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β‐Endorphin Cells in the Arcuate Nucleus: Projections to the Supraoptic Nucleus and Changes in Expression During Pregnancy and Parturition
Author(s) -
Douglas A. J.,
Bicknell R. J.,
Leng G.,
Russell J. A.,
Meddle S. L.
Publication year - 2002
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.2002.00837.x
Subject(s) - supraoptic nucleus , arcuate nucleus , oxytocin , nucleus , endocrinology , medicine , hypothalamus , neuropeptide , beta endorphin , chemistry , biology , microbiology and biotechnology , receptor
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 β‐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 β‐endorphin fluorescent microbeads retrogradely transported from the supraoptic nucleus, and double‐labelled neurones (β‐endorphin plus microbeads), showing that β‐endorphin neurones throughout the arcuate nucleus project to the supraoptic nucleus. There was an increase in the number of β‐endorphin‐immunoreactive cells in the arcuate nucleus and an increase in the density of β‐endorphin fibres within the supraoptic nucleus and peri‐supraoptic region in late pregnancy and parturition, suggesting enhanced expression of β‐endorphin and increased β‐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 β‐endorphin neurones in both proestrus and parturient rats, but the number of positive cells did not increase during parturition, suggesting lack of activation of β‐endorphin neurones at birth. Thus, β‐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.