RESUMEN
Postural orthostatic tachycardia syndrome (POTS) is a common autonomic disorder of largely unknown etiology that presents with sustained tachycardia on standing, syncope and elevated norepinephrine spillover. Some individuals with POTS experience anxiety, depression and cognitive dysfunction. Previously, we identified a mutation, A457P, in the norepinephrine (NE; also known as noradrenaline) transporter (NET; encoded by SLC6A2) in POTS patients. NET is expressed at presynaptic sites in NE neurons and plays a crucial role in regulating NE signaling and homeostasis through NE reuptake into noradrenergic nerve terminals. Our in vitro studies demonstrate that A457P reduces both NET surface trafficking and NE transport and exerts a dominant-negative impact on wild-type NET proteins. Here we report the generation and characterization of NET A457P mice, demonstrating the ability of A457P to drive the POTS phenotype and behaviors that are consistent with reported comorbidities. Mice carrying one A457P allele (NET(+/P)) exhibited reduced brain and sympathetic NE transport levels compared with wild-type (NET(+/+)) mice, whereas transport activity in mice carrying two A457P alleles (NET(P/P)) was nearly abolished. NET(+/P) and NET(P/P) mice exhibited elevations in plasma and urine NE levels, reduced 3,4-dihydroxyphenylglycol (DHPG), and reduced DHPG:NE ratios, consistent with a decrease in sympathetic nerve terminal NE reuptake. Radiotelemetry in unanesthetized mice revealed tachycardia in NET(+/P) mice without a change in blood pressure or baroreceptor sensitivity, consistent with studies of human NET A457P carriers. NET(+/P) mice also demonstrated behavioral changes consistent with CNS NET dysfunction. Our findings support that NET dysfunction is sufficient to produce a POTS phenotype and introduces the first genetic model suitable for more detailed mechanistic studies of the disorder and its comorbidities.
Asunto(s)
Técnicas de Sustitución del Gen , Proteínas Mutantes/metabolismo , Proteínas de Transporte de Noradrenalina a través de la Membrana Plasmática/metabolismo , Síndrome de Taquicardia Postural Ortostática/metabolismo , Animales , Barorreflejo , Conducta Animal , Transporte Biológico , Catecolaminas/metabolismo , Modelos Animales de Enfermedad , Femenino , Humanos , Metoxihidroxifenilglicol/análogos & derivados , Metoxihidroxifenilglicol/metabolismo , Ratones , Norepinefrina , Síndrome de Taquicardia Postural Ortostática/fisiopatología , TelemetríaRESUMEN
Healthy cardiovascular function relies on a balanced and responsive integration of noradrenergic and cholinergic innervation of the heart. High-affinity choline uptake by cholinergic terminals is pivotal for efficient ACh production and release. To date, the cardiovascular impact of diminished choline transporter (CHT) expression has not been directly examined, largely due to the transporter's inaccessibility in vivo. Here, we describe findings from cardiovascular experiments using transgenic mice that bear a CHT genetic deficiency. Whereas CHT knockout (CHT(-/-)) mice exhibit early postnatal lethality, CHT heterozygous (CHT(+/-)) mice survive, grow, and reproduce normally and exhibit normal spontaneous behaviors. However, the CHT(+/-) mouse heart displays significantly reduced levels of high-affinity choline uptake accompanied by significantly reduced levels of ACh. Telemeterized recordings of cardiovascular function in these mice revealed tachycardia and hypertension at rest. After treadmill exercise, CHT(+/-) mice exhibited slower heart rate recovery, consistent with a diminished cholinergic reserve, a contention validated through direct vagal nerve stimulation. Echocardiographic and histological experiments revealed an age-dependent decrease in fractional shortening, increased left ventricular dimensions, and increased ventricular fibrosis, consistent with ventricular dysfunction. These cardiovascular phenotypes of CHT(+/-) mice encourage an evaluation of humans bearing reduced CHT expression for their resiliency in maintaining proper heart function as well as risk for cardiovascular disease.
Asunto(s)
Cardiomegalia/metabolismo , Proteínas de Transporte de Catión/metabolismo , Colina/metabolismo , Taquicardia/metabolismo , Disfunción Ventricular/metabolismo , Factores de Edad , Análisis de Varianza , Animales , Sistema Nervioso Autónomo/metabolismo , Western Blotting , Peso Corporal/genética , Cardiomegalia/genética , Proteínas de Transporte de Catión/genética , Ecocardiografía , Frecuencia Cardíaca/genética , Hipertensión/genética , Hipertensión/metabolismo , Masculino , Ratones , Ratones Transgénicos , Condicionamiento Físico Animal , Taquicardia/genética , Telemetría , Disfunción Ventricular/genéticaRESUMEN
Human subjects with impaired baroreflex function cannot buffer rises or falls in blood pressure (BP), thus allowing BP effects of endogenous or environmental stimuli that previously escaped detection to emerge dramatically. Studies in these patients led us to discover that water ingestion induced a robust increase in BP and vascular resistance. Here, using a mouse model of baroreflex impairment, we show that the increase in blood pressure after water ingestion is mediated through sympathetic nervous system activation and that the osmosensitive transient receptor potential vanilloid 4 channel (Trpv4) is an essential component of the response. Although portal osmolality decreases after water ingestion in both wild-type and Trpv4(-/-) mice, only the wild-type animals show a pressor response. The same volume of physiological saline does not elicit an increase in BP, suggesting osmolality as the stimulus. The osmopressor response to water, and Trpv4 thus represent new factors now implicated in the physiology of BP regulation.
