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The rat cauda epididymidis receives sympathetic innervation from the inferior mesenteric ganglion (IMG). We have previously demonstrated that surgical removal of the IMG and proximal hypogastric nerves (IMG denervation) results in significant and cauda-specific changes in epididymal sperm transport, sperm motility, luminal fluid protein composition, and tissue histology. In the present study we used natural mating trials and intrauterine insemination (IUI) techniques to determine whether or not IMG denervation affects male fertility and reproductive capacity. For the initial studies, adult male Sprague Dawley rats were mated with estrous females 1 and 4 weeks following IMG denervation. Nine days after mating, uterine implantation sites and corpora lutea (CL) were counted. In females mated with sham-operated control males, 85.8% of ovulated oocytes were fertilized and subsequently implanted. In contrast, females mated with IMG-denervated males 1 or 4 weeks following surgery had 0% and 3.5%, respectively, of ovulated oocytes fertilized and implanted. For rats maintained 21 days after mating, an average of 13 +/- 1 pups were delivered by each of nine females mated with sham-operated control male rats; whereas, only seven morphologically normal pups were delivered by one of 14 females mated with IMG-denervated male rats. Additional experiments demonstrated that the decrement in offspring was, in part, due to a significant decrease in the number of spermatozoa in the female uterus following mating with IMG-denervated males. To determine whether IMG denervation exerted an additional effect directly on the fertilizing ability of spermatozoa, IUI experiments were performed. Six million cauda epididymal spermatozoa from 1- or 4-week IMG-denervated males were inseminated into the uterine horns of luteinzing hormone-releasing hormone (LHRH)-synchronized females and 9 days later implantation sites and CL were counted. Implantations were observed for 78%, 28%, and 25% of ovulated oocytes following IUI with spermatozoa from sham-operated controls and from 1- and 4-week IMG-denervated rats, respectively. To determine whether the reduction in implantation sites following IUI with spermatozoa from IMG-denervated rats resulted from impaired oocyte fertilization, studies were performed in which oocytes were retrieved and stained 24 hours after IUI. Comparable fertilization rates of 76.5% and 89.0% were observed using cauda epididymal spermatozoa from IMG-denervated and sham-operated control males, respectively, indicating that oocyte fertilization was not affected by the loss of innervation. These studies establish the importance of innervation from the IMG for ejaculatory competence and sperm reproductive capacity in the male rat. These data further suggest that sympathetic innervation in the epididymis critically influences paternal factors associated with embryonic development.