Differential effects of the 5HT1B/1D receptor agonist naratriptan on trigeminal versus spinal nociceptive responses.

In vivo electrophysiological assays in anesthetized rats have been used to compare the effects of the 5HT1B/1D receptor agonist, naratriptan, on central trigeminal nociceptive processing from dural and cutaneous inputs with its effects on nociceptive processing in the spinal cord. Naratriptan inhibited responses of single trigeminal neurons, to noxious electrical and mechanical stimulation of the dura and face, dose dependently by a maximum of 67+/-3% and 70+/-18%, respectively, at 3 mg kg(-1) i.v. In contrast, naratriptan did not affect spinal dorsal horn neuronal responses to noxious mechanical stimulation of the hind-paw. These findings suggest that 5HT1B/1D receptors have differential effects on nociceptive processing in the trigeminal versus spinal dorsal horns and provide a potential explanation for the lack of general analgesic effects of brain penetrant 5HT(1B/1D) agonist antimigraine drugs.