Role of hindbrain adenosine 5'-monophosphate-activated protein kinase (AMPK) in hypothalamic AMPK and metabolic neuropeptide adaptation to recurring insulin-induced hypoglycemia in the male rat

Genetic Architecture and Functional Implications of the CSF-Contacting Nucleus

We previously identified a unique nucleus, the cerebrospinal fluid (CSF)-contacting nucleus. This study aims to understand its gene architecture and preliminarily suggest its functions. The results showed that there were about 19,666 genes in this nucleus, of which 913 were distinct from the dorsal raphe nucleus (non-CSF contacting). The top 40 highly-expressed genes are mainly related to energy metabolism, protein synthesis, transport, secretion, and hydrolysis. The main neurotransmitter is 5-HT. The receptors of 5-HT and GABA are abundant. The channels for Cl-, Na+, K+, and Ca2+ are routinely expressed. The signaling molecules associated with the CaMK, JAK, and MAPK pathways were identified accurately. In particular, the channels of transient receptor potential associated with nociceptors and the solute carrier superfamily members associated with cell membrane transport were significantly expressed. The relationship between the main genes of the nucleus and life activities is preliminarily verified.

Modulation of hypothalamic AMPK and hypothalamic neuropeptides in the control of eating behavior: A systematic review

Eating behavior is regulated by central and peripheral signals, which interact to modulate the response to nutrient intake. Central control is mediated by the hypothalamus through neuropeptides that activate the orexigenic and anorexigenic pathways. Energy homeostasis depends on the efficiency of these regulatory mechanisms. This neuroendocrine regulation of hunger and appetite can be modulated by nutritional sensors such as adenosine monophosphate-activated protein kinase (AMPK). Thus, this systematic review discusses the literature on correlations between AMPK and hypothalamic neuropeptides regarding control of eating behavior. Lilacs, PubMed/Medline, ScienceDirect, and Web of Science were searched for articles published from 2009 to 2021 containing combinations of the following descriptors: "eating behavior," "hypothalamus," "neuropeptide," and "AMPK." Of the 1330 articles found initially, 27 were selected after application of the inclusion and exclusion criteria. Of the selected articles, 15 reported decreased AMPK activity, due to interventions using angiotensin II infusion, fructose, glucose, cholecystokinin, leptin, or lipopolysaccharide (LPS) injection; dietary control through a low-protein diet or a high-fat diet (60 % fat); induction of hyperthyroidism; or injection of AMPK inhibitors. Seven studies showed a decrease in neuropeptide Y (NPY) through CV4 AICAR administration; fructose, glucose, leptin, or angiotensin II injections; or infusion of LPS from Escherichia coli and liver kinase B1 (LKB1) overexpression. Eleven studies reported a decrease in food consumption due to a decrease in AMPK activity and/or hypothalamic neuropeptides such as NPY. The results indicate that there is a relationship between AMPK and the control of eating behavior: a decrease in AMPK activity due to a dietary or non-dietary stimulus is associated with a consequent decrease in food intake. Furthermore, AMPK activity can be modulated by glucose, thyroid hormones, estradiol, leptin, and ghrelin.

Glycogen Phosphorylase Isoform Regulation of Ventromedial Hypothalamic Nucleus Gluco-Regulatory Neuron 5'-AMP-Activated Protein Kinase and Transmitter Marker Protein Expression

