ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

2pPP3. Effect of anticholinergic drugs on human spontaneous and click-evoked otoacoustic emissions, frequency discrimination, and lateralization using interaural intensity differences.

Narriman Lee Callaway

Dennis McFadden

Dept. of Psychol., Mezes Hall 330, Univ. of Texas, Austin, TX 78712

The primary neurotransmitter for the cochlear efferent system is widely believed to be acetylcholine. If anticholinergic drugs reduce neurotransmitter activity in the efferent pathway, they should produce effects in accord with those seen in animal studies where the olivocochlear bundle (OCB) was severed. Experiments were conducted to measure effects of three common anticholinergic drugs, diphenhydramine (Benadryl[sup (registered)]), hyoscyamine (Levsin[sup (registered)]), and scopolamine (Transderm-Scop[sup (registered)]) on two psychophysical tasks and two physiological measures. There was no evidence of impaired performance in a complex frequency-discrimination task or in a lateralization task using interaural intensity differences. Also, no compelling evidence was found to indicate that either spontaneous or click-evoked otoacoustic emissions were enhanced by these drugs. After the beginning of these experiments, a report appeared [S. G. Kujawa et al., Hear. Res. 74, 122--134 (1994)] indicating that, in guinea pigs, suppression of distortion-product otoacoustic emissions was reversed by anticholinergics having antinicotinic action, but less so by those having antimuscarinic action. The three anticholinergic drugs used here are primarily antimuscarinic in their action, which may explain the failure to observe the predicted effects. [Work supported by NIDCD.]