• drugs of abuse;
  • dyskinesia;
  • immediate-early genes;
  • motor stereotypy;
  • Parkinson's disease


ΔFosB-like proteins are particularly stable transcription factors that accumulate in the brain in response to chronic perturbations. In this study we have compared the time-course of striatal FosB/ΔFosB-like immunoreactivity and prodynorphin mRNA expression after discontinuation of chronic cocaine treatment to intact rats and chronic L-DOPA treatment to unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats. The animals were killed between 3 h and 16 days after the last drug injection. In both treatment paradigms, the drug-induced FosB/ΔFosB immunoreactivity remained significantly elevated in the caudate putamen even at the longest withdrawal period examined. The concomitant upregulation of prodynorphin mRNA, a target of ΔFosB, paralleled the time-course of ΔFosB-like immunoreactivity in the 6-OHDA-lesion/L-DOPA model, but was more transient in animals treated with cocaine. These results suggest that ΔFosB-like proteins have exceptional in vivo stability. In the dopamine-denervated striatum, these proteins may exert sustained effects on the expression of their target genes long after discontinuation of L-DOPA pharmacotherapy.