RESUMEN
Obstructive sleep apnea (OSA) is a highly prevalent sleep disorder that is associated with many cardiovascular complications. Similar to OSA, chronic intermittent hypoxia (CIH) (a model for OSA) leads to oxidative stress and impairs baroreflex control of the heart rate (HR) in rodents. The baroreflex arc includes the aortic depressor nerve (ADN), vagal efferent, and central neurons. In this study, we used mice as a model to examine the effects of CIH on baroreflex sensitivity, aortic baroreceptor afferents, and central and vagal efferent components of the baroreflex circuitry. Furthermore, we tested whether human Cu/Zn Superoxide Dismutase (SOD1) overexpression in transgenic mice offers protection against CIH-induced deficit of the baroreflex arc. Wild-type C57BL/6J and SOD1 mice were exposed to room air (RA) or CIH and were then anesthetized, ventilated, and catheterized for measurement of mean arterial pressure (MAP) and HR. Compared with wild-type RA control, CIH impaired baroreflex sensitivity but increased maximum baroreceptor gain and bradycardic response to vagal efferent stimulation. Additionally, CIH reduced the bradycardic response to ADN stimulation, indicating a diminished central regulation of bradycardia. Interestingly, SOD1 overexpression prevented CIH-induced attenuation of HR responses to ADN stimulation and preserved HR responses to vagal efferent stimulation in transgenic mice. We suggest that CIH decreased central mediation of the baroreflex and SOD1 overexpression may prevent the CIH-induced central deficit.
Asunto(s)
Barorreflejo , Bradicardia/prevención & control , Encéfalo/enzimología , Sistema Cardiovascular/inervación , Frecuencia Cardíaca , Presorreceptores/fisiopatología , Superóxido Dismutasa-1/metabolismo , Nervio Vago/fisiopatología , Animales , Presión Arterial , Bradicardia/enzimología , Bradicardia/etiología , Bradicardia/fisiopatología , Encéfalo/fisiopatología , Enfermedad Crónica , Modelos Animales de Enfermedad , Estimulación Eléctrica , Humanos , Hipoxia/complicaciones , Hipoxia/enzimología , Hipoxia/fisiopatología , Masculino , Ratones Endogámicos C57BL , Ratones Transgénicos , Superóxido Dismutasa-1/genética , Regulación hacia ArribaRESUMEN
Excessive reactive oxygen species (ROS) (such as the superoxide radical) are commonly associated with cardiac autonomic dysfunctions. Though superoxide dismutase 1 (SOD1) overexpression may protect against ROS damage to the autonomic nervous system, superoxide radical reduction may change normal physiological functions. Previously, we demonstrated that human SOD1 (hSOD1) overexpression does not change baroreflex bradycardia and tachycardia but rather increases aortic depressor nerve activity in response to arterial pressure changes in C57B6SJL-Tg (SOD1)2 Gur/J mice. Since the baroreflex arc includes afferent, central, and efferent components, the objective of this study was to determine whether hSOD1 overexpression alters the central and vagal efferent mediation of heart rate (HR) responses. Our data indicate that SOD1 overexpression decreased the HR responses to vagal efferent nerve stimulation but did not change the HR responses to aortic depressor nerve (ADN) stimulation. Along with the previous study, we suggest that SOD1 overexpression preserves normal baroreflex function but may differentially alter the functions of the ADN, vagal efferents, and central components. While SOD1 overexpression likely enhanced ADN function and the central mediation of bradycardia, it decreased vagal efferent control of HR.
Asunto(s)
Barorreflejo/fisiología , Frecuencia Cardíaca/fisiología , Superóxido Dismutasa-1/metabolismo , Nervio Vago/metabolismo , Animales , Presión Sanguínea/fisiología , Bradicardia/metabolismo , Humanos , Ratones TransgénicosRESUMEN
Transient receptor potential canonical 6 (TRPC6) channels are permeable to Na+ and Ca2+ and are widely expressed in the brain. In this study, the role of TRPC6 was investigated following ischemia/reperfusion (I/R) and oxygen-glucose deprivation (OGD). We found that TRPC6 expression was increased in wild-type (WT) mice cortical neurons following I/R and in primary neurons with OGD, and that deletion of TRPC6 reduced the I/R-induced brain infarct in mice and the OGD- /neurotoxin-induced neuronal death. Using live-cell imaging to examine intracellular Ca2+ levels ([Ca2+] i ), we found that OGD induced a significant higher increase in glutamate-evoked Ca2+ influx compared to untreated control and such an increase was reduced by TRPC6 deletion. Enhancement of TRPC6 expression using AdCMV-TRPC6-GFP infection in WT neurons increased [Ca2+] i in response to glutamate application compared to AdCMV-GFP control. Inhibition of N-methyl-d-aspartic acid receptor (NMDAR) with MK801 decreased TRPC6-dependent increase of [Ca2+] i in TRPC6 infected cells, indicating that such a Ca2+ influx was NMDAR dependent. Furthermore, TRPC6-dependent Ca2+ influx was blunted by blockade of Na+ entry in TRPC6 infected cells. Finally, OGD-enhanced Ca2+ influx was reduced, but not completely blocked, in the presence of voltage-dependent Na+ channel blocker tetrodotoxin (TTX) and dl-α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) blocker CNQX. Altogether, we concluded that I/R-induced brain damage was, in part, due to upregulation of TRPC6 in cortical neurons. We postulate that overexpression of TRPC6 following I/R may induce neuronal death partially through TRPC6-dependent Na+ entry which activated NMDAR, thus leading to a damaging Ca2+ overload. These findings may provide a potential target for future intervention in stroke-induced brain damage.
