Douglas A J, Bicknell R J, Leng G, Russell J A, Meddle S L
Division of Biomedical Sciences, University of Edinburgh, George Square, Edinburgh, UK.
J Neuroendocrinol. 2002 Oct;14(10):768-77. doi: 10.1046/j.1365-2826.2002.00837.x.
Supraoptic nucleus oxytocin neurone activity and secretion are inhibited in late pregnancy and parturition by endogenous opioids. Here, we investigated alterations in the projections and gene expression of beta-endorphin/pro-opiomelanocortin neurones in the arcuate nucleus in the pregnant rat. All regions of the arcuate nucleus were found to contain cells immunoreactive for beta-endorphin fluorescent microbeads retrogradely transported from the supraoptic nucleus, and double-labelled neurones (beta-endorphin plus microbeads), showing that beta-endorphin neurones throughout the arcuate nucleus project to the supraoptic nucleus. There was an increase in the number of beta-endorphin-immunoreactive cells in the arcuate nucleus and an increase in the density of beta-endorphin fibres within the supraoptic nucleus and peri-supraoptic region in late pregnancy and parturition, suggesting enhanced expression of beta-endorphin and increased beta-endorphin innervation of the supraoptic nucleus. Pro-opiomelanocortin mRNA expression in the arcuate nucleus increased in late compared to early pregnancy: the number of positive neurones significantly increased in the caudal region. Fos expression (an indicator of neuronal activation) in the arcuate nucleus was colocalized in beta-endorphin neurones in both proestrus and parturient rats, but the number of positive cells did not increase during parturition, suggesting lack of activation of beta-endorphin neurones at birth. Thus, beta-endorphin cells in the arcuate nucleus project to the supraoptic nucleus and increased innervation during pregnancy may explain the enhanced endogenous opioid inhibition of oxytocin neurones.
在妊娠晚期和分娩期，内源性阿片类物质会抑制视上核催产素神经元的活动和分泌。在此，我们研究了妊娠大鼠弓状核中β-内啡肽/阿黑皮素原神经元投射和基因表达的变化。发现弓状核的所有区域都含有对视上核逆行转运的β-内啡肽荧光微珠呈免疫反应的细胞，以及双标记神经元（β-内啡肽加微珠），这表明整个弓状核中的β-内啡肽神经元投射到视上核。在妊娠晚期和分娩期，弓状核中β-内啡肽免疫反应性细胞数量增加，视上核和视上核周围区域内β-内啡肽纤维密度增加，提示β-内啡肽表达增强以及视上核的β-内啡肽神经支配增加。与妊娠早期相比，妊娠晚期弓状核中阿黑皮素原mRNA表达增加：尾侧区域阳性神经元数量显著增加。在动情前期和分娩期大鼠的弓状核中，Fos表达（神经元激活的指标）与β-内啡肽神经元共定位，但分娩期间阳性细胞数量未增加，提示出生时β-内啡肽神经元未激活。因此，弓状核中的β-内啡肽细胞投射到视上核，妊娠期间神经支配增加可能解释了内源性阿片类物质对催产素神经元抑制作用增强的原因。
