The effects of intrathecally applied noradrenaline and 5-hydroxytryptamine on spinal nocifensive reflexes and the rostral transmission of noxious information to the thalamus in the rat.
The effects of intrathecally applied noradrenaline (NA) and 5-hydroxytryptamine (5-HT) on a spinal nocifensive reflex and nociceptive responses recorded from rat ventrobasal thalamus have been compared. A dose of 15 nmol NA increased the tail flick latency (TFL) for approximately 120 min (n = 12) in rats lightly anaesthetised with Saffan. A dose of 260 nmol 5-HT increased the TFL for approximately 21 min (n = 7). In rats anaesthetised with urethane, 15 nmol NA produced a reversible reduction in the response of 15 ventrobasal thalamic units to noxious stimulation lasting approximately 36 min (n = 15). A dose of 260 nmol 5-HT reduced thalamic nociceptive responses for approximately 25 min (n = 12). This suggests that spinal interneurones subserving the tail flick reflex are more sensitive to NA than spinal neurones involved in the transmission of noxious information supraspinally. In contrast, intrathecally applied 5-HT is equipotent in its action on both groups of neurones involved in nociceptive mechanisms.
Barasi
S
S
Clatworthy
A
A
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004305:Dose-Response Relationship, Drug; D007278:Injections, Spinal; D008297:Male; D009638:Norepinephrine / Q000008:administration & dosage* / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D012018:Reflex / Q000502:physiology; D012701:Serotonin / Q000008:administration & dosage* / Q000494:pharmacology; D013116:Spinal Cord / Q000503:physiopathology*; D009435:Synaptic Transmission / Q000187:drug effects*; D013788:Thalamus / Q000503:physiopathology*
D012701:Serotonin; D009638:Norepinephrine