RESUMEN
Hypothermia was induced in European hamsters (hibernators) and Wistar rats (nonhibernators), and changes in the firing rate and spike duration of extracellularly recorded action potentials were investigated in hypothalamic slices in vitro. At slice temperatures close to normal body temperature (37 +/- 3 degreesC), 32 and 57% of spontaneously active neurons in the medial preoptic area were classified as warm-sensitive in rats and hamsters, respectively. With decreasing slice temperature, the number of active neurons decreased progressively without a significant difference between rats and hamsters. At a slice temperature of 10 degreesC, 57% of all hypothalamic neurons in rats and 42% in hamsters were still spontaneously active. The average temperature at which activity ceased completely when the temperature was decreased further (the cut-off temperature) was 7.9 +/- 0.3 degreesC (n = 14) in rats but was significantly lower at 4.9 +/- 0.4 degreesC (n = 8) in hamsters (P < 0.001). Firing rates and temperature coefficients did not differ in their temperature dependence between rats and hamsters. Action potential duration increased with decreasing slice temperature in both species, but the increase in duration was significantly greater in rats.
Asunto(s)
Hibernación/fisiología , Hipotermia/fisiopatología , Neuronas/fisiología , Área Preóptica/fisiopatología , Potenciales de Acción , Animales , Regulación de la Temperatura Corporal/fisiología , Cricetinae , Técnicas In Vitro , Masculino , Ratas , Ratas Wistar , Especificidad de la Especie , TemperaturaRESUMEN
The depression of physiological processes characteristic of mammalian hibernation is precisely regulated by the central nervous system, especially by the neuropeptidergic apparatus of the hypothalamus. Because of inhibitory influences on neuronal circuits within the brain and suppressive effects on the metabolism via the endocrine axis, somatostatin has been implicated in the regulation of hibernation. The somatostatin system of the brain was investigated with immunocytochemistry, in situ hybridization, and radioimmunoassays in euthermic summer, euthermic winter, and hibernating European hamsters (Cricetus cricetus). Numerous somatostatin-immunoreactive perikarya were observed in the periventricular hypothalamic nucleus. The striatum, amygdala, and cortex contained only scattered immunoreactive perikarya. These entities also contained immunoreactive fiber profiles, although the highest density of immunoreactive fibers was found in the median eminence. Immunocytochemistry and radioimmunoassays showed that the number of somatostatin-immunoreactive perikarya and fibers and the content of somatostatin in the hypothalamus and the median eminence was conspicuously lower in euthermic winter animals than in euthermic summer animals. This decrease was more pronounced in hibernating specimens. In situ hybridization also demonstrated a decrease in the expression and synthesis rate of somatostatin in euthermic winter animals; again, this was even more dramatic in hibernating hamsters. These changes were less pronounced or non-significant in the extrahypothalamic somatostatin-immunoreactive perikarya and fiber systems, as shown by immunocytochemistry and radioimmunoassay, respectively.
