Attenuation of Fos-like immunoreactivity in the trigeminal nucleus caudalis following trigeminovascular activation in the anaesthetised guinea-pig

The present study has examined the involvement of sensory neurotransmitters in activating neurones in the trigeminal nucleus caudalis following stimulation of the trigeminovascular system in anaesthetised guinea-pigs. Electrical stimulation of the right trigeminal ganglion produced a unilateral expression of Fos-like immunoreactivity (Fos-LI) in the trigeminal nucleus caudalis. The tachykinin NK, receptor antagonist, GR205171 (100 mu g/kg i.v.) and the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (1 mg/kg i.v.) each inhibited expression of Fos-LI following electrical stimulation. The calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37) (1.3 mg/kg i.v.), administered following rostral intracarotid infusion of mannitol to disrupt the blood-brain barrier, tended to reduce Fos-LI evoked by electrical stimulation, although this failed to reach statistical significance. Capsaicin (10 nmol in 0.1 ml), administered intracisternally, produced a bilateral expression of Fos-LI in the trigeminal nucleus caudalis. This expression was unaffected by the peripherally acting NK, receptor antagonist, GR82334 (0.2 mg/kg i.v.) or CGRP(8-37) (1.3 mg/kg i.v.). The centrally penetrant Nk(1) receptor antagonist, GR205171 (100 mu g/kg i.v.), inhibited significantly Fos-LI evoked by intracisternal capsaicin administration. is concluded that the sensory neurotransmitters, substance P and glutamate are released centrally following activation of the trigeminovascular system and that each may be involved in activation of cells in the trigeminal nucleus caudalis. (C) 1997 Elsevier Science B.V.