Effects of prazosin, clonidine, and propranolol on the elevations in brain reward thresholds and somatic signs associated with nicotine withdrawal in rats

Tobacco withdrawal is characterized by a negative mood state and relatively mild somatic symptoms. Increased noradrenergic transmission has been reported to play an important role in opioid withdrawal, but little is known about the role of noradrenergic transmission in nicotine withdrawal. The aim of these experiments was to investigate the effects of prazosin, clonidine, and propranolol on the negative mood state and somatic signs associated with nicotine withdrawal in rats. A discrete-trial intracranial self-stimulation procedure was used to assess the negative affective state of nicotine withdrawal. Elevations in brain reward thresholds are indicative of a deficit in brain reward function. In all the experiments, the nicotinic acetylcholine receptor antagonist mecamylamine (3 mg/kg) elevated the brain reward thresholds of the nicotine-treated rats and did not affect those of the control rats. The alpha 1-adrenergic receptor antagonist prazosin (0.0625 and 0.125 mg/kg) dose-dependently attenuated the elevations in brain reward thresholds associated with precipitated nicotine withdrawal. The alpha 2-adrenergic receptor agonist clonidine (10-40 mu g/kg) and the nonselective beta-adrenergic receptor antagonist propranolol (2.5-10 mg/kg) did not attenuate the elevations in brain reward thresholds associated with nicotine withdrawal. Furthermore, mecamylamine (2 mg/kg) induced more somatic signs in the nicotine-treated rats than in the control rats. Clonidine and propranolol, but not prazosin, decreased the total number of somatic signs associated with nicotine withdrawal. Blockade of alpha 1-adrenergic receptors attenuates the deficit in brain reward function associated with nicotine withdrawal. Antagonism of beta-adrenergic receptors or stimulation of alpha 2-adrenergic receptors attenuates the somatic symptoms of nicotine withdrawal.