Nonuniformity of sympathetic nerve activity to the skin and kidney

Facial skin blood flow responses during exposures to emotionally charged movies

The changes in regional facial skin blood flow and vascular conductance have been assessed for the first time with noninvasive two-dimensional laser speckle flowmetry during audiovisually elicited emotional challenges for 2 min (comedy, landscape, and horror movie) in 12 subjects. Limb skin blood flow and vascular conductance and systemic cardiovascular variables were simultaneously measured. The extents of pleasantness and consciousness for each emotional stimulus were estimated by the subjective rating from -5 (the most unpleasant; the most unconscious) to +5 (the most pleasant; the most conscious). Facial skin blood flow and vascular conductance, especially in the lips, decreased during viewing of comedy and horror movies, whereas they did not change during viewing of a landscape movie. The decreases in facial skin blood flow and vascular conductance were the greatest with the comedy movie. The changes in lip, cheek, and chin skin blood flow negatively correlated (P < 0.05) with the subjective ratings of pleasantness and consciousness. The changes in lip skin vascular conductance negatively correlated (P < 0.05) with the subjective rating of pleasantness, while the changes in infraorbital, subnasal, and chin skin vascular conductance negatively correlated (P < 0.05) with the subjective rating of consciousness. However, none of the changes in limb skin blood flow and vascular conductance and systemic hemodynamics correlated with the subjective ratings. The mental arithmetic task did not alter facial and limb skin blood flows, although the task influenced systemic cardiovascular variables. These findings suggest that the more emotional status becomes pleasant or conscious, the more neurally mediated vasoconstriction may occur in facial skin blood vessels.

Perinatal taurine exposure programs patterns of autonomic nerve activity responses to tooth pulp stimulation in adult male rats

Perinatal taurine excess or deficiency influences adult health and disease, especially relative to the autonomic nervous system. This study tests the hypothesis that perinatal taurine exposure influences adult autonomic nervous system control of arterial pressure in response to acute electrical tooth pulp stimulation. Female Sprague-Dawley rats were fed with normal rat chow with 3% β-alanine (taurine depletion, TD), 3% taurine (taurine supplementation, TS), or water alone (control, C) from conception to weaning. Their male offspring were fed with normal rat chow and tap water throughout the experiment. At 8-10 weeks of age, blood chemistry, arterial pressure, heart rate, and renal sympathetic nerve activity were measured in anesthetized rats. Age, body weight, mean arterial pressure, heart rate, plasma electrolytes, blood urea nitrogen, plasma creatinine, and plasma cortisol were not significantly different among the three groups. Before tooth pulp stimulation, low- (0.3-0.5 Hz) and high-frequency (0.5-4.0 Hz) power spectral densities of arterial pressure were not significantly different among groups while the power spectral densities of renal sympathetic nerve activity were significantly decreased in TD compared to control rats. Tooth pulp stimulation did not change arterial pressure, heart rate, renal sympathetic nerve, and arterial pressure power spectral densities in the 0.3-4.0 Hz spectrum or renal sympathetic nerve firing rate in any group. In contrast, perinatal taurine imbalance disturbed very-low-frequency power spectral densities of both arterial pressure and renal sympathetic nerve activity (below 0.1 Hz), both before and after the tooth pulp stimulation. The power densities of TS were most sensitive to ganglionic blockade and central adrenergic inhibition, while those of TD were sensitive to both central and peripheral adrenergic inhibition. The present data indicate that perinatal taurine imbalance can lead to aberrant autonomic nervous system responses in adult male rats.

