RESUMEN
Fluid intake is an essential innate behaviour that is mainly caused by two distinct types of thirst1-3. Increased blood osmolality induces osmotic thirst that drives animals to consume pure water. Conversely, the loss of body fluid induces hypovolaemic thirst, in which animals seek both water and minerals (salts) to recover blood volume. Circumventricular organs in the lamina terminalis are critical sites for sensing both types of thirst-inducing stimulus4-6. However, how different thirst modalities are encoded in the brain remains unknown. Here we employed stimulus-to-cell-type mapping using single-cell RNA sequencing to identify the cellular substrates that underlie distinct types of thirst. These studies revealed diverse types of excitatory and inhibitory neuron in each circumventricular organ structure. We show that unique combinations of these neuron types are activated under osmotic and hypovolaemic stresses. These results elucidate the cellular logic that underlies distinct thirst modalities. Furthermore, optogenetic gain of function in thirst-modality-specific cell types recapitulated water-specific and non-specific fluid appetite caused by the two distinct dipsogenic stimuli. Together, these results show that thirst is a multimodal physiological state, and that different thirst states are mediated by specific neuron types in the mammalian brain.
Asunto(s)
Neuronas/clasificación , Neuronas/fisiología , Sed/fisiología , Animales , Secuencia de Bases , Ingestión de Líquidos/fisiología , Femenino , Hipovolemia/prevención & control , Masculino , Ratones , Ratones Endogámicos C57BL , Modelos Animales , Organum Vasculosum/citología , Organum Vasculosum/fisiología , Presión Osmótica , Análisis de la Célula Individual , Órgano Subfornical/citología , Órgano Subfornical/fisiología , Privación de AguaRESUMEN
Neural circuits for appetites are regulated by both homeostatic perturbations and ingestive behaviour. However, the circuit organization that integrates these internal and external stimuli is unclear. Here we show in mice that excitatory neural populations in the lamina terminalis form a hierarchical circuit architecture to regulate thirst. Among them, nitric oxide synthase-expressing neurons in the median preoptic nucleus (MnPO) are essential for the integration of signals from the thirst-driving neurons of the subfornical organ (SFO). Conversely, a distinct inhibitory circuit, involving MnPO GABAergic neurons that express glucagon-like peptide 1 receptor (GLP1R), is activated immediately upon drinking and monosynaptically inhibits SFO thirst neurons. These responses are induced by the ingestion of fluids but not solids, and are time-locked to the onset and offset of drinking. Furthermore, loss-of-function manipulations of GLP1R-expressing MnPO neurons lead to a polydipsic, overdrinking phenotype. These neurons therefore facilitate rapid satiety of thirst by monitoring real-time fluid ingestion. Our study reveals dynamic thirst circuits that integrate the homeostatic-instinctive requirement for fluids and the consequent drinking behaviour to maintain internal water balance.
Asunto(s)
Ingestión de Líquidos/fisiología , Vías Nerviosas , Área Preóptica/citología , Área Preóptica/fisiología , Órgano Subfornical/citología , Órgano Subfornical/fisiología , Sed/fisiología , Animales , Apetito/fisiología , Femenino , Neuronas GABAérgicas/metabolismo , Receptor del Péptido 1 Similar al Glucagón/metabolismo , Homeostasis , Instinto , Masculino , Ratones , Óxido Nítrico Sintasa/metabolismo , Respuesta de Saciedad/fisiología , Equilibrio HidroelectrolíticoRESUMEN
Thirst motivates animals to drink in order to maintain fluid balance. Thirst has conventionally been viewed as a homeostatic response to changes in blood volume or tonicity. However, most drinking behaviour is regulated too rapidly to be controlled by blood composition directly, and instead seems to anticipate homeostatic imbalances before they arise. How this is achieved remains unknown. Here we reveal an unexpected role for the subfornical organ (SFO) in the anticipatory regulation of thirst in mice. By monitoring deep-brain calcium dynamics, we show that thirst-promoting SFO neurons respond to inputs from the oral cavity during eating and drinking and then integrate these inputs with information about the composition of the blood. This integration allows SFO neurons to predict how ongoing food and water consumption will alter fluid balance in the future and then to adjust behaviour pre-emptively. Complementary optogenetic manipulations show that this anticipatory modulation is necessary for drinking in several contexts. These findings provide a neural mechanism to explain longstanding behavioural observations, including the prevalence of drinking during meals, the rapid satiation of thirst, and the fact that oral cooling is thirst-quenching.