Brain glycogen is remodeled during metabolic homeostasis and provides oxidizable L-lactate equivalents. Brain glycogen phosphorylase (GP)-brain (GPbb; AMP-sensitive) and -muscle (GPmm; norepinephrine-sensitive) type isoforms facilitate stimulus-specific control of glycogen disassembly. Here, a whole animal model involving stereotactic-targeted delivery of GPmm or GPbb siRNA to the ventromedial hypothalamic nucleus (VMN) was used to investigate the premise that these variants impose differential control of gluco-regulatory transmission. Intra-VMN GPmm or GPbb siRNA administration inhibited glutamate decarboxylate_65/67 (GAD), a protein marker for the gluco-inhibitory transmitter γ--aminobutyric acid (GABA), in the caudal VMN. GPbb knockdown, respectively overturned or exacerbated hypoglycemia-associated GAD suppression in rostral and caudal VMN. GPmm siRNA caused a segment-specific reversal of hypoglycemic augmentation of the gluco-stimulatory transmitter indicator, neuronal nitric oxide synthase (nNOS). In both cell types, GP siRNA down-regulated 5′-AMP-activated protein kinase (AMPK) during euglycemia, but hypoglycemic suppression of AMPK was reversed by GPmm targeting. GP knockdown elevated baseline GABA neuron phosphoAMPK (pAMKP) content, and amplified hypoglycemic augmentation of pAMPK expression in each neuron type. GPbb knockdown increased corticosterone secretion in eu- and hypoglycemic rats. Outcomes validate efficacy of GP siRNA delivery for manipulation of glycogen breakdown in discrete brain structures in vivo, and document VMN GPbb control of local GPmm expression. Results document GPmm and/or -bb regulation of GABAergic and nitrergic transmission in discrete rostro-caudal VMN segments. Contrary effects of glycogenolysis on metabolic-sensory AMPK protein during eu- versus hypoglycemia may reflect energy state-specific astrocyte signaling. Amplifying effects of GPbb knockdown on hypoglycemic stimulation of pAMPK infer that glycogen mobilization by GPbb limits neuronal energy instability during hypoglycemia.

Ventrolateral ventromedial hypothalamic nucleus GABA neuron adaptation to recurring Hypoglycemia correlates with up-regulated 5'-AMP-activated protein kinase activity

Gamma-aminobutyric acid (GABA) acts on ventromedial hypothalamic targets to suppress counter-regulatory hormone release, thereby lowering blood glucose. Maladaptive up-regulation of GABA signaling is implicated in impaired counter-regulatory outflow during recurring insulin-induced hypoglycemia (RIIH). Ventromedial hypothalamic nucleus (VMN) GABAergic neurons express the sensitive energy gauge 5'-AMP-activated protein kinase (AMPK). Current research used high-neuroanatomical resolution single-cell microdissection tools to address the premise that GABAergic cells in the VMNvl, the primary location of 'glucose-excited' metabolic-sensory neurons in the VMN, exhibit attenuated sensor activation during RIIH. Data show that during acute hypoglycemia, VMNvl glutamate decarboxylase65/67 (GAD)-immunoreactive neurons maintain energy stability, yet a regional subset of this population exhibited decreased GAD content. GABA neurons located along the rostrocaudal length of the VMNvl acclimated to RIIH through a shift to negative energy imbalance, e.g. increased phosphoAMPK expression, alongside amplification/gain of inhibition of GAD profiles. Acquisition of negative GAD sensitivity may involve altered cellular receptivity to noradrenergic input via α2-AR and/or β1-AR. Suppression of VMNvl GABA nerve cell signaling during RIIH may differentiate this neuroanatomical population from other, possibly non-metabolic-sensory GABA neurons in the MBH. Data here also provide novel evidence that VMNvl GABA neurons are direct targets of glucocorticoid control, and show that glucocorticoid receptors may inhibit RIIH-associated GAD expression in rostral VMNvl GABAergic cells through AMPK-independent mechanisms.

Metabolic functions of flavonoids: From human epidemiology to molecular mechanism

Dietary flavonoid intake is associated with the regulation of nutrient metabolism in the living body. Observational and cohort studies have reported a negative association between flavonoid intake and the risk of metabolic and cardiovascular diseases. Several intervention trials in humans have also supported the benefits of dietary flavonoids. In experimental studies using animal models, a daily diet rich in typical flavonoids such as catechins, anthocyanin, isoflavone, and quercetin was shown to improve whole-body energy expenditure, mitochondrial activity, and glucose tolerance. For some flavonoids, molecular targets for the metabolic modulations have been suggested. Although the effect of flavonoids on neurons has been unclear, several flavonoids have been shown to regulate thermogenesis and feeding behavior through modulating autonomic and central nervous systems. Based on epidemiological and experimental studies, this review summarizes the evidence on the metabolic benefits of flavonoids and their potential mechanism of action in metabolic regulation.