RESUMEN
The murine model has been used to investigate the role of cardiac sensory axons in various disease states. However, the distribution and morphological structures of cardiac nociceptive axons in normal murine tissues have not yet been well characterized. In this study, whole-mount atria from FVB mice were processed with calcitonin gene-related peptide (CGRP) and substance P (SP) primary antibodies followed by secondary antibodies, and then examined using confocal microscopy. We found: 1) Large CGRP-IR axon bundles entered the atria with the major veins, and these large bundles bifurcated into small bundles and single axons that formed terminal end-nets and free endings in the epicardium. Varicose CGRP-IR axons had close contacts with muscle fibers, and some CGRP-IR axons formed varicosities around principle neurons (PNs) within intrinsic cardiac ganglia (ICGs). 2) SP-IR axons also were found in the same regions of the atria, attached to veins, and within cardiac ganglia. Similar to CGRP-IR axons, these SP-IR axons formed terminal end-nets and free endings in the atrial epicardium and myocardium. Within ICGs, SP-IR axons formed varicose endings around PNs. However, SP-IR nerve fibers were less abundant than CGRP-IR fibers in the atria. 3) None of the PNs were CGRP-IR or SP-IR. 4) CGRP-IR and SP-IR often colocalized in terminal varicosities around PNs. Collectively, our data document the distribution pattern and morphology of CGRP-IR and SP-IR axons and terminals in different regions of the atria. This knowledge provides useful information for CGRP-IR and SP-IR axons that can be referred to in future studies of pathological remodeling.
Asunto(s)
Axones/ultraestructura , Péptido Relacionado con Gen de Calcitonina/metabolismo , Corazón/anatomía & histología , Corazón/inervación , Neuronas/citología , Sustancia P/metabolismo , Animales , Axones/metabolismo , Atrios Cardíacos/anatomía & histología , Atrios Cardíacos/inervación , Inmunohistoquímica , Intestino Delgado/anatomía & histología , Intestino Delgado/inervación , Masculino , Ratones , Microscopía Confocal , Neuronas/metabolismo , Sistema Nervioso Parasimpático/anatomía & histología , Sistema Nervioso Parasimpático/metabolismo , Pericardio/anatomía & histología , Pericardio/inervación , Terminales Presinápticos/metabolismo , Venas/anatomía & histologíaRESUMEN
Large-conductance Ca2(+)-activated K+ channels (BK) regulate action potential (AP) properties and excitability in many central neurons. However, the properties and functional roles of BK channels in parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal 7-9 days. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. Using excised patch single-channel recordings, we identified voltage-gated and Ca(2+)-dependent BK channels in PCMNs. The majority of BK channels exhibited persistent channel opening during voltage holding. These BK channels had a conductance of 237 pS and a 50% opening probability at +27.9 mV, the channel open time constant was 3.37 ms at +20 mV, and dwell time increased exponentially as the membrane potential depolarized. At the +20-mV holding potential, the [Ca2+]50 was 15.2 µM with a P0.5 of 0.4. Occasionally, some BK channels showed a transient channel opening and fast inactivation. Using whole cell voltage clamp, we found that BK channel mediated outward currents and afterhyperpolarization currents (IAHP). Using whole cell current clamp, we found that application of BK channel blocker iberiotoxin (IBTX) increased spike half-width and suppressed fast afterhyperpolarization (fAHP) amplitude following single APs. In addition, IBTX application increased spike half-width and reduced the spike frequency-dependent AP broadening in trains and spike frequency adaption (SFA). Furthermore, BK channel blockade decreased spike frequency. Collectively, these results demonstrate that PCMNs have BK channels that significantly regulate AP repolarization, fAHP, SFA, and spike frequency. We conclude that activation of BK channels underlies one of the mechanisms for facilitation of PCMN excitability.
Asunto(s)
Potenciales de Acción/fisiología , Tronco Encefálico/citología , Canales de Potasio de Gran Conductancia Activados por el Calcio/fisiología , Neuronas Motoras/fisiología , Fibras Parasimpáticas Posganglionares/fisiología , Pericardio/fisiología , Animales , Animales Recién Nacidos , Tronco Encefálico/fisiología , Músculos Laríngeos/citología , Músculos Laríngeos/fisiología , Masculino , Ratones , Técnicas de Cultivo de Órganos , Faringe/citología , Faringe/inervación , Faringe/fisiologíaRESUMEN
BACKGROUND: Autonomic imbalances including parasympathetic withdrawal and sympathetic overactivity are cardinal features of heart failure regardless of etiology; however, mechanisms underlying these imbalances remain unknown. Animal model studies of heart and visceral organ hypertrophy predict that nerve growth factor levels should be elevated in heart failure; whether this is so in human heart failure, though, remains unclear. We tested the hypotheses that neurons in cardiac ganglia are hypertrophied in human, canine, and rat heart failure and that nerve growth factor, which we hypothesize is elevated in the failing heart, contributes to this neuronal hypertrophy. METHODS AND RESULTS: Somal morphology of neurons from human (579.54±14.34 versus 327.45±9.17 µm(2); P<0.01) and canine hearts (767.80±18.37 versus 650.23±9.84 µm(2); P<0.01) failing secondary to ischemia and neurons from spontaneously hypertensive rat hearts (327.98±3.15 versus 271.29±2.79 µm(2); P<0.01) failing secondary to hypertension reveal significant hypertrophy of neurons in cardiac ganglia compared with controls. Western blot analysis shows that nerve growth factor levels in the explanted, failing human heart are 250% greater than levels in healthy donor hearts. Neurons from cardiac ganglia cultured with nerve growth factor are significantly larger and have greater dendritic arborization than neurons in control cultures. CONCLUSIONS: Hypertrophied neurons are significantly less excitable than smaller ones; thus, hypertrophy of vagal postganglionic neurons in cardiac ganglia would help to explain the parasympathetic withdrawal that accompanies heart failure. Furthermore, our observations suggest that nerve growth factor, which is elevated in the failing human heart, causes hypertrophy of neurons in cardiac ganglia.
