Preserved reticular neuronal activity during selective delivery of supra-clinical isoflurane concentrations to brain in goats and its association with spontaneous movement

We have previously observed spontaneous movement when supra-clinical concentrations of isoflurane were selectively delivered to the in situ goat brain. We presently examined whether neurons in the midbrain reticular formation (MRF) remained active during such delivery. Isoflurane (5.1±1.6%) was selectively delivered to the goat cranial circulation while the torso isoflurane was decreased to 0.2-0.3%. At the high cranial/low torso isoflurane combination, spontaneous movement occurred that usually consisted of running motions, stiffening and twitching. Seventeen MRF neurons recorded in six goats exhibited high spontaneous firing (33±20 Hz) despite the presence of an isoelectric electroencephalogram. We conclude that some MRF neurons are resistant to the depressant effect of isoflurane, and may contribute to the observed spontaneous movement.