Peptide immunocytochemistry in afferent neurons from lower gut in rats

Several peptides were detected in primary sensory neurons located in nodose and dorsal root ganglia and projecting from rat cecum and rectosigmoid, through a combination of retrograde staining by the fluorescent tracer DY-2HCl and of the immunofluorescent procedure of Coons. The three larger cell populations thus identified stored immunoreactive components respectively similar to calcitonin gene-related peptide (CGRP), substance P (SP), and a peptide related to peptide histidine methionine (PHM). The later immunoreactivity consisted of a single molecular form with an apparent molecular weight smaller than PHM itself. Fewer cells contained components immunologically similar to somatostatin 14 (ST14), to the 1-14 N-terminal sequence of somatostatin 28 (1-14 S28), and to neuropeptide Y (NPY). Neonatal treatment with capsaicin resulted in a drastic reduction of immunoreactivity for SP, PHM, ST14, 1-14 S28, and in a partial reduction of CGRP-like positive perikarya. These results demonstrate that several peptides are potentially involved in the sensory innervation of the lower gut in rat.