Differential control of efferent sympathetic activity revisited

This article reviews 40 years of research (1970-2010) into the capability of the efferent sympathetic nervous system to display differential responsiveness. Discovered first were antagonistic changes of activity in sympathetic filaments innervating functionally different sections of the cardiovascular system in response to thermal stimulation. During the subsequent four decades of investigation, a multitude of differential sympathetic efferent response patterns were identified, ranging from opposing activity changes at the level of multi-fiber filaments innervating different organs to the level of single fibers controlling functionally different structures in the same organ. Differential sympathetic responsiveness was shown to be displayed in response to exogenous or artificial stimulation of afferent sensory fibers transmitting particular exogenous stimuli, especially those activating peripheral nociceptors. Moreover, sympathetic differentiation was found to be characteristic of autonomic responses to environmental changes by which homeostasis in the broadest sense would be challenged. Heat or cold loads or their experimental equivalents, altered composition of inspired air or changes in blood gas composition, imbalances of body fluid control, and exposure to agents challenging the immune system were shown to elicit differential efferent sympathetic response patterns which often displayed a high degree of specificity. In summary, autonomic adjustments to changes of biometeorological parameters may be considered as representative of the capability of the sympathetic nervous system to exert highly specific efferent control of organ functions by which bodily homeostasis is maintained.

Sympathetic nervous system overactivity and its role in the development of cardiovascular disease

This review examines how the sympathetic nervous system plays a major role in the regulation of cardiovascular function over multiple time scales. This is achieved through differential regulation of sympathetic outflow to a variety of organs. This differential control is a product of the topographical organization of the central nervous system and a myriad of afferent inputs. Together this organization produces sympathetic responses tailored to match stimuli. The long-term control of sympathetic nerve activity (SNA) is an area of considerable interest and involves a variety of mediators acting in a quite distinct fashion. These mediators include arterial baroreflexes, angiotensin II, blood volume and osmolarity, and a host of humoral factors. A key feature of many cardiovascular diseases is increased SNA. However, rather than there being a generalized increase in SNA, it is organ specific, in particular to the heart and kidneys. These increases in regional SNA are associated with increased mortality. Understanding the regulation of organ-specific SNA is likely to offer new targets for drug therapy. There is a need for the research community to develop better animal models and technologies that reflect the disease progression seen in humans. A particular focus is required on models in which SNA is chronically elevated.

Methods of analysis and physiological relevance of rhythms in sympathetic nerve discharge

1. Like virtually all other physiological control systems, the sympathetic nervous system controlling cardiovascular function is characterized by the presence of rhythmic activity. Despite the prevalence of rhythms, their function is often not obvious, which leads to the question, what can one learn about the neural control of autonomic function by studying sympathetic nervous system rhythms? 2. Sympathetic nerve discharge (SND) is characterized by a mixture of periodicities ranging between approximately 0.04 and 10 Hz, depending on the physiological conditions, type of nerve being analysed and the species. The present article illustrates why frequency domain (power density spectral) analysis is more suitable than time domain (autocorrelation) analysis to quantify a complex signal (i.e. one with multiple frequency components) such as SND. 3. The present article entertains the possibilities that rhythmic activity may lead to more effective activation of sympathetic neurons than randomly occurring activity, that rhythmicity is important for coordinating activity in different sympathetic nerves and in formulating complex cardiovascular response patterns and that sympathetic rhythmicity may help maintain homeostasis.

Problems, possibilities, and pitfalls in studying the arterial baroreflexes’ influence over long-term control of blood pressure

While there is no disputing the critical role of baroreflexes in buffering rapid changes in arterial pressure, their role in long-term pressure control has become an area of controversy. Recent experiments using novel techniques have challenged the traditional view that arterial baroreflexes are not involved in setting chronic arterial pressure levels. Resetting of the arterial baroreflex, often used as an argument against the arterial baroreflex playing a role in long-term pressure control is rarely complete. The arterial baroreflex is just one of the many neural, hormonal, and intrinsic mechanisms involved in arterial pressure control and while the removal of the arterial baroreflex alone has little effect on mean arterial pressure it is too simplistic to suggest that the baroreflex has no role in long-term pressure control. Renal sympathetic nerve activity appears to be particularly resistant to resetting in response to ANG II-induced hypertension. Given the important role of the kidneys in long-term pressure control, we suggest there is a clear need to develop experimental techniques whereby sympathetic nerve activity to the kidneys and other organs can be monitored over periods of weeks to months.

What sets the long-term level of sympathetic nerve activity: is there a role for arterial baroreceptors?

