Overall our results show that rats exhibited heightened

Overall, our results show that rats exhibited heightened anxiety-like behaviors both 24h and 2 weeks following the last repeated injection of amphetamine. The distance traveled in the EPM was nearly identical between saline- and amphetamine-treated groups at both time points measured, suggesting that differences observed in anxiety-like measures were not due to differences in the activity between the treatment groups. Therefore, these findings suggest that chronic amphetamine treatment increases anxiety states, which persist during protracted drug withdrawal. Infusion of a CRF ARRY-380 antagonist directly into the dRN reduced anxiety-like behaviors exhibited by amphetamine pre-treated rats at 2 weeks of withdrawal, with no effect on locomotion within the maze. These results extend those of Pringle et al. showing increased CRF receptors in the dRN up to 6 weeks following 14 days of amphetamine treatment, and of Sarnyai et al. and Basso et al. demonstrating increased anxiety-like behaviors of rats at 48h of withdrawal following 14 days of cocaine treatment, which were ameliorated by icv CRF antiserum or a CRF receptor antagonist. Combined, these findings suggest that one of the mechanisms by which chronic psychostimulant treatment and withdrawal results in elevated anxiety states may be increased CRF receptor activity in the dRN. Given that CRF receptor activation within the dRN leads to increases in 5-HT release in limbic regions such as the amygdala and nucleus accumbens , , heightened CRF receptor activity in the dRN during amphetamine withdrawal may amplify serotonergic activity within the limbic system to result in increased anxiety states. Interestingly, ASV-30 infusion in the dRN of saline pre-treated rats had no effect on anxiety-like behaviors. This result may be due to the saline pre-treated group exhibiting relatively low levels of anxiety-like behaviors (when compared to saline pre-treated rat of the first experiment that were not acclimated to handling prior to EPM testing). Our result is consistent with a number of studies showing that general CRF receptor antagonists administered intracranially or icv have little effect on the behavior of non-stressed animals (see ). However, in some studies, icv administration of ASV-30 decreases anxiety-like behavior of rats in the EPM without prior exposure to stress or drugs . The discrepancy in findings may be due to the site of infusion, with CRF receptor antagonism specific to the dRN only effective in rats that show heightened CRF receptor levels in this region. This implies that chronic exposure to amphetamine results in dRN CRF receptor regulation of behavior that is not typically mediated by the activity of these receptors in drug naive rats. In summary, the current data suggest that chronic amphetamine treatment of rats results in an increased anxiety state which persists following drug abstinence, and that CRF receptor antagonism within the dRN reverses this anxiety state. Future research should confirm these findings using different anxiety paradigms with more global antagonism of central CRF receptors. Such future studies may suggest CRF receptor antagonism as a possible direction for therapeutic treatment to reduce anxiety states during amphetamine withdrawal.