Asunto(s)
Encéfalo/fisiología , Hibernación/fisiología , Hipófisis/fisiología , Somatostatina/análisis , Animales , Encéfalo/citología , Química Encefálica , Corteza Cerebral/fisiología , Cricetinae , Sistema Hipotálamo-Hipofisario/fisiología , Hipotálamo/fisiología , Inmunohistoquímica , Hibridación in Situ , Masculino , Especificidad de Órganos , Hipófisis/citología , Radioinmunoensayo , Estaciones del Año , Conducta Sexual Animal , Somatostatina/biosíntesisAsunto(s)
Regulación de la Temperatura Corporal , Tronco Encefálico/fisiología , Cricetinae/fisiología , Hibernación , Adenilil Ciclasas/metabolismo , Animales , Colforsina/farmacología , AMP Cíclico/metabolismo , Proteínas de Unión al GTP/metabolismo , Guanilil Imidodifosfato/farmacología , Receptores Adrenérgicos alfa 1/fisiología , Receptores Adrenérgicos beta/fisiología , Transducción de SeñalRESUMEN
Mammalian hibernation, an adaptation to survive harsh winter conditions, is one of the most prominent seasonal rhythmic processes exactly regulated on a low metabolic level. Diurnal variations in vegetative physiology are missing during hibernation; however, a precisely working diurnal system is mandatory for both the proper initiation and termination of the annual hibernation phase and the periodical arousal reactions. Biorhythms and the vegetative physiological processes connected with hibernation are, among others, controlled by hypothalamic noradrenaline systems. In this study, the density, binding capacity, and relative proportions of beta 1- and beta 2-adrenergic receptors (AR) within the hypothalamus of: 1) motorically inactive summer; 2) motorically active summer; 3) aroused, motorically active winter; and 4) deeply hibernating winter European hamsters (Cricetus cricetus) were studied. For further analysis of the beta-adrenergic signal transduction cascade, the activity of adenylyl cyclase (AC) was measured by formation of cAMP in controls, after stimulation of G proteins, or after forskolin stimulation without or in presence of manganese ions. While beta 1- and beta 2-AR subtypes were nearly equally abundant (50% beta 1:50% beta 2) in active summer, inactive summer, and hibernating hamsters, a significant redistribution in favor of beta 2-AR occurred after arousal (40% beta 1:60% beta 2). The activity of AC was much higher in active summer hamsters than in inactive summer, aroused winter, and hibernating winter hamsters. When AC was stimulated by guanylylimidophosphate [Gpp(NH)p], MnCl2, forskolin, or by forskolin in presence of MnCl2 instead of MgCl2, the potency to stimulate AC was found to show the following rank order: basal < Gpp(NH)p < MnCl2 < or = forskolin + MnCl2 < forskolin.
Asunto(s)
Ritmo Circadiano/fisiología , Cricetinae/fisiología , Hibernación/fisiología , Receptores Adrenérgicos beta 1/fisiología , Receptores Adrenérgicos beta 2/fisiología , Transducción de Señal/fisiología , 1-Metil-3-Isobutilxantina/farmacología , Adenilil Ciclasas/fisiología , Agonistas Adrenérgicos beta/farmacología , Antagonistas Adrenérgicos beta/farmacología , Animales , Nivel de Alerta/fisiología , Cloruros/farmacología , Ritmo Circadiano/efectos de los fármacos , Ritmo Circadiano/efectos de la radiación , Colforsina/farmacología , AMP Cíclico/biosíntesis , Activación Enzimática/efectos de los fármacos , Guanilil Imidodifosfato/farmacología , Hibernación/efectos de los fármacos , Hibernación/efectos de la radiación , Hipotálamo/efectos de los fármacos , Hipotálamo/fisiología , Imidazoles/farmacología , Luz , Masculino , Compuestos de Manganeso/farmacología , Propanolaminas/farmacología , Receptores Adrenérgicos beta 1/efectos de los fármacos , Receptores Adrenérgicos beta 2/efectos de los fármacos , Estaciones del Año , Transducción de Señal/efectos de los fármacosRESUMEN
This investigation of the relationship between cardiac beta-adrenoceptors and adenosine 3',5'-cyclic monophosphate (cAMP) formation in cardiac ventricles of the nocturnally active European hamster both during euthermia under a 12:12-h dark-light cycle and during hibernation under constant-darkness conditions showed that neither the densities, affinities, nor distribution of the beta 1- and beta 2-receptor subtypes differed between the dark phase, light phase, and hibernation. Basal formation of cAMP by the cardiac adenylyl cyclase of euthermic hamsters was higher in ventricles obtained at night [core temperature (Tcore) = 37.8 degrees C] than in ventricles obtained during the day (Tcore = 36.4 degrees C). Basal formation of cAMP was also significantly lower in hibernating hamsters (Tcore = 7.0 degrees C) than in euthermic hamsters. When adenylyl cyclase activity was stimulated by isoprenaline, guanylylimidodiphosphate [Gpp(NH)p], or forskolin, the rank order of potency was the same in euthermic hamsters and hibernating hamsters: isoprenaline < Gpp(NH)p < forskolin. Functional competition curves indicated that in the euthermic hamsters beta 1-receptors were responsible for 67% of the response to isoprenaline at night and 62% of the response during the day. In hibernating hamsters, in contrast, most of the response to isoprenaline (58%) was mediated via beta 2-receptors. This shift in the relative importance of the receptor subtypes may facilitate arousal from hibernation by making the heart more sensitive to circulating epinephrine.
