ATTENUATION OF FOS-LIKE IMMUNOREACTIVITY IN THE TRIGEMINAL NUCLEUS CAUDALIS FOLLOWING TRIGEMINOVASCULAR ACTIVATION IN THE ANESTHETIZED GUINEA-PIG

The present study has examined the involvement of sensory neurotransmi tters in activating neurones in the trigeminal nucleus caudalis follow ing stimulation of the trigeminovascular system in anaesthetised guine a-pigs. Electrical stimulation of the right trigeminal ganglion produc ed a unilateral expression of Fos-like immunoreactivity (Fos-LI) in th e trigeminal nucleus caudalis. The tachykinin NK, receptor antagonist, GR205171 (100 mu g/kg i.v.) and the N-methyl-D-aspartate (NMDA) recep tor antagonist, MK-801 (1 mg/kg i.v.) each inhibited expression of Fos -LI following electrical stimulation. The calcitonin gene-related pept ide (CGRP) receptor antagonist, CGRP(8-37) (1.3 mg/kg i.v.), administe red following rostral intracarotid infusion of mannitol to disrupt the blood-brain barrier, tended to reduce Fos-LI evoked by electrical sti mulation, although this failed to reach statistical significance. Caps aicin (10 nmol in 0.1 ml), administered intracisternally, produced a b ilateral expression of Fos-LI in the trigeminal nucleus caudalis. This expression was unaffected by the peripherally acting NK, receptor ant agonist, 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 capsaici n administration. is concluded that the sensory neurotransmitters, sub stance P and glutamate are released centrally following activation of the trigeminovascular system and that each may be involved in activati on of cells in the trigeminal nucleus caudalis. (C) 1997 Elsevier Scie nce B.V.