Effects of GABAB receptor agonists and antagonists on glycemia regulation in mice

Association of long-term benzodiazepine hypnotic use and prediabetes in US population: A cross-sectional analysis of national health and nutrition examination survey data

Benzodiazepine hypnotics' effects on glucose metabolism are seldom reported, and the association between long-term (≥4 weeks) benzodiazepine usage and prediabetes has not been studied. This study was aimed to investigate the association between benzodiazepine hypnotic usage for ≥ 3 months and the prevalence of prediabetes. We analyzed cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) during 2005 to 2008, selecting adult participants without diabetes who used benzodiazepine hypnotics for at least 3 months or did not take any hypnotics. Individuals taking other hypnotics, antipsychotics, glucocorticoids, or hypoglycemic drugs were excluded. We defined prediabetes as an hemoglobin A1C (HbA1C) 5.7-6.4%, as suggested by the American Diabetes Association. Prescribed drug information was self-reported and checked by official interviewers, and HbA1C data in NHANES was recognized by the National Glycohemoglobin Standardization Program. We calculated the propensity score according to the covariates and adjusted it using multivariate logistic regression. Lower thresholds of HbA1C ≥ 5.5% or ≥ 5.3% were also analyzed. Among 4694 eligible participants, 38 received benzodiazepine hypnotics; using these hypnotics for ≥ 3 months was not significantly associated with the prevalence of prediabetes, as well as HbA1C ≥ 5.5% or ≥ 5.3%. Adjusted for propensity score, the respective odds ratios for prediabetes, HbA1C ≥ 5.5%, and HbA1C ≥ 5.3% were 1.09 (95% confidence interval [CI] 0.19-6.32), 0.83 (95% CI 0.22-3.13), and 1.22 (95% CI 0.3-4.93). No significant association was found between benzodiazepine hypnotic usage ≥ 3 months and the prevalence of prediabetes.

Deletion of GABAB receptors from Kiss1 cells affects glucose homeostasis without altering reproduction in male mice

Kisspeptin and γ-amino butyric acid (GABA), synthesized in the central nervous system, are critical for reproduction. Both are also expressed in peripheral organs/tissues critical to metabolic control (liver/pancreas/adipose). Many kisspeptin neurons coexpress GABAB receptors (GABABR) and GABA controls kisspeptin expression and secretion. We developed a unique mouse lacking GABABR exclusively from kisspeptin cells/neurons (Kiss1-GABAB1KO) to evaluate the impact on metabolism/reproduction. We confirmed selective deletion of GABABR from Kiss1 cells in the anteroventral periventricular nucleus/periventricular nucleus continuum (AVPV/PeN; immunofluorescence and PCR) and arcuate nucleus (ARC), medial amygdala (MeA), pituitary, liver, and testes (PCR). Young Kiss1-GABAB1KO males were fertile, with normal LH and testosterone. Kiss1 expression was similar between genotypes in AVPV/PeN, ARC, MeA, bed nucleus of the stria terminalis (BNST), and peripheral organs (testis, liver, pituitary). Kiss1-GABAB1KO males presented higher fasted glycemia and insulin levels, an impaired response to a glucose overload, reduced insulin sensitivity, and marked insulin resistance. Interestingly, when Kiss1-GABAB1KO males got older (9 mo old) their body weight (BW) increased, in part due to an increase in white adipose tissue (WAT). Old Kiss1-GABAB1KO males showed higher fasted insulin, increased pancreatic insulin content, insulin resistance, and significantly decreased pancreatic kisspeptin levels. In sum, lack of GABABR specifically in Kiss1 cells severely impacts glucose homeostasis in male mice, reinforcing kisspeptin involvement in metabolic regulation. These alterations in glucose homeostasis worsened with aging. We highlight the impact of GABA through GABABR in the regulation of the pancreas kisspeptin system in contrast to liver kisspeptin that was not affected.NEW & NOTEWORTHY We developed a unique mouse lacking GABAB receptors specifically in Kiss1 cells to evaluate the impact on reproduction and metabolism. Knockout males showed a severe impact on glucose homeostasis, which worsened with aging. These results reinforce the proposed kisspeptin involvement in metabolic regulation and highlight the impact of GABA through GABABR in the regulation of the peripheral pancreas kisspeptin system.

