CHARACTERIZATION OF NEURONS IN THE AREA OF THE MEDULLARY LATERAL RETICULAR NUCLEUS RESPONSIVE TO NOXIOUS VISCERAL AND CUTANEOUS STIMULI

In halothane-anesthetized rats, 283 caudal medullary neurons responsiv e to colorectal distension (CRD) were characterized using extracellula r electrodes. Neurons inhibited by CRD (n = 82) were in the area dorsa l to the lateral reticular nucleus (LRN). Most neurons excited by CRD (n = 130) were located within or immediately adjacent to the LRN, were excited by noxious heat and/or noxious pinch of at least half the bod y surface and were called bilateral nociceptive specific (bNS) neurons . bNS neurons had accelerating responses to graded CRD (threshold: 20 +/- 2 mmHg). Ten of twelve bNS neurons tested could be antidromically activated by electrical stimulation of the midline cerebellum. Other n eurons excited by CRD (n = 71) had mixed responses to cutaneous stimul i and were generally located in the area dorsal to the LRN. Increases in blood pressure due to intravenous phenylephrine did not significant ly alter the spontaneous activity of neurons excited by CRD, but alter ed spontaneous activity (12 excited, four inhibited) in all neurons te sted which were inhibited by CRD. Decreases in blood pressure produced by intravenous nitroprusside produced a reciprocal response in most n eurons inhibited by CRD and had a delayed onset (20-30 s after bolus a dministration) excitatory effect on 21 of 27 units excited by CRD. Com bined with other studies, these data suggest a role for neurons within and adjacent to the LRN in the modulation of visceral nociception. Th ey also implicate a role for the cerebellum in visceral nociceptive pr ocessing. (C) 1998 Elsevier Science B.V. All rights reserved.