Asunto(s)
Ingestión de Líquidos/fisiología , Ingestión de Alimentos/fisiología , Homeostasis , Neuronas/fisiología , Órgano Subfornical/citología , Sed/fisiología , Equilibrio Hidroelectrolítico/fisiología , Animales , Sangre , Calcio/metabolismo , Retroalimentación Fisiológica , Femenino , Masculino , Ratones , Boca/inervación , Boca/fisiología , Vías Nerviosas , Optogenética , Órgano Subfornical/fisiología , Factores de TiempoRESUMEN
Thirst is the basic instinct to drink water. Previously, it was shown that neurons in several circumventricular organs of the hypothalamus are activated by thirst-inducing conditions. Here we identify two distinct, genetically separable neural populations in the subfornical organ that trigger or suppress thirst. We show that optogenetic activation of subfornical organ excitatory neurons, marked by the expression of the transcription factor ETV-1, evokes intense drinking behaviour, and does so even in fully water-satiated animals. The light-induced response is highly specific for water, immediate and strictly locked to the laser stimulus. In contrast, activation of a second population of subfornical organ neurons, marked by expression of the vesicular GABA transporter VGAT, drastically suppresses drinking, even in water-craving thirsty animals. These results reveal an innate brain circuit that can turn an animal's water-drinking behaviour on and off, and probably functions as a centre for thirst control in the mammalian brain.
Asunto(s)
Conducta de Ingestión de Líquido/fisiología , Órgano Subfornical/citología , Órgano Subfornical/fisiología , Sed/fisiología , Animales , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Proteínas de Unión al ADN/metabolismo , Deshidratación/fisiopatología , Ingestión de Líquidos , Agua Potable , Rayos Láser , Ratones , Optogenética , Respuesta de Saciedad , Factores de Transcripción/metabolismo , Proteínas del Transporte Vesicular de Aminoácidos Inhibidores/metabolismoRESUMEN
Subfornical organ (SFO) neurons exhibit heterogeneity in current expression and spiking behavior, where the two major spiking phenotypes appear as tonic and burst firing. Insight into the mechanisms behind this heterogeneity is critical for understanding how the SFO, a sensory circumventricular organ, integrates and selectively influences physiological function. To integrate efficient methods for studying this heterogeneity, we built a single-compartment, Hodgkin-Huxley-type model of an SFO neuron that is parameterized by SFO-specific in vitro patch-clamp data. The model accounts for the membrane potential distribution and spike train variability of both tonic and burst firing SFO neurons. Analysis of model dynamics confirms that a persistent Na+ and Ca2+ currents are required for burst initiation and maintenance and suggests that a slow-activating K+ current may be responsible for burst termination in SFO neurons. Additionally, the model suggests that heterogeneity in current expression and subsequent influence on spike afterpotential underlie the behavioral differences between tonic and burst firing SFO neurons. Future use of this model in coordination with single neuron patch-clamp electrophysiology provides a platform for explaining and predicting the response of SFO neurons to various combinations of circulating signals, thus elucidating the mechanisms underlying physiological signal integration within the SFO. NEW & NOTEWORTHY Our understanding of how the subfornical organ (SFO) selectively influences autonomic nervous system function remains incomplete but theoretically results from the electrical responses of SFO neurons to physiologically important signals. We have built a computational model of SFO neurons, derived from and supported by experimental data, which explains how SFO neurons produce different electrical patterns. The model provides an efficient system to theoretically and experimentally explore how changes in the essential features of SFO neurons affect their electrical activity.
Asunto(s)
Potenciales de Acción , Canales de Calcio/metabolismo , Modelos Neurológicos , Neuronas/fisiología , Canales de Sodio/metabolismo , Órgano Subfornical/fisiología , Animales , Células Cultivadas , Neuronas/metabolismo , Ratas , Ratas Sprague-Dawley , Órgano Subfornical/citología , Órgano Subfornical/metabolismoRESUMEN
Inflammation is thought to play a fundamental role in the pathophysiology of hypertension and heart failure, although the mechanisms for this remain unclear. Proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), influence the subfornical organ (SFO) to modulate sympathetic activity and blood pressure. The pressor effects of TNF-α in the SFO are partially mediated by angiotensin II (ANG II) receptor type 1 (AT1R), and TNF-α is known to potentiate ANG II-induced hypertension. However, the cellular mechanism of the interaction between TNF-α and ANG II/AT1R signaling remains unknown. In the present study, we performed Ca2+ imaging on dissociated SFO neurons in vitro from male Sprague-Dawley rats to determine whether TNF-α modulates ANG II-induced increases in intracellular Ca2+ in SFO neurons. We first established that a proportion of SFO neurons respond to ANG II, an effect that required AT1R signaling and extracellular Ca2+. We then tested the hypothesis that TNF-α may modulate the effects of ANG II on SFO neurons by examining the effects of TNF-α treatment on the ANG II-induced rise in intracellular Ca2+. We discovered that TNF-α potentiated the ANG II-induced rise in intracellular Ca2+, an effect that was dependent on the duration of TNF-α treatment. Finally, we determined that this potentiation of ANG II-induced Ca2+ activity relied on tetrodotoxin-sensitive voltage-gated Na+ (vgNa+) channels. These data suggest that the potentiation of ANG II/AT1R activity by TNF-α in SFO neurons results from the previously demonstrated ability of this cytokine to modulate the activation threshold of vgNa+ currents.
