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.

Poly(ADP-ribose) polymerase 1 (PARP1) is a multifunctional protein involved in diverse cellular functions, notably DNA damage repair. Pharmacological inhibition of PARP1 has therapeutic benefits for various pathologies. Despite the increased use of PARP inhibitors, challenges persist in achieving PARP1 selectivity and effective blood-brain barrier (BBB) penetration. The development of a PARP1-specific positron emission tomography (PET) radioligand is crucial for understanding disease biology and performing target occupancy studies, which may aid in the development of PARP1-specific inhibitors. In this study, we leverage the recently identified PARP1 inhibitor, AZD9574, to introduce the design and development of its ¹⁸F-isotopologue ([¹⁸F]AZD9574). Our comprehensive approach, encompassing pharmacological, cellular, autoradiographic, and in vivo PET imaging evaluations in non-human primates, demonstrates the capacity of [¹⁸F]AZD9574 to specifically bind to PARP1 and to successfully penetrate the BBB. These findings position [¹⁸F]AZD9574 as a viable molecular imaging tool, poised to facilitate the exploration of pathophysiological changes in PARP1 tissue abundance across various diseases.

Norepinephrine (NE) control of hypothalamic gluco-regulation involves astrocyte-derived energy fuel supply. In male rats, exogenous NE regulates astrocyte glycogen metabolic enzyme expression in vivo through 5’-AMP-activated protein kinase (AMPK)-dependent mechanisms. Current research utilized a rat hypothalamic astrocyte primary culture model to investigate the premise that NE imposes sex-specific direct control of AMPK activity and glycogen mass and metabolism in these glia. In male rats, NE down-regulation of pAMPK correlates with decreased CaMMKB and increased PP1 expression, whereas noradrenergic augmentation of female astrocyte pAMPK may not involve these upstream regulators. NE concentration is a critical determinant of control of hypothalamic astrocyte glycogen enzyme expression, but efficacy varies between sexes. Data show sex variations in glycogen synthase expression and glycogen phosphorylase-brain and –muscle type dose-responsiveness to NE. Narrow dose-dependent NE augmentation of astrocyte glycogen content during energy homeostasis infers that NE maintains, over a broad exposure range, constancy of glycogen content despite possible changes in turnover. In male rats, beta₁- and beta₂-adrenergic receptor (AR) profiles displayed bi-directional responses to increasing NE doses; female astrocytes exhibited diminished beta₁-AR content at low dose exposure, but enhanced beta₂-AR expression at high NE dosages. Thus, graded variations in noradrenergic stimulation may modulate astrocyte receptivity to NE in vivo. Sex dimorphic NE regulation of hypothalamic astrocyte AMPK activation and glycogen metabolism may be mediated, in part, by one or more ARs characterized here by divergent sensitivity to this transmitter.

Hindbrain A2 noradrenergic neurons assimilate estrogenic and metabolic cues. In female mammals, negative- versus positive-feedback patterns of estradiol (E) secretion impose divergent regulation of the gonadotropin-releasing hormone (GnRH)-pituitary-gonadal (HPG) neuroendocrine axis. Current research used retrograde tracing, dual-label immunocytochemistry, single-cell laser-microdissection, and multiplex qPCR methods to address the premise that E feedback modes uniquely affect metabolic regulation of A2 neurons involved in HPG control. Ovariectomized female rats were given E replacement to replicate plasma hormone levels characteristic of positive (high-E dose) or negative (low-E dose) feedback. Animals were either full-fed (FF) or subjected to short-term, e.g., 18-h food deprivation (FD). After FF or FD, rostral preoptic area (rPO)-projecting A2 neurons were characterized by the presence or absence of nuclear glucokinase regulatory protein (nGKRP) immunostaining. FD augmented or suppressed mRNAs encoding the catecholamine enzyme dopamine-beta-hydroxylase (DβH) and the metabolic-sensory biomarker glucokinase (GCK), relative to FF controls, in nGKRP-immunoreactive (ir)-positive A2 neurons from low-E or high-E animals, respectively. Yet, these transcript profiles were unaffected by FD in nGKRP-ir-negative A2 neurons at either E dosage level. FD altered estrogen receptor (ER)-alpha and ATP-sensitive potassium channel subunit sulfonylurea receptor-1 gene expression in nGKRP-ir-positive neurons from low-E, but not high-E animals. Results provide novel evidence that distinct hindbrain A2 neuron populations exhibit altered versus unaffected transmission to the rPO during FD-associated metabolic imbalance, and that the direction of change in this noradrenergic input is controlled by E feedback mode. These A2 cell types are correspondingly distinguished by FD-sensitive or -insensitive GCK, which correlates with the presence versus absence of nGKRP-ir. Further studies are needed to determine how E signal volume regulates neurotransmitter and metabolic sensor responses to FD in GKRP-expressing A2 neurons.

