Interaction between cholinergic neurons and substance P or calcitonin gene-related peptide terminals of the rat sacral intermediolateral nucleus: double immunostaining at the light and electron microscopic levels

The relationships both between cholinergic neurons and substance P (SP) and between cholinergic neurons and calcitonin gene-related peptide (CGRP) terminals were examined in the rat sacral intermediolateral nucleus at the light and electron microscopic levels by means of double-immunostaining methods. Cholinergic neurons were labeled by a monoclonal antibody to choline acetyltransferase (CAT) with the avidin-biotin technique and stained bluish-green by indolyl-beta-galactoside reaction products with beta-galactosidase as a marker. On the same sections, SP or CGRP fibers were labeled by polyclonal antisera to SP or CGRP after application of the peroxidase-antiperoxidase (PAP) method and stained brown by the p-dimethylaminoazobenzene (DAB) reaction. After embedding in Epon, light and electron microscopic sections were examined. At the light microscopic level, CGRP-like immunoreactive (CGRP-I) fibers and SP-like immunoreactive (SP-I) fibers were found to pass through the lateral edge of the dorsal horn and then into the dorsal region of the sacral intermediolateral nucleus. In addition, SP-I fibers also extend from the dorsolateral funiculus into the entire sacral intermediolateral region. At the electron microscopic level, many axosomatic and axodendritic synapses were found between CAT-I structures and SP-I terminals in the intermediolateral nucleus, whereas most of the CGRP-I terminals in this area made axodendritic synapses with CAT-I dendrites. These results indicate that cholinergic neurons in the sacral intermediolateral nucleus receive direct synaptic input from SP-I and CGRP-I terminals.(ABSTRACT TRUNCATED AT 250 WORDS)