Asunto(s)
Ritmo Circadiano , Cricetinae/fisiología , Sistema de Conducción Cardíaco/fisiología , Estaciones del Año , Transducción de Señal , Sistema Nervioso Simpático/fisiología , Adenilil Ciclasas/metabolismo , Animales , Colforsina/farmacología , AMP Cíclico/biosíntesis , Guanilil Imidodifosfato/farmacología , Hibernación , Isoproterenol/farmacología , Receptores Adrenérgicos beta/metabolismoRESUMEN
This study was concerned with the interactive effects of cold-induced vasodilatation, blockade of voltage-sensitive Ca2+ channels and sympathetic nerve stimulation in the nasal vascular bed of anesthetized dogs. To estimate the distribution of the internal maxillary artery blood flow to capillaries and to arteriovenous anastomoses (AVA), the microsphere technique in combination with electromagnetic flowmetry was used. Intraarterial infusion of verapamil resulted in a dose-dependent vasodilatation and a redistribution of the internal maxillary artery blood flow. Simultaneously applied electrical stimulation of the cervical sympathetic trunk resulted in a significant fall in blood flow, caused mainly by a decrease in capillary flow. Verapamil infusion combined with cold exposure led to a simultaneous elevation of the AVA and capillary flows. When electrical stimulation of the cervical sympathetic trunk was also applied, the AVA and capillary flows were affected in different manners, depending on the sequence of the stimulations. Analysis of capillary flow data in the various nasal and facial tissue compartments indicates that cold exposure, blockade of the voltage-dependent Ca2+ channels and an elevated sympathetic tone modify the local nutritive blood flow.
Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Arteria Maxilar/efectos de los fármacos , Nifedipino/farmacología , Vasodilatación/efectos de los fármacos , Verapamilo/farmacología , Animales , Anastomosis Arteriovenosa/efectos de los fármacos , Anastomosis Arteriovenosa/fisiología , Velocidad del Flujo Sanguíneo/efectos de los fármacos , Velocidad del Flujo Sanguíneo/fisiología , Bloqueadores de los Canales de Calcio/administración & dosificación , Capilares/efectos de los fármacos , Capilares/fisiología , Frío , Perros , Estimulación Eléctrica , Cara/irrigación sanguínea , Femenino , Infusiones Intraarteriales , Masculino , Arteria Maxilar/inervación , Arteria Maxilar/fisiología , Microesferas , Nifedipino/administración & dosificación , Nariz/irrigación sanguínea , Sistema Nervioso Simpático/efectos de los fármacos , Sistema Nervioso Simpático/fisiología , Vasodilatación/fisiología , Verapamilo/administración & dosificaciónRESUMEN
The effects of the intra-arterial infusion of ATP, ADP and AMP into the internal maxillary artery (IMA), which provides the blood supply to the nasal and forehead regions of the dog, were analyzed. Total blood flow and perfusion pressure measurements in the IMA after administration of each adenyl compound indicated dose-dependent and active vasodilatory responses that were restricted to the ipsilateral vessels. The rank order of potency was ADP > or = ATP > AMP. In order to determine the microcirculatory effects caused by ADP, the tracer microsphere technique combined with absolute blood flow measurement was used. Intra-arterial infusion of ADP in the range 1-200 nmol/min produced elevations in the IMA flow on the stimulated side that ranged between 11 and 74%. The responses to low doses of ADP were mainly confined to the capillaries (CAP), whereas the arteriovenous anastomoses too were sensitive to high doses. The relative contributions of the anatomically and functionally different compartments of the forehead and nose to ADP-produced relaxations of the CAP were dependent upon their location. The CAP flows in the tissues which play a crucial role in conditioning the inspired air increased significantly, while the compartments of the furred surfaces were less sensitive to ADP. The results suggest that, since ATP, ADP and AMP are effective vasodilatory agents in all the regions examined, purines could have a regulatory or modulatory role in the complex vascular regulation of the nasal and forehead regions.
