RESUMO
Intracerebroventricular (icv) injection of hydrogen peroxide (H2O2), a reactive oxygen species, or the blockade of catalase (enzyme that degrades H2O2 into H2O and O2) with icv injection of 3-amino-1,2,4-triazole (ATZ) reduces the pressor effects of angiotensin II also injected icv. In the present study, we investigated the effects of ATZ injected icv or intravenously (iv) on the pressor responses induced by icv injections of the cholinergic agonist carbachol, which similar to angiotensin II induces pressor responses that depend on sympathoexcitation and vasopressin release. In addition, the effects of H2O2 icv on the pressor responses to icv carbachol were also tested to compare with the effects of ATZ. Normotensive non-anesthetized male Holtzman rats (280-300 g, n = 8-9/group) with stainless steel cannulas implanted in the lateral ventricle were used. Previous injection of ATZ (5 nmol/1 µl) or H2O2 (5 µmol/1 µl) icv similarly reduced the pressor responses induced by carbachol (4 nmol/1 µl) injected icv (13 ± 4 and 12 ± 4 mmHg, respectively, vs. vehicle + carbachol: 30 ± 5 mmHg). ATZ (3.6 mmol/kg of body weight) injected iv also reduced icv carbachol-induced pressor responses (21 ± 2 mmHg). ATZ icv or iv and H2O2 icv injected alone produced no effect on baseline arterial pressure. The treatments also produced no significant change of heart rate. The results show that ATZ icv or iv reduced the pressor responses to icv carbachol, suggesting that endogenous H2O2 acting centrally inhibits the pressor mechanisms (sympathoactivation and/or vasopressin release) activated by central cholinergic stimulation.
Assuntos
Pressão Sanguínea/efeitos dos fármacos , Catalase/farmacologia , Hipertensão/fisiopatologia , Amitrol (Herbicida)/farmacologia , Angiotensina II , Animais , Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Frequência Cardíaca/efeitos dos fármacos , Peróxido de Hidrogênio/farmacologia , Hipertensão/tratamento farmacológico , Injeções Intraventriculares , Masculino , Ratos , Ratos Sprague-Dawley , Espécies Reativas de Oxigênio , Vasoconstritores/farmacologia , VasopressinasRESUMO
NEW FINDINGS: What is the central question of this study? Acute acidosis that results from short-term exercise is involved in delayed gastric emptying in rats and the lower responsiveness of gastric fundus strips to carbachol. Does extracellular acidosis decrease responsiveness to carbachol in tissues of sedentary rats? How? What is the main finding and its importance? Extracellular acidosis inhibits cholinergic signalling in the rat gastric fundus by selectively influencing the Gq/11 protein signalling pathway. Acute acidosis that results from short-term exercise delays gastric emptying in rats and decreases the responsiveness to carbachol in gastric fundus strips. The regulation of cytosolic Ca2+ concentrations appears to be a mechanism of action of acidosis. The present study investigated the way in which acidosis interferes with gastric smooth muscle contractions. Rat gastric fundus isolated strips at pH 6.0 presented a lower magnitude of carbachol-induced contractions compared with preparations at pH 7.4. This lower magnitude was absent in carbachol-stimulated duodenum and KCl-stimulated gastric fundus strips. In Ca2+ -free conditions, repeated contractions that were induced by carbachol progressively decreased, with no influence of extracellular pH. In fundus strips, CaCl2 -induced contractions were lower at pH 6.0 than at pH 7.4 but only when stimulated in the combined presence of carbachol and verapamil. In contrast, verapamil-sensitive contractions that were induced by CaCl2 in the presence of KCl did not change with pH acidification. In Ca2+ store-depleted preparations that were treated with thapsigargin, the contractions that were induced by extracellular Ca2+ restoration were smaller at pH 6.0 than at pH 7.4, but relaxation that was induced by SKF-96365 (an inhibitor of store-operated Ca2+ entry) was unaltered by extracellular acidification. At pH 6.0, the phospholipase C inhibitor U-73122 relaxed carbachol-induced contractions less than at pH 7.4, and this phenomenon was absent in tissue that was treated with the RhoA kinase blocker Y-27632. Thus, extracellular acidosis inhibited pharmacomechanical coupling in gastric fundus by selectively inhibiting the Gq/11 protein signalling pathway, whereas electromechanical coupling remained functionally preserved.
