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Brain insulin action regulates hypothalamic glucose sensing and the counterregulatory response to hypoglycemia.

Diggs-Andrews KA, Zhang X, Song Z, Daphna-Iken D, Routh VH, Fisher SJ - Diabetes (2010)

Bottom Line: Subsequently, counterregulatory responses, hypothalamic neuronal activation (with transcriptional marker c-fos), and regional brain glucose uptake (via (14)C-2deoxyglucose autoradiography) were measured.Additionally, electrophysiological activity of individual glucose-inhibited neurons and hypothalamic glucose sensing protein expression (GLUTs, glucokinase) were measured.Chronically, insulin acts in the brain to regulate the counterregulatory response to hypoglycemia by directly altering glucose sensing in hypothalamic neurons and shifting the glycemic levels necessary to elicit a normal sympathoadrenal response.

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Metabolism and Lipid Research, Department of Internal Medicine, Washington University School of Medicine, Saint Louis, Missouri, USA.

ABSTRACT

Objective: An impaired ability to sense and appropriately respond to insulin-induced hypoglycemia is a common and serious complication faced by insulin-treated diabetic patients. This study tests the hypothesis that insulin acts directly in the brain to regulate critical glucose-sensing neurons in the hypothalamus to mediate the counterregulatory response to hypoglycemia.

Research design and methods: To delineate insulin actions in the brain, neuron-specific insulin receptor knockout (NIRKO) mice and littermate controls were subjected to graded hypoglycemic (100, 70, 50, and 30 mg/dl) hyperinsulinemic (20 mU/kg/min) clamps and nonhypoglycemic stressors (e.g., restraint, heat). Subsequently, counterregulatory responses, hypothalamic neuronal activation (with transcriptional marker c-fos), and regional brain glucose uptake (via (14)C-2deoxyglucose autoradiography) were measured. Additionally, electrophysiological activity of individual glucose-inhibited neurons and hypothalamic glucose sensing protein expression (GLUTs, glucokinase) were measured.

Results: NIRKO mice revealed a glycemia-dependent impairment in the sympathoadrenal response to hypoglycemia and demonstrated markedly reduced (3-fold) hypothalamic c-fos activation in response to hypoglycemia but not other stressors. Glucose-inhibited neurons in the ventromedial hypothalamus of NIRKO mice displayed significantly blunted glucose responsiveness (membrane potential and input resistance responses were blunted 66 and 80%, respectively). Further, hypothalamic expression of the insulin-responsive GLUT 4, but not glucokinase, was reduced by 30% in NIRKO mice while regional brain glucose uptake remained unaltered.

Conclusions: Chronically, insulin acts in the brain to regulate the counterregulatory response to hypoglycemia by directly altering glucose sensing in hypothalamic neurons and shifting the glycemic levels necessary to elicit a normal sympathoadrenal response.

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Related in: MedlinePlus

NIRKO mice display normal physiological responses to heat stress. NIRKO (n = 6, closed bars) and littermate controls (n = 6, open bars) were subjected to heat stress for 90 min. A and B: Plasma epinephrine (A) and norepinephrine (B) levels were not significantly different between NIRKO and control mice. C: Representative images of matched hypothalamic sections highlighting heat stress induced c-fos staining in the PVN. D: The quantity of c-fos positive cells was similar between NIRKO and controls. (A high-quality color representation of this figure is available in the online issue.)
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Figure 6: NIRKO mice display normal physiological responses to heat stress. NIRKO (n = 6, closed bars) and littermate controls (n = 6, open bars) were subjected to heat stress for 90 min. A and B: Plasma epinephrine (A) and norepinephrine (B) levels were not significantly different between NIRKO and control mice. C: Representative images of matched hypothalamic sections highlighting heat stress induced c-fos staining in the PVN. D: The quantity of c-fos positive cells was similar between NIRKO and controls. (A high-quality color representation of this figure is available in the online issue.)

Mentions: NIRKO and control mice were subjected to a mild stressor (restraint stress) and a more profound stressor (heat stress) to evaluate sympathoadrenal activation in response to glycemia-independent stress. In response to milder restraint stress, plasma epinephrine levels rose similarly twofold in both littermate controls and NIRKO mice (Fig. 5A). The physiological increased heart rate to restraint stress was also similar in control and NIRKO mice (Fig. 5B). Heat stress induced a more pronounced catecholamine elevation than restraint stress (to levels observed with hypoglycemia), but the rise in both epinephrine and norepinephrine in response to heat stress was again not significantly different between groups (Fig. 6C and D). To determine whether this defect in neuronal activation was unique to hypoglycemia, c-fos expression was also assessed in response to heat stress. Increased c-fos expression was again noted in the PVN in response to heat stress (Fig. 6A), to levels observed with hypoglycemia; however, in response to heat stress, there was no difference in c-fos expression between groups (Control: 123 ± 4 vs. NIRKO: 129 ± 10, P = NS) (Fig. 6B).