Asunto(s)
Ganglios Autónomos/metabolismo , Insuficiencia Cardíaca/metabolismo , Corazón/inervación , Factor de Crecimiento Nervioso/metabolismo , Adulto , Anciano , Animales , Estudios de Casos y Controles , Células Cultivadas , Modelos Animales de Enfermedad , Perros , Femenino , Ganglios Autónomos/patología , Insuficiencia Cardíaca/etiología , Insuficiencia Cardíaca/patología , Humanos , Hipertensión/complicaciones , Hipertrofia , Masculino , Persona de Mediana Edad , Isquemia Miocárdica/complicaciones , Isquemia Miocárdica/metabolismo , Miocardio/metabolismo , Ratas , Ratas Endogámicas SHR , Ratas Endogámicas WKYRESUMEN
We tested the feasibility of stimulating upper-intercostal and abdominal muscles plus the diaphragm by using chronically implanted intramuscular electrodes.During two survival surgeries with six dogs, intramuscular electrodes were implanted bilaterally in the three respiratory muscles. Standard stimulation of the diaphragm was conducted. The dorsolateral and ventrolateral abdominal wall areas were stimulated with a 25 mA current. The second to fourth intercostal spaces were stimulated to elicit the largest tidal volume associated with the least coactivation of the serratus and latissimus muscles. Lone diaphragm and upper-intercostal muscle pacing produced inhaled tidal volumes (mean +/- standard error of the mean) of 293 +/- 36 mL and 59 +/- 17 mL, respectively. Lone abdominal muscle pacing produced an exhaled volume of 55 +/- 17 mL. Combined pacing of diaphragm and intercostal muscles increased the inhaled volume to 389 +/- 39 mL. The addition of abdominal pacing following the combined stimulation of diaphragm and intercostals increased the exhaled volume to 472 +/- 54 mL. During autopsy, dislodgement of the electrodes overlying the ribs was a concern and probably resulted from loose animal jackets. Chronic intramuscular Permaloc electrodes can be implanted in several respiratory muscles and increase tidal volumes more than diaphragm stimulation alone.
Asunto(s)
Músculos Abdominales/fisiología , Diafragma/fisiología , Electrodos Implantados , Músculos Intercostales/fisiología , Respiración , Animales , Perros , Estimulación Eléctrica/instrumentación , Estimulación Eléctrica/métodos , Estudios de Factibilidad , Femenino , Masculino , Frecuencia Respiratoria , Volumen de Ventilación PulmonarRESUMEN
Previously, we demonstrated that maternal diabetes reduced the excitability and increased small-conductance Ca(2+)-activated K(+) (SK) currents of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA). In addition, blockade of SK channels with apamin completely abolished this reduction. In the present study, we examined whether maternal diabetes affects large-conductance Ca(2+)-activated K(+) (BK) channels and whether BK channels contribute to the attenuation of PCMN excitability observed in neonates of diabetic mothers. Neonatal mice from OVE26 diabetic mothers (NMDM) and normal FVB mothers (control) were used. The pericardial sac of neonatal mice at postnatal days 7-9 was injected with the tracer X-rhodamine-5 (and 6)-isothiocyanate 2 days prior to the experiment to retrogradely label PCMNs in the NA. Whole cell current- and voltage-clamps were used to measure spike frequency, action potential (AP) repolarization (half-width), afterhyperpolarization potential (AHP), transient outward currents, and afterhyperpolarization currents (I(AHP)). In whole cell voltage clamp mode, we confirmed that maternal diabetes increased transient outward currents and I(AHP) compared with normal cells. Using BK channel blockers charybdotoxin (CTx) and paxilline, we found that maternal diabetes increased CTx- and paxilline-sensitive transient outward currents but did not change CTx- and paxilline-sensitive I(AHP). In whole cell current-clamp mode, we confirmed that maternal diabetes increased AP half-width and AHP, and reduced excitability of PCMNs. Furthermore, we found that after blockade of BK channels with CTx or paxilline, maternal diabetes induced a greater increase of AP half-width but similarly decreased fast AHP without affecting medium AHP. Finally, blockade of BK channels decreased spike frequency in response to current injection in both control and NMDM without reducing the difference of spike frequency between the two groups. Therefore, we conclude that although BK transient outward currents, which may alter AP repolarization, are increased in NMDM, BK channels do not directly contribute to maternal diabetes-induced attenuation of PCMN excitability. In contrast, based on evidence from our previous and present studies, reduction of PCMN excitability in neonates of diabetic mothers is largely dependent on altered SK current associated with maternal diabetes.
