Alterations in neurokinin A-, substance P- and calcitonin gene-related peptide immunoreactivities in the caudal trigeminal nucleus of the rat following electrical stimulation of the trigeminal ganglion

We have carried out an immunohistochemical study on the presence of neuroki nin A (NKA) and substance P (SP) in the rat caudal trigeminal nucleus (CTN) after electrical stimulation of the trigeminal ganglion (TG), used as an e xperimental model to induce alterations, some of which may occur during mig raine attacks (release of vasoactive peptides from perivascular trigeminal axons and neurogenic inflammation). Both unilateral, 30 min electrical stim ulation (5 Hz, 5 ms, 0.1-1 mA) of the TG and 5 min stimulation with a sligh t increase in the stimulating parameters (7.5 Hz, 5 ms, 1.4 mA) caused a si gnificant depletion of the NKA and SP immunoreactivities (-IR) of the TG ne rve central terminals in the ipsilateral CTN. Calcitonin gene-related pepti de (CGRP)-IR of the ipsilateral CTN was also studied in the CTN using the i ncreased stimulating parameters and a marked depletion of CGRP-IR was also observed following TG stimulation. Such depletion may be due to the release of neuropeptides from the trigeminal central terminals, These findings sug gest that NKA, SP and CGRP could act as neurotransmitters at the first cent ral synapses of the trigeminal nociceptive pathway to transmit the sensory stimuli to the higher brain centers. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.