The relationship between cocaine-induced increases in NAC1 and behavioral sensitization.

Repeated exposure to cocaine can cause long-term behavioral changes in mammals, including an augmented locomotor response known as behavioral sensitization. A major goal of research is the identification of molecules associated with these behaviors. NAC1, a member of the POZ/BTB transcription factor family, exhibited increased mRNA levels in the nucleus accumbens of the rat weeks after cocaine use. NAC1 exists as two isoforms, each demonstrating the ability to inhibit transcription, but to different extents. The present experiments examined the time course for both NAC1 isoforms after five consecutive days of systemic cocaine administration in male rats. Tissues were collected from several central nervous system regions and underwent Western blot analysis. There was significantly greater expression of the long isoform, lNAC1 (cocaine 1.341+/-0.641; saline 1+/-0.321; P=.044), and the short isoform, sNAC1 (cocaine 3.038+/-2.816; saline 1+/-0.720; P=.001), in the nucleus accumbens of cocaine-treated rats. The olfactory tubercle also showed a significant increase, but only in sNAC1 expression and at only one time period. No other significant differences were observed for either isoform of NAC1 in any other brain region. The expression of lNAC1 exhibited an inverse relationship with behavioral sensitization in rats 1-3 months following repeated cocaine injections predicting approximately 40% of the variance in the behavior variables (R(2)=.387; and P=.031 for distance and P=.025 for ambulatory count). These results indicate that NAC1 expression is increased for a period of several months after chronic cocaine exposure. Furthermore, these data suggest that NAC1 may function as an endogenous inhibitor of behavioral sensitization. NAC1 represents a target for future studies examining cocaine-induced behavioral changes.