Embora seja bem estabelecido que a exposição a baixas temperaturas resulte em ativação simpática e hiperglicemia, os mecanismos moleculares envolvidos na regulação neural da produção hepática de glicose ainda não são bem conhecidos. Portanto, o objetivo do presente estudo foi investigar o papel da inervação simpática na regulação de genes e enzimas chaves da neoglicogênese hepática, em roedores expostos agudamente ao frio. Para isso, foram utilizados dois modelos experimentais de desnervação simpática: a simpatectomia química em camundongos induzida pelo tratamento com 6-hidroxidopamina (100 mg.kg-1.dia-1; 1º, 2º e 7º dia de vida pós-natal; i.p). e a desnervação local dos nervos hepáticos por fenol (95%) em ratos. A exposição de camundongos ao frio (4ºC), durante 1, 3 e/ou 6h, induziu hiperglicemia, hipotermia, depleção do conteúdo de glicogênio hepático e ativação da neoglicogênese, estimada pela elevada expressão gênica e atividade das enzimas glicose-6-fosfatase e fosfoenolpiruvato carboxiquinase (PEPCK). Em paralelo, verificou-se que a exposição ao frio induziu um drástico aumento na expressão do RNAm do Nr4a1 e do PGC1-?, dois genes-alvos de CREB que participam do complexo de ativação transcricional dos genes que codificam as enzimas neoglicogênicas estudadas. A simpatectomia não afetou a depleção dos estoques de glicogênio hepático induzida pelo frio, mas reduziu o aumento do conteúdo hepático de noradrenalina e AMPc e acentuou a hipotermia, bem como preveniu a hiperglicemia, sendo este efeito associado ao bloqueio da expressão gênica e atividade da glicose-6-fosfatase e da PEPCK e do RNAm do Nr4a1, em todos os tempos estudados. Resultados bastante semelhantes foram observados em ratos submetidos à lesão dos nervos hepáticos com fenol e expostos ao frio durante 24h. Tanto a adrenalectomia como a adrenodemedulação (remoção da medula da adrenal) não alteraram o efeito estimulatório do frio na atividade e expressão gênica das enzimas neoglicogênicas de camundongos. Porém, em ratos expostos ao frio, a adrenodemedulação bloqueou aIII hiperglicemia e reduziu parcialmente a hiperexpressão dos genes da glicose-6-fosfatase e PEPCK. Estes resultados mostram a importância fisiológica da inervação simpática do fígado de roedores na estimulação do programa gênico da neoglicogênese, durante o estresse térmico agudo. / Although it is well established that exposure to low temperatures leads to sympathetic activation and hyperglycemia, the molecular mechanisms related to the neural regulation of hepatic glucose production remain elusive. Therefore, the goal of the present study was to investigate the role of sympathetic innervation in the regulation of genes and key enzymes of hepatic gluconeogenesis in liver of rodents exposed to acute cold. For this, two experimental models of sympathetic denervation were used: the chemical sympathectomy in mice induced by 6-hydroxydopamine treatment (100 mg.kg-1.day-1; 1º, 2º and 7ºdays of neonatal life; i.p.) and local denervation of hepatic nerves by phenol (95%) in rats. Exposure of mice to cold (4° C) for 1, 3 and / or 6 h induced hyperglycemia, hypothermia, depletion of hepatic glycogen content and activation of gluconeogenesis, estimated by high gene expression and activity of the enzymes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase (PEPCK). In parallel, it was found that exposure to cold induced a dramatic increase in Nr4a1 and PGC1-? mRNA expression, two CREB target genes that participate in the transcriptional activation complex of the genes encoding the gluconeogenesis enzymes studied. The sympathectomy did not affect the depletion of cold-induced hepatic glycogen stores but reduced the hepatic content of noradrenaline and cAMP and increased hypothermia, as well as prevented hyperglycemia, and this effect was associated with the blockade of gene expression and enzymatic activity of glucose-6-phosphatase and PEPCK and Nr4a1 mRNA levels, at all time intervals investigated. Similar results were observed in rats submitted to hepatic nerve damage with phenol and exposed to cold for 24h. Either adrenalectomy or adrenodemedullation (surgical removal of the adrenal medulla) did not alter the stimulatory effect of cold on the activity and gene expression of the gluconeogenesis enzymes of mice. However, in cold-exposed rats, adrenodemedullation blocked hyperglycemia and partially reduced overexpression of the glucose-6-phosphatase and PEPCK mRNA.V These results show the physiological role of the hepatic sympathetic innervation in the transcriptional program associated with gluconeogenesis, during acute thermal stress.