Asunto(s)
Adenosina Difosfato/farmacología , Adenosina Monofosfato/farmacología , Adenosina Trifosfato/farmacología , Cara/irrigación sanguínea , Nariz/irrigación sanguínea , Animales , Perros , Relación Dosis-Respuesta a Droga , Femenino , Inyecciones Intraarteriales , Masculino , Arteria Maxilar/efectos de los fármacos , Microcirculación/efectos de los fármacos , Microesferas , Flujo Sanguíneo Regional/efectos de los fármacosRESUMEN
The effects of the close arterial infusion of histamine upon the microcirculation of facial and nasal tissues were examined in dogs. Blood flow through arteriovenous anastomoses (AVA flow), capillaries (CAP flow) and collaterals (COL flow) were determined by electromagnetic flowmetry and the tracer-microsphere technique following an infusion of histamine at doses ranging from 0.5 to 50 nmol/min. Low doses of histamine (0.5-5.0 nmol/min) resulted in an increase in blood flow through the ipsilateral internal maxillary artery (IMA), which could be mainly attributed to a significant elevation of the CAP flow. A concomitant marked increase in AVA flow was observed only after the administration of higher doses (20-50 nmol/min). Significant changes in systemic blood pressure, heart rate and cardiac output occurred only after the infusion of histamine at doses of 20 and 50 nmol/min. Significant increases in the CAP flow of tissues with relatively low perfusion were observed after the infusion of histamine at lower doses. The CAP flow of structures which play an essential role in conditioning the inspired air and exhibit high perfusion rates under control conditions exhibited significant increases only after the administration of higher doses. The present experiments provide direct evidence for a dose-dependent vasodilatory effect of histamine on different microcirculatory compartments of cutaneous and mucosal vascular beds supplied by the IMA in the dog. The results indicate that at low blood histamine levels, an increase in CAP flow predominates, and at higher doses, both elevated CAP flow and elevated AVA flow contribute to the vasodilatory response to histamine.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Cara/irrigación sanguínea , Histamina/farmacología , Mucosa Nasal/irrigación sanguínea , Nariz/irrigación sanguínea , Animales , Presión Sanguínea/efectos de los fármacos , Gasto Cardíaco/efectos de los fármacos , Perros , Relación Dosis-Respuesta a Droga , Femenino , Frecuencia Cardíaca/efectos de los fármacos , Masculino , Microcirculación/efectos de los fármacos , Microesferas , Mucosa Nasal/efectos de los fármacosRESUMEN
Eighteen beagles were chronically instrumented with an anterior third ventricular (A3V) infusion device to analyze, in conscious dogs, the involvement of central atrial natriuretic peptide (ANP) in body fluid and blood pressure control. The dogs' osmotic and body fluid homeostasis was challenged by 24 h water deprivation or blood withdrawal (12 ml/kg body wt) to elucidate possible modifying influences on the release of arginine vasopressin (AVP), angiotensin II (ANG II), and drinking. Three series of experiments were performed: 1) infusion of ANP (500 ng/min) dissolved in artificial cerebrospinal fluid (aCSF) and given for 10 min, 2) infusion of aCSF alone for the same length of time, and 3) time control experiments without infusion. Plasma AVP and ANG II were analyzed by radioimmunoassay, and in several experiments on dehydrated dogs, plasma norepinephrine and epinephrine were additionally determined by high-performance liquid chromatography. Various blood parameters and rectal and ear skin temperatures were measured. Arterial pressure and heart rate were recorded in three animals additionally equipped with carotid loops. Changes in plasma AVP and ANG II induced by dehydration and bleeding were not significantly modified by A3V infusions of ANP and aCSF in comparison to time controls. Blood pressure changes were similar in experiments with A3V ANP infusion and time controls during bleeding and reinfusion. It is concluded that central ANP is not important in the control of vasopressin and renin-angiotensin systems during osmotic and volume challenges in conscious dogs.
