PREGNANCY-INDUCED UTERINE NEURONAL DEGENERATION IN THE RAT

We studied the location, distribution, and density of uterine nerve bu ndles in virgin, full-term pregnant, and early postpartum female rats. In the virgin, a low-magnification analysis of uterine whole-mounts s tained for acetylcholinesterase revealed fibers both in close associat ion with blood vessels and coursing freely within muscle or connective tissue in the mesometrium and the uterine body. Higher magnification analysis of sections treated immunohistochemically with antibodies to the ubiquitous neuronal protein gene product 9.5, tyrosine hydroxylase , and calcitonin gene-related peptide indicated that the greatest dens ity of nerve bundles was in the mesometrial triangle and intramyometri al region. Although the majority of bundles were associated with blood vessels, many coursed freely, particularly in the myometrial and endo metrial layers. The density of innervation within the body of the uter us was heterogeneous. For instance, both innervated and noninnervated spiral arteries branched from the same innervated circumferential arte ry. In the term pregnant rat, we observed a profound denervation withi n all layers of the body of the uterus. The few remaining nerve bundle s tended to be associated with blood vessels, and they were confined t o the intramyometrial region. Within 48 h postpartum, both the number and density of nerve bundles increased. Long tortuous bundles, not see n in the full-term rat, were observed. The present study is the first to describe and illustrate the pattern of uterine innervation in virgi n, full-term pregnant, and early postpartum rats over a wide range of magnifications.