Haider A, Alshamrani A, Alhamyani A, Bheemanapally K, Ibrahim MM. Hindbrain catecholamine regulation of ventromedial hypothalamic nucleus glycogen metabolism during acute versus recurring insulin-induced hypoglycemia in male versus female rat

Ventromedial hypothalamic nucleus (VMN) glycogen metabolism affects local glucoregulatory signaling. The hindbrain metabolic-sensitive catecholamine (CA) neurotransmitter norepinephrine controls VMN glycogen phosphorylase (GP)-muscle (GPmm) and -brain (GPbb) type expression in male rats. Present studies addressed the premise that CA regulation of hypoglycemic patterns of VMN glycogen metabolic enzyme protein expression is sex-dimorphic, and that this signal is responsible for sex differences in acclimation of these profiles to recurrent insulin-induced hypoglycemia (RIIH). VMN tissue was acquired by micropunch-dissection from male and female rats pretreated by caudal fourth ventricular administration of the CA neurotoxin 6-hydroxydopamine (6OHDA) before single or serial insulin injection. 6-OHDA averted acute hypoglycemic inhibition of VMN glycogen synthase (GS) and augmentation of GPmm and GPbb protein expression in males, and prevented GPmm and -bb down-regulation in females. Males recovered from antecedent hypoglycemia (AH) exhibited neurotoxin-preventable diminution of baseline GS profiles, whereas acclimated GPmm and -bb expression in females occurred irrespective of pretreatment. RIIH did not alter VMN GS, GPmm, and GPbb expression in vehicle- or 6-OHDA-pretreated animals of either sex. VMN glycogen content was correspondingly unchanged or increased in males versus females following AH; 6-OHDA augmented glycogen mass in AH-exposed animals of both sexes. RIIH did not alter VMN glycogen accumulation in vehicle-pretreated rats of either sex, but diminished glycogen in neurotoxin-pretreated animals. AH suppresses baseline GS (CA-dependent) or GPmm/GPbb (CA-independent) expression in male and female rats, respectively, which corresponds with unaltered or augmented VMN glycogen content in those sexes. AH-associated loss of sex-distinctive CA-mediated enzyme protein sensitivity to hypoglycemia (male: GS, GPmm, GPbb; female: GPmm, Gpbb) may reflect, in part, VMN target desensitization to noradrenergic input.

Sex differences in ventromedial hypothalamic nucleus glucoregulatory transmitter biomarker protein during recurring insulin-induced hypoglycemia

Recurring insulin-induced hypoglycemia (RIIH) in males correlates with maladaptive glucose counter-regulatory collapse and acclimated expression of ventromedial hypothalamic nucleus (VMN) nitric oxide (NO) and γ-aminobutyric acid (GABA) metabolic transmitter biomarkers, e.g., neuronal nitric oxide synthase (nNOS) and glutamate decarboxylase_65/67 (GAD). Hindbrain noradrenergic neurons innervate the VMN, where norepinephrine regulates nNOS and GAD expression. Current research investigated the hypothesis that antecedent hypoglycemia (AH) exposure causes sex-dimorphic habituation of VMN glucoregulatory biomarker proteins between and/or during serial hypoglycemic bouts, and that hindbrain catecholaminergic (CA) signaling may control sex-specific adaptation of one or more of these proteins. Data show that upon recovery from AH, females exhibit CA-mediated reductions in baseline VMN nNOS, GAD, steroidogenic factor-1 (SF-1), and brain-derived neurotrophic factor (BNDF) expression compared to euglycemic profiles. In males, however, AH caused 6-OHDA-insensitive suppression of only basal SF-1 levels in the VMN. VMN transmitter protein acclimation to RIIH was sex-contingent, as differential nNOS, GAD, SF-1, and BDNF responses to a single vs final bout of hypoglycemia occur in males, whereas females show acclimated reactivity of GAD and SF-1 only to renewed hypoglycemia. CA-mediated and -independent habituation of distinctive VMN protein profiles occurred in each sex. Further research is necessary to evaluate, in each sex, effects of altered baseline VMN metabolic neurotransmitter signals on glucose homeostasis as well as non-metabolic functions under the control of those neurochemicals. It would also be insightful to learn if and how sex-contingent habituation of VMN transmitter responses to hypoglycemia contribute to sex-dimorphic patterns of glucose counter-regulation during RIIH.