Asunto(s)
Potenciales de Acción , Corazón/inervación , Canales de Potasio de Gran Conductancia Activados por el Calcio/metabolismo , Bulbo Raquídeo/metabolismo , Neuronas Motoras/metabolismo , Sistema Nervioso Parasimpático/metabolismo , Embarazo en Diabéticas/metabolismo , Efectos Tardíos de la Exposición Prenatal , Potenciales de Acción/efectos de los fármacos , Animales , Animales Recién Nacidos , Femenino , Canales de Potasio de Gran Conductancia Activados por el Calcio/antagonistas & inhibidores , Bulbo Raquídeo/efectos de los fármacos , Bulbo Raquídeo/fisiopatología , Ratones , Neuronas Motoras/efectos de los fármacos , Sistema Nervioso Parasimpático/efectos de los fármacos , Sistema Nervioso Parasimpático/fisiopatología , Técnicas de Placa-Clamp , Bloqueadores de los Canales de Potasio/farmacología , Embarazo , Embarazo en Diabéticas/fisiopatología , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/efectos de los fármacos , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Factores de TiempoRESUMEN
Small conductance Ca(2+)-activated K(+) channels (SK) regulate action potential (AP) firing properties and excitability in many central neurons. However, the functional roles of SK channels of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal days 7-9. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. With the use of whole cell current clamp, single APs and spike trains of different frequencies were evoked by current injections. We found that 1) PCMNs have two different firing patterns: the majority of PCMNs (90%) exhibited spike frequency adaptation (SFA) and the rest (10%) showed less or no adaptation; 2) application of the specific SK channel blocker apamin significantly increased spike half-width in single APs and trains and reduced the spike frequency-dependent AP broadening in trains; 3) SK channel blockade suppressed afterhyperpolarization (AHP) amplitude following single APs and trains and abolished spike-frequency dependence of AHP in trains; and 4) SK channel blockade increased the spike frequency but did not alter the pattern of SFA. Using whole cell voltage clamp, we measured outward currents and afterhyperpolarization current (I(AHP)). SK channel blockade revealed that SK-mediated outward currents had both transient and persistent components. After bath application of apamin and Ca(2+)-free solution, we found that apamin-sensitive and Ca(2+)-sensitive I(AHP) were comparable, confirming that SK channels may contribute to a major portion of Ca(2+)-activated K(+) channel-mediated I(AHP). These results suggest that PCMNs have SK channels that significantly regulate AP repolarization, AHP, and spike frequency but do not affect SFA. We conclude that activation of SK channels underlies one of the mechanisms for negative control of PCMN excitability.
Asunto(s)
Corazón/inervación , Corazón/fisiología , Bulbo Raquídeo/fisiología , Neuronas Motoras/fisiología , Sistema Nervioso Parasimpático/fisiología , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/fisiología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Animales , Apamina/farmacología , Femenino , Masculino , Ratones , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/efectos de los fármacosRESUMEN
Parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) play a key role in regulating cardiac functions. In this study, we examined the effects of maternal diabetes on excitability, action potential (AP) properties, and small conductance Ca(2+)-activated K(+) (SK) currents of PCMNs. Neonatal mice from diabetic (OVE26 female, NMDM) and normal (FVB female, control) mothers that had been mated with nondiabetic fathers (FVB male) were used. Tracer XRITC was injected into the pericardial sac at P7-9 to retrogradely label PCMNs. Two days later, XRITC-labeled PCMNs were identified in brain stem slices. The responses of spike frequency, AP repolarization (half-width) and afterhyperpolarization (AHP) of PCMNs to current injections were studied using whole cell current clamp. Outward and afterhyperpolarization currents (I(AHP)) in response to voltage steps were measured using whole cell voltage clamp. In examining the effects of maternal diabetes on excitability and AP properties, we found that in NMDM spike frequency decreased, the half-width and AHP peak amplitude increased, and the peak amplitude of outward transient currents and I(AHP) increased compared with those measured in control. In examining the effects of maternal diabetes on SK channels, we found that after blockage of SK channels with a specific SK channel blocker apamin, maternal diabetes significantly increased apamin-sensitive outward transient currents and I(AHP), and suppressed AHP amplitude in NMDM more than those in control. Further, apamin application increased the firing rate to current injections and completely abolished the difference of the firing rate between control and NMDM. We suggest that the augmented SK-mediated currents may contribute to the increased AHP amplitude and the attenuated excitability of PCMNs in NMDM.