Asunto(s)
Factor Natriurético Atrial/farmacología , Volumen Sanguíneo , Encéfalo/fisiología , Deshidratación/fisiopatología , Animales , Temperatura Corporal , Deshidratación/sangre , Perros , Electrólitos/sangre , Femenino , Masculino , Concentración Osmolar , Equilibrio HidroelectrolíticoRESUMEN
The potency of parasympathetic vasomotor efferent nerves in controlling blood flow of the face and nose was indicated by the following features attributed to the maxillary artery and their vascular compartments in dogs. Electrical stimulation of the vidian nerve induced a frequency-dependent increase in maxillary flow, which was due to a significant decrease in resistance to flow in nutrient and shunt vessels. Pronounced increases in perfusion rates mainly occurred in evaporative tissues of the nose, in particular the naso-maxilloturbinates and alar fold during vidian nerve stimulation, while those, for example, of the skin remained unchanged. Adrenergic and subsequent cholinergic blockade left the response pattern of maxillary flow to vidian nerve stimulation basically unaffected. Both nutrient and shunt flows contributed to the parasympathetically induced increases in maxillary flow while responses were compartmentalized similar to that found in untreated animals. Apart from sympathetic vasoconstrictor inputs, these results show that cholinergic and non-cholinergic parasympathetic vasodilator inputs contribute to the adjustment of vasomotor tone in the maxillary vascular bed.
Asunto(s)
Cara/irrigación sanguínea , Mucosa Nasal/irrigación sanguínea , Sistema Nervioso Parasimpático/fisiología , Animales , Resistencia Capilar , Perros , Estimulación Eléctrica , Cara/inervación , Arteria Maxilar/fisiología , Flujo Sanguíneo RegionalRESUMEN
Total blood flow and perfusion pressure (PP) of the internal maxillary artery (IMA) were recorded bilaterally during electrical stimulation (8 V, 2ms) of the right cervical sympathetic nerve at frequencies (f) of 0.3, 0.5, 1.0 and 3.0 Hz in anesthetized, paralyzed and artificially ventilated dogs. Distribution of IMA-FLOW to precapillaries (CAP-FLOW) and arteriovenous anastomoses (AVA-FLOW) was determined by the tracer microspheres technique. During electrical stimulation (ES) IMA-FLOW was affected only unilaterally and decreased in a hyperbola-like fashion with the increase of f, while contralateral IMA-FLOW remained unchanged. Systemic blood pressure as well as PP of both IMA remained unchanged while heart rate was only increased during ES at maximal f. The reduction of IMA-FLOW was mainly due to marked vasoconstrictor responses of the AVAs, which were already attained at low f while significant vasoconstrictor responses of precapillaries occurred at higher f and were less pronounced. The early response of AVAs to increasing sympathetic activation enables IMA-FLOW to be adjusted in a physiological range of sympathetic activities, before CAP-FLOW is substantially reduced. The predominance of AVA-FLOW in blood flow control of the IMA was also supported by the conformity in their hyperbolic relationship with maxillary resistance at rest and during enhanced levels of sympathetic vasoconstrictor activity.
