Reflex activity in postganglionic fibres within skin and muscle nerves elicited by somatic stimuli in chronic spinal cats

1.Reflex and spontaneous activity in cutaneous and muscle postganglionic neurones of the hind leg were investigated in 10 chloralose anaesthetized cats which were spinalized at Th₈ 7 to 96 days before the experiments. The reflexes were elicited by electrical stimulation of cutaneous Group II to Group IV afferent fibres in the sural nerve and by natural stimulation of hairs and of cutaneous nociceptors.2.Electrical stimulation of cutaneous afferent fibres elicited the same reflex pattern in both cutaneous and muscle postganglionic neurons. Group II fibres had — if any effects — mostly inhibitory effects on the postganglionic neurones. Stimulation of Group III and Group IV fibres induced excitation followed by a depression of the spontaneous activity in the postganglionic neurones.3.Natural stimulation of hairs by air jets induced depression of the spontaneous activity in both types of postganglionic neurones. Noxious mechanical or thermal stimuli to the skin induced excitation in both types of postganglionic neurones. The spontaneous activity in cutaneous postganglionic neurones could additionally be depressed by noxious stimuli applied to the skin area which is very close to the area innervated by these neurones.4.Reflexes and spontaneous activity recovered partially in cutaneous postganglionic neurones in about 10 weeks after spinalization. Those in muscle postganglionic neurones recovered partially after about 4 weeks. They were stronger in muscle postganglionic neurones than in cutaneous postganglionic neurones.5.The results are discussed in relation to the central organization of the sympathetic nervous system in the neuraxis and in relation to other investigations of the somato-sympathetic reflexes in spinal animals.