GABAergic control of rhythmic activity in the presence of strychnine in the lamprey spinal cord.

Rhythmic ventral root activity has been induced in the spinal cord of the lamprey in vitro in the presence of strychnine. Bicuculline (a GABAA blocker) increases the initial frequency and decreases the episode duration of such activity, whereas diazepam (which potentiates GABA action) has the opposite effect. In addition, bicuculline slows the depolarisation of ventral horn neurones. However, voltage clamp at potentials positive to the interburst potential does not reveal net outward current, even in the presence of diazepam, indicating that the effects of GABA on the rhythmic activity must be presynaptic to the impaled cells.