Assuntos
Acidose/metabolismo , Sinalização do Cálcio/efeitos dos fármacos , Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Subunidades alfa Gq-G11 de Proteínas de Ligação ao GTP/metabolismo , Esvaziamento Gástrico/efeitos dos fármacos , Fundo Gástrico/efeitos dos fármacos , Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Animais , Relação Dose-Resposta a Droga , Fundo Gástrico/metabolismo , Concentração de Íons de Hidrogênio , Técnicas In Vitro , Masculino , Músculo Liso/metabolismo , Ratos WistarRESUMO
Previously we have demonstrated that microinjection of acetylcholine (ACh) into the intermediate nucleus of the solitary tract (iNTS) induced sympatho-inhibition combined with a decrease in the phrenic nerve activity (PNA), whereas in the commissural NTS (cNTS), ACh did not change sympathetic nerve activity (SNA), but increased the PNA. In view of these demonstrated distinctive effects of ACh in different subnuclei of the NTS the current studies were undertaken to examine, using patch clamp techniques, the specific effects of ACh on the excitability of individual neurons in the NTS, as well as the neuropharmacology of these actions. Coronal slices of the brainstem containing either cNTS or iNTS subnuclei were used, and whole cell patch clamp recordings obtained from individual neurons in these two subnuclei. In cNTS, 58% of recorded neurons (n=12) demonstrated rapid reversible depolarizations in response to ACh (10mM), effects which were inhibited by the nicotinic antagonist mecamylamine (10µM), but unaffected by the muscarinic antagonist atropine (10µM). Similarly, bath application of ACh depolarized 76% of iNTS neurons (n=17), although in this case both atropine and mecamylamine reduced the ACh-induced depolarization. These data demonstrate that ACh depolarizes cNTS neurons through actions on nicotinic receptors, while depolarizing effects in iNTS are apparently mediated by both receptors.
Assuntos
Antagonistas Colinérgicos/farmacologia , Antagonistas Muscarínicos/farmacologia , Neurônios/efeitos dos fármacos , Antagonistas Nicotínicos/farmacologia , Núcleo Solitário/efeitos dos fármacos , Acetilcolina/farmacologia , Animais , Atropina/farmacologia , Agonistas Colinérgicos/farmacologia , Masculino , Mecamilamina/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Neurônios/metabolismo , Técnicas de Patch-Clamp , Ratos Sprague-Dawley , Núcleo Solitário/metabolismo , Técnicas de Cultura de TecidosRESUMO
Heart rate (HR) is a periodic activity that is variable over time due to intrinsic cardiac factors and extrinsic neural control, largely by the autonomic nervous system. Heart rate variability (HRV) is analyzed by measuring consecutive beat-to-beat intervals. This variability can contain information about the factors regulating cardiac activity under normal and pathological conditions, but the information obtained from such analyses is not yet fully understood. In this article, HRV in zebrafish larvae was evaluated under normal conditions and under the effect of substances that modify intrinsic cardiac activity and cardiac activity modulated by the nervous system. We found that the factors affecting intrinsic activity have negative chronotropic and arrhythmogenic effects at this stage of development, whereas neural modulatory factors have a lesser impact. The results suggest that cardiac activity largely depends on the intrinsic properties of the heart tissue in the early stages of development and, to a lesser extent, in the maturing nervous system. We also report, for the first time, the influence of the neurotransmitter gamma amino butyric acid on HRV. The results demonstrate the larval zebrafish model as a useful tool in the study of intrinsic cardiac activity and its role in heart diseases.
