THE DUAL EFFECT OF ENFLURANE ON GILL WITHDRAWAL REFLEX OF APLYSIA

Superfusion of clinical concentrations of enflurane (0.5% or 1.0%), an inhalation anaesthetic, over the abdominal ganglion of Aplysia signif icantly affected the amplitude of the gill withdrawal reflex evoked by tactile stimulation of the siphon. Enflurane superfusion (0.5%) suppr essed the gill withdrawal reflex amplitude (to 46.1% of control; P<0.0 01 vs control) in eight of ten experiments. In the remaining two exper iments, enflurane superfusion of the abdominal ganglion significantly facilitated the gill withdrawal reflex amplitude (174.5% of control; P <0.01). In addition, enflurane superfusion significantly reduced the n umber of action potentials evoked in central gill motor neurons by the siphon stimulation (to 47.1% of control; P<0.01) in six out of nine e xperiments. In one of the remaining three experiments, enflurane incre ased the number of action potentials evoked by the stimulus (to 200.0% of control). In two of the three, enflurane did not alter the number of action potentials. Behavioural responses were 'uncoupled' from the neuronal responses as a result of enflurane superfusion.