Carrageenan-induced changes in spinal nociception and its modulation by the brain stem.
Carrageenan was used to study inflammation-induced changes in spinal nociception and its brain stem modulation in the pentobarbitone-anesthetized rat. Carrageenan was administered intraplantarly into one hindpaw 2 h before the start of electrophysiological single unit recordings of wide-dynamic range (WDR) neurons of the spinal dorsal horn. Carrageenan produced a significant leftward shift in the stimulus-response function for mechanical stimuli, whereas that for noxious heat stimuli was short of statistical significance. Conditioning electrical stimulation in the rostroventromedial medulla (RVM) significantly attenuated noxious heat-evoked, but not mechanically evoked, responses to spinal dorsal horn WDR neurons in the control (contralateral) side. However, in the carrageenan-treated side RVM stimulation had no significant effect on mechanically or noxious heat-evoked responses. Following direct spinal administration of neuropeptide FF (NPFF), noxious heat-evoked responses, but not mechanically evoked responses, were attenuated by RVM-stimulation also in the carrageenan-treated side. This selective NPFF-induced enhancement of brain stem-spinal inhibition was not reversed by naloxone. The results indicate that carrageenan-induced inflammation significantly changes the response properties of spinal nociceptive neurons and their brain stem-spinal modulation. During inflammation, NPFF in the spinal cord produces a submodality-selective potentiation of the antinociceptive effect induced by brain stem-spinal pathways, independent of naloxone-sensitive opioid receptors.
Pertovaara
A
A
Department of Physiology, Institute of Biomedicine, University of Helsinki, Finland.
Hämäläinen
M M
MM
Kauppila
T
T
Panula
P
P
D000818:Animals; D001933:Brain Stem / Q000378:metabolism / Q000503:physiopathology*; D002351:Carrageenan; D004558:Electric Stimulation; D004594:Electrophysiology; D006358:Hot Temperature; D007249:Inflammation / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D009479:Neuropeptides / Q000378:metabolism; D009619:Nociceptors / Q000378:metabolism / Q000502:physiology*; D009842:Oligopeptides / Q000378:metabolism; D010812:Physical Stimulation; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000378:metabolism / Q000503:physiopathology*
D009479:Neuropeptides; D009842:Oligopeptides; D002351:Carrageenan; C053651:phenylalanyl-leucyl-phenylalanyl-glutaminyl-prolyl-glutaminyl-arginyl-phenylalaninamide