Ethanol-Induced Motor Impairment Mediated by Inhibition of α7 Nicotinic Receptors

Nicotine and ethanol (EtOH) are among the most widely co-abused substances, and nicotinic acetylcholine receptors (nAChRs) contribute to the behavioral effects of both drugs. Along with their role in addiction, nAChRs also contribute to motor control circuitry. The alpha 7 nAChR subtype is highly expressed in the laterodorsal tegmental nucleus (LDTg), a brainstem cholinergic center that contributes to motor performance through its projections to thalamic motor relay centers, including the mediodorsal thalamus. We demonstrate that EtOH concentrations just above the legal limits for intoxication in humans can inhibit alpha 7 nAChRs in LDTg neurons from rats. This EtOH-induced inhibition is mediated by a decrease in cAMP/PKA signaling. The alpha 7 nAChR-positive allosteric modulator PNU120596 [N-(5-chloro-2,4-dimethoxyphenyl)-N'-(5-methyl-3-isoxazolyl)-urea], which interferes with receptor desensitization, completely eliminated EtOH modulation of these receptors. These data suggest that EtOH inhibits alpha 7 responses through a PKA-dependent enhancement of receptor desensitization. EtOH also inhibited the effects of nicotine at presynaptic alpha 7 nAChRs on glutamate terminals in the mediodorsal thalamus. In vivo administration of PNU120596 either into the cerebral ventricles or directly into the mediodorsal thalamus attenuated EtOH-induced motor impairment. Thus, alpha 7 nAChRs are likely important mediators of the motor impairing effects of moderate EtOH consumption.