Segmental origin of sympathetic preganglionic neurones regulating the tail circulation in the rat

The spinal segments of origin of the sympathetic preganglionic neurones (SPNs) influencing the activity of sympathetic postganglionic neurones innervating the tail have been studied using a neurophysiological approach. Activity was recorded from the ventral collector nerve that carries 70% of the sympathetic fibres innervating targets within the tail and provides 80% of the innervation of the caudal ventral artery. When recording activity from the ventral collector nerve at the tail base, the largest responses were evoked following electrical stimulation within spinal segments lumbar (L) 1 and 2 and smaller responses from thoracic (T) 13 (n = 5). Although similar responses to those recorded from the tail base were elicited from spinal segments L1 and L2, when activity was recorded from mid-tail only minimal responses were evoked from T13 (n = 6). On average robust responses were never elicited following stimulation beyond these segments. Responses had latencies compatible with conduction over C-fibre axons and were absent following ganglionic blockade. It is concluded that SPNs influencing the tail circulation reside mainly in L1 and L2 spinal segments and there is also a substantial but lesser contribution arising from segment T13.