Sex-dimorphic Rostro-caudal Patterns of 5'-AMP-activated Protein Kinase Activation and Glucoregulatory Transmitter Marker Protein Expression in the Ventrolateral Ventromedial Hypothalamic Nucleus (VMNvl) in Hypoglycemic Male and Female Rats: Impact of Estradiol

The ventromedial hypothalamic nucleus-ventrolateral part (VMNvl) is an estradiol-sensitive structure that controls sex-specific behavior. Electrical reactivity of VMNvl neurons to hypoglycemia infers that cellular energy stability is monitored there. Current research investigated the hypothesis that estradiol elicits sex-dimorphic patterns of VMNvl metabolic sensor activation and gluco-regulatory neurotransmission during hypoglycemia. Rostral-, middle-, and caudal-VMNvl tissue was separately micropunch-dissected from letrozole (Lz)- or vehicle-injected male and estradiol- or vehicle-implanted ovariectomized (OVX) female rats for Western blot analysis of total and phosphorylated 5'-AMP-activated protein kinase (AMPK) protein expression and gluco-stimulatory [neuronal nitric oxide synthase (nNOS); steroidogenic factor-1 (SF1) or -inhibitory (glutamate decarboxylase_65/67 (GAD)] transmitter marker proteins after sc insulin (INS) or vehicle injection. In both sexes, hypoglycemic up-regulation of phosphoAMPK was estradiol-dependent in rostral and middle, but not caudal VMNvl. AMPK activity remained elevated after recovery from hypoglycemia over the rostro-caudal VMNvl in female, but only in the rostral segment in male. In each sex, hypoglycemia correspondingly augmented or suppressed nNOS profiles in rostral and middle versus caudal VMNvl; these segmental responses persisted longer in female. Rostral and middle segment SF1 protein was inhibited by estradiol-independent mechanisms in hypoglycemic males, but increased by estradiol-reliant mechanisms in female. After INS injection, GAD expression was inhibited in the male rostral VMNvl without estradiol involvement, but this hormone was required for broader suppression of this profile in the female. Neuroanatomical variability of VMNvl metabolic transmitter reactivity to hypoglycemia underscores the existence of functionally different subgroups in that structure. The regional distribution and estradiol sensitivity of hypoglycemia-sensitive VMNvl neurons of each neurochemical phenotype evidently vary between sexes.

Sex-dimorphic aromatase regulation of ventromedial hypothalamic nucleus glycogen content in euglycemic and insulin-induced hypoglycemic rats

Estrogen receptors control hypothalamic astrocyte glycogen accumulation in vitro. Glycogen metabolism impacts metabolic transmitter signaling in the ventromedial hypothalamic nucleus (VMN), a key glucoregulatory structure. Aromatase, the enzyme that converts testosterone to estradiol, is expressed at high levels in the VMN. Here, the aromatase inhibitor letrozole (Lz) was used alongside high-resolution microdissection/UPHLC-electrospray ionization-mass spectrometric methods to determine if neuroestradiol imposes sex-specific control of VMN glycogen content during glucostasis and/or glucoprivation. Testes-intact male and estradiol-replaced ovariectomized female rats were pretreated by lateral ventricular letrozole (Lz) infusion prior to subcutaneous insulin (INS) injection. Vehicle-treated female controls exhibited higher VMN glycogen content compared to males. Lz increased VMN glycogen levels in males, not females. INS-induced hypoglycemia (IIH) elevated (males) or diminished (females) rostral VMN glycogen accumulation. Induction of IIH in Lz-pretreated animals reduced male VMN glycogen mass, but augmented content in females. Data provide novel evidence for regional variation, in both sexes, in glycogen reactivity to IIH. Results highlight sex-dimorphic neuroestradiol regulation of VMN glycogen amassment during glucostasis, e.g. inhibitory in males versus insignificant in females. Locally-generated estradiol is evidently involved in hypoglycemic enhancement of male VMN glycogen, but conversely limits glycogen content in hypoglycemic females. Further research is needed to characterize mechanisms that underlie the directional shift in aromatase regulation of VMN glycogen in eu- versus hypoglycemic male rats and gain in negative impact in hypoglycemic females.

