DIFFERENTIAL EFFECT OF MK-801 AND SCOPOLAMINE ON C-FOS EXPRESSION INDUCED BY L-DOPA IN THE STRIATUM OF 6-HYDROXYDOPAMINE LESIONED RATS

In rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigro-striatal pathway, striatal D-1-receptor-stimulated c-fos expression and turning behavior are positively modulated by D-2 receptor stimulation and by blockade of N-methyl-D-aspartate (NMDA) or muscarinic receptors. Combined D-1/D-2 receptor stimulation by L-dopa activates c-fos in a manner not additive with muscarinic receptor blockade by scopolamine. On the other hand, blockade of NMDA receptors by MK 801 reduced c-fos expression induced by L-dopa while, depending on the dose of L-dopa, differentially affecting contralateral turning behavior. The results are interpreted to suggest that D-2 receptor stimulation amplifies D-1-receptor-mediated c-fos expression by two mechanisms differentially related to muscarinic and NMDA receptors. (C) 1994 Wiley-Liss, Inc.