Localization of Substance P-Immunoreactive Nerve Structures in the Rat Colon

Abstract

The tachykinins, including their major representative substance P (SP), are an essential component of its non-adrenergic, non-cholinergic transmission of the myenteric plexus of the enteric nervous system. Hence, the understanding of the role that SP plays in the conduction of a wide variety of motility and secretory reflexes lies in the evidence-based understanding of the sites of its expression. In the present study, the presence, distribution and staining intensity of the SP-positive nerve structures in the myenteric plexus of the proximal and distal colon of the adult rat have been investigated by means of immunohistochemistry at the light microscopic level. We observed an abundance of intensely stained beaded SP-immunopositive fibres, surrounding the SP-immunonegative myenteric neuronal cell bodies in a basket-like manner. Fine bundles of SP-immunostained varicose fibres were also registered in the adjacent smooth muscle layers. The statistical analysis revealed discernible prevalence of the staining intensity in the proximal colon, compared to the distal one. In summary, our findings provide immunohistochemical evidence for the occurrence of abundant SP-immunopositive nerve structures in the colonic region of the rat. Taken together with previous morphological and pharmacological research the results of this study suggest that the SP-mediated neurotransmission is of physiological and likely of pathological significance for the examined region.