CENTRAL PROJECTION OF CALCITONIN-GENE-RELATED PEPTIDE (CGRP)-IMMUNOREACTIVE AND SUBSTANCE-P (SP)-IMMUNOREACTIVE TRIGEMINAL PRIMARY NEURONS IN THE RAT

Substance P (SP) is implicated in transmission of primary afferent noc iceptive signals. In primary neurons, SP is colocalized with calcitoni n gene-related peptide (CORP), which is another neuropeptide marker fo r small to medium primary neurons. CORP coreleased with SP augments th e postsynaptic effect of SP and thereby modulates the nociceptive tran smission. This study demonstrates the distribution of CORP-like immuno reactivity (-ir) and SP-ir in the lower brainstem of normal rats and a fter trigeminal rhizotomy or tractotomy at the level of subnucleus int erpolaris (Vi). By comparing the results obtained from normal and deaf ferented rats, we analyzed the central projection of trigeminal primar y nociceptors. The CGRP-immunoreactive (-ir) trigeminal primaries proj ected to the entire rostrocaudal extent of the spinal trigeminal nucle us, the principal nucleus (PrV), the paratrigeminal nucleus (paraV), a nd the lateral subnucleus of solitary tract nucleus (STN) on the ipsil ateral side. The trigeminal primaries projecting to the spinal trigemi nal nucleus, paraV and STN also contained SP-ir. The ipsilateral trige minal primaries were the exclusive source of CGRP-ir terminals in the PrV, the Vi and the dorsomedial nucleus within the subnucleus oralis ( Vo). The medullary dorsal horn (MDH) and the lateral edge of Vo receiv ed convergent CGRP-ir projection from the ipsilateral trigeminal prima ries and other neurons. The glossopharyngeal and vagal primaries are c andidates for the source of CGRP-ir projection to the Vo and the MDH, while the dorsal root axons supply the MDH with CGRP-ir terminals. In addition, contralateral primary neurons crossing the midline appear to contain CORP and to terminate in the MDH. (C) 1997 Wiley-Liss, Inc.