DA and homovanillic acid (HVA): DA by 20%-60% at 10 days post-lesioning, which suggest compensatory increases of DA metabolism. While no change in total striatal tyrosine hydroxylase (TH) polypeptide concentration was found at any post-lesion time, TH catalytic activity was decreased slightly (-25%) at 10 days. Among individual rats, at 3, 10 and 27 days post-lesioning, striatal DA concentration was inversely related to striatal glial fibrillary acidic protein (GFAP) concentration, a marker of astrocytic activity. The loss of DA was observed whether or not DA was normalized to striatal protein, which suggests that DA loss cannot be simply attributed to increased astrocytic proteins. These data suggest reciprocal relationships between the extent of astrocytic reactions after cortical deafferentation and striatal DA loss, which could involve local remodelling without primary damage to the nigro-striatal terminals.