Apparent hyperalgesia after lesions of the descending serotonergic pathways is due to increased tail skin temperature.
It has been suggested that the descending serotonergic pathways exercise a tonic inhibition on nociception in the spinal cord. In this study 5,6-dihydroxytryptamine (5,6-DHT, 20 micrograms base) injected intrathecally in rats reduced spinal serotonin concentration to 3.5% of control levels without significantly affecting spinal noradrenaline. The lesion reduced the mean tail-flick latency by approximately 35% and increased the mean tail skin temperature by approximately 3.5 degrees C; both parameters gradually returned to normal values within 2-3 weeks. Both in controls and in lesioned animals there was a highly significant negative correlation between tail skin temperature and tail-flick latency. Multiple regression analysis showed that the effect of lesioning on tail-flick latency was non-significant when the effect of skin temperature was taken into account. Thus the reduced tail-flick latency after lesions of descending serotonergic pathways, usually interpreted as increased nociception, may be due to changes in tail skin temperature.
Tjølsen
Arne
A
Department of Physiology, University of Bergen, N-5009 BergenNorway Department of Pharmacology, University of Bergen, N-5009 BergenNorway.
Berge
Odd-Geir
OG
Eide
Per Kristian
PK
Broch
Ole Jacob
OJ
Hole
Kjell
K
D015115:5,6-Dihydroxytryptamine / Q000494:pharmacology; D000818:Animals; D006930:Hyperalgesia / Q000503:physiopathology*; D006941:Hyperesthesia / Q000503:physiopathology*; D008297:Male; D009619:Nociceptors / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*; D012881:Skin Temperature; D013116:Spinal Cord / Q000502:physiology
D012701:Serotonin; D015115:5,6-Dihydroxytryptamine