Asunto(s)
Potenciales de Acción/fisiología , Bulbo Raquídeo/fisiología , Neuronas Motoras/fisiología , Embarazo en Diabéticas/metabolismo , Embarazo en Diabéticas/fisiopatología , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/fisiología , Animales , Animales Recién Nacidos , Femenino , Masculino , Potenciales de la Membrana/fisiología , Ratones , Ratones Transgénicos , Neuronas Motoras/patología , Embarazo , Embarazo en Diabéticas/patologíaRESUMEN
Diabetes-induced structural changes of vagal aortic afferent and cardiac efferent axons are not well understood. FVB control and OVE26 diabetic mice at different ages received injections of the tracer tetramethylrhodamine dextran (TMR-D) into the nodose ganglion to label vagal aortic afferents (at 3 and 6 months), or DiI injections into the nucleus ambiguus to label vagal cardiac efferents (at 3, 6, and 9 months). The aortic arch and atria were examined by using confocal microscopy. In the aortic arch, TMR-D labeled large and small vagal afferent axons (axons(L) and axons(S)) that formed different types of terminals: axons(L) produced large flower-sprays (flower-sprays(L)) and end-nets (end-nets(L)), whereas axons(S) produced small flower-sprays (flower-sprays(S)) and end-nets (end-nets(S)). In the atria, DiI-labeled vagal efferent axons formed basket endings around ganglion principle neurons (PNs). The vagal afferents, PNs and vagal cardiac efferents in diabetic mice were compared with age-matched control mice. We found (P < 0.05) that: 1) the size of axons(L), flower-sprays(L), flower-sprays(S) and end-nets(S) were reduced at 6 and 9 months; 2) the size of cardiac ganglia and the somatic area of the PNs were decreased, and the PN density in cardiac ganglia was increased at all ages and the PN nuclei/soma area ratio was increased at 9 months; and 3) the percentage of DiI-labeled axons-innervated PNs was decreased at all ages. Furthermore, the number of synaptic-like terminal varicosities around PNs was decreased. Compared with 3 months, more advanced diabetes at 9 months further reduced the number of varicosities/PN. In addition to these changes, swollen axons and terminals, as well as leaky-like DiI-labeled terminals, were observed in long-term diabetic mice (6 and 9 months of age). Taken together, our data show that chronic diabetes induces a significant structural atrophy of vagal aortic afferent and cardiac efferent axons and terminals. Although different morphologies of vagal afferent terminals in the aortic arch may serve as substrates for the future investigation of aortic depressor afferent physiology, structural remodeling of vagal afferents and efferents provides a foundation for further analysis of diabetes-induced impairment of cardiac autonomic regulation.
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Aorta Torácica/inervación , Diabetes Mellitus Tipo 1/patología , Ganglios/patología , Bulbo Raquídeo/patología , Neuronas Aferentes/patología , Nervio Vago/patología , Vías Aferentes/patología , Envejecimiento/patología , Animales , Aorta Torácica/patología , Axones/patología , Corazón/inervación , Ratones , Ratones Transgénicos , Neuronas Eferentes/patología , Ganglio Nudoso/patologíaRESUMEN
OBJECTIVE: To test the feasibility of implanting intramuscular electrodes (Permaloc, Synapse Biomedical Inc, Oberlin OH) with self-securing polypropylene anchors to stimulate upper-intercostal and abdominal muscles plus the diaphragm. METHODS/RESULTS: In 6 anesthetized dogs, 12 Permaloc electrodes were implanted in the 3 respiratory muscles (4 in each muscle group). Tidal volume with diaphragmatic stimulation was 310 +/- 38 mL (mean +/- SE); with upper intercostal stimulation, it was 68 +/- 18 mL; and with combined diaphragm intercostal stimulation, it was 438 +/- 78 mL. By study design, stimulation in the upper intercostal muscles was limited to not more than slight/moderate contraction of the serratus and latissimus muscles overlying the ribs. Abdominal muscle stimulation produced exhaled volumes of 38 +/- 20 mL (this stimulation was limited by the maximal output of the stimulator of 25 milliamperes). Combined diaphragm intercostal stimulation followed by abdominal muscle stimulation increased exhaled volumes from 312 +/- 31 mL to 486 +/- 58 mL (P = 0.024). CONCLUSIONS: Permaloc electrodes can be successfully implanted in upper intercostal and abdominal muscles in addition to the diaphragm. Combined diaphragm intercostal stimulation followed by abdominal muscle stimulation increased the exhaled volumes recorded with diaphragmatic stimulation alone.
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Diafragma/fisiología , Estimulación Eléctrica/instrumentación , Estimulación Eléctrica/métodos , Electrodos Implantados , Músculos Abdominales/fisiología , Animales , Biofisica , Perros , Femenino , Masculino , Tórax/inervación , Factores de TiempoRESUMEN
Baroreflex control of heart rate (HR) is impaired in human diabetes mellitus and in large experimental models. However, baroreflex impairment in diabetic mouse models and diabetes-induced remodeling of baroreflex circuitry are not well studied. We examined the impairment of baroreflex control of heart rate (HR) and assessed structural remodeling of cardiac ganglia in the streptozotocin (STZ)-induced diabetic mouse model. FVB mice were either injected with vehicle or STZ. Group 1: mice were anesthetized and the femoral artery and vein were catheterized at the 30th day after vehicle or STZ injection. On the second day after surgery, baroreflex-mediated HR responses to sodium nitroprusside (SNP) and phenylephrine (PE)-induced mean arterial blood pressure (MABP) changes were measured in conscious mice. Group 2: Fluoro-Gold was administered (i.p.) to label cardiac ganglia in each mouse at the 25th day after vehicle or STZ injection. After another five days, animals were perfused and cardiac ganglia were examined using confocal microscopy. Compared with control, we found in STZ mice: 1) the HR decreased, but MABP did not. 2) The PE-induced increases of MABP were decreased. 3) Baroreflex bradycardia was attenuated in the rapid MABP ascending phase but the steady-state DeltaHR/DeltaMABP was not different at all PE doses. 4) SNP-induced MABP decreases were not different. 5) Baroreflex tachycardia was attenuated. 6) The sizes of cardiac ganglia and ganglionic principal neurons were decreased. 7) The ratio of nucleus/cell body of cardiac ganglionic neurons was increased. We conclude that baroreflex control of HR is impaired in conscious STZ mice. In addition, diabetes may induce a significant structural remodeling of cardiac ganglia. Such an anatomical change of cardiac ganglia may provide new information for the understanding of diabetes-induced remodeling of the multiple components within the baroreflex circuitry.