Asunto(s)
Angiotensina II/farmacología , Señalización del Calcio/efectos de los fármacos , Neuronas/efectos de los fármacos , Órgano Subfornical/efectos de los fármacos , Factor de Necrosis Tumoral alfa/farmacología , Animales , Células Cultivadas , Sinergismo Farmacológico , Masculino , Potenciales de la Membrana , Neuronas/metabolismo , Ratas Sprague-Dawley , Receptor de Angiotensina Tipo 1/agonistas , Receptor de Angiotensina Tipo 1/metabolismo , Órgano Subfornical/citología , Órgano Subfornical/metabolismo , Factores de Tiempo , Canales de Sodio Activados por Voltaje/efectos de los fármacos , Canales de Sodio Activados por Voltaje/metabolismoRESUMEN
Tumor necrosis factor-α (TNF-α) is a proinflammatory cytokine implicated in cardiovascular and autonomic regulation via actions in the central nervous system. TNF-α-/- mice do not develop angiotensin II (ANG II)-induced hypertension, and administration of TNF-α into the bloodstream of rats increases blood pressure and sympathetic tone. Recent studies have shown that lesion of the subfornical organ (SFO) attenuates the hypertensive and autonomic effects of TNF-α, while direct administration of TNF-α into the SFO increases blood pressure, suggesting the SFO to be a key site for the actions of TNF-α. Therefore, we used patch-clamp techniques to examine both acute and long-term effects of TNF-α on the excitability of Sprague-Dawley rat SFO neurons. It was observed that acute bath application of TNF-α depolarized SFO neurons and subsequently increased action potential firing rate. Furthermore, the magnitude of depolarization and the proportion of depolarized SFO neurons were concentration dependent. Interestingly, following 24-h incubation with TNF-α, the basal firing rate of the SFO neurons was increased and the rheobase was decreased, suggesting that TNF-α elevates SFO neuron excitability. This effect was likely mediated by the transient sodium current, as TNF-α increased the magnitude of the current and lowered its threshold of activation. In contrast, TNF-α did not appear to modulate either the delayed rectifier potassium current or the transient potassium current. These data suggest that acute and long-term TNF-α exposure elevates SFO neuron activity, providing a basis for TNF-α hypertensive and sympathetic effects.NEW & NOTEWORTHY Considerable recent evidence has suggested important links between inflammation and the pathological mechanisms underlying hypertension. The present study describes cellular mechanisms through which acute and long-term exposure of tumor necrosis factor-α (TNF-α) influences the activity of subfornical organ neurons by modulating the voltage-gated transient Na+ current. This provides critical new information regarding the specific pathological mechanisms through which inflammation and TNF-α in particular may result in the development of hypertension.
Asunto(s)
Potenciales de Acción , Neuronas/efectos de los fármacos , Órgano Subfornical/efectos de los fármacos , Factor de Necrosis Tumoral alfa/farmacología , Animales , Células Cultivadas , Masculino , Neuronas/metabolismo , Neuronas/fisiología , Canales de Potasio/metabolismo , Ratas , Ratas Sprague-Dawley , Canales de Sodio/metabolismo , Órgano Subfornical/citología , Órgano Subfornical/fisiologíaRESUMEN
It is known that the median preoptic nucleus (POMe) sends dense projections to the subfornical organ (SFO). However, the functional significance of these projections have not been well discussed. In this electron microscopic study, we investigated the presence of synapses between POMe-derived axon terminals and SFO neurons that project to the paraventricular hypothalamic nucleus (PVN). After injection of a retrograde tracer, wheat germ agglutinin-conjugated horseradish peroxidase-colloidal gold complex, into the PVN, many labeled neurons were found in the SFO. In contrast, after injection of an anterograde tracer, biotinylated dextran amine, in the POMe, abundant labeled axon varicosities were observed in the SFO. Using electron microscopy, synapses were identified between retrogradely labeled dendrites and cell bodies, and anterogradely labeled axon terminals, indicating that POMe neurons innervate SFO neurons projecting to the PVN. The possibility that POMe neurons play multiple roles in the neuronal circuit responsible for vasopressin release and/or cardiovascular regulation is also discussed.