Inflammatory bowel disease (IBD) alters neuronal regulation of the gastrointestinal (GI) tract. The superior mesenteric ganglia (SMG) contain sympathetic neurons that modulate GI functions such, as motility and blood flow. IBD reduces the release of noradrenaline, a sympathetic neurotransmitter. We hypothesized that the reduction in NA release is due to inhibition of voltage-gated calcium current (ICa), as calcium influx is a regulator of neurotransmitter release. We also hypothesized that tumor necrosis factor α (TNFα), a proinflammatory cytokine elevated during IBD, can also inhibit the ICa of SMG neurons. Therefore, we compared ICa amplitude in neurons from normal mice and mice with dextran sulphate sodium (DSS; 5% w/v)-induced colitis. Neurons dissociated from the SMG were cultured overnight and changes to ICa were investigated using electrophysiological, Ca2+ imaging, PCR and neurotransmitter release techniques. Colitis significantly reduced ICa of SMG neurons by selectively inhibiting N-type Ca2+ channels. This was accompanied by a reduction in mRNA encoding the N-type channel alpha subunit (CaV 2.2) and a rightward shift in the voltage dependence of activation of ICa. Colitis reduced the NA release from the colon and jejunum. Depolarization-induced release of tritiated-NA was inhibited by ω-Conotoxin GVIA (300 nM). These results suggest that the changes in VGCC observed at the cell bodies of SMG neurons were also occurring at the nerve terminals during colitis. Similar experimental techniques were performed using SMG neurons incubated overnight in TNFα (1nM). TNFα decreased ICa and depolarization-induced Ca2+ influx in SMG neurons. Similar to DSS-induced colitis, the reduction in ICa was limited to N-type Ca2+ channels. Preincubation of neurons with SC 514 (20μM) and Bay 11 7082 (1µM), inhibitors of nuclear factor kappa B signaling, prevented the reduction in ICa. Preincubation with the p38 MAPK inhibitor, PD 169316 (30µM), recovered a smaller portion of the reduction in Ca2+ influx. These data suggest that DSS colitis and TNFα inhibit N-type VGCC ICa in sympathetic neurons and identify a novel role for NF-κB and p38 MAPK in the regulation of neurotransmitter release. These findings also suggest that DSS colitis inhibits NA release by altering sympathetic N-type VGCC in the colon and jejunum. / Thesis (Master, Physiology) -- Queen's University, 2008-09-02 12:06:20.438

Embora seja bem estabelecido que a exposição a baixas temperaturas resulte em ativação simpática e hiperglicemia, os mecanismos moleculares envolvidos na regulação neural da produção hepática de glicose ainda não são bem conhecidos. Portanto, o objetivo do presente estudo foi investigar o papel da inervação simpática na regulação de genes e enzimas chaves da neoglicogênese hepática, em roedores expostos agudamente ao frio. Para isso, foram utilizados dois modelos experimentais de desnervação simpática: a simpatectomia química em camundongos induzida pelo tratamento com 6-hidroxidopamina (100 mg.kg-1.dia-1; 1º, 2º e 7º dia de vida pós-natal; i.p). e a desnervação local dos nervos hepáticos por fenol (95%) em ratos. A exposição de camundongos ao frio (4ºC), durante 1, 3 e/ou 6h, induziu hiperglicemia, hipotermia, depleção do conteúdo de glicogênio hepático e ativação da neoglicogênese, estimada pela elevada expressão gênica e atividade das enzimas glicose-6-fosfatase e fosfoenolpiruvato carboxiquinase (PEPCK). Em paralelo, verificou-se que a exposição ao frio induziu um drástico aumento na expressão do RNAm do Nr4a1 e do PGC1-?, dois genes-alvos de CREB que participam do complexo de ativação transcricional dos genes que codificam as enzimas neoglicogênicas estudadas. A simpatectomia não afetou a depleção dos estoques de glicogênio hepático induzida pelo frio, mas reduziu o aumento do conteúdo hepático de noradrenalina e AMPc e acentuou a hipotermia, bem como preveniu a hiperglicemia, sendo este efeito associado ao bloqueio da expressão gênica e atividade da glicose-6-fosfatase e da PEPCK e do RNAm do Nr4a1, em todos os tempos estudados. Resultados bastante semelhantes foram observados em ratos submetidos à lesão dos nervos hepáticos com fenol e expostos ao frio durante 24h. Tanto a adrenalectomia