Impact of caudal hindbrain glycogen metabolism on A2 noradrenergic neuron AMPK activation and ventromedial hypothalamic nucleus norepinephrine activity and glucoregulatory neurotransmitter marker protein expression

The brain glycogen reserve is a source of oxidizable substrate fuel. Lactoprivic-sensitive hindbrain A2 noradrenergic neurons provide crucial metabolic-sensory input to downstream hypothalamic glucose-regulatory structures. Current research examined whether hindbrain glycogen fuel supply impacts A2 energy stability and governance of ventromedial hypothalamic nucleus (VMN) metabolic transmitter signaling. Male rats were injected into the caudal fourth ventricle (CV4) with the glycogen phosphorylase inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) prior to continuous intra-CV4 infusion of L-lactate or vehicle. Lactate reversed DAB suppression of A2 neuron AMPK protein and up-regulated phosphoAMPK profiles. A2 dopamine-β-hydroxylase expression was refractory to DAB, but elevated by DAB/lactate. Lactate normalized A2 estrogen receptor-alpha and GPER proteins and up-regulated estrogen receptor-beta levels in DAB-treated rats. VMN norepinephrine content was decreased by DAB, but partially restored by lactate. DAB caused lactate-reversible or -irreversible augmentation of VMN glycogen phosphorylase-brain (GPbb) and -muscle type (GPmm) variant profiles, and correspondingly up- or down-regulated VMN protein markers of glucose-stimulatory nitrergic and glucose-inhibitory γ-aminobutyric acid transmission. DAB did not alter plasma glucose, but suppressed or elevated circulating glucagon and corticosterone in that order. Results show that diminished hindbrain glycogen breakdown is communicated to the VMN, in part by NE signaling, to up-regulate VMN glycogen breakdown and trigger neurochemical signaling of energy imbalance in that site. DAB effects on GPmm, VMN glycogen content, and counter-regulatory hormone secretion were unabated by lactate infusion, suggesting that aside from substrate fuel provision rate, additional indicators of glycogen metabolism such as turnover rate may be monitored in the hindbrain.

Estrogen Receptor Involvement in Noradrenergic Regulation of Ventromedial Hypothalamic Nucleus Glucoregulatory Neurotransmitter and Stimulus-Specific Glycogen Phosphorylase Enzyme Isoform Expression

