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The effect of gammahydroxy-butyrate on the H-reflex

Pilot study

Sleep Disorders Centre and Department of Psychiatry (Dr. Marnelak), and the Department of Rehabilitation Medicine (Dr. Sowden), Sunnybrook Medical Centre, University of Toronto, Toronto, Ontario, Canada.

Gammahydroxybutyrate (GHB) promotes cataplexy when given during the day, but decreases the incidence of daytime cataplexy when given at night. To understand the effects of GHB on this form of motor inhibition, we studied its actions on the H- and F-responses. The H-response is attenuated or abolished during cataplexy. GHB markedly inhibited the H-reflex response in normal and narcoleptic subjects, whether or not sleep was induced. It had no effect on the F-response. Prolonged motor inhibition at night by GHB may raise the threshold for inhibition during the day, accounting for the decrease in daytime cataplexy. The failure to affect the F-response suggests that GHB has a presynaptic site of action.

Address correspondence and reprint requests to Dr. Marnelak, 2075 Bay-view Avenue, Toronto, Ontario, Canada M4N 3M5.

Accepted for publication February 23, 1983.