Assuntos
Cafeína/farmacologia , Etanol/farmacologia , Frequência Cardíaca/efeitos dos fármacos , Coração/efeitos dos fármacos , Coração/inervação , Ácido gama-Aminobutírico/metabolismo , Acetilcolina/farmacologia , Animais , Bicuculina/farmacologia , Depressores do Sistema Nervoso Central/farmacologia , Estimulantes do Sistema Nervoso Central/farmacologia , Agonistas Colinérgicos/farmacologia , Dopamina/farmacologia , Dopaminérgicos/farmacologia , Agonistas de Receptores de GABA-A/farmacologia , Antagonistas de Receptores de GABA-A/farmacologia , Regulação da Expressão Gênica no Desenvolvimento , Larva , Lidocaína/farmacologia , Cloreto de Metacolina/farmacologia , Agonistas Muscarínicos/farmacologia , Muscimol/farmacologia , Peixe-ZebraRESUMO
BACKGROUND: It is actually known that acetylcholine works as a signaling molecule in non-neuronal cells and tissues, in addition to its neuronal function as neurotransmitter. It can act on two types of receptors nicotinic and muscarinic receptors (mAChRs). The latter belong to the G protein coupled receptor family and there are five subtypes genetically cloned. Their activation triggers classical and non-classical intracellular signals that could be linked to the proliferation of normal and/or transformed cells. The M3 subtype was identified in different types of tumors and its stimulation with agonists triggers cell proliferation, migration, invasion and metastasis. RESULTS: Our laboratory has extensively investigated the expression and function of mAChRs in breast tumors from animal and human origins. We found a profuse expression of mAChRs in breast tumors, but opposite to this, an absence of these receptors in normal breast cells and tissues. The stimulation of mAChRs with the cholinergic agonist carbachol for 20 h increased tumor cell death. Moreover, the combination of subthreshold concentrations of the agonist with paclitaxel potentiates cell death. The usage of low dose chemotherapy with short drug free intervals was named metronomic therapy and it has emerged as a novel regimen for cancer treatment with very low incidence of side effects. CONCLUSION: Our work and that of others indicate that mAChRs that are over-expressed in different types of tumor cells could be a useful target for metronomic therapy in cancer treatment.
Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/farmacologia , Neoplasias da Mama/tratamento farmacológico , Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Paclitaxel/farmacologia , Receptores Muscarínicos/metabolismo , Administração Metronômica , Animais , Protocolos de Quimioterapia Combinada Antineoplásica/administração & dosagem , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Carbacol/administração & dosagem , Agonistas Colinérgicos/administração & dosagem , Feminino , Humanos , Paclitaxel/administração & dosagem , Receptores Muscarínicos/genéticaRESUMO
Higher cognitive functions require the integration and coordination of large populations of neurons in cortical and subcortical regions. Oscillations in the gamma band (30-45 Hz) of the electroencephalogram (EEG) have been involved in these cognitive functions. In previous studies, we analysed the extent of functional connectivity between cortical areas employing the 'mean squared coherence' analysis of the EEG gamma band. We demonstrated that gamma coherence is maximal during alert wakefulness and is almost absent during rapid eye movement (REM) sleep. The nucleus pontis oralis (NPO) is critical for REM sleep generation. The NPO is considered to exert executive control over the initiation and maintenance of REM sleep. In the cat, depending on the previous state of the animal, a single microinjection of carbachol (a cholinergic agonist) into the NPO can produce either REM sleep [REM sleep induced by carbachol (REMc)] or a waking state with muscle atonia, i.e. cataplexy [cataplexy induced by carbachol (CA)]. In the present study, in cats that were implanted with electrodes in different cortical areas to record polysomnographic activity, we compared the degree of gamma (30-45 Hz) coherence during REMc, CA and naturally-occurring behavioural states. Gamma coherence was maximal during CA and alert wakefulness. In contrast, gamma coherence was almost absent during REMc as in naturally-occurring REM sleep. We conclude that, in spite of the presence of somatic muscle paralysis, there are remarkable differences in cortical activity between REMc and CA, which confirm that EEG gamma (≈40 Hz) coherence is a trait that differentiates wakefulness from REM sleep.