The role of GABA in islet function

Gamma aminobutyric acid (GABA) is a non-proteinogenic amino acid and neurotransmitter that is produced in the islet at levels as high as in the brain. GABA is synthesized by the enzyme glutamic acid decarboxylase (GAD), of which the 65 kDa isoform (GAD65) is a major autoantigen in type 1 diabetes. Originally described to be released via synaptic-like microvesicles or from insulin secretory vesicles, beta cells are now understood to release substantial quantities of GABA directly from the cytosol via volume-regulated anion channels (VRAC). Once released, GABA influences the activity of multiple islet cell types through ionotropic GABAA receptors and metabotropic GABAB receptors. GABA also interfaces with cellular metabolism and ATP production via the GABA shunt pathway. Beta cells become depleted of GABA in type 1 diabetes (in remaining beta cells) and type 2 diabetes, suggesting that loss or reduction of islet GABA correlates with diabetes pathogenesis and may contribute to dysfunction of alpha, beta, and delta cells in diabetic individuals. While the function of GABA in the nervous system is well-understood, the description of the islet GABA system is clouded by differing reports describing multiple secretion pathways and effector functions. This review will discuss and attempt to unify the major experimental results from over 40 years of literature characterizing the role of GABA in the islet.

Beta-Cell Ion Channels and Their Role in Regulating Insulin Secretion

Beta cells of the pancreatic islet express many different types of ion channels. These channels reside in the β-cell plasma membrane as well as subcellular organelles and their coordinated activity and sensitivity to metabolism regulate glucose-dependent insulin secretion. Here, we review the molecular nature, expression patterns, and functional roles of many β-cell channels, with an eye toward explaining the ionic basis of glucose-induced insulin secretion. Our primary focus is on K_ATP and voltage-gated Ca²⁺ channels as these primarily regulate insulin secretion; other channels in our view primarily help to sculpt the electrical patterns generated by activated β-cells or indirectly regulate metabolism. Lastly, we discuss why understanding the physiological roles played by ion channels is important for understanding the secretory defects that occur in type 2 diabetes. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.

GABAB Receptor Chemistry and Pharmacology: Agonists, Antagonists, and Allosteric Modulators

The GABA_B receptors are metabotropic G protein-coupled receptors (GPCRs) that mediate the actions of the primary inhibitory neurotransmitter, γ-aminobutyric acid (GABA). In the CNS, GABA plays an important role in behavior, learning and memory, cognition, and stress. GABA is also located throughout the gastrointestinal (GI) tract and is involved in the autonomic control of the intestine and esophageal reflex. Consequently, dysregulated GABA_B receptor signaling is associated with neurological, mental health, and gastrointestinal disorders; hence, these receptors have been identified as key therapeutic targets and are the focus of multiple drug discovery efforts for indications such as muscle spasticity disorders, schizophrenia, pain, addiction, and gastroesophageal reflex disease (GERD). Numerous agonists, antagonists, and allosteric modulators of the GABA_B receptor have been described; however, Lioresal^® (Baclofen; β-(4-chlorophenyl)-γ-aminobutyric acid) is the only FDA-approved drug that selectively targets GABA_B receptors in clinical use; undesirable side effects, such as sedation, muscle weakness, fatigue, cognitive deficits, seizures, tolerance and potential for abuse, limit their therapeutic use. Here, we review GABA_B receptor chemistry and pharmacology, presenting orthosteric agonists, antagonists, and positive and negative allosteric modulators, and highlight the therapeutic potential of targeting GABA_B receptor modulation for the treatment of various CNS and peripheral disorders.

GABAB-Receptor Agonist-Based Immunotherapy for Type 1 Diabetes in NOD Mice

Some immune system cells express type A and/or type B γ-aminobutyric acid receptors (GABA_A-Rs and/or GABA_B-Rs). Treatment with GABA, which activates both GABA_A-Rs and GABA_B-Rs), and/or a GABA_A-R-specific agonist inhibits disease progression in mouse models of type 1 diabetes (T1D), multiple sclerosis, rheumatoid arthritis, and COVID-19. Little is known about the clinical potential of specifically modulating GABA_B-Rs. Here, we tested lesogaberan, a peripherally restricted GABA_B-R agonist, as an interventive therapy in diabetic NOD mice. Lesogaberan treatment temporarily restored normoglycemia in most newly diabetic NOD mice. Combined treatment with a suboptimal dose of lesogaberan and proinsulin/alum immunization in newly diabetic NOD mice or a low-dose anti-CD3 in severely hyperglycemic NOD mice greatly increased T1D remission rates relative to each monotherapy. Mice receiving combined lesogaberan and anti-CD3 displayed improved glucose tolerance and, unlike mice that received anti-CD3 alone, had some islets with many insulin⁺ cells, suggesting that lesogaberan helped to rapidly inhibit β-cell destruction. Hence, GABA_B-R-specific agonists may provide adjunct therapies for T1D. Finally, the analysis of microarray and RNA-Seq databases suggested that the expression of GABA_B-Rs and GABA_A-Rs, as well as GABA production/secretion-related genes, may be a more common feature of immune cells than currently recognized.

