Increased striatal expression of glutamate decarboxylase 67 after priming of 6-hydroxydopamine-lesioned rats

Previous single exposure (priming) to a dopamine receptor agonist greatly e nhances the contralateral turning behaviour elicited by dopamine D-1 recept or agonists in unilaterally 6-hydroxydopamine lesioned rats. In the present study we have investigated the levels of glutamate decarboxylase 67 and gl utamate decarboxylase 65 messenger RNA in the striatum of 6-hydroxydopamine -lesioned rats primed with L-3,4-dihydroxyphenylalanine (L-DOPA) and challe nged with the D-1 receptor agonist SKF 38393, three days thereafter. As pre viously reported, levels of glutamate decarboxylase 67 messenger RNA increa sed in the striatum denervated by the 6-hydroxydopamine lesion as compared with the intact one. Striatal glutamate decarboxylase 67 messenger RNA leve ls, measured three days after priming with L-DOPA (50 mg/kg), further incre ased in the lesioned striatum while were not modified in the intact one. Ad ministration of SKF 38393 (3 mg/kg) elicited a more intense contralateral t urning behaviour in primed than in drug-naive 6-hydroxydopamine-lesioned ra ts but did not induce any change in striatal glutamate decarboxylase 67 mes senger RNA. In contrast, striatal levels of glutamate decarboxylase 65 mess enger RNA were not modified by either 6-hydroxydopamine lesions or priming with L-DOPA. The results show that priming with L-DOPA induces long-lasting changes in G ABAergic neurons of the 6-hydroxydopamine-lesioned striatum. These changes might play a role in the increased behavioural response of striatal D-1 rec eptors induced by priming. (C) 1999 IBRO. Published by Elsevier Science Ltd .