The acute effects of nicotine on physiological responses from the auditory systems of nonsmokers

Indirect information about the afferent and efferent functions of the auditory brainstem, midbrain, and cortical cholinergic nuclei in the transmission of sound was provided by assessing the effects of nicotine on electrophysiological responses from different levels of the auditory system. The electroencephalogram and auditory evoked potentials were measured from 20 normal-hearing, non-smokers (10 male, 10 female) under two conditions (nicotine patch, placebo patch). The presence of nicotine did appear to acutely affect cholinergic nuclei involved in afferent and efferent transmission.; Auditory evoked potentials believed to reflect the conduction of sound from the cochlear nucleus to the cortex in the primary auditory pathway were unaffected or increased in amplitude and decreased in latency with nicotine (generally interpreted as signs of excitation within neural networks). Measures affected by arousal state were also enhanced with nicotine. These responses probably reflect activation of the cholinergic reticular formation and hippocampal neurons involved in a secondary afferent auditory pathway.; Auditory evoked potentials and electroencephalographic measures believed to reflect cortical activity were enhanced with nicotine. Thus, it appears nicotine-enhanced excitation in the afferent pathways resulted in increased activity in the cortex. Enhanced cortical activity has been shown to activate the efferent auditory pathway, which projects back to the thalamus, reticular activating system, and hippocampus. Responses believed to be influenced by the nuclei of the efferent pathway were decreased with nicotine, possibly reflecting improved stimulus filtering. This efferent system modulates neural changes occurring along the afferent pathways in response to auditory stimulation.; The results of this study are consistent with past results in animals and human smokers. These findings demonstrate nicotine's unique ability to activate inhibitory mechanisms of the nervous system without simultaneous reductions. in excitation. The regions most influenced by the presence of nicotine appear to be central. Some measures from the peripheral auditory system were suppressed, probably due to centrally- activated efferent inhibition occurring at the level of the cochlea and/or eighth nerve. Some interactions were found between sex and nicotine in the human auditory pathway, particularly at the cortical level. Evidence of interactions between auditory lateralization and nicotine was also reported.