Asunto(s)
Neuronas/fisiología , Núcleo Hipotalámico Paraventricular/citología , Área Preóptica/citología , Órgano Subfornical/citología , Sinapsis/fisiología , Animales , Biotina/análogos & derivados , Biotina/metabolismo , Dextranos/metabolismo , Oro Coloide/metabolismo , Masculino , Microinyecciones , Microscopía Inmunoelectrónica , Vías Nerviosas/fisiología , Neuronas/metabolismo , Neuronas/ultraestructura , Ratas , Ratas Sprague-Dawley , Sinapsis/ultraestructura , Aglutininas del Germen de Trigo/metabolismoRESUMEN
The subfornical organ (SFO) plays a pivotal role in body fluid homeostasis through its ability to integrate neurohumoral signals and subsequently alter behavior, neuroendocrine function, and autonomic outflow. The purpose of the present study was to evaluate whether selective activation of SFO neurons using virally mediated expression of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) stimulated thirst and salt appetite. Male C57BL/6 mice (12-15 wk) received an injection of rAAV2-CaMKII-HA-hM3D(Gq)-IRES-mCitrine targeted at the SFO. Two weeks later, acute injection of clozapine N-oxide (CNO) produced dose-dependent increases in water intake of mice with DREADD expression in the SFO. CNO also stimulated the ingestion of 0.3 M NaCl. Acute injection of CNO significantly increased the number of Fos-positive nuclei in the SFO of mice with robust DREADD expression. Furthermore, in vivo single-unit recordings demonstrate that CNO significantly increases the discharge frequency of both ANG II- and NaCl-responsive neurons. In vitro current-clamp recordings confirm that bath application of CNO produces a significant membrane depolarization and increase in action potential frequency. In a final set of experiments, chronic administration of CNO approximately doubled 24-h water intake without an effect on salt appetite. These findings demonstrate that DREADD-induced activation of SFO neurons stimulates thirst and that DREADDs are a useful tool to acutely or chronically manipulate neuronal circuits influencing body fluid homeostasis.
Asunto(s)
Apetito/efectos de los fármacos , Drogas de Diseño/farmacología , Receptores Acoplados a Proteínas G/metabolismo , Cloruro de Sodio/metabolismo , Órgano Subfornical/efectos de los fármacos , Sed/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/genética , Angiotensina II/farmacología , Animales , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Clozapina/análogos & derivados , Clozapina/farmacología , Ingestión de Líquidos/efectos de los fármacos , Ingestión de Líquidos/genética , Humanos , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Neuronas/efectos de los fármacos , Proteínas Oncogénicas v-fos/metabolismo , Receptores Acoplados a Proteínas G/genética , Solución Salina Hipertónica/administración & dosificación , Órgano Subfornical/citologíaRESUMEN
Hydrogen sulfide (H2S) is an endogenously found gasotransmitter that has been implicated in a variety of beneficial physiological functions. This study was performed to investigate the cellular mechanisms underlying actions of H2S previously observed in subfornical organ (SFO), where H2S acts to regulate blood pressure through a depolarization of the membrane and an overall increase in the excitability of SFO neurons. We used whole cell patch-clamp electrophysiology in the voltage-clamp configuration to analyze the effect of 1 mM NaHS, an H2S donor, on voltage-gated potassium, sodium, and calcium currents. We observed no effect of NaHS on potassium currents; however, both voltage-gated sodium currents (persistent and transient) and the N-type calcium current had a depolarized activation curve and an enhanced peak-induced current in response to a series of voltage-step and ramp protocols run in the control and NaHS conditions. These effects were not responsible for the previously observed depolarization of the membrane potential, as depolarizing effects of H2S were still observed following block of these conductances with tetrodotoxin (5 µM) and ω-conotoxin-GVIA (100 nM). Our studies are the first to investigate the effect of H2S on a variety of voltage-gated conductances in a single brain area, and although they do not explain mechanisms underlying the depolarizing actions of H2S on SFO neurons, they provide evidence of potential mechanisms through which this gasotransmitter influences the excitability of neurons in this important brain area as a consequence of the modulation of multiple ion channels.
