Highlights • Insulin-induced hypoglycemia (IIH) is exacerbated by hindbrain lactate repletion. • IIH augments pAMPKα1/2 protein expression in A1, C1, and A2, but not C2 cells. • Ventricular l ...-lactate infusion normalizes pAMPKα1/2 level content in A2 and C1 but not A1 cells. • Lactate also regularizes hypothalamic norepinephrine and epinephrine content in a site-specific manner. • IIH-associated lactoprivation is selectively signaled to the hypothalamus by A2 and C1 cells.
Highlights • Estradiol (E)- or oil-implanted ovariectomized female rats were injected with insulin. • Laser-dissected hypothalamic astrocytes were evaluated for glycogen enzyme protein levels. • E ...stimulates ventromedial and lateral hypothalamic astrocyte glycogen synthase protein. • E also augments glycogen phosphorylase expression in those sites during hypoglycemia. • E may regulate hypothalamic glycogen volume and turnover in a site-specific manner.
Abstract The neurochemical phenotype(s) of metabolic sensing neurons in the dorsal vagal complex (DVC) remains unclear. These studies utilized single-cell quantitative real-time RT–PCR, in ...conjunction with laser–catapult microdissection, to address the hypothesis that DVC A2 neurons express genes that encode the characterized metabolic transducers, e.g. glucokinase (GCK) and the energy-dependent potassium channel, KATP . Studies show that either glucose or lactate alters synaptic firing of DVC chemosensory neurons, and that delivery of the latter fuel into the caudal hindbrain amplifies insulin-induced hypoglycemia (IIH) and elevates neuronal glucose and monocarboxylate transporter, GCK, and sulfonylurea-1 mRNA in the DVC. We thus examined the additional premise that IIH modifies A2 substrate transporter and metabolic transducer gene profiles, and that such transcriptional responses may be reversed by exogenous lactate and/or glucose. Individual tyrosine hydroxylase (TH)-immunoreactive (-ir) A2 neurons were microdissected from the caudal DVC 2 h after injection of insulin or saline, and continuous caudal fourth ventricular (CV4) infusion of lactate, glucose, or artificial cerebrospinal fluid. The data show that IIH decreased MCT2, but elevated GLUT3, GLUT4, GCK, and SUR-1 transcripts in A2 neurons. Blood glucose levels in insulin-injected rats were further reduced by CV4 infusion of either lactate or glucose. Lactate plus insulin reversed hypoglycemic reductions in MCT2 mRNA and further augmented GLUT3 transcripts in A2 neurons, whereas glucose infusion in insulin-injected rats further increased GLUT3 and GCK gene profiles. The present results demonstrate that caudal DVC A2 neurons express molecular markers for metabolic sensing, and genes that encode glucose and monocarboxylate transporters. Evidence that IIH reduces A2 MCT2, but elevates GLUT3 and GLUT4 gene profiles suggests that glucose may be a primary energy source to these cells during hypoglycemia, while decreased lactate uptake, alone or relative to glucose uptake, may be a critical manifestation of systemic glucose deficiency at the cellular level. Findings that singular fuel repletion does not normalize hypoglycemic patterns of glucose transporter, GCK, or SUR-1 mRNA expression in A2 neurons imply that sufficient supply of both energy substrates is required for metabolic balance, and that cellular adaptation to the prevalence of either fuel may increase cellular dependence on glucose-specific metabolites or other products.
Highlights • Compound C (Cc) was injected to estradiol- or oil-implanted ovariectomized rat hindbrain. • Cc inhibits hindbrain adenosine 5′-monophosphate-activated protein kinase (AMPK). • Estradiol ...regulates hindbrain Cc effects on hypothalamic AMPK. • Estradiol determines hypothalamic targets of Cc-altered norepinephrine signaling. • Cc completely or partially represses feeding in presence versus absence of estradiol.