The catecholamine norepinephrine (NE) links hindbrain metabolic-sensory neurons with key glucostatic control structures in the brain, including the ventromedial hypothalamic nucleus (VMN). In the brain, the glycogen reserve is maintained within the astrocyte cell compartment as an alternative energy source to blood-derived glucose. VMN astrocytes are direct targets for metabolic stimulus-driven noradrenergic signaling due to their adrenergic receptor expression (AR). The current review discusses recent affirmative evidence that neuro-metabolic stability in the VMN may be shaped by NE influence on astrocyte glycogen metabolism and glycogen-derived substrate fuel supply. Noradrenergic modulation of estrogen receptor (ER) control of VMN glycogen phosphorylase (GP) isoform expression supports the interaction of catecholamine and estradiol signals in shaping the physiological stimulus-specific control of astrocyte glycogen mobilization. Sex-dimorphic NE control of glycogen synthase and GP brain versus muscle type proteins may be due, in part, to the dissimilar noradrenergic governance of astrocyte AR and ER variant profiles in males versus females. Forthcoming advances in the understanding of the molecular mechanistic framework for catecholamine stimulus integration with other regulatory inputs to VMN astrocytes will undoubtedly reveal useful new molecular targets in each sex for glycogen mediated defense of neuronal metabolic equilibrium during neuro-glucopenia.

The enzyme aromatase is expressed at high levels in the ventromedial hypothalamic nucleus (VMN), a principal component of the brain gluco-regulatory network. Current research utilized selective gene knockdown tools to investigate the premise that VMN neuroestradiol controls glucostasis. Intra-VMN aromatase siRNA administration decreased baseline aromatase protein expression and tissue estradiol concentrations and either reversed or attenuated the hypoglycemic regulation of these profiles in a VMN segment-specific manner. Aromatase gene repression down-regulated protein biomarkers for gluco-stimulatory (nitric oxide; NO) and -inhibitory (gamma-aminobutyric acid; GABA) neurochemical transmitters. Insulin-induced hypoglycemia (IIH) up- or down-regulated neuronal nitric oxide synthase (nNOS) and glutamate decarboxylase_65/67 (GAD), respectively, throughout the VMN. Interestingly, IIH caused divergent changes in tissue aromatase and estradiol levels in rostral (diminished) versus middle and caudal (elevated) VMN. Aromatase knockdown prevented hypoglycemic nNOS augmentation in VMN middle and caudal segments, but abolished the GAD inhibitory response to IIH throughout this nucleus. VMN nitrergic and GABAergic neurons monitor stimulus-specific glycogen breakdown. Here, glycogen synthase (GS) and phosphorylase brain- (GPbb; AMP-sensitive) and muscle- (GPmm; noradrenergic –responsive) type isoform responses to aromatase siRNA were evaluated. Aromatase repression reduced GPbb and GPmm content in euglycemic controls and prevented hypoglycemic regulation of GPmm but not GPbb expression while reversing glycogen accumulation. Aromatase siRNA elevated baseline glucagon and corticosterone secretion and abolished hypoglycemic hyperglucagonemia and hypercorticosteronemia. Outcomes document the involvement of VMN neuroestradiol signaling in brain control of glucose homeostasis. Aromatase regulation of VMN gluco-regulatory signaling of hypoglycemia-associated energy imbalance may entail, in part, control of GP variant-mediated glycogen disassembly.