Total and acylated ghrelin plasma levels as potential long-term response markers in alcohol-dependent patients receiving high-dose of the GABA-B receptor agonist baclofen

The orexigenic hormone ghrelin is involved in the regulation of food intake and energy balance. Previous findings suggest its involvement in the modulation of mesolimbic reward pathways, thus potentially being relevant in the pathophysiology of substance use disorders such as alcohol dependence. In the present study, we assessed plasma levels of total and acylated ghrelin within the BACLAD trial, where alcohol-dependent patients received individually titrated high-dose baclofen (30-270 mg/d) within a randomized, placebo-controlled design. Plasma levels of total ghrelin and acylated ghrelin were measured at baseline, during treatment with individually titrated high-dose baclofen and after termination of the study medication within a timeframe of up to 20 weeks. Multivariate longitudinal non-parametric analysis revealed that plasma levels of total ghrelin significantly decreased in the group of abstinent patients receiving high-dose baclofen. In addition, plasma levels of total ghrelin correlated negatively with days of abstinence during treatment with high-dose baclofen. Plasma levels of acylated ghrelin increased during the study in the group of relapsed patients under baclofen and placebo treatment. These findings suggest that the long-term response to baclofen treatment in alcohol use disorder (AUD) might be monitored by assessing total and acylated ghrelin plasma levels.

Neuroendocrine response to GABA-B receptor agonism in alcohol-dependent individuals: Results from a combined outpatient and human laboratory experiment

Gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the nervous system, plays an important role in biobehavioral processes that regulate alcohol seeking, food intake, and stress response. The metabotropic GABA-B receptor has been investigated as a potential therapeutic target for alcohol use disorder, by using orthosteric agonists (e.g., baclofen) and positive allosteric modulators. Whether and how pharmacological manipulation of the GABA-B receptor, in combination with alcohol intake, may affect feeding- and stress-related neuroendocrine pathways remains unknown. In the present randomized, double-blind, placebo-controlled study, thirty-four alcohol-dependent individuals received baclofen (30 mg/day) or placebo in a naturalistic outpatient setting for one week, and then performed a controlled laboratory experiment which included alcohol cue-reactivity, fixed-dose priming, and self-administration procedures. Blood samples were collected, and the following neuroendocrine markers were measured: ghrelin, leptin, amylin, glucagon-like peptide-1 (GLP-1), insulin, prolactin, thyroid-stimulating hormone, growth hormone, cortisol, and adrenocorticotropic hormone (ACTH). During the outpatient phase, baclofen significantly increased blood concentrations of acyl-ghrelin (p = 0.01), leptin (p = 0.01), amylin (p = 0.004), and GLP-1 (p = 0.02). Significant drug × time-point interaction effects for amylin (p = 0.001) and insulin (p = 0.03), and trend-level interaction effects for GLP-1 (p = 0.06) and ACTH (p = 0.10) were found during the laboratory experiment. Baclofen, compared to placebo, had no effect on alcohol drinking in this study (p's ≥ 0.05). Together with previous studies, these findings shed light on the role of the GABAergic system and GABA-B receptors in the shared neurobiology of alcohol-, feeding-, and stress-related behaviors.

Intestinal resection-associated metabolic syndrome

BACKGROUND

Short bowel syndrome occurs following massive small bowel resection (SBR) and is one of the most lethal diseases of childhood. We have previously demonstrated hepatic steatosis, altered gut microbiome, and increased fat deposition in our murine model of SBR. These novel findings prompted us to investigate potential alterations in glucose metabolism and systemic inflammation following intestinal resection.

METHODS

Male C57BL6 mice underwent 50% proximal SBR or sham operation. Body weight and composition were measured. Fasting blood glucose (FBG), glucose, and insulin tolerance testing were performed. Small bowel, pancreas, and serum were collected at sacrifice and analyzed.

