EXCITATION BY ETHANOL OF RAT MUSCLE SPINDLES

¹ Department of Pharmacology, State University of New York at Buffalo, Buffalo, New York

The effects of ethanol on the activity of afferent nerves from primary and secondary endings in the muscle spindles and from tendon organs of the rat caudal muscle in situ were studied. Addition of ethanol in concentrations of 17 mM and above to a Krebs' solution bath surrounding the muscle caused a concentration-dependent increase in afferent activity from the sensory organs. At concentrations above 417 mM the excitation of muscle spindles and tendon organs was followed by an abrupt cessation of repetitive activity even though the afferents in the nerve trunk remained capable of conducting electrically evoked activity. Faster conducting afferents exhibited a greater ethanol-induced increment in discharge frequency than slower conducting fibers. The maximum increase in afferent discharge frequency in response to ethanol was consistently smaller than that obtainable with sustained muscle stretch or succinylcholine. Fibers from muscle spindles with a low threshold to static muscle stretch were activated first and fired continuously at lower concentrations of ethanol than those of higher mechanical threshold. The effects of ethanol were not altered by the concomitant presence of tubocurarine in concentrations blocking extra- and intrafusal neuromuscular transmission. It is suggested that ethanol alters the generator potential or effectiveness thereof in causing repetitive activity. It is suggested that alterations in muscle afferent function may be involved in the motor incoordination of ethanol intoxication.