Immunohistochemical localization of Met5-enkephalin-Arg6-Gly7-Leu8 in the female genital organs and in the paracervical ganglion of the pig.

Indirect immunofluorescence method was used to study the localization and distribution of the proenkephalin A-derived octapeptide, Met5-enkephalin-Arg6-Gly7-Leu8 (MEAGL), in the paracervical ganglion and in the female genital organs of the pig. In the paracervical ganglion, a subpopulation of principal neurons and nerve fibers contained MEAGL immunoreactivity. In the vagina, numerous MEAGL-immunoreactive nerve fibers were localized in the muscular membrane, under the serous membrane and in the submucous layer. The uterine cervix contained a great number of immunoreactive nerve fibers in muscular membrane and in submucous and subserous layers. The pattern of distribution of MEAGL-immunoreactive nerve fibers in the uterine horns was similar to that of cervix, but their number in the uterine horns was lower. MEAGL-immunoreactive fibers were also observed through different oviductal layers. In the ovary a low number of immunoreactive fibers were seen in the medullary and cortical parts of the organ. The results of this study indicate that the female genital organs, particularly the uterus and vagina, of the pig receive dense innervation by nerve fibers containing the proenkephalin A-derived octapeptide MEAGL. The presence of MEAGL in principal neurons and fibers of the paracervical ganglion suggests that a large proportion of them originate from neurons of the paracervical ganglion.