Activation of the mesolimbic dopamine system is a critical component underlying addictive behaviors, including smoking. It has been hypothesized that the initial effect of nicotine on the dopamine system is to activate high affinity nicotinic acetylcholine receptors (nAChRs) containing the beta2 subunit, but that these receptors rapidly desensitize and are not critical for ongoing dopaminergic activation. To clarify the role of beta2-subunit-containing (beta2*) nAChRs in activation of the dopamine system and subsequent locomotor activation by repeated nicotine administration, C57BL/6J (B6) mice were administered 200 microg/ml of nicotine in the drinking water and the onset of locomotor activation was measured. B6 mice showed an increase in locomotor activity in response to chronic nicotine which was blocked by oral administration of the dopamine receptor antagonist pimozide. Knockout mice lacking the beta2 subunit of the nAChR did not show locomotor activation in response to chronic nicotine exposure, suggesting that beta2* nAChRs are critical for ongoing activation of the dopamine system by chronic nicotine administration and the resulting locomotor activation in mice.