RESUMO
The application of sodium cyanide (NaCN) to the carotid body receptors (CBR) (CBR stimulation) induces rapid blood hyperglycemia and an increase in brain glucose retention. The commissural nucleus tractus solitarius (cNTS) is an essential relay nucleus in this hyperglycemic reflex; it receives glutamatergic afferents (that also release brain derived neurotrophic factor, BDNF) from the nodose-petrosal ganglia that relays CBR information. Previous work showed that AMPA in NTS blocks hyperglycemia and brain glucose retention after CBR stimulation. In contrast, BDNF, which attenuates glutamatergic AMPA currents in NTS, enhances these glycemic responses. Here we investigated the combined effects of BDNF and AMPA (and their antagonists) in NTS on the glycemic responses to CBR stimulation. Microinjections of BDNF plus AMPA into the cNTS before CBR stimulation in anesthetized rats, induced blood hyperglycemia and an increase in brain arteriovenous (a-v) of blood glucose concentration difference, which we infer is due to increased brain glucose retention. By contrast, the microinjection of the TrkB antagonist K252a plus AMPA abolished the glycemic responses to CBR stimulation similar to what is observed after AMPA pretreatments. In BDNF plus AMPA microinjections preceding CBR stimulation, the number of c-fos immunoreactive cNTS neurons increased. In contrast, in the rats microinjected with K252a plus AMPA in NTS, before CBR stimulation, c-fos expression in cNTS decreased. The expression of AMPA receptors GluR2/3 did not change in any of the studied groups. These results indicate that BDNF in cNTS plays a key role in the modulation of the hyperglycemic reflex initiated by CBR stimulation.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/metabolismo , Corpo Carotídeo/efeitos dos fármacos , Corpo Carotídeo/metabolismo , Hiperglicemia/metabolismo , Núcleo Solitário/metabolismo , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/metabolismo , Animais , Fator Neurotrófico Derivado do Encéfalo/administração & dosagem , Ensaio de Imunoadsorção Enzimática , Glucose/metabolismo , Hiperglicemia/induzido quimicamente , Hiperglicemia/patologia , Imuno-Histoquímica , Masculino , Microinjeções , Neurotransmissores/farmacologia , Proteínas Proto-Oncogênicas c-fos/metabolismo , Distribuição Aleatória , Ratos Wistar , Receptor trkB/agonistas , Receptor trkB/antagonistas & inibidores , Receptor trkB/metabolismo , Receptores de AMPA/agonistas , Receptores de AMPA/antagonistas & inibidores , Receptores de AMPA/metabolismo , Cianeto de Sódio/farmacologia , Núcleo Solitário/citologia , Núcleo Solitário/efeitos dos fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/administração & dosagemRESUMO
Neuronal nitric oxide synthase (nNOS), which catalyzes the generation of nitric oxide (NO), is expressed by neuron subpopulations in the CNS. Nitric oxide is involved in neurotransmission and central glucose homeostasis. Our prior studies have shown that carotid body receptors participate in brain glucose regulation in vivo, and suggest the presence of a NO tonic mechanism in the solitary tract nucleus (STn). However, the role of NO within STn in glucose control remains unknown. In this study, we explored the potential regulatory role of NO on brain glucose retention induced by carotid body chemoreceptor anoxic stimulation with sodium cyanide (NaCN) which inhibits oxidative metabolism. Intracisternal infusions of nitroxidergic drugs before carotid chemoreceptor stimulation in anesthetized rats, elicited changes in nitrite concentration in plasma and hypothalamus-pituitary (H-P) tissue, as well as in gene expression of neuronal and inducible isoforms (nNOS and iNOS) in H-P tissue. The changes observed in above variables modified brain glucose retention in an opposite direction. When the NO donor, sodium nitroprusside (SNP), was given before carotid stimulation, nitrite concentration in plasma and H-P tissue, and gene expression of nNOS and iNOS in H-P tissue increased, whereas brain glucose retention decreased. In contrast, when the NOS inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) was infused immediately before carotid chemoreceptor stimulation, nitrite levels and nNOS expression decreased in plasma and H-P tissue, whereas brain glucose retention increased. Anoxic stimulation by itself induced an increase in the expression of both genes studied. All these results indicate that de novo expression of the nNOS gene in H-P tissue may be critically involved in central glucose changes observed after anoxic carotid chemoreceptor stimulation in conjunction with NO.