Asunto(s)
Barorreflejo/fisiología , Diabetes Mellitus Experimental/fisiopatología , Ganglios Autónomos/patología , Corazón/fisiopatología , Neuronas Eferentes/patología , Animales , Bradicardia/fisiopatología , Estado de Conciencia , Corazón/inervación , Frecuencia Cardíaca/fisiología , Masculino , Ratones , Ratones Transgénicos , Microscopía Confocal , EstreptozocinaRESUMEN
Baroreflex control of heart rate (HR) is impaired in human type 1 diabetes mellitus. The goal of this study is to use a transgenic mouse model of type 1 diabetes (OVE26) to assess the diabetes-induced baroreflex impairment in the conscious state. OVE26 transgenic mice (which develop hyperglycemia within the first three weeks after birth due to the specific damage of beta cells) and normal control mice (FVB) 5-6months of age were anesthetized, and the left femoral artery and both veins were catheterized. On the second day after surgery, baroreflex-mediated HR responses to arterial blood pressure (ABP) changes that were induced by separate microinfusion of phenylephrine (PE) and sodium nitroprusside (SNP) at different doses (0.03-0.4microg/min) were measured in the conscious state. Compared with FVB control, we found that in OVE26 diabetic mice 1) mean ABP (MABP) and HR were decreased (p<0.05). 2) PE-induced MABP increases were comparable to those in FVB mice (p>0.05). 3) Baroreflex-mediated bradycardia was attenuated (p<0.05). 4) SNP-induced MABP decreases was reduced (p<0.05). 5) Baroreflex-mediated tachycardia was attenuated (p<0.05). Since baroreflex control of HR in conscious OVE26 mice is impaired in a similar fashion to human diabetes mellitus, we suggest that OVE26 mice may provide a useful model to study the neural mechanisms of diabetes-induced baroreflex impairment.
Asunto(s)
Barorreflejo/fisiología , Diabetes Mellitus Experimental/fisiopatología , Diabetes Mellitus Tipo 1/fisiopatología , Frecuencia Cardíaca , Animales , Presión Sanguínea/efectos de los fármacos , Bradicardia/prevención & control , Relación Dosis-Respuesta a Droga , Corazón/efectos de los fármacos , Corazón/fisiopatología , Frecuencia Cardíaca/efectos de los fármacos , Masculino , Ratones , Ratones Transgénicos , Nitroprusiato/administración & dosificación , Nitroprusiato/farmacología , Fenilefrina/administración & dosificación , Fenilefrina/farmacología , Taquicardia/prevención & control , Vasoconstrictores/administración & dosificación , Vasoconstrictores/farmacología , Vasodilatadores/administración & dosificación , Vasodilatadores/farmacología , VigiliaRESUMEN
BACKGROUND: Better methods are needed for recording urethral function for complex urologic problems involving the bladder, urethra, and pelvic floor. OBJECTIVE: To evaluate a balloon catheter for recording urethral pressure and function using bench-top testing and evaluation in an animal model. METHODS: Balloon pressure-recording methods included slightly inflating the balloon with water and placing the pressure transducer on the distal end of the catheter. For bench-top testing, manual procedures and a silastic tube with a restriction were used. In 3 anesthetized dogs, pressure recorded from the skeletal urethral sphincter was induced with electrical stimulation of the sphincter. Anal sphincter pressure was also recorded. RESULTS: Bench-top testing showed good pressure recordings, including a confined peak at the tube restriction. Animal tests showed urethral pressure records with rapid responses when electrical stimulation was applied. Peak pressure at the urethral skeletal sphincter was 55.7 +/- 15 cmH2O, which was significantly higher than the peak pressure recorded 2 cm distally in the proximal urethra (3.3 +/- 2.3 cmH2O). Peak anal pressures were smaller and unchanged for the 2 stimulations. CONCLUSIONS: Balloon-pressure recordings showed rapid responses that were adequate for the tests conducted. In the animal model, high-pressure contractions specific to the skeletal urethral sphincter were shown. Balloon-tipped catheters warrant further investigation and may have applications for the evaluation of detrusor-sphincter dyssynergia after spinal cord injury or for stress urinary incontinence.
