INTRACELLULAR RECORDING FROM THALAMIC NEURONS DURING RETICULOCORTICAL ACTIVATION

Abstract

Intracellularly recorded activities of thalamic neurons during recruiting responses have been compared with activities elicited by high-frequency (25- 75/sec.) midline thalamic (CM) stimulation in encephale isole cats. Neurons in which long-latency inhibitory postsynaptic potentials (IPSP''s)were prominent during recruiting responses evoked by low-frequency (7/sec.) CM stimulation showed either increased discharge frequency without significant membrane depolarization or long-latency sustained depolarization during high-frequency CM stimulation. Neurons with prominent excitatory synaptic drives during recruitment exhibited short-latency depolarization during high-frequency CM stimulation. Synaptically induced depolarization inactivation of spikes was characteristically observed in these elements after variable periods of repetitive firing. Persisting effects of high-frequency CM stimulation on thalamic neurons consisted in elimination of evoked IPSP''s and marked potentiation of excitatory synaptic bombardment. These effects were observed in cells with residual postactivation depolarization and elements in which repolarization was complete. Blockade of inhibition and the development of sustained excitatory synaptic drives are major intrathalamic synaptic events involved in the transition from synchronization to desynchronization of thalamic neuronal activity.