NICOTINIC ACETYLCHOLINE-RECEPTORS ON CAPSAICIN-SENSITIVE NERVES

TO study the density of nicotinic acetylcholine receptors on primary afferents and central nociceptive pathways, [H-3](-)-nicotine binding was conducted in the cerebral cortex and spinal cord including dorsal roots and ganglia (DRG), of control rats and rats desensitized by neonatal capsaicin treatment. [H-3](-)-nicotine binding in capsaicin-treated rats was reduced in cerebral cortex by 35% and spinal cord+DRG by 46% (p<0.05). Functionally, both iontophoretically applied acetylcholine- and capsaicin-evoked flares (measured by laser Doppler flowmetry) were reduced in capsaicin-treated animals (p<0.05); similarly, electrical stimulation-evoked nares were significantly lower in the same group, compared with controls (p<0.05). These data provide direct evidence that many neuronal nicotinic acetylcholine receptors are associated with capsaicin-sensitive peptidergic neurones, including primary afferents, DRG and central nociceptive pathways.