Much of our knowledge of the influence of the sympathetic nervous system on the control of blood pressure is built on experimental approaches that focus very much on time scales <24 h. Although direct recordings of sympathetic nerve activity (SNA) over short time scales provide important information, it is difficult to place their relevance over the longer term where the development of chronic changes in blood pressure are likely to be a mixture of hormonal, renal, and neural influences. Recently new experimental approaches are now revealing a possible role for arterial baroreceptors in the chronic regulation of SNA. These studies reveal that chronic increases in blood pressure are associated with chronic changes in SNA that may be due to nonresetting of the blood pressure-SNA baroreflex relationship. This review discusses the implications of such information, highlighting new technologies for long-term recording of SNA that appear to hold much promise for revealing the role of SNA to the kidney for the long-term control of blood pressure.

Involvement of sympathetic nerve activity in skin blood flow oscillations in humans

We have used the wavelet transform to evaluate the time-frequency content of laser-Doppler flowmetry (LDF) signals measured simultaneously on the surfaces of free microvascular flaps deprived of sympathetic nerve activity (SNA), and on adjacent intact skin, in humans. It was thereby possible to determine the frequency interval within which SNA manifests itself in peripheral blood flow oscillations. The frequency interval from 0.0095 to 2 Hz was examined and was divided into five subintervals: I, approximately 0.01 Hz; II, approximately 0.04 Hz; III, approximately 0.1 Hz; IV, approximately 0.3 Hz; and V, approximately 1 Hz. The average value of the LDF signal in the time domain as well as the mean amplitude and total power in the interval from 0.0095 to 2 Hz and amplitude and power within each of the five subintervals were significantly lower for signals measured on the free flap (P < 0.002). The normalized spectral amplitude and power in the free flap were significantly lower in only two intervals: I, from 0.0095 to 0.021 Hz; and II, from 0.021 to 0.052 Hz (P < 0.05); thus indicating that SNA is manifested in at least one of these frequency intervals. Because interval I has recently been shown to be the result of vascular endothelial activity, we conclude that we have identified SNA as influencing blood flow oscillations in normal tissues with repetition times of 20-50 s or frequencies of 0.02-0.05 Hz.

Rhythmic activities of the sympatho-excitatory neurons in the medulla of rabbits: neurons controlling cutaneous vasomotion

Spontaneous activities of the reticulospinal neurons in the reticular formation of the rostroventral medulla, of the ear sympathetic nerve (ESNA) and of the renal sympathetic nerve (RSNA) were analyzed with regard to cardiac cycle- and respiration-related rhythm in the anesthetized, vagotomized and immobilized rabbits. A reticulospinal neuron that was concurrently excited with increase in the ESNA and/or reduction of the blood flow of the ear skin by electrical stimulation of the dorsomedial hypothalamus was tentatively named as a cutaneous sympatho-excitatory neuron (Cu neuron). More than half of the Cu neurons (13/22) had a respiration-related rhythmic activity as well as the ESNA. Activity of most of the Cu neurons (19/22) was not modulated with the frequency of the heartbeat and the ESNA had little or no cardiac cycle-related activity. Simultaneous recording shows that the degree of modulation (relative power of the power spectrum of the post event time histogram at the frequency of the respiration) of activity of the Cu neurons correlated with that of the ESNA. On the other hand, most (13/18) of the barosensitive sympatho-excitatory reticulospinal neurons in the rostral ventrolateral medulla (RVLM neurons) had both cardiac cycle- and respiration-related activity as well as the RSNA had. The Cu neurons were located at the medial sites to the location of the RVLM neurons. These results further showed that the Cu neurons controlled the cutaneous vasoconstrictor fibers and that the sympatho-excitatory neurons were located at the different sites in the ventral medulla according to their function.