Assuntos
Carbacol/farmacologia , Cataplexia/fisiopatologia , Agonistas Colinérgicos/farmacologia , Neurônios/efeitos dos fármacos , Sono REM/efeitos dos fármacos , Animais , Cataplexia/induzido quimicamente , Gatos , Eletroencefalografia/métodos , Neocórtex/efeitos dos fármacos , Neurônios/fisiologia , Ponte/efeitos dos fármacos , Ponte/fisiologia , Vigília/efeitos dos fármacosRESUMO
The autonomic control of heart rate was studied throughout development in embryos of the green iguana, Iguana iguana by applying receptor agonists and antagonists of the parasympathetic and sympathetic systems. Acetylcholine (Ach) slowed or stopped the heart and atropine antagonized the response to Ach indicating the presence of muscarinic cholinoceptors on the heart of early embryos. However, atropine injections had no impact on heart rate until immediately before hatching, when it increased heart rate by 15%. This cholinergic tonus increased to 34% in hatchlings and dropped to 24% in adult iguanas. Although epinephrine was without effect, injection of propranolol slowed the heart throughout development, indicating the presence of ß-adrenergic receptors on the heart of early embryos, possibly stimulated by high levels of circulating catecholamines. The calculated excitatory tonus varied between 33% and 68% until immediately before hatching when it fell to 25% and 29%, a level retained in hatchlings and adults. Hypoxia caused a bradycardia in early embryos that was unaffected by injection of atropine indicating that hypoxia has a direct effect upon the heart. In later embryos and hatchlings hypoxia caused a tachycardia that was unaffected by injection of atropine. Subsequent injection of propranolol reduced heart rate both uncovering a hypoxic bradycardia in late embryos and abolishing tachycardia in hatchlings. Hypercapnia was without effect on heart rate in late stage embryos and in hatchlings.
Assuntos
Embrião não Mamífero/fisiologia , Frequência Cardíaca/fisiologia , Coração/fisiologia , Iguanas/fisiologia , Acetilcolina/farmacologia , Adrenérgicos/farmacologia , Agonistas Adrenérgicos beta/farmacologia , Antagonistas Adrenérgicos beta/farmacologia , Animais , Atropina/farmacologia , Sistema Nervoso Autônomo/efeitos dos fármacos , Sistema Nervoso Autônomo/embriologia , Sistema Nervoso Autônomo/fisiologia , Colinérgicos/farmacologia , Agonistas Colinérgicos/farmacologia , Eletrocardiografia , Embrião não Mamífero/efeitos dos fármacos , Embrião não Mamífero/embriologia , Epinefrina/farmacologia , Coração/efeitos dos fármacos , Coração/embriologia , Frequência Cardíaca/efeitos dos fármacos , Iguanas/embriologia , Antagonistas Muscarínicos/farmacologia , Miocárdio/metabolismo , Propranolol/farmacologia , Receptores Adrenérgicos beta/metabolismo , Receptores Colinérgicos/metabolismoRESUMO
The administration of cholinergic agonists like pilocarpine intraperitoneally (i.p.) or carbachol intracerebroventricularly (i.c.v.) induces water, but non significant hypertonic NaCl intake. These treatments also produce pressor responses, which may inhibit sodium intake. Noradrenaline (NOR) acting on α2-adrenoceptors in the lateral parabrachial nucleus (LPBN) deactivates inhibitory mechanisms increasing fluid depletion-induced sodium intake. In the present study, we investigated: (1) water and 1.8% NaCl intake in rats treated with pilocarpine i.p. or carbachol i.c.v. combined with NOR into the LPBN; (2) if inhibitory signals from cardiovascular receptors are blocked by NOR in the LPBN. Male Holtzman rats with stainless steel guide-cannulas implanted in the lateral ventricle and bilaterally in the LPBN were used. Bilateral injections of NOR (80nmol/0.2µl) into the LPBN decreased water intake (0.8±0.3, vs. saline (SAL): 2.9±0.3ml/180min) induced by pilocarpine (1mg/kg of body weight) i.p., without changing 1.8% NaCl intake (0.8±2.4, vs. SAL: 0.5±0.3ml/180min). Prazosin (1mg/kg of body weight) i.p. blocked pressor responses and increased water and 1.8% NaCl intake (6.3±1.7 and 14.7±3.5ml/180min, respectively) in rats treated with pilocarpine combined with NOR into the LPBN. Prazosin i.p. also increased 1.8% NaCl intake in rats treated with carbachol i.c.v combined with NOR into the LPBN. The results suggest that different signals inhibit sodium intake in rats treated with cholinergic agonists, among them those produced by increases of arterial pressure that are not efficiently deactivated by NOR acting in the LPBN.
