ANTICHOLINERGIC EFFECTS OF STRYCHNINE IN THE COCHLEA DO NOT INVOLVE MUSCARINIC RECEPTORS

CENTRAL control of cochlear function is mediated by the cholinergic (m edial) efferent system and both muscarinic and nicotinic acetylcholine receptors are thought to be present on outer hair cells. All the phys iological effects of acetylcholine in the cochlea are blocked by stryc hnine and we therefore investigated whether strychnine interacts with muscarinic receptors in the cochlea. The effects of strychnine on both (H-3)-quinuclidinyl benzylate binding and atropine sensitive carbacho l-induced (H-3)-inositol phosphate formation were examined. Strychnine (1 to 50 muM) has no effect on either quinuclidinyl benzylate binding or carbachol (1 mM)-induced inositol phosphate synthesis. Moreover, s trychnine does not change basal inositol phosphate metabolism. These d ata indicate that muscarinic receptors are not sensitive to strychnine at concentrations which are known to block the effects of acetylcholi ne on outer hair cells.