RESULTS

SBR mice gained less weight than shams after 10weeks. Despite this, FBG in resected mice was significantly higher than sham animals. After SBR, mice demonstrated perturbed body composition, higher blood glucose, increased pancreatic islet area, and increased systemic inflammation compared with sham mice. Despite these changes, we found no alteration in insulin tolerance after resection.

CONCLUSIONS

After massive SBR, we present evidence for abnormal body composition, glucose metabolism, and systemic inflammation. These findings, coupled with resection-associated hepatic steatosis, suggest that massive SBR (independent of parenteral nutrition) results in metabolic consequences not previously described and provides further evidence to support the presence of a novel resection-associated metabolic syndrome.

Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men

The pancreatic β-cell plays a key role in glucose homeostasis by secreting insulin, the only hormone capable of lowering the blood glucose concentration. Impaired insulin secretion results in the chronic hyperglycemia that characterizes type 2 diabetes (T2DM), which currently afflicts >450 million people worldwide. The healthy β-cell acts as a glucose sensor matching its output to the circulating glucose concentration. It does so via metabolically induced changes in electrical activity, which culminate in an increase in the cytoplasmic Ca2+ concentration and initiation of Ca2+-dependent exocytosis of insulin-containing secretory granules. Here, we review recent advances in our understanding of the β-cell transcriptome, electrical activity, and insulin exocytosis. We highlight salient differences between mouse and human β-cells, provide models of how the different ion channels contribute to their electrical activity and insulin secretion, and conclude by discussing how these processes become perturbed in T2DM.

Baclofen systemic toxicity: Experimental histopathological and biochemical study

OBJECTIVE

The present study was designed to highlight the toxic impact of baclofen on both biochemical and histopathological aspects in rats' liver, gastric, lung, kidney, and brain tissues.

METHODS

The study was performed on 30 healthy adult male albino rats divided into four groups with 5 rats in each control group, and 10 rats in either experimental groups (two experimental and two control groups). Five rats (negative control) were kept in a quite non-stressful environment, provided with food ad libitum and free access to water. Normal saline (1 ml) was given orally as placebo in the positive control group ( n = 5). Experimental group III, baclofen acute toxicity group (10 rats): Each animal received a single dose of lethal dose (LD₅₀) of baclofen orally by gavage. It equals 145 mg/kg body weight. The rats were observed for acute toxicity manifestations as well as for LD₅₀ deaths. Group IV, (baclofen-dependent group, 10 rats): Each animal received baclofen (1/10th LD₅₀) in gradually increasing doses for 1 month.

RESULTS

The levels of blood urea nitrogen, creatinine kinase, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, γ-glutamyl transpeptidase, cardiac troponin I, and prothrombin time in both baclofen-treated groups showed significant elevation when compared to controls. There were brain, lung, gastric, hepatic, and renal histopathological changes in baclofen-treated rats whose severity varied between the two experimental groups.

CONCLUSION AND RECOMMENDATION

Baclofen toxicity is an under diagnosed emergency. Physicians should consider baclofen toxicity in users having hepatorenal dysfunction, presenting with altered mental status, bradycardia, and hypotension.

Disruptions of sensorimotor gating, cytokines, glycemia, monoamines, and genes in both sexes of rats reared in social isolation can be ameliorated by oral chronic quetiapine administration

The pathogenesis of schizophrenia in patients with metabolic abnormalities remains unclear. Our previous study demonstrated that isolation rearing (IR) induced longitudinal concomitant changes of pro-inflammatory cytokine (pro-CK) levels and metabolic abnormalities with a developmental origin. However, the general consensus, believes that these abnormalities are caused by antipsychotic treatment in schizophrenic patients. The IR paradigm presents with face, construct, and predictive validity for schizophrenia. Therefore, we employed IR rats of both sexes to examine whether chronic quetiapine (QTP, a second-generation antipsychotic medication) treatment induces disruptions of metabolism (body weight, blood pressure, and the glycemic and lipid profiles) or cytokines [interleukin (IL)-1 beta, IL-6, IL-10, interferon-gamma, and tumor necrosis factor (TNF)-alpha], and further, whether it reverses deficits of behaviors [locomotor activity and prepulse inhibition (PPI)] and the expression of monoamines (dopamine and serotonin) and related genes (Htr1a, Htr2a, Htr3a, Drd1a, and Gabbr2). IR induced higher levels of pro-CK, dysglycemia, blood pressure, locomotor activity, and impaired PPI, simultaneously destabilizing cortico-striatal monoamines and relevant genes in both sexes, while QTP demonstrated dose-dependent reversal of these changes, suggesting that QTP might reduce the pro-CKs to regulate these abnormalities. Our data implied that antipsychotics may not be the solitary factor causing metabolic problems in schizophrenia and suggested that inflammatory changes may play a vital role in the developmental pathophysiology of schizophrenia and related metabolic abnormalities.

