Long-term Estradiol-17β Administration Decreases the Number of Neurons in the Caudal Mesenteric Ganglion Innervating the Ovary in Sexually Mature Gilts

The effect of estradiol-17 beta (E-2) on the number and distribution of neurons in the caudal mesenteric ganglion (CaMG) supplying the ovary of adult pigs was investigated. Also, the numbers of ovarian dopamine-beta-hydroxylase (D beta H-), neuropeptide Y (NPY-), somatostatin (SOM-), galanin (GAL-) and estrogen receptor (ER)-immunoreactive perikarya as well as the density of the intraganglionic nerve fibers containing D beta H and/or NPY, SOM, GAL were determined. E-2 was administered i.m. from day 4 of the first studied estrous cycle to the expected day 20 of the second studied cycle. Injections of E-2 (1) increased the E-2 level in the peripheral blood approximately 4-5 fold, (2) decreased the number of small-sized Fast Blue-positive postganglionic neurons in the CaMG, (3) decreased the number of small perikarya in the ventral, dorsal and central regions of the CaMG, (4) decreased the number of large perikarya in the dorsal and central regions, (5) decreased the number of small and large perikarya in the CaMG that were D beta H+/NPY+, (6) decreased the number of small D beta H+ but NPY- perikarya, (7) decreased the number of small perikarya coded D beta H+/SOM+ and D beta H+/SOM-, (8) decreased the number of small D beta H+/GAL(-) perikarya, (9) decreased the number of small and large perikarya expressing ER subtypes alpha and beta and (10) decreased the total number of nerve fibers in the CaMG containing D beta H and/or NPY and D beta H and/or GAL. These results show that long-term E-2 treatment of adult gilts downregulates the populations of both noradrenergic and ERs expressing ovarian neurons in the CaMG. Our findings suggest also that elevated E-2 levels that occur during pathological states may regulate gonadal function(s) by affecting ovary supplying neurons.