Assuntos
Encéfalo/metabolismo , Células Quimiorreceptoras/metabolismo , Inibidores Enzimáticos/farmacologia , Glucose/metabolismo , Sistema Hipotálamo-Hipofisário/metabolismo , Óxido Nítrico/metabolismo , Cianeto de Sódio/farmacologia , Animais , Corpo Carotídeo/metabolismo , Hipotálamo/metabolismo , Óxido Nítrico Sintase Tipo I/antagonistas & inibidores , Óxido Nítrico Sintase Tipo I/genética , Óxido Nítrico Sintase Tipo I/metabolismo , Hipófise/metabolismo , RatosRESUMO
We evaluate in rats the role of NO in the solitary tract nucleus (STn) after an anoxic stimulus to carotid body chemoreceptor cells (CChrc) with cyanide (NaCN), on the hyperglycemic reflex with glucose retention by the brain (BGR) and FOS expression (FOS-ir) in the STn. The results suggest that nitroxidergic pathways in the STn may play an important role in glucose homeostasis. A NO donor such as sodium nitroprusside (NPS) in the STn before CChrc stimulation increased arterial glucose level and significantly decreased BGR. NPS also induced a higher FOS-ir expression in STn neurons when compared to neurons in control rats that only received artificial cerebrospinal fluid (aCSF) before CChrc stimulation. In contrast, a selective NOS inhibitor such as Nomega-nitro-L-arginine methyl ester (L-NAME) in the STn before CChrc stimulation resulted in an increase of both, systemic glucose and BGR above control values. In this case, the number of FOS-ir positive neurons in the STn decreased when compared to control or to NPS experiments. FOS-ir expression in brainstem cells suggests that CChrc stimulation activates nitroxidergic pathways in the STn to regulate peripheral and central glucose homeostasis. The study of these functionally defined cells will be important to understand brain glucose homeostasis.
Assuntos
Corpo Carotídeo/metabolismo , Regulação da Expressão Gênica , Glucose/metabolismo , Homeostase , Óxido Nítrico/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , Núcleo Solitário/metabolismo , Animais , Corpo Carotídeo/efeitos dos fármacos , Regulação da Expressão Gênica/efeitos dos fármacos , Homeostase/efeitos dos fármacos , Masculino , Neurônios/metabolismo , Nitroprussiato/farmacologia , Fotomicrografia , Ratos , Ratos Wistar , Cianeto de Sódio/farmacologia , Núcleo Solitário/efeitos dos fármacos , Fatores de TempoRESUMO
Hypothalamic arginine-vasopressin (AVP) plays an important role both as a neurotransmitter and hormone in the regulation of blood glucose and feeding behavior. AVP-containing axons from the parvocellular subdivision of paraventricular nucleus of the hypothalamus terminate in the nucleus of the tractus solitarius (NTS), but the function of this projection is not known. Interestingly, the NTS also receives afferent information from the carotid body and other peripheral receptors involved in glucose homeostasis. We have previously reported that stimulation of the carotid body receptors initiates a hyperglycemic reflex and increases brain glucose retention. Here we show that direct administration of micro-doses of AVP into the NTS of anesthetized or awake rats rapidly increased the levels of blood glucose concentration and brain arterio-venous (A-V) glucose difference. This effect was not observed when the same doses of AVP were injected in the brainstem outside NTS. Arginine-vasopressin antagonist microinjections alone produced a small but significant reduction in brain A-V glucose. Pre-administered VP1-receptor antagonist [beta-mercapto-beta,beta-cyclopentamethylene-propionyl(1),O-Me-Tyr(2),Arg(8)]vasopressin blocked the effects of AVP. These results indicate that AVP acting on its receptors locally within the NTS participates in glucose homeostasis, increasing both blood glucose concentration and brain A-V glucose differences. Hypothalamic AVP may facilitate hyperglycemic responses initiated by peripheral signals processed at the level of the NTS.
