DESTRUCTION OF THE NIGROSTRIATAL PATHWAY INCREASES FOS-LIKE IMMUNOREACTIVITY PREDOMINANTLY IN STRIATOPALLIDAL NEURONS

Unilateral destruction of the nigrostriatal pathway by injection of 6- hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB) produc es a long-lasting ( > 3 months) increase in the expression of Fos-like immunoreactivity (FLI) in medium-sized neurons (12-18 mum) of the ips ilateral striatum. In order to determine the nature of neurons which c ontain FLI in the 6-OHDA-denervated striatum, striatonigral and striat opallidal neurons were retrogradely labelled with the fluorescent trac er Fluoro-Gold. Nuclei displaying FLI were frequently found in striato pallidal neurons (72% overlap) but seldom in striatonigral neurons (11 % overlap). These results are consistent with studies suggesting that dopamine tonically inhibits striatopallidal neurons which become more active in its absence. Moreover, the preferential localization of FLI in striatopallidal neurons supports the proposal that the AP-1 transcr iptional regulating factor may contribute to neuropeptide and/or D2 do pamine receptor increases which occur in these neurons after 6-OHDA le sions.