Chronic nicotine exposure enhances cutaneous axon reflexes in the rat

The effect of chronic nicotine exposure on the cutaneous neurogenic flare response was investigated non-invasively in rats. Axon reflexes were evoked by transdermal iontophoresis of acetylcholine, and resultant changes in skin microvascular blood flux were measured by laser Doppler flowmetry. Rats given five injections of nicotinesulphate (1 mg kg-1 i.p.) daily for 14 days were compared to saline-injected littermates. Axon reflexes were enhanced by 143% after 7 days exposure to nicotine, and by 336% after 14 days exposure. Controls did not display these increases. Axon reflexes measured 7 days after nicotine cessation were similar to pre-nicotine levels. These results may suggest that nicotinic cholinoceptors on skin nociceptors and primary afferents upregulate in response to chronic nicotine exposure, and return to normal following nicotine cessation.