Compartmentalization of GABA synthesis by GAD67 differs between pancreatic beta cells and neurons

The inhibitory neurotransmitter GABA is synthesized by the enzyme glutamic acid decarboxylase (GAD) in neurons and in pancreatic β-cells in islets of Langerhans where it functions as a paracrine and autocrine signaling molecule regulating the function of islet endocrine cells. The localization of the two non-allelic isoforms GAD65 and GAD67 to vesicular membranes is important for rapid delivery and accumulation of GABA for regulated secretion. While the membrane anchoring and trafficking of GAD65 are mediated by intrinsic hydrophobic modifications, GAD67 remains hydrophilic, and yet is targeted to vesicular membrane pathways and synaptic clusters in neurons by both a GAD65-dependent and a distinct GAD65-independent mechanism. Herein we have investigated the membrane association and targeting of GAD67 and GAD65 in monolayer cultures of primary rat, human, and mouse islets and in insulinoma cells. GAD65 is primarily detected in Golgi membranes and in peripheral vesicles distinct from insulin vesicles in β-cells. In the absence of GAD65, GAD67 is in contrast primarily cytosolic in β-cells; its co-expression with GAD65 is necessary for targeting to Golgi membranes and vesicular compartments. Thus, the GAD65-independent mechanism for targeting of GAD67 to synaptic vesicles in neurons is not functional in islet β-cells. Therefore, only GAD65:GAD65 homodimers and GAD67:GAD65 heterodimers, but not the GAD67:GAD67 homodimer gain access to vesicular compartments in β-cells to facilitate rapid accumulation of newly synthesized GABA for regulated secretion and fine tuning of GABA-signaling in islets of Langerhans.

Adaptive human CDKAL1 variants underlie hormonal response variations at the enteroinsular axis

Recent analyses have identified positively selected loci that explain differences in immune responses, body forms, and adaptations to extreme climates, but variants that describe adaptations in energy-balance regulation remain underexplored. To identify variants that confer adaptations in energy-balance regulation, we explored the evolutionary history and functional associations of candidate variants in 207 genes. We screened single nucleotide polymorphisms in genes that had been associated with energy-balance regulation for unusual genetic patterns in human populations, followed by studying associations among selected variants and serum levels of GIP, insulin, and C-peptide in pregnant women after an oral glucose tolerance test. Our analysis indicated that 5′ variants in CDKAL1, CYB5R4, GAD2, and PPARG are marked with statistically significant signals of gene–environment interactions. Importantly, studies of serum hormone levels showed that variants in CDKAL1 are associated with glucose-induced GIP and insulin responses (p<0.05). On the other hand, a GAD2 variant exhibited a significant association with glucose-induced C-peptide response. In addition, simulation analysis indicated that a type 2 diabetes risk variant in CDKAL1 (rs7754840) was selected in East Asians ∼6,900 years ago. Taken together, these data indicated that variants in CDKAL1 and GAD2 were targets of prior environmental selection. Because the selection of the CDKAL1 variant overlapped with the selection of a cluster of GIP variants in the same population ∼11,800 to 2,000 years ago, we speculate that these regulatory genes at the human enteroinsular axis could be highly responsive to environmental selection in recent human history.

