ACTIVE SLEEP-RELATED DEPOLARIZATION OF FELINE TRIGEMINO-THALAMIC AFFERENT TERMINALS

PRESYNAPTIC depolarization of trigemino-thalamic (TGT) terminals may c ontribute to modulation of ascending ore-facial somatosensory informat ion during active (or rapid eye movement) sleep. The relative excitabi lity of TGT terminals was inferred from changes in the current require d to maintain an antidromic firing probability of 50% (EC50) during qu iet wakefulness as compared to active sleep. Depolarization or hyperpo larization of TGT terminals was defined as a decrease or increase, res pectively, in the EC50. Overall, the EC50 of 8 TGT terminals was reduc ed by a mean 8.8 +/- 3.6 mu A during active sleep relative to quiet wa kefulness. This result suggests that depolarization of TGT terminals, which may act to suppress the transfer of sensory information from the trigeminal nucleus to the thalamus, occurs during active sleep.