Estrogen biphasically modifies hypothalamic GABAergic function concomitantly with negative and positive control of
E J Wagner1, O K Ronnekleiv, M A Bosch
1Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, Oregon 97201, USA. wagnere@ohsu.edu
Summary
Estrogen influences the ovulatory cycle by altering hypothalamic GABAergic neurons. Estradiol benzoate (EB) initially reduces GABAergic neuron inhibition, then decreases GABAergic function, modulating luteinizing hormone (LH) secretion.
Area of Science:
- Neuroendocrinology
- Reproductive Biology
- Hormonal Regulation
Background:
- Estrogen primarily controls the female ovulatory cycle through feedback mechanisms on gonadotropin secretion.
- The precise regulation of hypothalamic neuronal excitability by estrogen remains incompletely understood.
Purpose of the Study:
- To investigate how estrogen affects GABAergic neurons in the preoptic area (POA).
- To test the hypothesis that estrogen elicits a biphasic luteinizing hormone (LH) secretion profile by acting on these neurons.
Main Methods:
- Utilized an ovariectomized female guinea pig model.
- Performed intracellular electrophysiological recordings to assess neuronal responses.
- Employed ribonuclease protection assays to measure gene expression.
Main Results:
- Estradiol benzoate (EB) treatment decreased the hyperpolarizing response to GABA(B) receptor agonist baclofen in GABAergic neurons 24 hours post-treatment.
- This effect persisted at 42 hours, while EB reduced glutamic acid decarboxylase mRNA expression at 42 hours but not 24 hours.
- Estrogen attenuated autoinhibition of GABAergic POA neurons during negative feedback and reduced GABAergic function during the positive feedback-induced LH surge.
Conclusions:
- Estrogen's effects on hypothalamic GABAergic neurons correlate with its biphasic modulation of LH secretion.
- These findings offer new insights into estrogen's mechanism for regulating hypothalamic GABAergic neurons.
- This regulation is crucial for the cyclical control of LH release in the female ovulatory cycle.
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