Estrogen receptor β is essential for sprouting of nociceptive primary afferents and for morphogenesis and maintenance of the dorsal horn interneurons

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Abstract
Estrogen is known to influence pain, but the specific roles of the two estrogen receptors (ERs) in the spinal cord are unknown. In the present study, we have examined the expression of ERα and ERβ in the spinal cord and have looked for defects in pain pathways in ERβ knockout (ERβ−/−) mice. In the spinal cords of 10-month-old WT mice, ERβ-positive cells were localized in lamina II, whereas ERα-positive cells were mainly localized in lamina I. In ERβ−/− mice, there were higher levels of calcitonin gene-regulated peptide and substance P in spinal cord dorsal horn and isolectin B4 in the dorsal root ganglion. In the superficial layers of the spinal cord, there was a decrease in the number of calretinin (CR)-positive neurons, and in the outer layer II, there was a loss of calbindin-positive interneurons. During embryogenesis, ERβ was first detectable in the spinal cord at embryonic day 13.5 (E13.5), and ERα was first detectable at E15.5. During middle and later embryonic stages, ERβ was abundantly expressed in the superficial layers of the dorsal horn. ERα was also expressed in the dorsal horn but was limited to fewer neurons. Double staining for ERβ and CR showed that, in the superficial dorsal horn of WT neonates [postnatal day 0 (P0)], most CR neurons also expressed ERβ. At this stage, few CR-positive cells were detected in the dorsal horn of ERβ−/− mice. Taken together, these findings suggest that, early in embryogenesis, ERβ is involved in dorsal horn morphogenesis and in sensory afferent fiber projections to the dorsal horn and that ERβ is essential for survival of dorsal horn interneurons throughout life.