Elsevier

Neuroscience

Volume 103, Issue 1, 28 February 2001, Pages 237-244
Neuroscience

Sympathetic hyperinnervation of the uterus in the estrogen receptor α knock-out mouse

https://doi.org/10.1016/S0306-4522(00)00549-2Get rights and content

Abstract

Uterine innervation undergoes cyclical remodeling in the adult virgin rat. Previous studies showed that ovariectomy leads to increased uterine sympathetic nerve density, and this can be reduced by estrogen administration. However, the receptor mechanism by which estrogen modulates sympathetic innervation is unknown. The present study assessed the role of the estrogen receptor α in establishing levels of uterine innervation by comparing the nerve abundance in mice with a null mutation of the estrogen receptor α with those of the wild-type cycling mouse. Immunostaining for total uterine innervation using antibodies against the pan-neuronal marker protein gene product 9.5 showed that nerve numbers in normally cycling wild-type mice were high in diestrus when circulating estrogen is at its nadir, and low at estrus, coincident with high plasma estrogen. Uteri of the estrogen receptor α knock-out mice were smaller than those of wild-type mice, but even when corrected for differences in size, total innervation was 188% and 355% greater than that of wild-type mice at diestrus and estrus, respectively. This hyperinnervation is associated with increased numbers of nerves immunoreactive for the noradrenergic enzyme dopamine β-hydroxylase, without obvious differences in those containing calcitonin gene-related peptide or the vesicular acetylcholine transporter. While estrogen supplementation of the ovariectomized wild-type mice significantly reduced total uterine innervation, neither ovariectomy nor estrogen supplementation affected uterine nerve density in estrogen receptor α knock-out mice.

We conclude that estrogen acting through the estrogen receptor α determines the number of sympathetic nerve terminal branches within uterine smooth muscle target. In mice with low circulating estrogen, or high estrogen but lacking the functional estrogen receptor α, the uterus contains abundant sympathetic nerves, whereas estrogen acts via the estrogen receptor α to regulate uterine innervation by reducing numbers of intact sympathetic nerves. Although it is not known whether estrogen acts on the target or neuron to initiate these changes, the estrogen receptor α apparently plays a major role in the cyclical modulation of uterine sympathetic innervation.

Section snippets

Animals and tissue preparation

Experiments were conducted on 16 wild-type C57BI/6J mice and eight littermate ERαKO mice. NIH guidelines of laboratory animal care were followed and experimental protocols were approved by the University of Kansas Medical Center Animal Care and Use Committee. All efforts were made to minimize animal suffering and to reduce the number of animals used.

Wild-type cycling mice were studied in the diestrus (n=4) or estrus (n=4) phases of the estrous cycle as determined by vaginal smear. Eight other

Uterine innervation of the cycling wild-type mouse

In wild-type mice, PGP 9.5-IR fibers were most abundant in the circular smooth muscle layer and vascular zone separating the myometrial layers, and were less frequent in the longitudinal smooth muscle and endometrium (Fig. 1a, b). Nerve density, as determined by the percentage of uterine cross-sectional area apparently occupied by PGP 9.5-IR nerves, was significantly lower in estrus (3.8±0.3%) than at diestrus (7.3±0.3%; Fig. 1, Fig. 2, P=0.027). Uterine cross-sectional area in the ovarian

Variations in uterine sympathetic nerve density during the estrous cycle

The present study shows that uterine innervation of the wild-type mouse undergoes cyclical remodeling in concert with the phases of the estrous cycle. Immunostaining for PGP 9.5-IR nerves indicates that mouse uterine nerve density is lower at estrus than at diestrus. PGP 9.5 is widely distributed in essentially all neural tissues56 and is a reliable indicator of intact innervation.30 Therefore, the decrease in PGP 9.5-IR nerve density at estrus is likely to reflect an actual loss of uterine

Conclusions

The numbers of intact nerves present in the ovarian region of the uterine horn in the wild-type mouse varies as a function of estrous cycle stage, with high estrogen levels correlating with low numbers of sympathetic nerves. Mice in which ERα has been rendered non-functional by way of homologous recombination were found to have uteri of diminished size, but with a marked elevation in the number of sympathetic nerves, which was not altered by variations in plasma estrogen. These findings support

Acknowledgements

This work was supported by NIH grant NS39570 with core facilities provided by center grant HD02528 from the NICHD. We thank Dr Dennis B. Lubahn (University of Missouri Medical School) for permission to use the ERαKO transgenic mouse line derived from his laboratory, and Drs S. K. Dey and Sanjoy K. Das (University of Kansas Medical Center) for generously providing and genotyping the animals in this study.

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