Hindbrain lactate regulation of hypoglycemia-associated patterns of catecholamine and metabolic-sensory biomarker gene expression in A2 noradrenergic neurons innervating the male versus female ventromedial hypothalamic nucleus.

ABSTRACT

Caudal hindbrain A2 noradrenergic neurons provide critical metabolic-sensory input to the brain glucostatic circuitry. In males, insulin-induced hypoglycemia (IIH)-associated patterns of A2 cell dopamine-beta-hydroxylase (DßH) protein expression reflect diminution of the oxidizable fuel L-lactate, yet DßH exhibits sex-dimorphic responses to IIH. Here, retrograde tracing and combinatory single-cell laser-microdissection/multiplex qPCR techniques were used to examine whether lactate imposes sex-specific control of hypoglycemia-associated metabolic-sensory function and noradrenergic neurotransmission in A2 neurons that innervate the ventromedial hypothalamic nucleus (VMN), a key glucose-regulatory structure. VMN-projecting A2 neurons from each sex were characterized by presence or absence of nuclear glucokinase regulatory protein (nGKRP) immunoreactivity (-ir). IIH caused lactate-reversible up- or down-regulation of DßH mRNA in male and female nGKRP-ir-positive A2 neurons, respectively, and stimulated glucokinase (GCK) and sulfonylurea receptor-1 (SUR-1) gene expression in these cells in each sex. Hypoglycemia did not alter DßH, GCK, and SUR-1 transcript profiles in nGKRP-ir-negative male or female A2 neurons innervating the VMN. Estrogen receptor (ER) gene profiles in nGKRP-ir-positive neurons showed sex-specific [ER-alpha; G-protein-coupled estrogen-receptor-1 (GPER)] or sex-monomorphic (ER-beta) transcriptional responses to IIH. Fewer ER gene profiles were affected by IIH in nGKRP-ir-negative A2 neurons from male or female rats. Results show that during IIH, VMN-projecting A2 neurons may deliver altered, sex-dependent (nGKRP-positive) or unaffected (nGKRP-negative) noradrenergic input to the VMN. In each sex, metabolic-sensory gene profiles were reactive to hypoglycemia in nGKRP-ir-positive, not -negative A2 cells. Further studies are needed to elucidate the role of GKRP in transduction of metabolic imbalance into noradrenergic signaling, and to determine if input by one or more ER variants establishes sex differences in DßH transcriptional sensitivity to IIH.