Asunto(s)
Anastomosis Arteriovenosa/fisiología , Cara/irrigación sanguínea , Arteria Maxilar/inervación , Nariz/irrigación sanguínea , Sistema Nervioso Simpático/fisiología , Animales , Velocidad del Flujo Sanguíneo , Presión Sanguínea , Capilares/fisiología , Perros , Estimulación Eléctrica , Arteria Maxilar/fisiología , Resistencia VascularRESUMEN
Lingual blood flow and its distribution were determined at rest and in response to local cooling of the tongue (32 degrees C) in 6 anaesthetized, paralyzed and artificially ventilated dogs before and after two intraarterial (i.a.) injections of capsaicin (2.5 mg) at an interval of about 40 min. In 3 dogs, the same protocol was performed after degeneration of the chorda-lingual and glossopharyngeal nerves due to prior transection. In general the first i.a. injection of capsaicin resulted in a marked and the second injection in a smaller decrease of lingual blood flow. Local cooling of the tongue induced significant increases in lingual blood flow before as well as after capsaicin treatment, regardless of whether sensory innervation was intact or degenerated. In both the untreated and capsaicin treated dogs the increase in lingual blood flow during local cooling of the tongue was solely due to an increase in blood flow through the arteriovenous anastomoses, while blood flow through the capillaries of the mucosa and muscles even decreased. The findings suggest that capsaicin-induced vasoconstriction of the tongue vessels is due to a direct effect on vascular receptors. It is further suggested that cold vasodilatation of the canine tongue is not mediated by axon collaterals releasing substance P. Direct thermal effects on the intramural ganglia and the postganglionic vasomotor efferents innervating the AVAs, or on AVAs basal tone itself are suggested as the underlying mechanism.
Asunto(s)
Capsaicina/farmacología , Lengua/irrigación sanguínea , Vasodilatación/efectos de los fármacos , Animales , Anastomosis Arteriovenosa/efectos de los fármacos , Anastomosis Arteriovenosa/inervación , Frío , Desnervación , Perros , Microcirculación/efectos de los fármacos , Flujo Sanguíneo Regional/efectos de los fármacos , Lengua/efectos de los fármacos , Lengua/inervaciónRESUMEN
A technique of reversible cold blockade was applied in decerebrate and vagotomized rabbits that were immobilized and artificially ventilated to study the modulation of spontaneous respiratory rhythms. Respiratory discharges were recorded from vagal and phrenic efferents before and during cold blockade at the second cervical segment (C2) with a coolant-circulated thermode (-15 degrees C). Measurement of the cooling profile demonstrated that there was significant hypothermia in the regions of the phrenic nucleus (+25 degrees C) and obex of the medulla (+26 degrees C). Arterial pressure was maintained by continual norepinephrine infusion, end-tidal carbon dioxide tension was held at hypercapnic levels, and rectal temperature was regulated near 38 degrees C. The cold blockade of descending respiratory drives to the cervical phrenic nucleus inhibited the spontaneous activity in the phrenic nerve for more than 90 min. Phrenic activity could be induced by the intravenous injection of strychnine, but not doxapram, although this was not of respiratory quality. These results show that in the absence of descending and pharmacologic drives, but in the presence of phrenic hypothermia, spinalized rabbits are incapable of generating rhythmic patterns of discharge. C2 cold blockade also significantly slowed the spontaneous central respiratory rhythm with no change in integrated vagal amplitude, presumably due to a direct cooling effect on brainstem oscillators for breathing.
