NICOTINE-INDUCED C-FOS EXPRESSION IN THE STRIATUM IS MEDIATED MOSTLY BY DOPAMINE-D1 RECEPTOR AND IS DEPENDENT ON NMDA STIMULATION

The powerful psychostimulant and positive reinforcing effects of nicotine have been speculated to be mediated by the dopaminergic neurons of the ventral tegemental area (VTA) and their terminals in the nucleus accumbens. To extend our understanding of nicotine and dopamine interactions, we mapped the pattern of c-fos expression in the striatum as an important marker of some of the earliest changes that occur at gene transcription level. Acute nicotine injections in rats led to Fos expression more prominently in the caudatoputamen than in the nucleus accumbens in a dose-dependent fashion. Fos-reactive cells were more prominent in the central and dorsomedial limbic caudatoputamen than in the dorsolateral sensory-motor striatum. Injections of mecamylamine completely blocked nicotine-induced Fos expression. Injections of the selective dopamine D1 antagonist SCH 23390, but not D2 antagonist YM 09151-2 or Clozapine, a drug with high affinity to D4 receptors, before nicotine injections, completely blocked Fos expression in the striatum. Nicotine induced Fos expression was also blocked completely by the NMDA receptor antagonists MK-801 and CPP. These results suggest that nicotine-induced Fos expression in the striatum is mediated mostly by dopamine D1 receptors and that the Fos expression is also dependent on N-methyl-D-aspartate (NMDA) stimulation.