The female ventromedial hypothalamic nucleus (VMN) is a focal substrate for estradiol (E) regulation of energy balance, feeding, and body weight, but how E shapes VMN gluco-regulatory signaling in ...each sex is unclear. This study investigated the hypothesis that estrogen receptor-alpha (ERα) and/or -beta (ERβ) control VMN signals that inhibit γ-aminobutyric acid or stimulate nitric oxide, steroidogenic factor-1 (SF-1) counter-regulation in a sex-dependent manner. VMN nitrergic neurons monitor astrocyte fuel provision; here, we examined how these ER regulate astrocyte glycogen metabolic enzyme, monocarboxylate transporter, and adrenoreceptor protein responses to insulin-induced hypoglycemia (IIH) in each sex. Testes-intact male and E-replaced ovariectomized female rats were pretreated by intracerebroventricular ERα antagonist (MPP) or ERβ antagonist (PHTPP) administration before IIH. Data implicate both ER in hypoglycemic inhibition of neuronal nitric oxide synthase protein in each sex and up-regulation of glutamate decarboxylase65/67 and SF-1 expression in females. ERα and -β enhance astrocyte AMPK and glycogen synthase expression and inhibit glycogen phosphorylase in hypoglycemic females, while ERβ suppresses the same proteins in males. Differential VMN astrocyte protein responses to IIH may partially reflect ERα and -β augmentation of ERβ and down-regulation of alpha1, alpha2, and beta1 adrenoreceptor proteins in females, versus ERβ repression of GPER and alpha2 adrenoreceptor profiles in males. MPP or PHTPP pretreatment blunted counter-regulatory hormone secretion in hypoglycemic males only, suggesting that in males one or more VMN neurotransmitters exhibiting sensitivity to forebrain ER may passively regulate this endocrine outflow, whereas female forebrain ERα and -β are apparently uninvolved in these contra-regulatory responses.
•Estrogen (E) control of ventromedial hypothalamic nucleus (VMN) gluco-regulation is unclear.•E receptor (ER) antagonists were given icv to male or female rats before insulin-induced hypoglycemia.•ER-alpha and -beta cause hypoglycemic inhibition of neuronal nitric oxide synthase protein in each sex.•ER stimulate glucogen synthase expression in females only, but inhibit glycogen phosphorylase in both sexes.•ER antagonism blunted counter-regulatory hormone secretion in hypoglycemic males, but not females.
Neural substrates for estrogen regulation of glucose homeostasis remain unclear. Female rat dorsal vagal complex (DVC) A2 noradrenergic neurons are estrogen- and metabolic-sensitive. The ventromedial ...hypothalamic nucleus (VMN) is a key component of the brain network that governs counter-regulatory responses to insulin-induced hypoglycemia (IIH). Here, the selective estrogen receptor-alpha (ERα) or -beta (ERβ) antagonists MPP and PHTPP were administered separately to the caudal fourth ventricle to address the premise that these hindbrain ER variants exert distinctive control of VMN reactivity to IIH in the female sex. Data show that ERα governs hypoglycemic patterns of VMN astrocyte glycogen metabolic enzyme, e.g. glycogen synthase and phosphorylase protein expression, whereas ERβ mediates local glycogen breakdown. DVC ERs also regulate VMN neurotransmitter signaling of energy sufficiency γ-aminobutyric acid or deficiency nitric oxide, steroidogenic factor-1 during IIH. Neither hindbrain ER mediates IIH-associated diminution of VMN norepinephrine (NE) content. Both ERs oppose hypoglycemic hyperglucagonemia, while ERβ contributes to reduced corticosterone output. Outcomes reveal that input from the female hindbrain to the VMN is critical for energy reserve mobilization, metabolic transmitter signaling, and counter-regulatory hormone secretion during hypoglycemia, and that ERs control those cues. Evidence that VMN NE content is not controlled by hindbrain ERα or -β implies that these receptors may regulate VMN function via NE-independent mechanisms, or alternatively, that other neurotransmitter signals to the VMN may control local substrate receptivity to NE.
