TRIGEMINAL-PARABRACHIAL CONNECTIONS - POSSIBLE PATHWAY FOR NOCICEPTION-INDUCED CARDIOVASCULAR REFLEX RESPONSES

Noxious stimulation of dental nerves elicits marked changes in cardiov ascular function. In order to investigate central pathways mediating r eflex changes in cardiovascular activity, immunohistochemical localiza tion of cells expressing the immediate-early gene, c-Sos, was used to identify central neurons responding to noxious electrical stimulation of mandibular, incisor tooth dentin or chemical (capsaicin) stimulatio n of tooth pulp in the anesthetized rat. Injections of Fluoro-Gold wer e made in the lateral parabrachial region to identify efferent project ions from the spinal trigeminal nucleus. Electrical and chemical stimu lation produced similar patterns of Fos-positive neurons in the spinal trigeminal nucleus: subnuclei caudalis, interpolaris and oralis. Fos- positive neurons were most dense in laminae I and LT, of the dorsomedi al subnucleus caudalis with fewer Fos-positive neurons located in the interpolaris and oralis subnuclei. Sham stimulation of tooth dentin an d control vehicle injections into the tooth pulp resulted in either a few weakly stained or no Fos-positive neurons in the spinal trigeminal nucleus. Cell bodies double labeled with Fluoro-Gold following inject ions into the parabrachial region and Fos-protein subsequent to electr ical stimulation of incisor tooth were present in all three subnuclei of the spinal trigeminal nucleus. The largest number of Fos-positive n eurons with efferent projections to the lateral parabrachial region we re located in subnucleus caudalis (32.2 +/- 5.3 S.E.M.) and fewer were located in the interpolaris (0.4 +/- 0.4 S.E.M.) and oralis (19.8 +/- 3.5 S.E.M.) subnuclei. The results demonstrate that nociceptive denta l input received by the three subnuclei of the spinal trigeminal nucle us, particularly the subnucleus caudalis, is relayed to the lateral pa rabrachial nucleus.