Time course of changes in nociception after 5,6-dihydroxytryptamine lesions of descending 5-HT pathways.
Intrathecal injection of 5,6-dihydroxytryptamine (5,6-DHT) in rats produced selective lesions of the descending 5-HT pathways. Spinal 5-HT levels gradually fell to less than 10% of controls within 10 days of 5,6-DHT administration with no recovery evident within 4 weeks. The uptake of 14C-5-HT into crude spinal synaptosomes was similarly reduced. The uptake of 3H-NA into spinal synaptosomes was unaffected, as was the uptake of 14C-5-HT and 3H-NA into cortical synaptosomes. Following 5,6-DHT, tail-flick latencies were reduced by 20-30% during the first post-injection week, but returned to control levels during the second week. Intrathecal or systemic administration of the 5-HT receptor antagonist metergoline significantly reduced latencies of normal rats and of 5,6-DHT treated rats tested after the second week when the response was normalized. Metergoline did not, however, further reduce the latencies of lesioned rats during the first post-injection week. It is concluded that functional adaptation involving 5-HT neurotransmission compensated for the selective lesion of descending 5-HT pathways induced by 5,6-DHT.
D015115:5,6-Dihydroxytryptamine / Q000494:pharmacology*; D000818:Animals; D001923:Brain Chemistry; D008297:Male; D008711:Metergoline / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects*; D009619:Nociceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*; D013997:Time Factors
D008711:Metergoline; D012701:Serotonin; D015115:5,6-Dihydroxytryptamine