Asunto(s)
Cateterismo/métodos , Presión , Uretra/fisiopatología , Animales , Perros , Femenino , Modelos Animales , Transductores de PresiónRESUMEN
Baroreflex sensitivity is impaired by diabetes mellitus. Previously, we found that diabetes induces a deficit of central mediation of baroreflex-mediated bradycardia. In this study, we assessed whether diabetes induces degeneration of the nucleus ambiguus (NA) and reduces heart rate (HR) responses to l-Glutamate (L-Glu) microinjection into the NA. FVB control and OVE26 diabetic mice (5-6 months) were anesthetized. Different doses of L-Glu (0.1-5 mM/l, 20 nl) were delivered into the left NA using a multi-channel injector. In other animals, the left vagus was electrically stimulated at 1-40 Hz (1 ms, 0.5 mA, 20 s). HR and mean arterial blood pressure (MAP) responses to L-Glu microinjections into the NA and to the electrical stimulation of the vagus were measured. The NA region was defined by tracer TMR-D injection into the ipsilateral nodose ganglion to retrogradely label vagal motoneurons in the NA. Brainstem slices at -600, -300, 0, +300, and +600 mum relative to the obex were processed using Nissl staining and the number of NA motoneurons was counted. Compared with FVB control, we found in OVE26 mice that: 1) HR responses to L-Glu injection into the NA at doses of 0.2-0.4 (mM/l, 20 nl) were attenuated (p<0.05), but MAP responses were unchanged (p>0.05). 2) HR responses to vagal stimulation were increased (p<0.05). 3) The total number of NA (left and right) motoneurons was reduced (p<0.05). Taken together, we concluded that diabetes reduces NA control of HR and induces degeneration of NA motoneurons. Degeneration of NA cardiac motoneurons may contribute to impairment of reflex-bradycardia in OVE26 diabetic mice.
Asunto(s)
Enfermedades del Sistema Nervioso Autónomo/fisiopatología , Complicaciones de la Diabetes/fisiopatología , Bulbo Raquídeo/fisiopatología , Enfermedades Neurodegenerativas/fisiopatología , Reflejo Anormal/fisiología , Enfermedades del Nervio Vago/fisiopatología , Animales , Enfermedades del Sistema Nervioso Autónomo/etiología , Enfermedades del Sistema Nervioso Autónomo/patología , Barorreflejo/efectos de los fármacos , Barorreflejo/fisiología , Bradicardia , Complicaciones de la Diabetes/patología , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Estimulación Eléctrica , Lateralidad Funcional/efectos de los fármacos , Lateralidad Funcional/fisiología , Ácido Glutámico/metabolismo , Ácido Glutámico/farmacología , Corazón/inervación , Corazón/fisiopatología , Sistema de Conducción Cardíaco/efectos de los fármacos , Sistema de Conducción Cardíaco/fisiopatología , Frecuencia Cardíaca/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Bulbo Raquídeo/efectos de los fármacos , Bulbo Raquídeo/patología , Ratones , Microinyecciones , Neuronas Motoras/efectos de los fármacos , Neuronas Motoras/metabolismo , Neuronas Motoras/patología , Degeneración Nerviosa/etiología , Degeneración Nerviosa/patología , Degeneración Nerviosa/fisiopatología , Enfermedades Neurodegenerativas/etiología , Enfermedades Neurodegenerativas/patología , Enfermedades del Nervio Vago/etiología , Enfermedades del Nervio Vago/patologíaRESUMEN
Chronic intermittent hypoxia (CIH), as occurs in sleep apnea, impairs baroreflex-mediated reductions in heart rate (HR) and enhances HR responses to electrical stimulation of vagal efferent. We tested the hypotheses that HR responses to activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the nucleus ambiguous (NA) are reduced in CIH-exposed rats and that this impairment is associated with degeneration of glutamate receptor (GluR)-immunoreactive NA neurons. Fischer 344 rats (3-4 mo) were exposed to room air (RA) or CIH for 35-50 days (n = 18/group). At the end of the exposures, AMPA (4 pmol, 20 nl) and NMDA (80 pmol, 20 nl) were microinjected into the same location of the left NA (-200 microm to +200 microm relative to caudal end of area postrema; n = 6/group), and HR and arterial blood pressure responses were measured. In addition, brain stem sections at the level of -800, -400, 0, +400, and +800 microm relative to obex were processed for AMPA and NMDA receptor immunohistochemistry. The number of NA neurons expressing AMPA receptors and NMDA receptors (NMDARs) was quantified. Compared with RA, we found that after CIH 1) HR responses to microinjection of AMPA into the left NA were reduced (RA -290 +/- 30 vs. CIH -227 +/- 15 beats/min, P < 0.05); 2) HR responses to microinjection of NMDA into the left NA were reduced (RA -302 +/- 16 vs. CIH -238 +/- 27 beats/min, P < 0.05); and 3) the number of NMDAR1, AMPA GluR1, and AMPA GluR2/3-immunoreactive cells in the NA was reduced (P < 0.05). These results suggest that degeneration of NA neurons expressing GluRs contributes to impaired baroreflex control of HR in rats exposed to CIH.