Assuntos
Arginina Vasopressina/metabolismo , Glucose/metabolismo , Hiperglicemia/metabolismo , Vias Neurais/metabolismo , Núcleo Hipotalâmico Paraventricular/metabolismo , Núcleo Solitário/metabolismo , Animais , Arginina Vasopressina/análogos & derivados , Arginina Vasopressina/antagonistas & inibidores , Glicemia/efeitos dos fármacos , Homeostase/efeitos dos fármacos , Homeostase/fisiologia , Antagonistas de Hormônios/farmacologia , Hiperglicemia/fisiopatologia , Masculino , Vias Neurais/citologia , Vias Neurais/efeitos dos fármacos , Ocitocina/análogos & derivados , Ocitocina/farmacologia , Núcleo Hipotalâmico Paraventricular/citologia , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Ratos , Ratos Wistar , Núcleo Solitário/citologia , Núcleo Solitário/efeitos dos fármacosRESUMO
The response of hypophysectomized (HYPOX) and sham-operated (S-HYPOX) female and male Wistar young rats (8 weeks old) to antigenic stimulation was compared. Humoral antigenic responses against hemocyanin were measured by ELISA. [3H]thymidine incorporation into cultured spleen cells was used to determine proliferative response to concanavalin A (ConA) or antigenic stimulation. Anti-hemocyanin serum titers in the HYPOX animals was about half of that observed in control S-HYPOX rats. Similarly, the cellular proliferative response was significantly decreased in HYPOX animals when compared to S-HYPOX rats; the blastogenic response to hemocyanin in UC rats (which did not receive the antigen injection) was close to zero. S-HYPOX control rats responded to direct ConA stimulation as UC controls. Body weight and the weight of pituitary target organs (adrenal, thyroid, ovary and testes) was about 1/4 of that of controls. Hypophysectomy also resulted in a striking reduction in spleen weight. These results indicate that the pituitary gland is involved in cellular and humoral immune regulation in young rats.
Assuntos
Hipofisectomia , Hipófise/imunologia , Animais , Técnicas de Cultura de Células , Feminino , Hemocianinas/farmacologia , Imunização , Masculino , Hipófise/efeitos dos fármacos , Ratos , Ratos WistarRESUMO
To test whether blood glucose concentration in the carotid body-sinus may influence the amount of glucose retained by the brain, the isolated carotid sinus was perfused with glucose-rich blood or glucose-poor blood from a second animal. The circulation of the right carotid body-sinus was temporarily isolated in rat A, and perfused with blood coming from rat B. Blood glucose in rat B was modified by injections of glucose or insulin. Changes in glucose retention by the brain were measured in rat A. When the isolated carotid body-sinus in rat A was perfused with hyperglycemic blood (16.7 mM), brain glucose retention in rat A decreased significantly from 0.14 +/- 0.02 mumol/g/min (t = 0) to 0.08 +/- 0.01 mumol/g/min at 4 min after the beginning of perfusion. In contrast, the perfusion of the isolated carotid body-sinus of rat A with hypoglycemic blood (2.7 mM) from rat B, had the opposite effect. Brain glucose retention in rat A increased (0.23 +/- 0.03 mumol/g/min) at t = 4 min in comparison to control values (0.13 +/- 0.01 mumol/g/min). Chemoreceptor activity was also manipulated by the injection of cyanide (NaCN) in rat B, under these conditions, brain glucose retention in rat A increased from 0.13 +/- 0.01 mumol/g/min to 0.28 +/- 0.03 mumol/g/min between 4 to 8 min after the beginning of perfusion. These results indicate that chemosensory activity within the carotid body-sinus, superfused in vivo with different glucose concentrations, modify glucose retention by the brain.