Norepinephrine (NE) directly regulates ventromedial hypothalamic nucleus (VMN) glucoregulatory neurons and also controls glycogen-derived fuel provision to those cells. VMN nitric oxide (NO) and γ-aminobutyric acid (GABA) neurons and astrocytes express estrogen receptor-alpha (ERα) and ER-beta (ERβ) proteins. Current research used selective ERα (1,3Bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride) or ERβ (4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol) antagonists to address the premise that these ERs govern basal and/or NE-associated patterns of VMN metabolic neuron signaling and astrocyte glycogen metabolism. Both ERs stimulate expression of the enzyme marker protein neuronal nitric oxide synthase, not glutamate decarboxylase_65/67. NE inhibition or augmentation of neuronal nitric oxide synthase and glutamate decarboxylase_65/67 profiles was ER-independent or -dependent, respectively. In both neuron types, VMN ERβ activity inhibited baseline alpha1- (α₁-) and/or alpha2- (α₂-)adrenergic receptor (AR) expression, but ERα and -β signaling was paradoxically crucial for noradrenergic upregulation of α₂-AR. NE inhibited glycogen synthase expression and exerted opposite effects on VMN adenosine monophosphate-sensitive glycogen phosphorylase (GP)-brain type (stimulatory) versus NE-sensitive GP muscle (inhibitory) via ERα or -β activity. Results document unique ERα and ERβ actions on metabolic transmitter and AR protein expression in VMN nitrergic versus GABAergic neurons. ER effects varied in the presence versus absence of NE, indicating that both neuron types are substrates for estradiol and noradrenergic regulatory interaction. NE-dependent ER control of VMN GP variant expression implies that these signals also act on astrocytes to direct physiological stimulus-specific control of glycogen metabolism, which may in turn influence GABA transmission.

High performance liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) methodology for analysis of amino acid energy substrates in microwave-fixed microdissected brain tissue

Hypoglycemia deprives the brain of its primary energy source glucose. Reductions in whole-brain amino acid energy substrate levels suggest that these non-glucose fuels may be metabolized during glucose shortage. Recurring hypoglycemia can cause mal-adaptive impairment of glucose counter-regulation; yet, it is unclear if amplified reliance upon alternative metabolic substrates impedes detection of continuing neuro-glucopenia. This research aimed to develop high-sensitivity UHPLC-electrospray ionization mass spectrometric (LC-ESI-MS) methodology, for complementary use with high-neuroanatomical resolution microdissection tools, for measurement of glucogenic amino acid, e.g. glutamine (Gln), glutamate (Glu), and aspartate (Asp) content in the characterized glucose-sensing ventromedial hypothalamic nucleus (VMN) during acute versus chronic hypoglycemia. Results show that VMN tissue Gln, Glu, and Asp levels were significantly decreased during a single hypoglycemic episode, and that Gln and Asp measures were correspondingly normalized or further diminished during renewed hypoglycemia. Results provide proof-of-principle that LC-ESI-MS has requisite sensitivity for amino acid energy substrate quantification in distinctive brain gluco-regulatory structures under conditions of eu- versus hypoglycemia. This novel combinatory methodology will support ongoing efforts to determine how amino acid energy yield may impact VMN metabolic sensory function during persistent hypoglycemia.

Effects of acute versus recurrent insulin-induced hypoglycemia on ventromedial hypothalamic nucleus metabolic-sensory neuron AMPK activity: Impact of alpha1-adrenergic receptor signaling

Mechanisms that underlie metabolic sensor acclimation to recurring insulin-induced hypoglycemia (RIIH) are unclear. Norepinephrine (NE) regulates ventromedial hypothalamic nucleus (VMN) gluco-stimulatory nitric oxide (NO) and gluco-inhibitory γ-aminobutryic acid (GABA) neuron signaling. Current research addressed the hypothesis that during RIIH, NE suppresses 5'-AMP-activated protein kinase (AMPK) reactivity in both populations and impedes counter-regulation. The brain is postulated to utilize non-glucose substrates, e.g. amino acids glutamine (Gln), glutamate (Glu), and aspartate (Asp), to produce energy during hypoglycemia. A correlated aim investigated whether NE controls pyruvate recycling pathway marker protein (glutaminase, GLT; malic enzyme, ME-1) expression in either metabolic-sensory cell population. Male rats were injected subcutaneously with vehicle or insulin on days 1-3, then pretreated on day 4 by intracerebroventricular delivery of the alpha₁-adrenergic receptor (α₁-AR) reverse-agonist prazocin (PRZ) or vehicle before final insulin therapy. PRZ prevented acute hypoglycemic augmentation of AMPK activation in each cell group. Antecedent hypoglycemic repression of sensor activity was reversed by PRZ in GABA neurons. During RIIH, nitrergic neurons exhibited α₁-AR - dependent up-regulated GLT and α₂-AR profiles, while GABA cells showed down-regulated α₁-AR. LC-ESI-MS analysis documented a decline in VMN Glu, Gln, and Asp concentrations during acute hypoglycemia, and habituation of the former two profiles to RIIH. PRZ attenuated glucagon and corticosterone secretion during acute hypoglycemia, but reversed decrements in output of both hormones during RIIH. Results implicate adjustments in impact of α₁-AR signaling in repressed VMN metabolic-sensory AMPK activation and counter-regulatory dysfunction during RIIH. Antecedent hypoglycemia may up-regulate NO neuron energy yield via α₁-AR - mediated up-regulated pyruvate recycling.