Asunto(s)
Barorreflejo/efectos de los fármacos , Hipertensión/fisiopatología , Sistema Nervioso Simpático/fisiología , Canales Catiónicos TRPV/fisiología , Agua/administración & dosificación , Animales , Barorreflejo/fisiología , Determinación de la Presión Sanguínea , Modelos Animales de Enfermedad , Humanos , Hipertensión/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Presión Osmótica , Prazosina/farmacología , Probabilidad , Distribución Aleatoria , Estadísticas no Paramétricas , Vagotomía/métodos , Resistencia Vascular/efectos de los fármacos , Resistencia Vascular/fisiología , Equilibrio Hidroelectrolítico/fisiologíaRESUMEN
Abnormal autonomic nerve traffic has been associated with a number of peripheral neuropathies and cardiovascular disorders prompting the development of genetically altered mice to study the genetic and molecular components of these diseases. Autonomic function in mice can be assessed by directly recording sympathetic nerve activity. However, murine sympathetic spikes are typically detected using a manually adjusted voltage threshold and no unsupervised detection methods have been developed for the mouse. Therefore, we tested the performance of several unsupervised spike detection algorithms on simulated murine renal sympathetic nerve recordings, including an automated amplitude discriminator and wavelet-based detection methods which used both the discrete wavelet transform (DWT) and the stationary wavelet transform (SWT) and several wavelet threshold rules. The parameters of the wavelet methods were optimized by comparing basal sympathetic activity to postmortem recordings and recordings made during pharmacological suppression and enhancement of sympathetic activity. In general, SWT methods were found to outperform amplitude discriminators and DWT methods with similar wavelet coefficient thresholding algorithms when presented with simulations with varied mean spike rates and signal-to-noise ratios. A SWT method which estimates the noise level using a "noise-only" wavelet scale and then selectively thresholds scales containing the physiologically important signal information was found to have the most robust spike detection. The proposed noise-level estimation method was also successfully validated during pharmacological interventions.
Asunto(s)
Potenciales de Acción/fisiología , Algoritmos , Diagnóstico por Computador/métodos , Electrodiagnóstico/métodos , Riñón/inervación , Riñón/fisiología , Reconocimiento de Normas Patrones Automatizadas/métodos , Sistema Nervioso Simpático/fisiología , Animales , Ratones , Ratones Endogámicos C57BLRESUMEN
BACKGROUND: Norepinephrine (NE) is a primary neurotransmitter of central autonomic regulation and sympathetic nerve conduction, and the norepinephrine transporter (NET) is crucial in limiting catecholaminergic signaling. NET is sensitive to antidepressants, cocaine, and amphetamine. NET blockade often is associated with cardiovascular side effects, and NET deficiency is linked to tachycardia in familial orthostatic intolerance. METHODS AND RESULTS: We telemetrically monitored NET-deficient (NET(-/-)) mice to determine the cardiovascular effects of reduced NE reuptake. Mean arterial pressure was elevated in resting NET(-/-) mice compared with NET(+/+) controls (103+/-0.6 versus 99+/-0.4 mm Hg; P<0.01), and corresponding pressures increased to 122+/-0.3 and 116+/-0.3 mm Hg (P<0.0001) with activity. Heart rate was also greater in resting NET(-/-) mice (565+/-5 versus 551+/-3 bpm; P<0.05), and genotypic differences were highly significant during the active phase (640+/-5 versus 607+/-3 bpm; P<0.0001). Conversely, the respiratory rate of resting NET(-/-) mice was dramatically reduced, whereas increases after the day/night shift surpassed those of controls. Plasma catecholamines in NET(-/-) and NET(+/+) mice were as follows: NE, 69+/-8 and 32+/-7; dihydroxyphenylglycol, 2+0.4 and 17+/-3; epinephrine, 15+/-3 and 4+/-0.6; and dopamine, 13+/-4 and 4+/-1 pmol/mL. Catechols in urine, brain, and heart also were determined. CONCLUSIONS: Resting mean arterial pressure and heart rate are maintained at nearly normal levels in NET-deficient mice, most likely as a result of increased central sympathoinhibition. However, sympathetic activation with wakefulness and activity apparently overwhelms central modulation, amplifying peripheral catecholaminergic signaling, particularly in the heart.