Long-Term Estradiol-17β Administration Changes the Population of Paracervical Ganglion Neurons Supplying the Ovary in Adult Gilts

The aim of this study was to determine the influence of estradiol-17β (E2) overdose on the number and distribution of ovarian parasympathetic neurons in the paracervical ganglion (PCG) in adult pigs. To identify the neurons innervating gonads on day 3 of the estrous cycle, the ovaries of both the control and experimental gilts were injected with retrograde neuronal tracer Fast Blue. From next day to the expected day 20 of the second studied cycle, experimental gilts were injected with E2, while control gilts received oil. The PCG were then collected and processed for double-labeling immunofluorescence. Injections of E2 increased the E2 level in the peripheral blood approximately four- to fivefold and reduced the following in the PCG: the total number of Fast Blue-positive neurons; the number of perikarya in the lateral part of the PCG; the numbers of vesicular acetylcholine transporter (VAChT)+/somatostatin+, VAChT+/vasoactive intestinal polypeptide (VIP)+, VAChT+/neuronal isoform of nitric oxide synthase+, VAChT+/VIP−, VAChT+/dopamine β-hydroxylase (DβH)−, VAChT−/VIP−, and VAChT−/DβH− perikarya; and the total number of perikarya expressing estrogen receptors (ERs) subtype α and/or β. In summary, long-term E2 treatment of adult gilts downregulates the population of both cholinergic and ERs expressing the PCG ovary-projecting neurons. Our results suggest that elevated E2 levels occurring during pathological states may regulate gonadal function(s) by affecting ovary-supplying neurons.