Effects of "in vivo" administration of baclofen on rat renal tubular function

The effects of the in vivo administration of baclofen on renal tubular transport and aquaporin-2 (AQP2) expression were evaluated. In conscious animals kept in metabolic cages, baclofen (0.01-1mg/kg, s.c.) induced a dose-dependent increment in the urine flow rate (UFR) and in sodium and potassium excretion, associated with an increased osmolal clearance (Closm), a diminished urine to plasma osmolality ratio (Uosm/Posm) and a decrease in AQP2 expression. The above mentioned baclofen effects on functional parameters were corroborated by using conventional renal clearance techniques. Additionally, this model allowed the detection of a diminution in glucose reabsorption. Some experiments were performed with water-deprived or desmopressin-treated rats kept in metabolic cages. Either water deprivation or desmopressin treatment decreased the UFR and increased the Uosm/Posm. Baclofen did not change the Uosm/Posm or AQP2 expression in desmopressin-treated rats; but it increased the UFR and diminished the Uosm/Posm and AQP2 expression in water-deprived animals. These results indicate that in vivo administration of baclofen promotes alterations in proximal tubular transport, since glucose reabsorption was decreased. The distal tubular function was also affected. The increased Closm indicates an alteration in solute reabsorption at the ascending limb of the Henle's loop. The decreased Uosm/Posm and AQP2 expression in controls and in water-deprived, but not in desmopressin-treated rats, lead us to speculate that some effect of baclofen on endogenous vasopressin availability could be responsible for the impaired urine concentrating ability, more than any disturbance in the responsiveness of the renal cells to the hormone.

Postnatal development of the endocrine pancreas in mice lacking functional GABAB receptors

Adult mice lacking functional GABAB receptors (GABAB1KO) have glucose metabolism alterations. Since GABAB receptors (GABABRs) are expressed in progenitor cells, we evaluated islet development in GABAB1KO mice. Postnatal day 4 (PND4) and adult, male and female, GABAB1KO, and wild-type littermates (WT) were weighed and euthanized, and serum insulin and glucagon was measured. Pancreatic glucagon and insulin content were assessed, and pancreas insulin, glucagon, PCNA, and GAD65/67 were determined by immunohistochemistry. RNA from PND4 pancreata and adult isolated islets was obtained, and Ins1, Ins2, Gcg, Sst, Ppy, Nes, Pdx1, and Gad1 transcription levels were determined by quantitative PCR. The main results were as follows: 1) insulin content was increased in PND4 GABAB1KO females and in both sexes in adult GABAB1KOs; 2) GABAB1KO females had more clusters (<500 μm(2)) and less islets than WT females; 3) cluster proliferation was decreased at PND4 and increased in adult GABAB1KO mice; 4) increased β-area at the expense of the α-cell area was present in GABAB1KO islets; 5) Ins2, Sst, and Ppy transcription were decreased in PND4 GABAB1KO pancreata, adult GABAB1KO female islets showed increased Ins1, Ins2, and Sst expression, Pdx1 was increased in male and female GABAB1KO islets; and 6) GAD65/67 was increased in adult GABAB1KO pancreata. We demonstrate that several islet parameters are altered in GABAB1KO mice, further pinpointing the importance of GABABRs in islet physiology. Some changes persist from neonatal ages to adulthood (e.g., insulin content in GABAB1KO females), whereas other features are differentially regulated according to age (e.g., Ins2 was reduced in PND4, whereas it was upregulated in adult GABAB1KO females).

Sex differences in insulin resistance in GABAB1 knockout mice

AIMS

We have previously demonstrated that the absence of functional GABA B receptors (GABABRs) disturbs glucose homeostasis in GABAB1KO mice. The aim of this work was to extend our studies of these alterations in GABAB1KO mice and investigate the sexual differences therein.

MAIN METHODS

Male and female, GABAB1KO and WT mice were used. Glucose and insulin tolerance tests (GTT and ITT), and insulin and glucagon secretion tests (IST and GST) were performed. Blood glucose, serum insulin and hyperglycemic hormones were determined, and HOMA-IR calculated. Skeletal muscle insulin receptor β subunit (IRβ), insulin receptor substrates 1/2 (IRS1, IRS2) and hexokinase-II levels were determined by Western blot. Skeletal muscle insulin sensitivity was assessed by in vivo insulin-induced Akt phosphorylation (Western blot). Food intake and hypothalamic NPY mRNA expression (by qPCR) were also evaluated.

KEY FINDINGS

Fasted insulin and HOMA-IR were augmented in GABAB1KO males, with no alterations in females. Areas under the curve (AUC) for GTT and ITT were increased in GABAB1KO mice of both genders, indicating compromised insulin sensitivity. No genotype differences were observed in IST, GST or in IRβ, IRS1, IRS2 and hexokinase-II expression. Akt activation was severely impaired in GABAB1KO males while no alterations were observed in females. GABAB1KO mice showed increased food intake and NPY expression.

SIGNIFICANCE

Glucose metabolism and energy balance disruptions were more pronounced in GABAB1KO males, which develop peripheral insulin resistance probably due to augmented insulin secretion. Metabolic alterations in females were milder and possibly due to previously described reproductive disorders, such as persistent estrus.