Differential control of sympathetic outflow

With advances in experimental techniques, the early views of the sympathetic nervous system as a monolithic effector activated globally in situations requiring a rapid and aggressive response to life-threatening danger have been eclipsed by an organizational model featuring an extensive array of functionally specific output channels that can be simultaneously activated or inhibited in combinations that result in the patterns of autonomic activity supporting behavior and mediating homeostatic reflexes. With this perspective, the defense response is but one of the many activational states of the central autonomic network. This review summarizes evidence for the existence of tissue-specific sympathetic output pathways, which are likely to include distinct populations of premotor neurons whose target specificity could be assessed using the functional fingerprints developed from characterizations of postganglionic efferents to known targets. The differential responses in sympathetic outflows to stimulation of reflex inputs suggest that the circuits regulating the activity of sympathetic premotor neurons must have parallel access to groups of premotor neurons controlling different functions but that these connections vary in their ability to influence different sympathetic outputs. Understanding the structural and physiological substrates antecedent to premotor neurons that mediate the differential control of sympathetic outflows, including those to noncardiovascular targets, represents a challenge to our current technical and analytic approaches.

T (tail)-rhythm oscillators: principles of nervous control of the vasculature revealed?

This review focuses on the nervous control of the caudal ventral artery of the rat tail, and aims to convince the reader that sympathetic control of the vasculature can be mediated via neural oscillators intrinsic to the sympathetic nervous system. The definitive functional significance of these oscillators is unknown at present. However, it is expected that through dynamic relationships with modulating and driving inputs, such oscillators would permit graded vascular responses.

Relationship of arousals from sleep to sympathetic nervous system activity and BP in obstructive sleep apnea

STUDY OBJECTIVE

Obstructive sleep apnea (OSA) patients have a high frequency of arousals. We hypothesized that arousals significantly influence tonic sympathetic nervous system function.

DESIGN

We examined the association of 11 variables measuring sympathetic activity, including plasma norepinephrine (NE), urinary NE, and BP measurements, with movement and cortical arousals.

PATIENTS

Sixty-seven subjects with various degrees of hypertension and OSA were evaluated. All patients were free from antihypertensive medications.

RESULTS

The age (range, 35 to 60 years), weight (range, 100 to 150% of ideal body weight), and diet of the subjects were similar. The movement arousal index was correlated with daytime baseline plasma NE (BNE), daytime urine NE, mean daytime diastolic BP, and systolic BP during rapid eye movement sleep (r = 0.39 to 0.53; p < or = 0.002). Cortical arousals did not correlate with any of the variables. A multiple regression procedure was performed to examine how well movement arousals predicted those variables with significant correlations. The respiratory disturbance index (RDI) and nighttime pulse oxyhemoglobin saturation were included in the regression equation due to their close association with movement arousals. Movement arousals independently predicted BNE (t [48] = 2.06; p < 0.05). No other variable independently predicted any of the measurements of sympathetic activity.

CONCLUSIONS

These findings suggest that movement arousals may influence daytime sympathetic tone independently of RDI and nighttime saturation.

Mechanisms of acute cardiovascular response to periodic apneas in sedated pigs

This study was designed to evaluate the importance of sympathoadrenal activation in the acute cardiovascular response to apneas and the role of hypoxemia in this response. In addition, we evaluated the contribution of the vagus nerve to apnea responses after chemical sympathectomy. In six pigs preinstrumented with an electromagnetic flow probe and five nonpreinstrumented pigs, effects of periodic nonobstructive apneas were tested under the following six conditions: room air breathing, 100% O2 supplementation, both repeated after administration of hexamethonium (Hex), and both repeated again after bilateral vagotomy in addition to Hex. With room air apneas, during the apnea cycle, there were increases in mean arterial pressure (MAP; from baseline of 108 +/- 4 to 124 +/- 6 Torr, P < 0.01), plasma norepinephrine (from 681 +/- 99 to 1,825 +/- 578 pg/ml, P < 0.05), and epinephrine (from 191 +/- 67 to 1,245 +/- 685 pg/ml, P < 0.05) but decreases in cardiac output (CO; from 3.3 +/- 0.6 to 2.4 +/- 0.3 l/min, P < 0.01) and cervical sympathetic nerve activity. With O2 supplementation relative to baseline, apneas were associated with small increases in MAP (from 112 +/- 4 to 118 +/- 3 Torr, P < 0.01) and norepinephrine (from 675 +/- 97 to 861 +/- 170 pg/ml, P < 0.05). After Hex, apneas with room air were associated with small increases in MAP (from 103 +/- 6 to 109 +/- 6 Torr, P < 0.05) and epinephrine (from 136 +/- 45 to 666 +/- 467 pg/ml, P < 0.05) and decreases in CO (from 3.6 +/- 0.4 to 3.2 +/- 0. 5 l/min, P < 0.05). After Hex, apneas with O2 supplementation were associated with decreased MAP (from 107 +/- 5 to 100 +/- 5 Torr, P < 0.05) and no other changes. After vagotomy + Hex, with room air and O2 supplementation, apneas were associated with decreased MAP (from 98 +/- 6 to 76 +/- 7 and from 103 +/- 7 to 95 +/- 6 Torr, respectively, both P < 0.01) but increased CO [from 2.7 +/- 0.3 to 3. 2 +/- 0.4 l/min (P < 0.05) and from 2.4 +/- 0.2 to 2.7 +/- 0.2 l/min (P < 0.01), respectively]. We conclude that sympathoadrenal activation is the major pressor mechanism during apneas. Cervical sympathetic nerve activity does not reflect overall sympathoadrenal activity during apneas. Hypoxemia is an important but not the sole trigger factor for sympathoadrenal activation. There is an important vagally mediated reflex that contributes to the pressor response to apneas.