Assuntos
Agonistas Colinérgicos/farmacologia , Ingestão de Líquidos/fisiologia , Norepinefrina/metabolismo , Núcleos Parabraquiais/metabolismo , Cloreto de Sódio na Dieta , Animais , Anti-Hipertensivos/farmacologia , Pressão Sanguínea/efeitos dos fármacos , Pressão Sanguínea/fisiologia , Carbacol/farmacologia , Cateteres de Demora , Ingestão de Líquidos/efeitos dos fármacos , Frequência Cardíaca/efeitos dos fármacos , Frequência Cardíaca/fisiologia , Masculino , Núcleos Parabraquiais/efeitos dos fármacos , Pilocarpina/farmacologia , Prazosina/farmacologia , Ratos Sprague-DawleyRESUMO
Esophageal atresia (EA) is characterized by esophageal and gastric motility changes secondary to developmental and postsurgical damage. This study evaluated the in vitro contractile profile of the distal esophagus and gastric fundus in an experimental model of EA induced by doxorubicin (DOXO). Wistar pregnant rats received DOXO 2.2 mg/kg on the 8th and 9th gestational days. On day 21.5, fetuses were collected, sacrificed, and divided into groups: control, DOXO without EA (DOXO-EA), and DOXO with EA (DOXO+EA). Strips from the distal esophagus and gastric fundus were mounted on a wire myograph and isolated organ-bath system, respectively, and subjected to increasing concentrations of carbamylcholine chloride (carbachol, CCh). The isolated esophagus was also stimulated with increasing concentrations of KCl. In esophagus, the concentration-effect curves were reduced in response to CCh in the DOXO+EA and DOXO-EA groups compared to the control group (P<0.05). The maximum effect values (Emax) for DOXO+EA and DOXO-EA were significantly lower than control (P<0.05), but the half-maximal effective concentration (EC50) values were not significantly different when the three groups were compared (P>0.05). In response to KCl, the distal esophagus samples in the three groups were not statistically different with regard to Emax or EC50 values (P>0.05). No significant difference was noted for EC50 or Emax values in fundic strips stimulated with CCh (P>0.05). In conclusion, exposure of dams to DOXO during gestation inhibited the contractile behavior of esophageal strips from offspring in response to CCh but not KCl, regardless of EA induction. The gastric fundus of DOXO-exposed offspring did not have altered contractile responsiveness to cholinergic stimulation.
Assuntos
Atresia Esofágica/fisiopatologia , Esôfago/fisiopatologia , Fundo Gástrico/fisiopatologia , Contração Muscular/fisiologia , Fístula Traqueoesofágica/diagnóstico , Animais , Antibióticos Antineoplásicos , Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Modelos Animais de Doenças , Doxorrubicina , Atresia Esofágica/induzido quimicamente , Feminino , Feto , Fundo Gástrico/efeitos dos fármacos , Técnicas In Vitro , Miografia , Gravidez , Ratos WistarRESUMO
The parasympathetic nervous system is important for ß-cell secretion and mass regulation. Here, we characterized involvement of the vagus nerve in pancreatic ß-cell morphofunctional regulation and body nutrient homeostasis in 90-day-old monosodium glutamate (MSG)-obese rats. Male newborn Wistar rats received MSG (4 g/kg body weight) or saline [control (CTL) group] during the first 5 days of life. At 30 days of age, both groups of rats were submitted to sham-surgery (CTL and MSG groups) or subdiaphragmatic vagotomy (Cvag and Mvag groups). The 90-day-old MSG rats presented obesity, hyperinsulinemia, insulin resistance, and hypertriglyceridemia. Their pancreatic islets hypersecreted insulin in response to glucose but did not increase insulin release upon carbachol (Cch) stimulus, despite a higher intracellular Ca(2+) mobilization. Furthermore, while the pancreas weight was 34% lower in MSG rats, no alteration in islet and ß-cell mass was observed. However, in the MSG pancreas, increases of 51% and 55% were observed in the total islet and ß-cell area/pancreas section, respectively. Also, the ß-cell number per ß-cell area was 19% higher in MSG rat pancreas than in CTL pancreas. Vagotomy prevented obesity, reducing 25% of body fat stores and ameliorated glucose homeostasis in Mvag rats. Mvag islets demonstrated partially reduced insulin secretion in response to 11.1 mM glucose and presented normalization of Cch-induced Ca(2+) mobilization and insulin release. All morphometric parameters were similar among Mvag and CTL rat pancreases. Therefore, the higher insulin release in MSG rats was associated with greater ß-cell/islet numbers and not due to hypertrophy. Vagotomy improved whole body nutrient homeostasis and endocrine pancreatic morphofunction in Mvag rats.