Hindbrain estrogen receptor-beta antagonism normalizes reproductive and counter-regulatory hormone secretion in hypoglycemic steroid-primed ovariectomized female rats

•Hypoglycemia elevates estrogen receptor-beta (ERβ) protein in A2 metabolo-sensory neurons.•Hindbrain ERβ antagonism normalizes LH release but not preoptic GnRH-I protein content.•The ERβ antagonist PHTPP attenuates counter-regulatory hormone output during hypoglycemia.•PHTPP prevents hypoglycemic augmentation of NE in the ARH, but not other forebrain loci.•PHTPP normalizes ARH, but not AVPV preprokisspeptin protein profiles in hypoglycemic rats.

Hindbrain dorsal vagal complex A2 noradrenergic signaling represses the pre-ovulatory luteinizing hormone (LH) surge in response to energy deficiency. Insulin-induced hypoglycemia augments A2 neuron adenosine 5′-monophosphate-activated protein kinase (AMPK) activity and estrogen receptor-beta (ERβ) expression, coincident with LH surge suppression. We hypothesized that ERβ is critical for hypoglycemia-associated patterns of LH secretion and norepinephrine (NE) activity in key reproduction-relevant forebrain structures. The neural mechanisms responsible for tight coupling of systemic energy balance and procreation remain unclear; here, we investigated whether ERβ-dependent hindbrain signals also control glucose counter-regulatory responses to hypoglycemia. Gonadal steroid-primed ovariectomized female rats were pretreated by caudal fourth ventricular administration of the ERβ antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP) or vehicle before insulin injection at LH surge onset. Western blot analysis of laser-microdissected A2 neurons revealed hypoglycemic intensification of AMPK activity and dopamine-β-hydroxylase protein expression; the latter response was attenuated by PHTPP pretreatment. PHTPP regularized LH release, but not preoptic GnRH-I precursor protein expression in insulin-injected rats, and reversed hypoglycemic stimulation of glucagon and corticosterone secretion. Hypoglycemia caused PHTPP-reversible changes in NE and prepro-kisspeptin protein content in the hypothalamic arcuate (ARH), but not anteroventral periventricular nucleus. Results provide novel evidence for ERβ-dependent caudal hindbrain regulation of LH and counter-regulatory hormone secretion during hypoglycemia. Observed inhibition of LH likely involves mechanisms at the axon terminal that impede GnRH neurotransmission. Data also show that caudal hindbrain ERβ exerts site-specific control of NE activity in forebrain projection sites during hypoglycemia, including the ARH where prepro-kisspeptin may be a target of that signaling.