•Estrogen receptor-alpha (ERα) or -beta (ERβ) antagonist was injected icv to hypoglycemic female rat hindbrain (HB).•HB ERα governs ventromedial hypothalamic nucleus (VMN) glycogen enzyme protein levels; ERβ controls VMN glycogen mass.•HB ERs regulate VMN transmitters that signal metabolic stability, e.g. γ-aminobutyric acid and nitric oxide.•Hypoglycemic diminution of VMN norepinephrine content is HB ER-independent.•HB ERα and -β oppose hypoglycemic hyperglucagonemia, while ERβ suppresses corticosterone output.
The ventromedial hypothalamic nucleus (VMN) is a critical component of the neural circuitry that regulates glucostasis. Astrocyte glycogen is a vital reserve of glucose and its oxidizable metabolite ...L-lactate. In hypoglycemic female rats, estradiol-dependent augmentation of VMN glycogen phosphorylase (GP) protein requires hindbrain catecholamine input. Research here investigated the premise that norepinephrine (NE) regulation of VMN astrocyte metabolism shapes local glucoregulatory neurotransmitter signaling in this sex. Estradiol-implanted ovariectomized rats were pretreated by intra-VMN administration of the monocarboxylate transporter inhibitor alpha-cyano-4-hydroxy-cinnamic acid (4CIN) or vehicle before NE delivery to that site. NE caused 4CIN-reversible reduction or augmentation of VMN glycogen synthase and phosphorylase expression. 4CIN prevented NE stimulation of gluco-inhibitory (glutamate decarboxylase65/67) and suppression of gluco-stimulatory (neuronal nitric oxide synthase) neuron marker proteins. These outcomes imply that effects of noradrenergic stimulation of VMN astrocyte glycogen depletion on glucoregulatory transmitter signaling may be mediated, in part, by glycogen-derived substrate fuel provision. NE control of astrocyte glycogen metabolism may involve down-regulated adrenoreceptor (AR), e.g. alpha1 and alpha2, alongside amplified beta1 AR and estrogen receptor-beta signaling. Noradrenergic hypoglycemia was refractory to 4CIN, implying that additional NE-sensitive VMN glucoregulatory neurochemicals may be insensitive to monocarboxylate uptake. Augmentation of circulating free fatty acids by combinatory NE and 4CIN, but not NE alone implies that acute hypoglycemia induced here is an insufficient stimulus for mobilization of these fuels, but is adequate when paired with diminished brain monocarboxylate fuel availability.
•The ventromedial hypothalamic nucleus (VMN) governs glucose counter-regulation.•VMN glycogen phosphorylase (GP) up-regulation in hypoglycemic females is catecholamine-reliant•Intra-VMN norepinephrine (NE) inhibited VMN glycogen synthase, while augmenting GP.•Monocarboxylate transporter inhibition prevented VMN gluco-regulatory marker protein responses to NE.•Monocarboxylate transporter inhibition during NE-induced hypoglycemia elevates free fatty acids.
