AN IMMUNOCYTOCHEMICAL INVESTIGATION OF THE RELATIONSHIP BETWEEN SUBSTANCE-P AND THE NEUROKININ-1 RECEPTOR IN THE LATERAL HORN OF THE RAT THORACIC SPINAL-CORD

The relationship between substance P-containing axons and sympathetic preganglionic neurons possessing the neurokinin-l receptor was investi gated in the lateral horn of the rat thoracic spinal cord, Sympathetic preganglionic neurons were labelled retrogradely with Fluorogold. Sec tions containing labelled cells were reacted with antibodies against c holine acetyltransferase. substance P and the neurokinin-l receptor an d examined with three-colour confocal laser scanning microscopy. In al l, 95 sympathetic preganglionic neurons were examined and 79% of these were immunoreactive for the neurokinin-l receptor. Substance P-immuno reactive axons not only made contacts with preganglionic neurons which were immunoreactive for the receptor but also made contacts with cell s which did not express the receptor. Dendrites, labelled with immunor eactivity for choline actyltransferase. also received contacts from su bstance P-immunoreactive varicosities but this was not related to the presence or the absence of receptor, An electron microscopic analysis was performed to investigate the relationship between substance P-cont aining boutons and dendrites possessing the neurokinin-1 receptor. Imm unoreactivity for substance P was detected with peroxidase immunocytoc hemistry and immunoreactivity for the receptor was detected with the s ilver-intensified gold method. Substance P-containing boutons made syn apses with dendrites which were positively and negatively labelled for the receptor. Receptor immunoreactivity was not usually present at sy napses formed by substance P boutons with neurokinin-l-immunoreactive dendrites. It is concluded that substance P may modulate much of the a ctivity of sympathetic preganglionic neurons through an indirect non-s ynaptic mechanism. (C) 1997 Elsevier Science B.V.