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Tronco Encefálico/efectos de los fármacos , Agonistas de Aminoácidos Excitadores/farmacología , Frecuencia Cardíaca/efectos de los fármacos , Corazón/inervación , Hipoxia/fisiopatología , N-Metilaspartato/farmacología , Receptores de Glutamato/efectos de los fármacos , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/farmacología , Animales , Barorreflejo/efectos de los fármacos , Presión Sanguínea/efectos de los fármacos , Tronco Encefálico/metabolismo , Tronco Encefálico/fisiopatología , Modelos Animales de Enfermedad , Regulación hacia Abajo , Agonistas de Aminoácidos Excitadores/administración & dosificación , Hipoxia/metabolismo , Microinyecciones , Neuronas Motoras/efectos de los fármacos , Neuronas Motoras/metabolismo , N-Metilaspartato/administración & dosificación , Degeneración Nerviosa/fisiopatología , Ratas , Ratas Endogámicas F344 , Receptores AMPA/agonistas , Receptores de Glutamato/metabolismo , Receptores de N-Metil-D-Aspartato/agonistas , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/administración & dosificaciónRESUMEN
PURPOSE: The neurotherapeutic effects of nerve electrical stimulation and gonadal steroids have independently been demonstrated. The purpose of this study was to investigate the therapeutic potential of a combinatorial treatment strategy of electrical stimulation and gonadal steroids on peripheral nerve regeneration. METHODS: Following a facial nerve crush axotomy in gonadectomized adult male rats, testosterone propionate (TP), dihydrotestosterone (DHT), or estradiol (E(2)) was systemically administered with/without daily electrical stimulation of the proximal nerve stump. Facial nerve outgrowth was assessed at 4 and 7 days post-axotomy using radioactive labeling. RESULTS: Administration of electrical stimulation alone reduced the estimated delay in sprout formation but failed to accelerate the overall regeneration rate. Conversely, TP treatment alone accelerated the regeneration rate by approximately 10% but had no effect on the sprouting delay. Combining TP with electrical stimulation, however, maintained the enhanced rate and reduced the sprouting delay. DHT treatment alone failed to alter the regeneration rate but combining it with electrical stimulation increased the rate by 10%. E(2) treatment alone increased the regeneration rate by approximately 5% but with electrical stimulation, there was no additional effect. CONCLUSIONS: Electrical stimulation and gonadal steroids differentially enhanced regenerative properties. TP, an aromatizable androgen, augmented regeneration most, suggesting a synergism between androgenic and estrogenic effects. Therapeutically, combining electrical stimulation with gonadal steroids may boost regenerative properties more than the use of either treatment alone.
Asunto(s)
Estimulación Eléctrica , Enfermedades del Nervio Facial/terapia , Regeneración Nerviosa/fisiología , Esteroides/uso terapéutico , Animales , Axotomía/métodos , Dihidrotestosterona/farmacología , Dihidrotestosterona/uso terapéutico , Modelos Animales de Enfermedad , Estradiol/farmacología , Estradiol/uso terapéutico , Enfermedades del Nervio Facial/tratamiento farmacológico , Leucina , Lisina , Masculino , Regeneración Nerviosa/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Esteroides/farmacología , Propionato de Testosterona/farmacología , Propionato de Testosterona/uso terapéutico , Factores de Tiempo , TritioRESUMEN
Nitric oxide and carbon monoxide are diffusible gas messengers, synthesized by nitric oxide synthase or heme oxygenase 2, respectively, that can activate soluble guanylyl cyclase in adjacent cells. Nitric oxide and carbon monoxide neuromodulation in cardiac ganglia has been demonstrated. However, identification of nitric oxide or carbon monoxide in human cardiac ganglia needs to be confirmed as suggested from animal model studies. Immunohistochemistry was used to demonstrate neuronal nitric oxide synthase, heme oxygenase 2, and soluble guanylyl cyclase immunoreactivity within neurons of adult human cardiac ganglia. Nitric oxide synthase immunoreactivity was present in 37% of neurons within cardiac ganglia, heme oxygenase 2 immunoreactivity in 79%, and soluble guanylyl cyclase in 53%. Our findings support the hypothesis that nitric oxide and carbon monoxide are modulators of neurotransmission in cardiac ganglia and in neural control of the adult human heart.
Asunto(s)
Monóxido de Carbono/metabolismo , Ganglios Parasimpáticos/enzimología , Guanilato Ciclasa/biosíntesis , Neuronas/enzimología , Óxido Nítrico/biosíntesis , Receptores Citoplasmáticos y Nucleares/biosíntesis , Adulto , Anciano , Nodo Atrioventricular/enzimología , Nodo Atrioventricular/metabolismo , Monóxido de Carbono/análisis , Células Cultivadas , Femenino , Ganglios Parasimpáticos/metabolismo , Guanilato Ciclasa/análisis , Hemo Oxigenasa (Desciclizante)/análisis , Hemo Oxigenasa (Desciclizante)/biosíntesis , Humanos , Masculino , Persona de Mediana Edad , Neuronas/metabolismo , Óxido Nítrico/análisis , Óxido Nítrico Sintasa de Tipo I/análisis , Óxido Nítrico Sintasa de Tipo I/biosíntesis , Receptores Citoplasmáticos y Nucleares/análisis , Nodo Sinoatrial/enzimología , Nodo Sinoatrial/metabolismo , Guanilil Ciclasa Soluble , Adulto JovenRESUMEN
Urinary retention is a serious urological problem associated with spinal cord injuries (SCIs) and other pelvic disorders. Effective methods of pelvic nerve stimulation were investigated for this problem. Following anesthesia in five dogs, the bladder was surgically exposed. Bladder and anal sphincter pressures were recorded. Testing was first conducted with probe electrodes. Barb electrodes were then implanted with a needle near the pelvic plexus nerves and the bladder wall. We tested different electrode arrangements and stimulating parameters to induce bladder contractions without skeletal muscle stimulation. The pelvic plexus nerves near the bladder were identified, and the barb electrodes were effectively implanted. Stimulation with bipolar and bilateral electrodes induced pressures over 30 cmH(2)O without skeletal muscle activation. Common stimulation parameters were 40 pps, 400 microseconds pulse duration, and 15 to 25 mA stimulating current applied for 3 s. Effective electrode implantation methods were shown. Also identified were electrode arrangements and stimulating parameters that induced strong bladder contractions without skeletal muscle activation. However, voiding studies were not conducted. Further studies with barb electrodes are warranted, and these methods may have applications for bladder stimulation following SCI.