The effect of diazepam and picrotoxin on brainstem evoked dorsal root potentials

Abstract

Diazepam has been demonstrated to have the effect of enhancing presynaptic inhibition or facilitation from supraspinal sites in cats as determined by increased negative or positive dorsal root potentials and inhibition or facilitation of the monosynaptic reflex. Experiments were performed on cats made decerebrate at the precollicular level. Dorsal root potentials were recorded from the most caudal rootlet of L6 or L7 and the monosynaptic reflex was recorded from the ventral root of L7. Stimulation was either a single shock to the gastrocnemius-soleus or common peroneal nerve or a 20msec train at 500 Hz to sites in the brainstem reticular formation. The initial negative dorsal root potentials were enhanced by diazepam regardless of origin. Diazepam also enhanced positive dorsal root potentials from the pontine reticular formation. Some pure positive dorsal root potentials from the caudal medullary reticular formation were depressed by diazepam. Picrotoxin was always found, including when diazepam depressed dorsal root potentials, to have the antagonistic action of diazepam; i.e., usually depressing the negative or positive supraspinal dorsal root potential.