Corticotropin-releasing factor (CRF) is a neuropeptide associated with the integration of the physiological and behavioral responses to stress. Recently, CRF1 receptor antagonists have been shown to decrease cocaine self-administration and inhibit stress-induced reinstatement of cocaine-seeking behavior. The exact mechanisms underlying this effect are not clear. Based on the large amount of literature demonstrating an association between dopaminergic neurotransmission and reward-related behavior, the aim of the present study was to examine the effects of acute versus chronic CRF1 receptor blockade on mesencephalic dopamine (DA) neuron activity (determined by in vivo extracellular recordings) and extracellular DA levels in the nucleus accumbens (Acb) (using in vivo microdialysis). In addition, the effect of CRF1 receptor antagonism on cocaine-induced DA overflow in the Acb was examined and correlated with DA neuron activity in the ventral tegmental area (VTA). Acute (but not chronic) CRF1 receptor blockade by CRA-0450 [1-[8-(2,4-dichlorophenyl)-2-methylquinolin-4-yl]-1,2,3,6-tetrahydropyridine-4-carboxamide benzenesulfonate] was found to significantly increase DA neuron population activity without affecting burst firing, average firing rate, or Acb DA levels. In addition, both acute and chronic CRF1 receptor antagonism significantly reduced cocaine-stimulated DA overflow in the Acb, and this reduction was correlated with an attenuated cocaine-induced inhibition of DA population activity. Taken as a whole, these data demonstrate that, although DA neuron population activity exhibits tolerance to chronic CRF1 receptor antagonism (by CRA-0450), tolerance does not develop to the selective inhibition of cocaine-induced DA release (in the Acb) and, as such, may be beneficial in the treatment of cocaine addiction.