Abstract
Unilateral injection of 6-hydroxydopamine into the locus ceruleus led to long lasting depletion of norepinephrine in the ipsilateral parietal cerebral cortex of the rat up to 8 weeks after injection. The uptake of both norepinephrine and dopamine by homogenates of parietal cortex was decreased markedly on the ipsilateral, but not on the contralateral, side. The uptake of four other neurotransmitter candidates or precursors was unaffected by the lesion. Desipramine (DMI) markedly inhibited the uptake of both norepinephrine and dopamine by cortical preparations from the contralateral side and from control rats, but this effect was not seen in preparations from the norepinephrine-depleted, ipsilateral cortex. The decreases DMI-sensitive uptake of norepinephrine or dopamine was highly correlated with decreased norepinephrine in the ipsilateral cortex. These results suggest that the specific uptake of norepinephrine and dopamine is a valid marker of noradrenergic innervation of the parietal cortex and that dopamine seems to be accumulated primarily by norepinephrine terminals in this region. Two and 8 weeks after locus ceruleus lesion, a DMI-insensitive, benztropine-sensitive dopamine uptake becomes apparent in ipsilateral cortical preparations, This may represent proliferation or increased function of dopaminergic cortical projections, compensating for noradrenergic denervation.