INTRINSIC AND SYNAPTIC PROPERTIES OF TURTLE RED NUCLEUS NEURONS INVITRO

Burst discharges in the red nucleus are correlated with discrete limb movements. Intracellular recordings from red nucleus neurons in the in vitro turtle brainstem-cerebellum was performed to elucidate mechanis ms underlying these bursts. Depolarizing intracellular current injecti on failed to demonstrate endogenous membrane currents that might produ ce burst discharges, and neurons did not exhibit significant spike fre quency adaptation, which is a characteristic of synaptically driven bu rsts. Responses of red nucleus neurons to synaptic input demonstrated a late, slow depolarizing synaptic potential (slow EPSP) having a late ncy of 9-12 ms, and a maximal duration of 600 ms. it is concluded that neither intrinsic membrane responses, nor the duration of the slow EP SP, can fully account for the behavior of red nucleus neurons during b urst discharge. We hypothesize that activity in the red nucleus is dri ven by a gradual recruitment of NMDA receptors, and1pr by polysynaptic excitatory pathways.