Asunto(s)
Sulfuro de Hidrógeno/metabolismo , Neuronas/metabolismo , Sodio/metabolismo , Órgano Subfornical/metabolismo , Canales de Sodio Activados por Voltaje/metabolismo , Potenciales de Acción , Animales , Calcio/metabolismo , Células Cultivadas , Masculino , Neuronas/efectos de los fármacos , Neuronas/fisiología , Ratas , Ratas Sprague-Dawley , Órgano Subfornical/citología , Órgano Subfornical/fisiología , Sulfuros/farmacologíaRESUMEN
The subfornical organ (SFO) is an important sensory circumventricular organ implicated in the regulation of fluid homeostasis and energy balance. We investigated whether the SFO is activated by the hormone cholecystokinin (CCK). CCK1 and CCK2 receptors were identified in the SFO by RT-PCR. Dissociated SFO neurons that responded to CCK (40/77), were mostly depolarized (9.2 ± 0.9 mV, 30/77), but some were hyperpolarized (-7.3 ± 1.1 mV, 10/77). We next examined the responses of SFO neurons in vivo to CCK (16 µg/kg ip), in the presence and absence of CCK1 or CCK2 receptor antagonists (devazepide; 600 µg/kg and L-365,260; 100 µg/kg, respectively), using the functional activation markers c-Fos and phosphorylated extracellular signal-related kinase (p-ERK). The nucleus of the solitary tract (NTS) served as a control for CCK-induced activity. There was a significant increase in c-Fos expression in the NTS (259.2 ± 20.8 neurons) compared with vehicle (47.5 ± 2.5). Similarly, in the SFO, c-Fos was expressed in 40.5 ± 10.6 neurons in CCK-treated compared with 6.6 ± 2.7 in vehicle-treated rats (P < 0.01). Devazepide significantly reduced the effects of CCK in the NTS but not in SFO. L-365,260 blocked the effects of CCK in both brain regions. CCK increased the number of p-ERK neurons in NTS (27.0 ± 4.0) as well as SFO (18.0 ± 4.0), compared with vehicle (8.0 ± 2.6 and 4.3 ± 0.6, respectively; P < 0.05). Both devazepide and L-365,260 reduced CCK-induced p-ERK in NTS, but only L-365,260 reduced it in the SFO. In conclusion, the SFO represents a novel brain region at which circulating CCK may act via CCK2 receptors to influence central autonomic control.
Asunto(s)
Colecistoquinina/farmacología , Fragmentos de Péptidos/farmacología , Órgano Subfornical/efectos de los fármacos , Animales , Benzodiazepinonas/farmacología , Devazepida/farmacología , Quinasas MAP Reguladas por Señal Extracelular/genética , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Regulación de la Expresión Génica/fisiología , Genes fos/genética , Genes fos/fisiología , Antagonistas de Hormonas/farmacología , Masculino , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Compuestos de Fenilurea/farmacología , ARN/genética , ARN/metabolismo , Ratas , Ratas Sprague-Dawley , Receptores de Colecistoquinina/antagonistas & inhibidores , Receptores de Colecistoquinina/genética , Receptores de Colecistoquinina/metabolismo , Órgano Subfornical/citología , Órgano Subfornical/fisiologíaRESUMEN
The blood-brain barrier (BBB) is a barrier that prevents free access of blood-derived substances to the brain through the tight junctions and maintains a specialized brain environment. Circumventricular organs (CVOs) lack the typical BBB. The fenestrated vasculature of the sensory CVOs, including the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO) and area postrema (AP), allows parenchyma cells to sense a variety of blood-derived information, including osmotic ones. In the present study, we utilized immunohistochemistry to examine changes in the expression of NG2 and platelet-derived growth factor receptor beta (PDGFRB) in the OVLT, SFO and AP of adult mice during chronic osmotic stimulation. The expression of NG2 and PDGFRB was remarkably prominent in pericytes, although these angiogenesis-associated proteins are highly expressed at pericytes of developing immature vasculature. The chronic salt loading prominently increased the expression of NG2 in the OVLT and SFO and that of PDGFRB in the OVLT, SFO and AP. The vascular permeability of low-molecular-mass tracer fluorescein isothiocyanate was increased significantly by chronic salt loading in the OVLT and SFO but not AP. In conclusion, the present study demonstrates changes in pericyte expression of NG2 and PDGFRB and vascular permeability in the sensory CVOs by chronic osmotic stimulation, indicating active participation of the vascular system in osmotic homeostasis.
