The dual effect of enflurane on gill withdrawal reflex ofAplysia

Superfusion of clinical concentrations of enflurane (0.5% or 1.0%), an inhalation anaesthetic, over the abdominal ganglion ofAplysia significantly affected the amplitude of the gill withdrawal reflex evoked by tactile stimulation of the siphon. Enflurane superfusion (0.5%) suppressed the gill withdrawal reflex amplitude (to 46.1% of control; P<0.001 vs control) in eight of ten experiments. In the remaining two experiments, 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 number 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 experiments. In one of the remaining three experiments, enflurane increased the number of action potentials evoked by the stimulus (to 200.0% of control). In two of the three, enflurane did not alter the numbet of action potentials. Behavioural responses were ‘uncoupled’ from the neuronal responses as a result of enflurane superfusion.