Estrogen receptor-alpha (ERα) and -beta (ERβ) occur in key elements of the brain gluco-homeostatic network in both sexes, including the hindbrain dorsal vagal complex (DVC), but the influence of ...distinct receptor populations on this critical function is unclear. The ventromedial hypothalamic nucleus (VMN) maintains glucose balance by integrating nutrient, endocrine, and neurochemical cues, including metabolic sensory information supplied by DVC A2 noradrenergic neurons. Current research utilized the selective ERα and ERβ antagonists MPP and PHTPP to characterize effects of DVC ERs on VMN norepinephrine (NE) activity and metabolic neurotransmitter signaling in insulin-induced hypoglycemic (IIH) male rats. Data show that ERβ inhibits VMN glycogen synthase and stimulates phosphorylase protein expression, while attenuating hypoglycemic augmentation of glycogen content. Furthermore, both ERs attenuate VMN glucose concentrations during IIH. Hypoglycemic up-regulation of nitric oxide (NO) and brain-derived neurotrophic factor (BDNF) signaling was correspondingly driven by ERα or -β, whereas GABA and steroidogenic factor-1 were respectively suppressed independently of ER input or by ERβ. IIH intensified VMN NE accumulation by ERβ-dependent mechanisms, but did not alter NE levels in other gluco-regulatory loci. ERβ amplified the magnitude of insulin-induced decline in blood glucose. Both ERs regulate corticosterone, but not glucagon secretion during IIH and oppose hypoglycemic diminution of circulating free fatty acids. These findings identify distinguishing versus common VMN functions targeted by DVC ERα and -β. Sex differences in hypoglycemic VMN NE accumulation, glycogen metabolism, and transmitter signaling may involve, in part, discrepant regulatory involvement or differential magnitude of impact of these hindbrain ERs.
•The ventromedial hypothalamic nucleus (VMN) shapes responses to insulin-induced hypoglycemia (IIH).•Hypoglycemic male rats were pretreated by estrogen receptor-alpha (ERα) or -beta (ERβ) antagonist hindbrain delivery.•ERβ regulates VMN norepinephrine activity, glycogen metabolic enzyme profiles, and glycogen content.•ERα regulates the VMN gluco-stimulatory transmitter nitric oxide.•These ERs do not regulate glucagon secretion, but ERβ suppresses corticosterone output.
•Dorsal vagal complex A2 neurons were microdissected after one or four daily insulin injections.•Acute hypoglycemia had opposite effects on A2 dopamine-β-hydroxylase (DBH) levels in the two ...sexes.•Recurring hypoglycemia (RH) decreased baseline DBH and 5’-AMP-activated protein kinase in females.•Estrogen receptor (ER)-α and G protein-coupled ER are inhibited in RH males, but not females.•RH males show inverse DBH reactivity whereas females exhibit loss of reactivity to RH.
Hindbrain estrogen receptors (ER) impose sex-dimorphic control of counter-regulatory hormone and hypothalamic glucoregulatory transmitter and glycogen metabolic responses to hypoglycemia. A2 noradrenergic neurons are estradiol- and metabolic-sensitive. Estradiol controls dopamine-beta-hydroxylase (DBH) protein habituation to recurrent insulin-induced hypoglycemia (RIIH) in females. Current research investigated the premise that sex-dimorphic patterns of A2 ER variant acclimation to RIIH correlate with differential A2 DBH and 5’-AMP-activated protein kinase (AMPK) adaptation to RIIH. A2 neurons were laser-catapult-microdissected from male and female rats after one or four insulin injections for Western blot analysis. A2 pAMPK and DBH levels were increased in males, but suppressed in females after single insulin dosing. ER-alpha (ERα) and -beta (ERβ) protein profiles were unaffected or decreased by acute hypoglycemia in each sex, whereas G protein-linked ER-1 (GPER) reactivity varied by sex. Antecedent hypoglycemia diminished basal A2 ERα/GPER and elevated ERβ content in each sex, yet reduced pAMPK and DBH levels in female rats only. Reintroduced hypoglycemia suppressed A2 ERβ levels in each sex, but altered DBH (↓), ERα (↓), and GPER (↑) levels in males only. Data document sex differences in A2 DBH adaptation to RIIH, e.g. a shift from positive-to-negative response in males versus loss of negative reactivity in females, as well as attenuated AMPK activation in both sexes. Between hypoglycemic episodes, A2 neurons in each sex likely exhibit diminished sensitivity to ERα/GPER signaling, but heightened receptivity to ERβ input. RIIH-induced changes in ERα and GPER expression in male but not female may contribute to DBH suppression (males) versus no change (females) relative to adapted baseline expression.
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