Asunto(s)
Antígenos/metabolismo , Área Postrema/metabolismo , Permeabilidad Capilar , Hipotálamo/metabolismo , Pericitos/metabolismo , Proteoglicanos/metabolismo , Receptor beta de Factor de Crecimiento Derivado de Plaquetas/metabolismo , Órgano Subfornical/metabolismo , Animales , Antígenos/genética , Área Postrema/irrigación sanguínea , Área Postrema/citología , Células Endoteliales/citología , Células Endoteliales/metabolismo , Hipotálamo/irrigación sanguínea , Hipotálamo/citología , Ratones , Ratones Endogámicos C57BL , Osmorregulación , Pericitos/citología , Proteoglicanos/genética , Receptor beta de Factor de Crecimiento Derivado de Plaquetas/genética , Cloruro de Sodio/farmacología , Órgano Subfornical/irrigación sanguínea , Órgano Subfornical/citologíaRESUMEN
Apelin is an adipocyte-derived hormone involved in the regulation of water balance, food intake and the cardiovascular system partially through actions in the CNS. The subfornical organ (SFO) is a circumventricular organ with identified roles in body fluid homeostasis, cardiovascular control and energy balance. The SFO lacks a normal blood-brain barrier, and is thus able to detect circulating signalling molecules such as angiotensin II and leptin. In this study, we investigated actions of apelin-13, the predominant apelin isoform in brain and circulatory system, on the excitability of dissociated SFO neurons using electrophysiological approaches, and determined the cardiovascular consequences of direct administration into the SFO of anaesthetized rats. Whole cell current clamp recording revealed that bath-applied 100 nm apelin-13 directly influences the excitability of the majority of SFO neurons by eliciting either depolarizing (31.8%, mean 7.0 ± 0.8 mV) or hyperpolarizing (28.6%, mean -10.4 ± 1.8 mV) responses. Using voltage-clamp techniques, we also identified modulatory actions of apelin-13 on specific ion channels, demonstrating that apelin-13 activates a non-selective cationic conductance to depolarize SFO neurons while activation of the delayed rectifier potassium conductance underlies hyperpolarizing effects. In anaesthetized rats, microinjection of apelin into SFO decreased both blood pressure (BP) (mean area under the curve -1492.3 ± 357.1 mmHg.s, n = 5) and heart rate (HR) (-32.4 ± 10.39 beats, n = 5). Our data suggest that circulating apelin can directly affect BP and HR as a consequence of the ability of this peptide to modulate the excitability of SFO neurons.
Asunto(s)
Péptidos y Proteínas de Señalización Intercelular/farmacología , Neuronas/efectos de los fármacos , Órgano Subfornical/citología , Potenciales de Acción/efectos de los fármacos , Animales , Presión Sanguínea/efectos de los fármacos , Frecuencia Cardíaca/efectos de los fármacos , Técnicas In Vitro , Masculino , Potenciales de la Membrana/efectos de los fármacos , Microinyecciones , Neuronas/fisiología , Ratas , Ratas Sprague-Dawley , Órgano Subfornical/fisiologíaRESUMEN
The sensory circumventricular organs (CVOs) are specialized collections of neurons and glia that lie in the midline of the third and fourth ventricles of the brain, lack a blood-brain barrier, and function as chemosensors, sampling both the cerebrospinal fluid and plasma. These structures, which include the organum vasculosum of the lamina terminalis (OVLT), subfornical organ (SFO), and area postrema (AP), are sensitive to changes in sodium concentration but the cellular mechanisms involved remain unknown. Epithelial sodium channel (ENaC)-expressing neurons of the CVOs may be involved in this process. Here we demonstrate with immunohistochemical and in situ hybridization methods that ENaC-expressing neurons are densely concentrated in the sensory CVOs. These neurons become c-Fos activated, a marker for neuronal activity, after various manipulations of peripheral levels of sodium including systemic injections with hypertonic saline, dietary sodium deprivation, and sodium repletion after prolonged sodium deprivation. The increases seen c-Fos activity in the CVOs were correlated with parallel increases in plasma sodium levels. Since ENaCs play a central role in sodium reabsorption in kidney and other epithelia, we present a hypothesis here suggesting that these channels may also serve a related function in the CVOs. ENaCs could be a significant factor in modulating CVO neuronal activity by controlling the magnitude of sodium permeability in neurons. Hence, some of the same circulating hormones controlling ENaC expression in kidney, such as angiotensin II and atrial natriuretic peptide, may coordinate ENaC expression in sensory CVO neurons and could potentially orchestrate sodium appetite, osmoregulation, and vasomotor sympathetic drive.