Assuntos
Glicemia/metabolismo , Química Encefálica/fisiologia , Corpo Carotídeo/metabolismo , Glucose/metabolismo , Animais , Corpo Carotídeo/citologia , Células Quimiorreceptoras/efeitos dos fármacos , Cianetos/farmacologia , Glucose/farmacologia , Insulina/farmacologia , Consumo de Oxigênio/fisiologia , Ratos , Ratos WistarRESUMO
A technique to excise the pituitary gland (hypophysis) in rats is described. The basisphenoid bone is reached from the ventral neck and is perforated to expose the pituitary gland and its stalk. An aspirator allows the removal of the hypophysis and the stalk, including pars tuberalis, in one piece. The advantages of this new technique include: 1) immediate verification of the entirety of hypophysectomy; 2) broad operating field which exposes the pituitary stalk up to the hypothalamus; 3) the use of tracheal intubation and artificial respiration to improve postoperative recovery and to allow expanded operation field even during prolonged surgery. Pre- and postoperative care are described. The mean survival rate after this type of operation was 79% in rats weighing 50 to 130 g and 90% in rats larger than 130 g.
Assuntos
Hipofisectomia/métodos , Ratos/cirurgia , Animais , Hipofisectomia/instrumentação , Ratos Endogâmicos , Trepanação/instrumentação , Trepanação/métodosRESUMO
No remnants of adenohypophyseal tissue were found in 83% of the 70 dogs studied; in 17% of the animals remnants amounting to from 1 to 3% of normal hypophyseal tissue were found. These traces showed significant histological and cytological changes, and were most frequently found located on the floor of the sella turcica at some distance from their usual site. It is doubtful whether these residua have any functional significance, since the hypophysectomized dogs with such remnants had a survival time that corresponded to that of dogs with total hypophysectomy (6 months). The microscopic structure of the fragment of transplanted parotid (salivary gland) presents rich vascularization, changes in cellular distribution and a loss of the excretory duct. A better histological aspect was observed in the transplanted cells of the dogs with longer survival time. An important correlation exists between functional behavior of the operated animals and the histological state of the transplanted parotid tissue.
Assuntos
Glândula Parótida/fisiologia , Sela Túrcica/fisiologia , Animais , Cães , Feminino , Hipofisectomia , Masculino , Glândula Parótida/transplante , Transplante AutólogoRESUMO
No remnants of adenohypophyseal tissue were found in 83
of the 70 dogs studied; in 17
of the animals remnants amounting to from 1 to 3
of normal hypophyseal tissue were found. These traces showed significant histological and cytological changes, and were most frequently found located on the floor of the sella turcica at some distance from their usual site. It is doubtful whether these residua have any functional significance, since the hypophysectomized dogs with such remnants had a survival time that corresponded to that of dogs with total hypophysectomy (6 months). The microscopic structure of the fragment of transplanted parotid (salivary gland) presents rich vascularization, changes in cellular distribution and a loss of the excretory duct. A better histological aspect was observed in the transplanted cells of the dogs with longer survival time. An important correlation exists between functional behavior of the operated animals and the histological state of the transplanted parotid tissue.
RESUMO
No remnants of adenohypophyseal tissue were found in 83
of the 70 dogs studied; in 17
of the animals remnants amounting to from 1 to 3
of normal hypophyseal tissue were found. These traces showed significant histological and cytological changes, and were most frequently found located on the floor of the sella turcica at some distance from their usual site. It is doubtful whether these residua have any functional significance, since the hypophysectomized dogs with such remnants had a survival time that corresponded to that of dogs with total hypophysectomy (6 months). The microscopic structure of the fragment of transplanted parotid (salivary gland) presents rich vascularization, changes in cellular distribution and a loss of the excretory duct. A better histological aspect was observed in the transplanted cells of the dogs with longer survival time. An important correlation exists between functional behavior of the operated animals and the histological state of the transplanted parotid tissue.