Journal
AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY INTEGRATIVE AND COMPARATIVE PHYSIOLOGY
Volume 289, Issue 4, Pages R977-R981Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpregu.00403.2005
Keywords
in vivo microdialysis; extracellular fluids; freely moving rats; glucosensing neurons
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Funding
- NIDDK NIH HHS [DK-59755, R01 DK059755] Funding Source: Medline
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During insulin-induced hypoglycemia, there is an increase in extracellular norepinephrine ( NE) in the ventromedial hypothalamus (VMH). This brain area is known to play an important role in integrated hormonal and behavioral responses to systemic hypoglycemia. Selective glucoprivation restricted to the VMH is both necessary and sufficient to initiate secretion of counterregulatory hormones. The present study was designed to investigate whether increased release of NE in the VMH depends on detection of glucoprivation localized in this area. In awake, chronically catheterized male Sprague-Dawley rats, extracellular NE in the VMH was monitored using 1-mm microdialysis probes perfused with Krebs Ringer buffer (KRB) or KRB + 100 mM D-glucose (D-Glc). During insulin-induced hypoglycemia (glycemic nadir similar to 2.4 mM) extracellular NE was increased to > 160% of baseline (P < 0.01) only in the KRB + insulin group. There was no increase in NE from baseline when glucose was added to the perfusate to maintain euglycemia at the periprobe environment. The sympathoadrenal response to hypoglycemia, present in the KRB + insulin group, was attenuated in the D-Glc + insulin group. The present results confirm that noradrenergic activation in the VMH during systemic hypoglycemia depends on detection of glucoprivation locally in this area. These data provide additional support for the importance of increased noradrenergic activity in the VMH in the counterregulatory hormonal responses to hypoglycemia.
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