Asunto(s)
Bloqueo Nervioso , Nervio Frénico/fisiología , Respiración , Médula Espinal/fisiología , Nervio Vago/fisiología , Animales , Gatos , Frío , Estado de Descerebración/fisiopatología , Doxapram/farmacología , Vías Eferentes/efectos de los fármacos , Vías Eferentes/fisiología , Masculino , Nervio Frénico/efectos de los fármacos , Conejos , Respiración/efectos de los fármacos , Médula Espinal/efectos de los fármacos , Estricnina/farmacología , Nervio Vago/efectos de los fármacosAsunto(s)
Regulación de la Temperatura Corporal , Mamíferos/fisiología , Lengua/irrigación sanguínea , Animales , Tiempo de Circulación Sanguínea , Velocidad del Flujo Sanguíneo , Tronco Encefálico/fisiología , Hipotálamo/fisiología , Neurotransmisores/fisiología , Consumo de Oxígeno , Sistema Nervioso Parasimpático/fisiología , Sistema Nervioso Simpático/fisiología , Lengua/metabolismo , Lengua/fisiología , Sistema Vasomotor/fisiologíaRESUMEN
The brain stem of anesthetized, immobilized and artificially ventilated dogs was probed with concentric bipolar electrodes, and those points were determined from which vasodilation or vasoconstriction of the nose and tongue could be elicited by electrical stimulation of the brain stem (ESB). Blood flow was measured with electromagnetic flowprobes in the lingual (LA) and the infraorbital (IA) arteries. Arterial blood pressure, heart rate and temperatures of the ear and hindlimb were measured. The following results were obtained: (1) vasodilatation by ESB in the LA and/or IA could be induced from an area extending parasagittally through the ventral part of the brain stem from the hypothalamus to the upper pontine region. The most potent area was in the supraoptic area of the anterior hypothalamus, but no representation was found in the dorsolateral part of the central gray matter, one of the most excitable mesencephalic vasodilatator areas in the defence reaction. Sites in which ESB was followed by vasoconstriction in LA and IA were distributed in regions closely related to the dilatator sites within the brain stem; (2) the vasodilatation in LA and IA was not correlated with changes in skin temperatures of the ear and hindlimb; (3) blood pressure and heart rate decreased, in general, during ESB; (4) the additional analysis revealed that vasodilatation by ESB; (a) was not altered by atropine; (b) was abolished by transection of the cervical vagosympathetic trunk only in IA; (c) was abolished by spinal cord transection at C2 only in IA; and (d) was abolished only in IA by either preceding catecholamine depletion with reserpine or by blockade of alpha-adrenergic receptors with phenoxybenzamine, and disappeared in both LA and IA after ganglionic blockade with hexamethonium; (5) the results demonstrate circumscribed vasoconstrictor as well as vasodilatator sites in the brain stem influencing nose and tongue blood flow. The centrally elicited atropine resistant vasomotor responses of the nose are mediated by adrenergic fibres, which are conducted in the cervical sympathetic trunk. In contrast, the centrally elicited vasodilatation of the tongue is due to non-adrenergic, non-cholinergic efferents with pre- and postganglionic synapses running apart from the cervical sympathetic trunk. The anatomical origin of these efferents suggests that they belong to the parasympathetic section of the autonomic nervous system.
Asunto(s)
Fibras Adrenérgicas/fisiología , Tronco Encefálico/fisiología , Nariz/irrigación sanguínea , Lengua/irrigación sanguínea , Vasodilatación , Animales , Arterias/inervación , Regulación de la Temperatura Corporal , Mapeo Encefálico , Perros , Hipotálamo/fisiología , Vías Nerviosas/fisiología , Médula Espinal/fisiología , Nervio Vago/fisiología , VasoconstricciónRESUMEN
Membrane potential trajectories were quantitatively assessed during the burst phase of cat phrenic motoneuron discharges. During burst progression the after-hyperpolarization shifted in the depolarizing direction with little change in spike threshold. Argument is made that these results constitute indirect evidence for the accumulation of potassium ions in the extracellular space of the phrenic motoneuron pool. Functional consequences regarding cell synchronization and recruitment are also discussed.
Asunto(s)
Neuronas Motoras/fisiología , Nervio Frénico/fisiología , Potenciales de Acción , Vías Aferentes/fisiología , Animales , Gatos , Cinética , Potenciales de la Membrana , Potasio/metabolismoRESUMEN
In anesthetized dogs total tongue blood flow and its distribution to mucosa and muscle capillaries and to arteriovenous anastomoses (AVA) was determined by combining venous outflow measurements with the radioactive microsphere technique. Local temperature changes of the tongue surface in the physiological range revealed an inverse relationship between lingual blood flow (8.6--30.4 ml . min-1) and tongue surface temperature (40.5 to 27.7 degrees C). The temperature dependent changes of tongue blood flow were exclusively due to changes of AVA blood flow (6.3--21.4 ml . min-1).