Brain insulin action regulates hypothalamic glucose sensing and the counterregulatory response to hypoglycemia.

Diggs-Andrews KA, Zhang X, Song Z, Daphna-Iken D, Routh VH, Fisher SJ - Diabetes (2010)

NIRKO mice display normal physiological responses to heat stress. NIRKO (n = 6, closed bars) and littermate controls (n = 6, open bars) were subjected to heat stress for 90 min. A and B: Plasma epinephrine (A) and norepinephrine (B) levels were not significantly different between NIRKO and control mice. C: Representative images of matched hypothalamic sections highlighting heat stress induced c-fos staining in the PVN. D: The quantity of c-fos positive cells was similar between NIRKO and controls. (A high-quality color representation of this figure is available in the online issue.)
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2927950&req=5

Figure 6: NIRKO mice display normal physiological responses to heat stress. NIRKO (n = 6, closed bars) and littermate controls (n = 6, open bars) were subjected to heat stress for 90 min. A and B: Plasma epinephrine (A) and norepinephrine (B) levels were not significantly different between NIRKO and control mice. C: Representative images of matched hypothalamic sections highlighting heat stress induced c-fos staining in the PVN. D: The quantity of c-fos positive cells was similar between NIRKO and controls. (A high-quality color representation of this figure is available in the online issue.)
Mentions: NIRKO and control mice were subjected to a mild stressor (restraint stress) and a more profound stressor (heat stress) to evaluate sympathoadrenal activation in response to glycemia-independent stress. In response to milder restraint stress, plasma epinephrine levels rose similarly twofold in both littermate controls and NIRKO mice (Fig. 5A). The physiological increased heart rate to restraint stress was also similar in control and NIRKO mice (Fig. 5B). Heat stress induced a more pronounced catecholamine elevation than restraint stress (to levels observed with hypoglycemia), but the rise in both epinephrine and norepinephrine in response to heat stress was again not significantly different between groups (Fig. 6C and D). To determine whether this defect in neuronal activation was unique to hypoglycemia, c-fos expression was also assessed in response to heat stress. Increased c-fos expression was again noted in the PVN in response to heat stress (Fig. 6A), to levels observed with hypoglycemia; however, in response to heat stress, there was no difference in c-fos expression between groups (Control: 123 ± 4 vs. NIRKO: 129 ± 10, P = NS) (Fig. 6B).

Bottom Line: Subsequently, counterregulatory responses, hypothalamic neuronal activation (with transcriptional marker c-fos), and regional brain glucose uptake (via (14)C-2deoxyglucose autoradiography) were measured.Additionally, electrophysiological activity of individual glucose-inhibited neurons and hypothalamic glucose sensing protein expression (GLUTs, glucokinase) were measured.Chronically, insulin acts in the brain to regulate the counterregulatory response to hypoglycemia by directly altering glucose sensing in hypothalamic neurons and shifting the glycemic levels necessary to elicit a normal sympathoadrenal response.

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Metabolism and Lipid Research, Department of Internal Medicine, Washington University School of Medicine, Saint Louis, Missouri, USA.

ABSTRACT

Objective: An impaired ability to sense and appropriately respond to insulin-induced hypoglycemia is a common and serious complication faced by insulin-treated diabetic patients. This study tests the hypothesis that insulin acts directly in the brain to regulate critical glucose-sensing neurons in the hypothalamus to mediate the counterregulatory response to hypoglycemia.

Research design and methods: To delineate insulin actions in the brain, neuron-specific insulin receptor knockout (NIRKO) mice and littermate controls were subjected to graded hypoglycemic (100, 70, 50, and 30 mg/dl) hyperinsulinemic (20 mU/kg/min) clamps and nonhypoglycemic stressors (e.g., restraint, heat). Subsequently, counterregulatory responses, hypothalamic neuronal activation (with transcriptional marker c-fos), and regional brain glucose uptake (via (14)C-2deoxyglucose autoradiography) were measured. Additionally, electrophysiological activity of individual glucose-inhibited neurons and hypothalamic glucose sensing protein expression (GLUTs, glucokinase) were measured.

Results: NIRKO mice revealed a glycemia-dependent impairment in the sympathoadrenal response to hypoglycemia and demonstrated markedly reduced (3-fold) hypothalamic c-fos activation in response to hypoglycemia but not other stressors. Glucose-inhibited neurons in the ventromedial hypothalamus of NIRKO mice displayed significantly blunted glucose responsiveness (membrane potential and input resistance responses were blunted 66 and 80%, respectively). Further, hypothalamic expression of the insulin-responsive GLUT 4, but not glucokinase, was reduced by 30% in NIRKO mice while regional brain glucose uptake remained unaltered.

Conclusions: Chronically, insulin acts in the brain to regulate the counterregulatory response to hypoglycemia by directly altering glucose sensing in hypothalamic neurons and shifting the glycemic levels necessary to elicit a normal sympathoadrenal response.

Show MeSH
Related in: MedlinePlus