Hindbrain lactoprivic regulation of hypothalamic neuron transactivation and gluco-regulatory neurotransmitter expression: Impact of antecedent insulin-induced hypoglycemia

Hindbrain energy state shapes hypothalamic control of glucostasis. Dorsal vagal complex (DVC) L-lactate deficiency is a potent glucose-stimulatory signal that triggers neuronal transcriptional activation in key hypothalamic metabolic loci. The energy gauge AMPK is activated in DVC metabolic-sensory A2 noradrenergic neurons by hypoglycemia-associated lactoprivation, but sensor reactivity is diminished by antecedent hypoglycemia (AH). Current research addressed the premise that AH alters hindbrain lactoprivic regulation of hypothalamic metabolic transmitter function. AH did not modify reductions in A2 dopamine-beta-hydroxylase and monocarboxylate-2 (MCT2) protein expression elicited by caudal fourth ventricular delivery of the MCT inhibitor alpha-cyano-4-hydroxycinnamic acid (4CIN), but attenuated 4CIN activation of A2 AMPK. 4CIN constraint of hypothalamic norepinephrine (NE) activity was averted by AH in a site-specific manner. 4CIN induction of Fos immunolabeling in hypothalamic arcuate (ARH), ventromedial (VMN), dorsomedial (DMN) and paraventricular (PVN) nuclei and lateral hypothalamic area (LHA) was avoided by AH. AH affected reactivity of select hypothalamic metabolic neurotransmitter/enzyme marker proteins, e.g. ARH neuropeptide Y, VMN glutamate decarboxylase, DMN RFamide-related peptide-1 and -3, and LHA orexin-A profiles to 4CIN, but did not alleviate drug inhibition of ARH proopiomelanocortin. AH prevented 4CIN augmentation of circulating glucagon, but did not alter hyperglycemic or hypocorticosteronemic responses to that treatment. Results identify hindbrain lactate deficiency as a stimulus for glucagon secretion, and imply that habituation of this critical counter-regulatory hormone to recurring hypoglycemia may involve one or more hypothalamic neurotransmitters characterized here by acclimation to this critical sensory stimulus.

Norepinephrine control of ventromedial hypothalamic nucleus glucoregulatory neurotransmitter expression in the female rat: Role of monocarboxylate transporter function

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.

Hypothalamic peroxisome proliferator-activated receptor gamma regulates ghrelin production and food intake

Peroxisome proliferator-activated receptor-γ (PPARγ) regulates fatty acid storage, glucose metabolism, and food intake. Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate appetite. However, the effects of PPARγ on ghrelin production are still unclear. In the present study, the effects of PPARγ on ghrelin production were examined in lean- or high-fat diet-induced obese (DIO) C57BL/6J mice and mHypoE-42 cells, a hypothalamic cell line. 3rd intracerebroventricular injection of adenoviral-directed overexpression of PPARγ (Ad-PPARγ) reduced hypothalamic and plasma ghrelin, food intake in both lean C57BL/6J mice and diet-induced obese mice. These changes were associated with a significant increase in mechanistic target of rapamycin complex 1 (mTORC1) activity. Overexpression of PPARγ enhanced mTORC1 signaling and suppressed ghrelin production in cultured mHypoE-42 cells. Our results suggest that hypothalamic PPARγ plays a vital role in ghrelin production and food intake in mice.