Differential arterial baroreflex regulation of renal, lumbar, and adrenal sympathetic nerve activity in the rat

Lumbar (LSNA), renal (RSNA), or adrenal sympathetic nerve activity (ASNA) is most commonly used as an index of sympathetic nerve activity in investigations of arterial baroreflex control in the rat. Although differential regulation of sympathetic outputs to different organs has been extensively studied, no direct and simultaneous comparisons of the full range of baroreflex reactivity have been described for these sympathetic outputs. Therefore, we compared steady-state sigmoidal baroreflex stimulus-response curves (via phenylephrine-nitroprusside infusion) for RSNA recorded simultaneously with LSNA or ASNA in urethan-chloralose-anesthetized male Sprague-Dawley rats. Characteristics of the baroreflex curves differed significantly between all three sympathetic outputs. ASNA exhibited the greatest range of baroreflex regulation, the highest upper level of activity, and the widest distribution of the gain over a broad range of mean arterial pressure (MAP). RSNA exhibited greater gain than LSNA. LSNA showed the smallest range and maximal inhibition in comparison to other sympathetic outputs. However, all three nerves responded similarly to baroreflex stimulation and unloading in the range in MAP close to the operating point. We conclude that baroreflex regulation of sympathetic activity shows wide regional variability in gain, range, and maximal inhibition. Therefore, the entire stimulus-response relationship should be considered in comparing regional sympathetic responses.

Arterial baroreflex modulation of heat-induced vasodilation in the rabbit ear

The purpose of this study was to determine whether nonthermal baroreflexes arising from cardiopulmonary and/or arterial baroreceptors modulate rabbit ear blood flow (EBF) during hyperthermia. Intact and sinoaortic-denervated (SAD) rabbits were chronically instrumented with a Doppler ultrasonic flow probe for measurement of EBF velocity (kHz). During whole body heating in conscious rabbits, EBF and ear vascular conductance (EVC) increased as core temperature increased until maximal plateau levels of EBF and EVC were reached. The maximal plateau level of EVC attained during heat stress was lower in SAD than in intact rabbits. Subsequent intrapericardial administration of procaine at maximal EBF blocked cardiac afferents but did not alter EVC in either animal group. In a second experiment, ramp decreases in mean arterial pressure were produced by vena caval occlusion at maximal EBF. In intact rabbits, EBF and EVC decreased linearly as mean arterial pressure fell, but EBF and EVC did not decrease during vena caval occlusion in SAD rabbits. Thus neither pharmacological nor mechanical unloading of cardiac baroreceptors results in reflex vasoconstriction in the heat-stressed rabbit ear. However, baroreflexes arising from arterial baroreceptors may modulate EBF in heat-stressed rabbits.