Asunto(s)
Canales Epiteliales de Sodio/metabolismo , Hipotálamo/citología , Neuronas/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Sodio/farmacología , Órgano Subfornical/citología , Animales , Área Postrema/citología , Canales Epiteliales de Sodio/genética , Femenino , Inmunohistoquímica , Hibridación in Situ , Masculino , Proteínas Proto-Oncogénicas c-fos/genética , RatasRESUMEN
Recently, receptors for the calcium-regulating glycoprotein hormone stanniocalcin-1 (STC-1) have been found within subfornical organ (SFO), a central structure involved in the regulation of electrolyte and body fluid homeostasis. However, whether SFO neurons produce STC-1 and how STC-1 may function in fluid homeostasis are not known. Two series of experiments were done in Sprague-Dawley rats to investigate whether STC-1 is expressed within SFO and whether it exerts an effect on water intake. In the first series, experiments were done to determine whether STC-1 was expressed within cells in SFO using immunohistochemistry, and whether protein and gene expression for STC-1 existed in SFO using Western blot and quantitative RT-PCR, respectively. Cells containing STC-1 immunoreactivity were found throughout the rostrocaudal extent of SFO. STC-1 protein expression within SFO was confirmed with Western blot, and SFO was also found to express STC-1 mRNA. In the second series, microinjections (200 nl) of STC-1, ANG II, a combination of the two or the vehicle were made into SFO in conscious, unrestrained rats. Water intake was measured at 0700 for a 1-h period after each injection in animals. Microinjections of STC-1 (17.6 or 176 nM) alone had no effect on water intake compared with controls. However, STC-1 not only attenuated the drinking responses to ANG II for about 30 min, but also decreased the total water intake over the 1-h period. These data suggest that STC-1 within the SFO may act in a paracrine/autocrine manner to modulate the neuronal responses to blood-borne ANG II. These findings also provide the first direct evidence of a physiological role for STC-1 in central regulation of body fluid homeostasis.
Asunto(s)
Angiotensina II/farmacología , Ingestión de Líquidos/efectos de los fármacos , Glicoproteínas/farmacología , Glicoproteínas/fisiología , Órgano Subfornical/fisiología , Angiotensina II/administración & dosificación , Animales , Ingestión de Líquidos/fisiología , Glicoproteínas/administración & dosificación , Homeostasis/efectos de los fármacos , Homeostasis/fisiología , Masculino , Microinyecciones , Modelos Animales , Ratas , Ratas Sprague-Dawley , Órgano Subfornical/citología , Equilibrio Hidroelectrolítico/efectos de los fármacos , Equilibrio Hidroelectrolítico/fisiologíaRESUMEN
Circumventricular organs (CVOs) are specialized brain structures located around the third and fourth ventricles. They differ from the rest of the brain parenchyma in that they are highly vascularised areas that lack a blood-brain barrier. These neurohaemal organs are classified as "sensory", when they contain neurons that can receive chemical inputs from the bloodstream. This review focuses on the sensory CVOs to describe their unique structure, and their functional roles in the maintenance of body fluid homeostasis and cardiovascular regulation, and in the generation of central acute immune and febrile responses. In doing so, the main neural connections to visceral regulatory centres such as the hypothalamus, the medulla oblongata and the endocrine hypothalamic-pituitary axis, as well as some of the relevant chemical substances involved, are described. The CVOs are vulnerable to circulating pathogens and can be portals for their entry in the brain. This review highlights recent investigations that show that the CVOs and related structures are involved in pathological conditions such as sepsis, stress, trypanosomiasis, autoimmune encephalitis, systemic amyloidosis and prion infections, while detailed information on their role in other neurodegenerative diseases such as Alzheimer's disease or multiple sclerosis is lacking. It is concluded that studies of the CVOs and related structures may help in the early diagnosis and treatment of such disorders.
