This study investigated the hypothesis that estrogen controls hindbrain AMP-activated protein kinase (AMPK) activity and regulation of blood glucose, counterregulatory hormone secretion, and hypothalamic nerve cell transcriptional status. Dorsal vagal complex A2 noradrenergic neurons were laser microdissected from estradiol benzoate (E)- or oil (O)-implanted ovariectomized female rats after caudal fourth ventricular (CV4) delivery of the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR), for Western blot analysis. E advanced AICAR-induced increases in A2 phospho-AMPK (pAMPK) expression and in blood glucose levels and was required for augmentation of Fos, estrogen receptor-α (ERα), monocarboxylate transporter-2, and glucose transporter-3 protein in A2 neurons and enhancement of corticosterone secretion by this treatment paradigm. CV4 AICAR also resulted in site-specific modifications in Fos immunolabeling of hypothalamic metabolic structures, including the paraventricular, ventromedial, and arcuate nuclei. The current studies demonstrate that estrogen regulates AMPK activation in caudal hindbrain A2 noradrenergic neurons during pharmacological replication of energy shortage in this area of the brain, and that this sensor is involved in neural regulation of glucostasis, in part, through control of corticosterone secretion. The data provide unique evidence that A2 neurons express both ERα and -β proteins and that AMPK upregulates cellular sensitivity to ERα-mediated signaling during simulated energy insufficiency. The results also imply that estrogen promotes glucose and lactate uptake by these cells under those conditions. Evidence for correlation between hindbrain AMPK and hypothalamic nerve cell genomic activation provides novel proof for functional connectivity between this hindbrain sensor and higher order metabolic brain loci while demonstrating a modulatory role for estrogen in this interaction.

Nerve cell metabolic activity is monitored in multiple brain regions, including the hypothalamus and hindbrain dorsal vagal complex (DVC), but it is unclear if individual metabolosensory loci operate autonomously or interact to coordinate central nervous system (CNS) reactivity to energy imbalance. This research addressed the hypothesis that hypoglycemia-associated DVC lactoprivation stimulates hypothalamic AMPK activity and metabolic neurotransmitter expression. As DVC catecholaminergic neurons express biomarkers for metabolic monitoring, we investigated whether these cells are a source of lactate deficit signaling to the hypothalamus. Caudal fourth ventricle (CV4) infusion of the glucose metabolite l-lactate during insulin-induced hypoglycemia reversed changes in DVC A2 noradrenergic, arcuate neuropeptide Y (NPY) and pro-opiomelanocortin (POMC), and lateral hypothalamic orexin-A (ORX) neuronal AMPK activity, coincident with exacerbation of hypoglycemia. Hindbrain lactate repletion also blunted hypoglycemic upregulation of arcuate NPY mRNA and protein. This treatment did not alter hypoglycemic paraventricular oxytocin (OT) and lateral hypothalamic ORX mRNA profiles, but exacerbated or reversed adjustments in OT and ORX neuropeptide synthesis, respectively. CV4 delivery of the monocarboxylate transporter inhibitor, 4-CIN, increased A2 phosphoAMPK (pAMPK), elevated circulating glucose, and stimulated feeding, responses that were attenuated by 6-hydroxydopamine pretreatment. 4-CIN-infused rats exhibited increased (NPY, ORX neurons) or decreased (POMC neurons) pAMPK concurrent with hyperglycemia. These data show that hindbrain lactoprivic signaling regulates hypothalamic AMPK and key effector neurotransmitter responses to hypoglycemia. Evidence that A2 AMPK activity is lactate-dependent, and that DVC catecholamine cells are critical for lactoprivic control of glucose, feeding, and hypothalamic AMPK, implies A2 derivation of this metabolic regulatory stimulus.

No abstract

The ability of estrogen to shield the brain from the bio-energetic insult, hypoglycemia, is unclear. Estradiol prevents hypoglycemic activation of the energy deficit sensor, adenosine 5′-monophosphate-activated protein kinase (AMPK), in hindbrain metabolo-sensory A2 noradrenergic neurons. Here, we investigated the hypothesis that estrogen regulates A2 AMPK through control of fuel metabolism and/or upstream protein kinase/phosphatase enzyme expression. A2 cells were harvested by laser-microdissection after insulin (INS) or vehicle (V) injection of estradiol (E)- or oil (O)-implanted ovariectomized female rats. Cell lysates were evaluated by immunoblot for glycolytic, tricarboxylic acid cycle (TCA), respiratory chain, and acetyl CoA-malonyl CoA pathway enzymes. A2 phosphofructokinase (PFKL), isocitrate dehydrogenase, and pyruvate dehydrogenase and ATP synthase subunit profiles were elevated in E/V versus O/V; hypoglycemia augmented PFKL and alpha-ketoglutarate dehydrogenase expression in E only. Hypoglycemia increased A2 Ca++/calmodulin-dependent protein kinase-beta in O, while reducing PP2A in both groups. A2 phosphoAMPK levels were equivalent in O/V versus E/V, but elevated during hypoglycemia in O only. These results implicate estradiol in compensatory up-regulation of substrate catabolism and corresponding maintenance of energy stability of A2 metabolo-sensory neurons during hypoglycemia, outcomes that support the potential viability of molecular substrates for hormone action as targets for therapies alleviating hypoglycemic brain injury.

Background Blood donations must be tested for evidence of syphilis, a transfusion‐transmitted infection. Screening blood for syphilis‐related antibodies greatly reduced the risk of transfusion‐transmitted syphilis (TTS). It is commonly believed that Treponema pallidum (Tp), the bacterium causing syphilis, does not survive in blood during cold storage—suggested as one reason why no cases of TTS have been recognized in the United States for many years. Some have suggested that routine syphilis screening of blood donations is no longer needed. To address the effect of storage, we investigated the survival of Tp experimentally spiked into blood and platelets stored under conventional conditions. Study design and methods We spiked fresh human blood products with high concentrations of Tp and inoculated samples at intervals into rabbits, a sensitive assay detecting infectious Tp. We tested whole blood (WB) stored refrigerated (1–6°C) for 9 days and platelets stored at room temperature for 7 days or refrigerated for 14 days. We assayed sera of the rabbits collected at intervals for seroconversion using two different tests and assessed orchitis. Rabbits were considered infected if one or both serological test results became positive. Results Viable Tp survived 7 days in WB and 6 days in platelets stored at both ambient and cold temperatures. Discussion Tp at concentrations much higher than those possibly present in an infected blood unit survived in cold blood products longer than previously reported and, thus, storage conditions cannot be relied upon to eliminate T. pallidum from blood or platelets. TTS remains a topic of concern for public health.