Effects of noxious skin heating on spontaneous cell activity in the magnocellular red nucleus of the cat.

Abstract

Neurones were extracellularly recorded in the magnocellular red nucleus (RNm) of decerebrated cats and identified by their monosynaptic responses to stimulation of the contralateral brachium conjunctivum (BC), and by their antidromic responses after stimulation of the rubrospinal tract in the cord. After each cell was isolated, noxious stimulation was applied to the skin, by touch-free radiant heat. The large majority of the cells (91.5%) responded to noxious stimulation of the skin, even after the RNm was deprived of cerebellar input by sectioning the contralateral BC. About half of this cell group was activated by noxious stimulation and the other half was inhibited. To obtain responses in RNm cells, the stimulus had to be above the thermal pain threshold, and the stimulation area had to be inside the somatic receptive field of the cell for low-threshold afferents. Thus, the receptive fields for nociceptive and low-threshold afferents are similarly organized somatotopically. Noxious stimulation sometimes induced a rhythmic pattern of spike bursts in RNm cells, which could be a reflection of the locomotor-like activity generated in the spinal cord. The results indicate that nociceptive information participates in sensorimotor control via the spinorubrospinal loop, which may also transmit low-threshold cutaneous input and corollary discharge of the activity in spinal motor centres to the RNm.