Regional differentiation of blood flow responses to microinjection of sodium nitroprusside into the nucleus tractus solitarius of anesthetized rats

This study was undertaken to examine the effects of the activation of the neurons in the nucleus tractus solitarius (NTS) via microinjection of sodium nitroprusside (SNP), which spontaneously releases nitric oxide (NO), on the blood flows of the spleen, kidney, liver, brain and spinal cord and to investigate the regional differentiation of the blood flow changes between those organs. Employing urethane-anesthetized (1.5 g kg-1, i.p.), paralyzed and artificially ventilated rats, regional blood flows of those organs were determined simultaneously using radiolabeled microspheres (109Cd, 51Cr and 85Sr) Unilateral microinjection of SNP into the NTS (n = 9) decreased brain blood flow from 71 +/- 8 (mean +/- S.E.) to 54 +/- 6 (P < 0.01) and spinal cord blood flow from 58 +/- 8 to 43 +/- 5 ml min-1 (100 g)-1 (P < 0.05) and increased brain vascular resistance from 1.18 +/- 0.13 to 1.48 +/- 0.15 (P < 0.01) and spinal cord vascular resistance from 1.46 +/- 0.17 to 1.80 +/- 0.16 (P < 0.05) mmHg per [ml min-1 (100 g)-1]. Whereas the microinjection of SNP into the NTS increased splenic blood flow from 127 +/- 25 to 188 +/- 27 (P < 0.01) and renal blood flow from 346 +/- 28 to 371 +/- 26 ml min-1 (100 g) (P < 0.05) and decreased splenic vascular resistance from 0.77 +/- 0.13 to 0.44 +/- 0.06 (P < 0.01) and renal vascular resistance from 0.24 +/- 0.02 to 0.21 +/- 0.01 mmHg per [ml min-1 (100 g)-1] (P < 0.05). The blood flow of the liver was not significantly altered. Unilateral microinjection of NG-monomethyl-L-arginine, an inhibitor of the formation of NO from L-arginine, into the NTS (n = 10) did not significantly change the blood flows of all organs examined except for an increase in blood flow of the kidney. Unilateral microinjections of SNP into the area adjacent to the NTS (n = 9), of artificial cerebrospinal fluid into the NTS (n = 7) and of light-inactivated SNP into the NTS (n = 6) did not significantly alter the blood flows of all organs examined. These results suggest than the neurons in the NTS have a vasoconstrictor effect on the brain and spinal cord circulation and a vasodilator effect on the splenic and renal circulation. There is a regional qualitative differentiation of the blood flow responses between these organs during activation of the neurons in the NTS.

Sympathetic nerve activity after discrete hypothalamic injections of L-glutamate

In these experiments L-glutamate, an amino acid which stimulates neuronal discharge, was microinjected into several hypothalamic nuclei and the resultant changes in electrical firing rate of sympathetic nerves innervating interscapular brown adipose tissue (IBAT) were measured. Three patterns of response were seen. A single large stimulatory response was seen when L-glutamate was microinjected into the ventromedial hypothalamus (VMH). Microinjection of L-glutamate into the paraventricular nucleus (PVN) produced a predominantly stimulatory response which was of smaller magnitude than the VMN. However in three animals L-glutamate in the PVN decreased firing rate and in one animal a biphasic response was observed. The second pattern was a decrease in sympathetic activity to IBAT which was the predominant pattern following injection of L-glutamate into the dorsomedial hypothalamus (DMH). However, a biphasic pattern was also observed. Injection of L-glutamate into the lateral hypothalamic area (LHA) produced 3 patterns of response; an increase, a decrease; or a biphasic response in nearly equal numbers of animals. The predominant response to L-glutamate in the preoptic area (POA) was biphasic. These data are consistent with the hypothesis that the VMH is the predominant stimulatory site for activation of the sympathetic nervous system to IBAT in the rat. The DMH and LHA appear to be the predominant inhibitory areas.

