SOMATOSENSORY AND MOVEMENT-RELATED PROPERTIES OF ROD NUCLEUS - A SINGLE-UNIT STUDY IN THE TURTLE

Extracellular recordings were performed from turtle red nucleus neuron s to examine their responsiveness to peripheral somatic stimulation an d to study differences between rubral sensory and movement-related res ponses. In pentobarbital sodium-anesthetized or decerebrate turtles, r ed nucleus neurons could be divided into two categories based on their response characteristics. The first group, which included 87% of neur ons studied, had low spontaneous rates of activity and responded with excitation to electrical stimulation of the spinal cord or the cerebel lum, or during active movement of the contralateral limbs. Neurons in this category were likely to be rubrospinal cells. The remaining 13% o f cells studied had higher rates of spontaneous discharge and were inh ibited by electrical stimulation or during active movement. These cell s might be rubral GABAergic interneurons. Single red nucleus neurons r esponded with excitation and/or inhibition to somatosensory stimulatio n. Unlike the motor fields, which were restricted to a single contrala teral limb, red nucleus sensory receptive fields were wide and often b ilaterally distributed. Rubral responsiveness to sensory stimulation w as found to be significantly diminished during active limb movements, thereby suggesting that sensory inputs to the red nucleus are not used for the on-line modification of motor commands. Inactivation of the c erebellar cortex enhanced the sensory responsiveness of rubral neurons and expanded the size of red nucleus receptive fields. These results suggest that the red nucleus receives substantial sensory input, and t hat the cerebellar cortex can modify the flow of sensory information t o the red nucleus.