Increased GABAergic tone in the ventromedial hypothalamus contributes to suppression of counterregulatory responses after antecedent hypoglycemia. 2008

Owen Chan, and Haiying Cheng, and Raimund Herzog, and Daniel Czyzyk, and Wanling Zhu, and Ajin Wang, and Rory J McCrimmon, and Margretta R Seashore, and Robert S Sherwin
Section of Endocrinology, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, USA.

OBJECTIVE We have previously demonstrated that modulation of gamma-aminobutyric acid (GABA) inhibitory tone in the ventromedial hypothalamus (VMH), an important glucose-sensing region in the brain, modulates the magnitude of glucagon and sympathoadrenal responses to hypoglycemia. In the current study, we examined whether increased VMH GABAergic tone may contribute to suppression of counterregulatory responses after recurrent hypoglycemia. METHODS To test this hypothesis, we quantified expression of the GABA synthetic enzyme, glutamic acid decarboxylase (GAD), in the VMH of control and recurrently hypoglycemic rats. Subsequently, we used microdialysis and microinjection techniques to assess changes in VMH GABA levels and the effects of GABA(A) receptor blockade on counterregulatory responses to a standardized hypoglycemic stimulus. RESULTS Quantitative RT-PCR and immunoblots in recurrently hypoglycemic animals revealed that GAD(65) mRNA and protein were increased 33 and 580%, respectively. Basal VMH GABA concentrations were more than threefold higher in recurrently hypoglycemic animals. Furthermore, whereas VMH GABA levels decreased in both control and recurrently hypoglycemic animals with the onset of hypoglycemia, the fall was not significant in recurrently hypoglycemic rats. During hypoglycemia, recurrently hypoglycemic rats exhibited a 49-63% reduction in glucagon and epinephrine release. These changes were reversed by delivery of a GABA(A) receptor antagonist to the VMH. CONCLUSIONS Our data suggest that recurrent hypoglycemia increases GABAergic inhibitory tone in the VMH and that this, in turn, suppresses glucagon and sympathoadrenal responses to subsequent bouts of acute hypoglycemia. Thus, hypoglycemia-associated autonomic failure may be due in part to a relative excess of the inhibitory neurotransmitter, GABA, within the VMH.

UI MeSH Term Description Entries
D007003 Hypoglycemia A syndrome of abnormally low BLOOD GLUCOSE level. Clinical hypoglycemia has diverse etiologies. Severe hypoglycemia eventually lead to glucose deprivation of the CENTRAL NERVOUS SYSTEM resulting in HUNGER; SWEATING; PARESTHESIA; impaired mental function; SEIZURES; COMA; and even DEATH. Fasting Hypoglycemia,Postabsorptive Hypoglycemia,Postprandial Hypoglycemia,Reactive Hypoglycemia,Hypoglycemia, Fasting,Hypoglycemia, Postabsorptive,Hypoglycemia, Postprandial,Hypoglycemia, Reactive
D008297 Male Males
D004195 Disease Models, Animal Naturally-occurring or experimentally-induced animal diseases with pathological processes analogous to human diseases. Animal Disease Model,Animal Disease Models,Disease Model, Animal
D005680 gamma-Aminobutyric Acid The most common inhibitory neurotransmitter in the central nervous system. 4-Aminobutyric Acid,GABA,4-Aminobutanoic Acid,Aminalon,Aminalone,Gammalon,Lithium GABA,gamma-Aminobutyric Acid, Calcium Salt (2:1),gamma-Aminobutyric Acid, Hydrochloride,gamma-Aminobutyric Acid, Monolithium Salt,gamma-Aminobutyric Acid, Monosodium Salt,gamma-Aminobutyric Acid, Zinc Salt (2:1),4 Aminobutanoic Acid,4 Aminobutyric Acid,Acid, Hydrochloride gamma-Aminobutyric,GABA, Lithium,Hydrochloride gamma-Aminobutyric Acid,gamma Aminobutyric Acid,gamma Aminobutyric Acid, Hydrochloride,gamma Aminobutyric Acid, Monolithium Salt,gamma Aminobutyric Acid, Monosodium Salt
D005968 Glutamate Decarboxylase A pyridoxal-phosphate protein that catalyzes the alpha-decarboxylation of L-glutamic acid to form gamma-aminobutyric acid and carbon dioxide. The enzyme is found in bacteria and in invertebrate and vertebrate nervous systems. It is the rate-limiting enzyme in determining GAMMA-AMINOBUTYRIC ACID levels in normal nervous tissues. The brain enzyme also acts on L-cysteate, L-cysteine sulfinate, and L-aspartate. EC 4.1.1.15. Glutamate Carboxy-Lyase,Glutamic Acid Decarboxylase,Acid Decarboxylase, Glutamic,Carboxy-Lyase, Glutamate,Decarboxylase, Glutamate,Decarboxylase, Glutamic Acid,Glutamate Carboxy Lyase
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D012333 RNA, Messenger RNA sequences that serve as templates for protein synthesis. Bacterial mRNAs are generally primary transcripts in that they do not require post-transcriptional processing. Eukaryotic mRNA is synthesized in the nucleus and must be exported to the cytoplasm for translation. Most eukaryotic mRNAs have a sequence of polyadenylic acid at the 3' end, referred to as the poly(A) tail. The function of this tail is not known for certain, but it may play a role in the export of mature mRNA from the nucleus as well as in helping stabilize some mRNA molecules by retarding their degradation in the cytoplasm. Messenger RNA,Messenger RNA, Polyadenylated,Poly(A) Tail,Poly(A)+ RNA,Poly(A)+ mRNA,RNA, Messenger, Polyadenylated,RNA, Polyadenylated,mRNA,mRNA, Non-Polyadenylated,mRNA, Polyadenylated,Non-Polyadenylated mRNA,Poly(A) RNA,Polyadenylated mRNA,Non Polyadenylated mRNA,Polyadenylated Messenger RNA,Polyadenylated RNA,RNA, Polyadenylated Messenger,mRNA, Non Polyadenylated
D014697 Ventromedial Hypothalamic Nucleus A nucleus of the middle hypothalamus, the largest cell group of the tuberal region with small-to-medium size cells. Hypothalamic Nucleus, Ventromedial,Nucleus, Ventromedial Hypothalamic
D015309 Glucose Clamp Technique Maintenance of a constant blood glucose level by perfusion or infusion with glucose or insulin. It is used for the study of metabolic rates (e.g., in glucose, lipid, amino acid metabolism) at constant glucose concentration. Euglycemic Clamping,Glucose Clamping,Euglycaemic Clamp,Euglycaemic Clamping,Euglycemic Clamp,Glucose Clamp,Glucose Clamp Technic,Clamp, Euglycaemic,Clamp, Euglycemic,Clamp, Glucose,Clamping, Euglycaemic,Clamping, Euglycemic,Clamping, Glucose,Clamps, Euglycaemic,Clamps, Euglycemic,Clamps, Glucose,Euglycaemic Clamps,Euglycemic Clamps,Glucose Clamp Technics,Glucose Clamp Techniques,Glucose Clamps,Technic, Glucose Clamp,Technics, Glucose Clamp,Technique, Glucose Clamp,Techniques, Glucose Clamp
D015971 Gene Expression Regulation, Enzymologic Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action in enzyme synthesis. Enzymologic Gene Expression Regulation,Regulation of Gene Expression, Enzymologic,Regulation, Gene Expression, Enzymologic

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