The potency of mu-opioid hyperpolarization of hypothalamic arcuate neurons is rapidly attenuated by 17 beta-estradiol.

Lagrange AH, Ronnekleiv OK, Kelly MJ
J Neurosci. 1994 14 (10): 6196-204

PMID: 7931572 · PMCID: PMC6576966

The mu-opioid agonist DAMGO (Tyr-D-Ala-Gly-MePhe-Gly-ol) hyperpolarizes the majority of arcuate hypothalamic (ARC) neurons by opening an inwardly rectifying potassium conductance. The EC50 for the DAMGO-induced hyperpolarization was 60 +/- 3 nM in ARC neurons from ovariectomized guinea pigs. Superfusion of 17 beta-estradiol (E2; 100 nM) for 20 min in vitro resulted in a significant decrease in DAMGO potency (EC50 = 212 +/- 16 nM) in 40% of the neurons that were tested. This rapid effect of E2 on the mu-opioid response was not mimicked by the biologically inactive isomer 17 alpha-estradiol. Multiple concentrations of E2 were used to generate an E2 concentration-response curve, with an EC50 of 9 nM and a maximal increase in the DAMGO EX50 of 411% of controls. The membrane properties and firing rate of E2-sensitive and E2-insensitive neurons were not different. Streptavidin-FITC labeling did not reveal any significant morphological differences between the groups, but a higher number of E2-sensitive cells was found in the lateral ARC and cell-poor zone. Moreover, immunocytochemical staining of the recorded cells revealed that beta-endorphin neurons were among those sensitive to E2. Therefore, E2 could increase beta-endorphin release by decreasing the potency of beta-endorphinergic autoinhibition, thus increasing the tonic opioid inhibition of E2-insensitive cells. Furthermore, the diffuse projections of hypothalamic beta-endorphin neurons would allow E2 to alter processes throughout the brain, as well as having local effects in the hypothalamus.

MeSH Terms (17)

Animals Arcuate Nucleus of Hypothalamus Dose-Response Relationship, Drug Enkephalin, Ala(2)-MePhe(4)-Gly(5)- Enkephalins Estradiol Female GTP-Binding Proteins Guinea Pigs In Vitro Techniques Membrane Potentials Narcotics Neurons Potassium Channels Receptors, Opioid, mu Sensitivity and Specificity Stereoisomerism

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