The effect of gammahydroxybutyrate on the H-reflex: pilot study

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.