Spinal and medullary reflex components of the somatosympathetic reflex discharges evoked by stimulation of the group IV somatic afferents

Abstract

Sympathetic reflex discharges were recorded from lumbar white rami (WR) in cats anaesthetized with chloralose. Stimulation of the group IV afferent fibres of either hindlimb nerves or adjacent spinal nerves evoked the group IV afferent reflex in CNS-intact as well as in acutely decerebrated cats. The group IV afferent reflex evoked by stimulation of hindlimb nerves in CNS-intact cats remained after decerebration, whereas it disappeared completely after spinal transection. However, in the long-kept chronic spinal cats, whose spinal cords were transected more than 8–12 weeks before experiments, this reflex reappeared. The group IV afferent reflex evoked by stimulation of adjacent spinal nerves in CNS-intact cats remained even in acute spinal cats. It could be evoked by single shock stimuli. The following conclusions are reached. (1) The group IV afferent reflex evoked by stimulation of hindlimb nerves has a central reflex pathway through the nedulla oblongata when the CNS neuraxis is intact. However, a spinal reflex pathway can also exist under special conditions such as in very long-kept chronic spinal animals. (2) The group IV afferent reflex evoked by stimulation of adjacent spinal nerves definitely has a spinal reflex pathway in CNS-intact cats.