The role of tail skin temperature in the facilitation of the tail-flick reflex after spinal transection or interference with descending serotonergic neurotransmission.
We examined in mice whether tail skin temperatures and tail-flick reflexes were changed after spinal transection or intrathecal (i.th.) injection of the serotonin (5-HT) neurotoxin 5,6-dihydroxytryptamine (5,6-DHT) or the 5-HT receptor antagonist metergoline. Transection of the spinal cord reduced tail-flick latency (the time needed to evoke the tail-flick reflex by radiant heat) and increased tail skin temperature 15-21 days after surgery. Analysis of covariance showed that the effect of tail skin temperature on tail-flick latency was far more pronounced than the effect of spinal transection. Intrathecal injection of 5,6-DHT (5 or 10 micrograms mouse-1), which extensively reduced the spinal levels of 5-HT, reduced tail-flick latency and increased tail skin temperature 1-5 days after treatment. Similarly, tail-flick latency was shortened and tail skin temperature elevated 15 min after i.th. injection of metergoline (0.5 micrograms mouse-1). Analysis of covariance showed no significant effect of i.th. 5,6-DHT or i.th. metergoline on tail-flick latency. Tail skin temperature, on the other hand, had a highly significant effect on tail-flick latency. The results show that the facilitation of the tail-flick reflex in spinally transected mice and mice injected i.th. with 5,6-DHT or metergoline is mainly caused by increased tail skin temperature. The data do not indicate that descending 5-HT pathways tonically inhibit the tail-flick reflex.
Eide
P K
PK
Department of Physiology, University of Bergen, Norway.
Rosland
J H
JH
D015115:5,6-Dihydroxytryptamine / Q000008:administration & dosage; D000818:Animals; D007278:Injections, Spinal; D008297:Male; D008711:Metergoline / Q000008:administration & dosage; D051379:Mice; D008815:Mice, Inbred Strains; D009619:Nociceptors / Q000502:physiology; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D012701:Serotonin / Q000008:administration & dosage; D012881:Skin Temperature / Q000187:drug effects; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects; D013623:Tail / Q000294:innervation / Q000502:physiology*
D011985:Receptors, Serotonin; D008711:Metergoline; D012701:Serotonin; D015115:5,6-Dihydroxytryptamine