The effects of thiamylal sodium on the tonic vibration reflex in man

The effects of barbiturate on the tonic vibration reflex (TVR) in man were studied. Motor unit spikes elicited during the TVR were recorded before and after an intravenous injection of thiamylal sodium. Thiamylal sodium at a dose between 1.5 and 5.8 mg/kg depressed the motor unit response to muscle vibration. Analysis using a cross-correlation between vibratory stimuli and motor unit spikes confirmed the previously reported existence of two types of motor unit response, i.e. spikes that are locked and those that are not locked to the vibratory stimuli. In addition, the latter type was susceptible to the depressant effects of thiamylal than the former type. Some possible explanations for the difference in susceptibility of the two types of motor unit to barbiturate are discussed, placing special emphasis on the probable participation of polysynaptic connections from group Ia afferents to motoneurons in the generation of the human TVR.