SYMPATHETICALLY-CORRELATED ACTIVITIES OF DORSAL HORN NEURONS IN SPINALLY- TRANSECTED RATS. David Chau, Namjin Kim and Lawrence P. Schramm. Departments of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2196.
APStracts 4:0065N, 1997.
ABSTRACT
In mammals with an intact neuraxis, most sympathetic nerve activity is generated by brainstem systems. Therefore, these systems have attracted much more attention than spinal systems that generate excitatory inputs to sympathetic preganglionic neurons. The purpose of this study was to determine whether, within hours of C1 spinal cord transection, spinal dorsal horn neurons (DHN) play a role in generating sympathetic nerve activity. Experiments were conducted in chloralose-anesthetized rats. We recorded renal sympathetic nerve activity (RSNA) in the left renal nerve, and we recorded the activities of neurons located in the left dorsal horn at T2, T8,T10 , T13, and L2. We also recorded the activity of neurons in the right dorsal horn at T10. The somatic fields and cutaneous modalities of most neurons were determined. Spike-triggered averaging was used to determine relationships between the ongoing activities of DHN and ongoing RSNA. In the left dorsal horn, bursts of ongoing activity of 16% of DHN at T8 and 43% of DHN at T10 were positively correlated with bursts of ongoing RSNA at latencies of 59 ñ 8ms. At no other level on the left side, nor in the T10 segment on the right side, were the activities of DHN correlated with RSNA. DHN with activities correlated with RSNA were located only in dorsal horn laminae III-V. Deeper laminae were not investigated in these experiments. The activities of all sympathetically- correlated DHN exhibited bursts of action potentials with interspike intervals shorter than 10ms. All but one sympathetically-correlated DHN exhibited wide- dynamic-range modalities. The modalities of sympathetically-uncorrelated neurons were more heterogeneous. Brief (5-10s) noxious cutaneous stimulation of mid- and lower-thoracic dermatomes on the left side excited all sympathetically-correlated DHN and simultaneously increased RSNA. The excitatory cutaneous fields of sympathetically-correlated neurons were circumscribed by the excitatory fields for RSNA. The excitatory cutaneous fields of some sympathetically-uncorrelated DHN extended beyond the excitatory fields for RSNA. Noxious cutaneous stimulation of the extremities on the left side which decreased RSNA simultaneously decreased the activities of all sympathetically-correlated DHN. These data provide electrophysiological evidence that, in spinally-transected rats, a population of DHN may generate or convey excitatory input to renal sympathetic preganglionic neurons. 

Received 13 December 1996; accepted in final form 5 February 1997.
APS Manuscript Number J969-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 20 February 1997