como a adrenodemedulação (remoção da medula da adrenal) não alteraram o efeito estimulatório do frio na atividade e expressão gênica das enzimas neoglicogênicas de camundongos. Porém, em ratos expostos ao frio, a adrenodemedulação bloqueou aIII hiperglicemia e reduziu parcialmente a hiperexpressão dos genes da glicose-6-fosfatase e PEPCK. Estes resultados mostram a importância fisiológica da inervação simpática do fígado de roedores na estimulação do programa gênico da neoglicogênese, durante o estresse térmico agudo. / Although it is well established that exposure to low temperatures leads to sympathetic activation and hyperglycemia, the molecular mechanisms related to the neural regulation of hepatic glucose production remain elusive. Therefore, the goal of the present study was to investigate the role of sympathetic innervation in the regulation of genes and key enzymes of hepatic gluconeogenesis in liver of rodents exposed to acute cold. For this, two experimental models of sympathetic denervation were used: the chemical sympathectomy in mice induced by 6-hydroxydopamine treatment (100 mg.kg-1.day-1; 1º, 2º and 7ºdays of neonatal life; i.p.) and local denervation of hepatic nerves by phenol (95%) in rats. Exposure of mice to cold (4° C) for 1, 3 and / or 6 h induced hyperglycemia, hypothermia, depletion of hepatic glycogen content and activation of gluconeogenesis, estimated by high gene expression and activity of the enzymes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase (PEPCK). In parallel, it was found that exposure to cold induced a dramatic increase in Nr4a1 and PGC1-? mRNA expression, two CREB target genes that participate in the transcriptional activation complex of the genes encoding the gluconeogenesis enzymes studied. The sympathectomy did not affect the depletion of cold-induced hepatic glycogen stores but reduced the hepatic content of noradrenaline and cAMP and increased hypothermia, as well as prevented hyperglycemia, and this effect was associated with the blockade of gene expression and enzymatic activity of glucose-6-phosphatase and PEPCK and Nr4a1 mRNA levels, at all time intervals investigated. Similar results were observed in rats submitted to hepatic nerve damage with phenol and exposed to cold for 24h. Either adrenalectomy or adrenodemedullation (surgical removal of the adrenal medulla) did not alter the stimulatory effect of cold on the activity and gene expression of the gluconeogenesis enzymes of mice. However, in cold-exposed rats, adrenodemedullation blocked hyperglycemia and partially reduced overexpression of the glucose-6-phosphatase and PEPCK mRNA.V These results show the physiological role of the hepatic sympathetic innervation in the transcriptional program associated with gluconeogenesis, during acute thermal stress.

In humans, various dietary and social factors led to the development of increased brain sizes alongside large adipose tissue stores. Complex reciprocal signaling mechanisms allow for a fine-tuned interaction between the two organs to regulate energy homeostasis of the organism. As an endocrine organ, adipose tissue secretes various hormones, cytokines, and metabolites that signal energy availability to the central nervous system (CNS). Vice versa, the CNS is a critical regulator of adipose tissue function through neural networks that integrate information from the periphery and regulate sympathetic nerve outflow. This review discusses the various reciprocal signaling mechanisms in the CNS and adipose tissue to maintain organismal energy homeostasis. We are focusing on the integration of afferent signals from the periphery in neuronal populations of the mediobasal hypothalamus as well as the efferent signals from the CNS to adipose tissue and its implications for adipose tissue function. Furthermore, we are discussing central mechanisms that fine-tune the immune system in adipose tissue depots and contribute to organ homeostasis. Elucidating this complex signaling network that integrates peripheral signals to generate physiological outputs to maintain the optimal energy balance of the organism is crucial for understanding the pathophysiology of obesity and metabolic diseases such as type 2 diabetes.