Early and late molecular events occurring following neuronal degeneration in the dopamine system.

We summarized here two distinctively interesting observations made in the DA neuronal circuitry implicated in Parkinson's disease. When a micro-knife lesion transecting the MFB was placed rostral to the SNc, the following two molecular events were observed. (i) There is a sequential gene expression of Fos, an immediate early gene, in the postsynaptic, presynaptic, and other related neurons in this circuitry. Interestingly, an induction of Fos was never demonstrated in the SNc at any time. (ii) In specific related neuronal populations, the increase in Fos was followed by the induction of the gene for the resident neurotransmitter synthesizing enzymes. The induction of these genes for Fos and neurotransmitter enzymes most likely indicates the distinctive activity of these neurons after the injury of the DA neurons in the SNc. Although these results are preliminary, the present results contribute to the understanding of the molecular processes in the neuronal circuitry implicated in PD.