Brain research
-
(1) Unitary extracellular recordings were made from 92 lumbar dorsal horn neurones in urethane-anaesthetised rats. These neurones were classed as 'noxious-only' (4), 'non-noxious-only' (33) or 'convergent' (55) by their responses to stimulation of their cutaneous receptive fields on the ipsilateral hindpaw. (2) Distension of abdominal viscera (colon, urinary bladder) depressed the activities of the vast majority (93%) of the convergent neurones but of only one other cell (a non-noxious-only neurone). ⋯ There were however, some small differences in the extent and temporal evolution of the inhibitory effects of the visceral and of the somatic stimuli--the visceral stimuli generally producing weaker inhibitions with slower rates of onset and recovery. It is proposed that these differences may have reflected different amounts and patterns of activity in the relevant primary afferent fibres rather than being due to different central neural mechanisms. (4) These results and the likely explanation that the effects of the visceral stimuli were mediated by a diffuse mechanism should be taken into account when interpreting the results of other studies in which inhibitory effects are produced by visceral stimulation.
-
Prostaglandin E2 (PGE2) microinjection (25 ng, 250 nl) into the preoptic area of the anterior hypothalamus (POAH) stimulated heat production in brown adipose tissue (BAT) and increased core temperature in urethane-anesthetized rats. These thermogenic and hyperthermic effects were attenuated by co-injection of NG-monomethyl-L-arginine (NMMA, 25 micrograms), a competitive inhibitor of nitric oxide (NO) production from L-arginine. ⋯ Intra-POAH injection of NMMA (25 micrograms) or L-arginine (50 micrograms) alone had no effect on IBAT and core temperatures. The results suggest that the effect on thermoregulation induced by action of PGE2 in the POAH is modulated by a local L-arginine-dependent and NMMA-sensitive NO-generating system.