Energy metabolism and hindbrain AMPK: regulation by estradiol

Nerve cell energy status is screened within multiple classically defined hypothalamic and hindbrain components of the energy balance control network, including the hindbrain dorsal vagal complex (DVC). Signals of caudal DVC origin have a physiological role in glucostasis, e.g., maintenance of optimal supply of the critical substrate fuel, glucose, through control of motor functions such as fuel consumption and gluco-counterregulatory hormone secretion. A2 noradrenergic neurons are a likely source of these signals as combinatory laser microdissection/high-sensitivity Western blotting reveals expression of multiple biomarkers for metabolic sensing, including adenosine 5'-monophosphate-activated protein kinase (AMPK). Hypoglycemia elicits estradiol-dependent sex differences in A2 AMPK activation as phospho-AMPK (pAMPK) expression is augmented in male and ovariectomized (OVX) female, but not estrogen-replaced, OVX rats. This dichotomy may reflect, in part, estradiol-mediated up-regulation of glycolytic and tricarboxylic acid cycle enzyme expression during hypoglycemia. Our new model for short-term feeding abstinence has physiological relevance to planned (dieting) or unplanned (meal delay) interruption of consumption in modern life, which is negatively correlated with appetite control and obesity, and is useful for investigating how estrogen may mitigate the effects of disrupted fuel acquisition on energy balance via actions within the DVC. Estradiol reduces DVC AMPK activity after local delivery of the AMP mimic, 5-aminoimidazole-4-carboxamide-riboside, or cessation of feeding for 12 h but elevates pAMPK expression when these treatments are combined. These data suggest that estrogen maintains cellular energy stability over periods of suspended fuel acquisition and yet optimizes, by DVC AMPK-dependent mechanisms, counter-regulatory responses to metabolic challenges that occur during short-span feeding abstinence.