Asunto(s)
Frío , Perros/fisiología , Lengua/irrigación sanguínea , Vasodilatación , Animales , Anastomosis Arteriovenosa/fisiología , Capilares/fisiología , Flujo Sanguíneo RegionalRESUMEN
Blood flow in vessels running to the nose and tongue was measured with electromagnetic flowmeters in anaesthetized dogs. In initial experiments the effect of electrical stimulation of the stellate ganglion on blood flow to the nose and tongue was studied and suitable doses of antagonist drugs to adrenergic and cholinergic receptors determined. In subsequent experiments the effect of receptor blockade on blood flow response was examined in animals subjected to hypothalamic heating at different body temperatures induced by whole body warming. It was found that heat load provoked an increase in blood flow to the nose which was due to a decrease in the activity of nerves supplying alpha adrenergic receptors. The heat induced vasodilatation observed in the tongue occurred by the same mechanism as in the nose when the thermal load was small and respiration rate was not increased from resting levels. However, when the thermal load was greater and panting was induced, a secondary "active" component became evident, and this was mediated neither by adrenergic nor cholinergic muscarinic receptors. Fibres responsible for this active vasodilatation to the tongue were postganglionic and ran apart from the vagosympathetic trunk.
Asunto(s)
Calor , Nariz/irrigación sanguínea , Lengua/irrigación sanguínea , Vasodilatación , Animales , Temperatura Corporal , Perros , Estimulación Eléctrica , Hipotálamo/fisiología , Parasimpatolíticos/farmacología , Ganglio Estrellado/fisiología , Simpaticolíticos/farmacologíaRESUMEN
1. The effects of increased ambient temperature (Ta) on blood-flow and -temperatures of the tongue were studied in the unanaesthetized dog. At Ta of 20 degrees C and a relative humidity (rh) of 30% the mean lingual blood flow was 11 ml-min-1 (0.15 ml-g-1-min-1) and the temperature difference between the lingual artery and vein (deltaTLAV) was 1.0 degrees C. Accordingly, a heat loss of 48.6 J-min-1 was calculated even for the dog breathing with the mouth closed. When Ta was elevated to 38 degrees C at constant rh, panting ensued. In parallel fashion lingual blood flow increased to 60.4 ml-min-1 (0.81 ml-g-1-min-1) in mean and to 74.7 ml-min-1 (0.99 ml-g-1-min-1) at peak rate of thermal tachypnoea (272 breaths-min-1). This flow increase resulted from a decrease in the local vascular resistance since the driving systemic pressure remained constant. It was accompanied by an increase in TLAV to 1.5 degrees C equivalent to a heat loss of 400.7J-min-1 in mean and 496.2J-min-1 at maximum respiratory rate. 2. The preoptic/anterior hypothalamic (PO/AH) region was heated with a water perfused thermode in urethane anaesthetized dogs at constant body temperature in order to study the relationship in time between the increase in lingual blood flow and the onset of thermal panting. Lingual blood flow was found to be 20 ml-min-1 at a respiratory rate of 60 breaths/min. During hypothalamic heating both respiratory rate and lingual blood flow increased markedly. At maximum respiratory rates (244 breaths-min-1) lingual blood flow reached a level of 60 ml-min-1. When perfusion of the thermode was stopped, both respiratory rate and lingual blood flow synchronously returned to control values within 5 min. Similar changes did not occur in dogs in which a ventilatory response failed to be elicited during hypothalamic heating. 3. The results suggest that the tongue contributes to the evaporative heat loss mechanism and they confirm the concept that panting, associated with increased lingual blood flow, is induced by a common autonomic outflow pattern which is mediated by the central mechanism controlling thermal homeostasis.