6-HYDROXYDOPAMINE LESIONS OF RAT SUBSTANTIA-NIGRA UP-REGULATE DOPAMINE-INDUCED PHOSPHORYLATION OF THE CAMP-RESPONSE ELEMENT-BINDING PROTEININ STRIATAL NEURONS

Destruction of the substantia nigra produces striatal D1 dopamine rece ptor supersensitivity without increasing receptor number or affinity, thus implicating postreceptor mechanisms. The nature of these mechanis ms is unknown. Increased striatal c-fos expression ipsilateral to a un ilateral lesion of the substantia nigra in rats treated with appropria te dopamine agonists provides a cellular marker of D1 receptor superse nsitivity. D1 receptors are positively linked to adenylate cyclase and therefore to cAMP-dependent protein kinase. Because expression of the c-fos gene in response to cAMP- and Ca2+/calmodulin-regulated protein kinases depends on phosphorylation of cAMP response element-binding p rotein (CREB) at Ser-133, we examined CREB phosphorylation after dopam inergic stimulation in cultured striatal neurons and in the striatum o f rats after unilateral 6-hydroxydopamine ablation of the substantia n igra. Using an antiserum specific for CREB phosphorylated at Ser-133, we found that dopamine increases CREB phosphorylation in cultured stri atal neurons. This effect was blocked by a D1 antagonist. L-Dopa produ ced marked CREB phosphorylation in striatal neurons in rats ipsilatera l, but not contralateral, to a 6-hydroxydopamine lesion. This response was blocked by a D1 antagonist, but not a D2 antagonist, and was repr oduced by a D1 agonist, but not a D2 agonist. These findings are consi stent with the hypothesis that D1 receptor supersensitivity is associa ted with upregulated activity of cAMP-dependent or Ca2+/calmodulin-dep endent protein kinases, or both, following dopamine denervation of str iatal neurons.