On the reduction of spontaneous and glutamate-driven spinocerebellar and spinoreticular tract neuronal activity during active sleep

The present study was performed to provide evidence that dynamic neural pro cesses underlie the reduction in dorsal spinocerebellar tract and spinoreti cular tract neuron activity that occurs during active sleep. To ascertain t he effect of local inhibition on the spontaneous and glutamate-evoked spike discharge of sensory tract neurons, preliminary control tests were perform ed during the state of quiet wakefulness, where GABA or glycine was co-admi nistered in a sustained fashion during pulsatile release of glutamate to do rsal spinocerebellar tract (n = 3) or spinoreticular tract (n = 2) neurons. Co administration of GABA or glycine also resulted in a significant marked suppression of spontaneous spike activity and glutamate-evoked responses o f these cells. Extracellular recording experiments combined with juxtacellu lar application of glutamate were then performed on 20 antidromically ident ified dorsal spinocerebellar tract and spinoreticular tract neurons in the chronic intact cat as a function of sleep and wakefulness. The glutamate-ev oked activity of a group of 10 sensory tract neurons (seven dorsal spinocer ebellar tract. three spinoreticular tract), which exhibited a significant d ecrease in their spontaneous spike activity during active sleep, was examin ed. Glutamate-evoked activity in these cells was significantly attenuated d uring active sleep compared with wakefulness. In contrast, the glutamate-ev oked activity of a second group of eight sensory tract neurons (four dorsal spinocerebellar tract, four spinoreticular tract). which exhibited a signi ficant increase in their spontaneous spike activity during active sleep, wa s not significantly altered in a state-dependent manner. These data indicate that, during natural active sleep, a dynamic neural pro cess is engaged onto certain dorsal spino cerebellar tract and spinoreticul ar tract neurons. which in turn dampens sensory throughput to higher brain centers. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reser ved.