Effects of cholinergic agonists and antagonists on frog cutaneous cold receptors

Sensitivity of cold receptors in frog skin is altered by acetylcholine and related compounds. Low concentrations of cholinergic agonists increase the sensitivity of cold receptors to thermal stimuli and also decrease threshold to electrical stimuli; higher concentrations decrease sensitivity to thermal stimuli and increase threshold to electrical stimulation. It is concluded that acetylcholine depolarizes the receptor terminals directly, higher concentrations of the drug producing inactivation. From experiments with cholinergic antagonists (atropine, tubocurarine, hexamethonium, tetraethylammonium) and anticholinesterases (neostigmine and edrophonium), it is concluded that the cold receptor behaves as if supplied by nicotinic and muscarinic pharmacological receptor sites.