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 ß1-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.

Hypoglycemic and post­hypoglycemic patterns of glycogen phosphorylase isoform expression in the ventrolateral ventromedial hypothalamic nucleus: impact of sex and estradiol.

Glycogen metabolism shapes ventromedial hypothalamic nucleus (VMN) control of glucose homeostasis. Brain glycogen mass undergoes compensatory expansion post­recovery from insulin­induced hypoglycemia (IIH). Current research utilized combinatory high­resolution microdissection/high­sensitivity Western blotting to investigate whether IIH causes residual adjustments in glycogen metabolism within the metabolic­sensory ventrolateral VMN (VMNvl). Micropunch­dissected tissue was collected from rostral, middle, and caudal levels of the VMNvl in each sex for analysis of glycogen synthase (GS) and glycogen phosphorylase (GP)­muscle type (GPmm; norepinephrine­sensitive) and GP­brain type (GPbb; glucoprivic­sensitive) isoform expression during and after IIH. Hypoglycemic suppression of VMNvl GS levels in males disappeared or continued after reestablishment of euglycemia, according to sampled segment. Yet, reductions in female VMNvl GS persisted after IIH. Males exhibited reductions in GPmm content in select rostro­caudal VMNvl segments, but this protein declined in each segment post­hypoglycemia. Females, rather, showed augmented or diminished GPmm levels during IIH, but no residual effects of IIH on this protein. In each sex, region­specific up­ or down­regulation of VMNvl GPbb profiles during glucose decrements were undetected post­recovery from IIH. Results provide novel proof of estradiol­dependent sex­dimorphic patterns of VMNvl GP variant expression at specific rostro­caudal levels of this critical gluco­regulatory structure. Sex differences in persistence of IIH­associated GS and GPmm patterns of expression after restoration of euglycemia infer that VMNvl recovery from this metabolic stress may involve dissimilar glycogen accumulation in male versus female.