Asunto(s)
Encefalopatías/patología , Encefalopatías/fisiopatología , Ventrículos Cerebrales/citología , Ventrículos Cerebrales/fisiología , Células Receptoras Sensoriales/citología , Células Receptoras Sensoriales/fisiología , Animales , Área Postrema/irrigación sanguínea , Área Postrema/citología , Área Postrema/fisiología , Ventrículos Cerebrales/irrigación sanguínea , Humanos , Hipotálamo/irrigación sanguínea , Hipotálamo/fisiología , Órgano Subfornical/irrigación sanguínea , Órgano Subfornical/citología , Órgano Subfornical/fisiologíaRESUMEN
The control of water-intake behavior is critical for life because an excessive water intake induces pathological conditions, such as hyponatremia or water intoxication. However, the brain mechanisms controlling water intake currently remain unclear. We previously reported that thirst-driving neurons (water neurons) in the subfornical organ (SFO) are cholecystokinin (CCK)-dependently suppressed by GABAergic interneurons under Na-depleted conditions. We herein show that CCK-producing excitatory neurons in the SFO stimulate the activity of GABAergic interneurons via CCK-B receptors. Fluorescence-microscopic Ca2+ imaging demonstrates two distinct subpopulations in CCK-positive neurons in the SFO, which are persistently activated under hyponatremic conditions or transiently activated in response to water drinking, respectively. Optical and chemogenetic silencings of the respective types of CCK-positive neurons both significantly increase water intake under water-repleted conditions. The present study thus reveals CCK-mediated neural mechanisms in the central nervous system for the control of water-intake behaviors.
Asunto(s)
Conducta de Ingestión de Líquido/fisiología , Neuronas/fisiología , Órgano Subfornical/citología , Animales , Masculino , Ratones , Microscopía Fluorescente/métodos , Sodio/metabolismo , Órgano Subfornical/fisiologíaRESUMEN
The subfornical organ, a circumventricular structure of the central nervous system, has efferent neural projections to sites within the brain known to be involved in drinking behavior and secretion of antidiuretic hormone. By using anterograde tracing techniques, it is shown that the subfornical organ projects to the nucleus medians of the medial preoptic area, to the organum vasculosum of the lamina terminalis, and to the supraoptic nuclei bilaterally. Its efferent connectivity is confirmed by retrograde transport of horseradish peroxidase. The organum vasculosum of the lamina terminalis, another circumventricular organ and a suspected receptor site for angiotensin II, is involved in the circuitry of the subfornical organ and also has an efferent projection to the supraoptic nuclei.
Asunto(s)
Ventrículos Cerebrales/citología , Sistemas Neurosecretores/fisiología , Órgano Subfornical/fisiología , Equilibrio Hidroelectrolítico , Animales , Encéfalo/citología , Conducta de Ingestión de Líquido/fisiología , Vías Eferentes/fisiología , Masculino , Área Preóptica/citología , Ratas , Órgano Subfornical/citología , Núcleo Supraóptico/citologíaRESUMEN
For thirsty animals, fluid intake provides both satiation and pleasure of drinking. How the brain processes these factors is currently unknown. Here, we identified neural circuits underlying thirst satiation and examined their contribution to reward signals. We show that thirst-driving neurons receive temporally distinct satiation signals by liquid-gulping-induced oropharyngeal stimuli and gut osmolality sensing. We demonstrate that individual thirst satiation signals are mediated by anatomically distinct inhibitory neural circuits in the lamina terminalis. Moreover, we used an ultrafast dopamine (DA) sensor to examine whether thirst satiation itself stimulates the reward-related circuits. Interestingly, spontaneous drinking behavior but not thirst drive reduction triggered DA release. Importantly, chemogenetic stimulation of thirst satiation neurons did not activate DA neurons under water-restricted conditions. Together, this study dissected the thirst satiation circuit, the activity of which is functionally separable from reward-related brain activity.
Asunto(s)
Neuronas GABAérgicas/fisiología , Red Nerviosa/fisiología , Vías Nerviosas/fisiología , Saciedad/fisiología , Estómago/inervación , Órgano Subfornical/citología , Animales , Calcio/metabolismo , Dopamina/metabolismo , Ingestión de Líquidos/fisiología , Femenino , Péptido 1 Similar al Glucagón/metabolismo , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Óxido Nítrico Sintasa de Tipo I/genética , Óxido Nítrico Sintasa de Tipo I/metabolismo , Optogenética , Concentración Osmolar , Fragmentos de Péptidos/metabolismo , Estimulación FísicaRESUMEN
Central injection of hypocretins/orexins in rats induces water intake. As the subfornical organ (SFO) plays an important role in drinking behavior, hypocretins may excite SFO neurons. In this study, effects of hypocretins on SFO neurons were investigated electrophysiologically in slice preparations. In extracellular recordings, hypocretin-1 excited SFO neurons, but hypocretin-2 did not or it was little. After the block of synaptic inputs, the excitatory responses to hypocretin-1 remained, but some disappeared. In whole-cell patch-clamp recordings, hypocretin-1 reduced the frequencies of miniature inhibitory presynaptic currents with inward currents occasionally in SFO neurons, but hypocretin-2 did not. These results suggest that hypocretin-1 excites SFO neurons via the activation of hcrtR1 on premembranes and postmembranes.