Synaptic Transmission in the Ventrolateral Thalamic Nucleus During Natural Sleep and Wakefulness: Its Relation to the Cerebellum and Sensorimotor Cortex

Abstract (1) The physiological features of cerebello-thalamic transmission during the sleep-waking cycle have been investigated after surgical interruption of projection fibers from either the cerebellum or the pericruciate cortex to the ventro-lateral thalamic nucleus in chronic, unrestrained, unanaesthetized cats. (2) In particular, both presynaptic and postsynaptic components of responses evoked in the VL by stimulation of the brachium conjunctivum were recorded during the different stages of sleep and wakefulness, and their changes in amplitude according to the level of vigilance were statistically evaluated. (3) It has been found that (a) the degree of patency of BC presynaptic endings remains practically unchanged throughout the sleep-waking cycle, while (b) the VL thalamic output upon stimulation of the BC is lower during light sleep than during deep sleep and wakefulness, thus paralleling the results previously obtained in the intact preparation. (4) Moreover, both antidromic and direct activation of VL thalamic nucleus show that the level of excitability of thalamic relay cells is lower during light sleep than during deep sleep and wakefulness. (5) These results support the view that the occurrence of synaptic transmission changes in the VL during the sleep-waking cycle does not depend either on cortico-thalamic or cerebello-thalamic influences.