Relative contribution of nervous system and hormones to CNS-mediated hyperglycemia is determined by the neurochemical specificity in the brain

To determine whether CNS regulatory pathways are organized so that differential sympathetic outflow patterns occur in response to stress, we injected various doses of neostigmine or bombesin into the third cerebral ventricle of fed rats, and then measured the hepatic venous plasma concentrations of glucose, glucagon, insulin, and epinephrine. The following four groups of rats were studied. Group 1 was intact rats. Group 2 comprised intact rats receiving the constant infusion of a) somatostatin to inhibit the endogenous secretion of insulin and glucagon, and b) insulin to maintain the plasma insulin concentration at basal levels. The infusion was started from -30 minutes and given via a catheter in the femoral vein. Group 3 consisted of rats that underwent bilateral adrenal medullectomy (ADMX) one week before the experiment. Group 4 was ADMX rats administered a constant infusion of somatostain with insulin through a femoral vein, as above. The administration of 1 x 10(-9) mol neostigmine caused hepatic venous hyperglycemia mediated by three distinct pathways: 1) direct innervation of the liver, 2) a direct action of epinephrine on the liver, and 3) the action of glucagon on the liver. We estimated the relative contribution of these three factors to be about 47, 32, and 21%, respectively. Relative contributions of three factors of the doses of 5 x 10(-9) and 5 x 10(-8) mol neostigmine demonstrated an effect similar to that of 1 x 10(-9) mol neostigmine. Epinephrine was shown to be the only agent involved in the hyperglycemic response to intraventricular bombesin at doses of 1 x 10(-10), 1 x 10(-9), and 1 x 10(-8) mol.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of catecholamines in the paravertebral sympathetic ganglia of the anesthetized dog

alpha-Adrenoceptor agonists decreased mean arterial pressure when injected into the arterial blood supply of the paraspinal sympathetic ganglia of pentobarbital-anesthetized open-chest dogs. The hypotensive response occurred concomitantly with selective decreases of vascular resistance in the vessels innervated by neurons arising from these ganglia, and both of these responses were blocked by the ganglionic blocking agent, hexamethonium. The hypotensive response to phenylephrine was selectively blocked by terazosin; alpha 1 selective agonist, and antagonist, respectively, while the hypotension produced by intra-arterial clonidine was blocked by rauwolscine; alpha 2 selective agonist and antagonist, respectively. Either terazosin or rauwolscine reduced the hypotension produced by noradrenaline or dopamine. These results demonstrated the presence of both alpha 1- and alpha 2-adrenoceptors in the paraspinal sympathetic ganglia. Activation of either alpha-adrenoceptor subtype inhibited ganglionic transmission.

Gustatory-salivary reflex: neural activity of sympathetic and parasympathetic fibers innervating the submandibular gland of the hamster

Electrophysiological experiments were performed to clarify the neural control mechanisms subserving gustatory-salivary reflex in anesthetized and decerebrate hamsters. Efferent neural activities of postganglionic sympathetic and preganglionic parasympathetic fibers, innervating the submandibular gland, were recorded when taste stimuli were infused into the oral cavity. Neural activities of primary gustatory afferents were also recorded from the chorda tympani (innervating the anterior part of the tongue) and the glossopharyngeal nerve (innervating the posterior part of the tongue). The parasympathetic fibers showed a low rate of spontaneous discharges (about 0.3 Hz), and responded tonically in an excitatory manner to taste stimulation. The magnitude of parasympathetic activity was highly correlated with the magnitude of gustatory afferent responses of the chorda tympani rather than that of the glossopharyngeal nerve. On the other hand, the sympathetic fibers showed irregular burst discharges (1.5 burst/s), and the rate of burst discharges was increased in response to high concentrations of HCl (0.03 M) or NaCl (1 M) solutions. Deafferentation experiments suggest that the parasympathetic activity is mainly influenced by gustatory information via the chorda tympani, while the sympathetic activity can be evoked by both the chorda tympani and glossopharyngeal nerve.

Cardiac vagal and sympathetic nerve responses to baroreceptor stimulation in the dog

The effects of ascending stepwise pressure changes in the isolated carotid sinuses on cardiac vagal and sympathetic nerve activities were studied in anesthetized, open chest dogs. The steady state responses of the cardiac vagal and the sympathetic nerve activity and arterial blood pressure were plotted against the sinus pressure and the relations were approximated by the normal distribution function (response curve). The sinus pressure- vs. "reflex gain" relations (reflex gain curve) were approximated by the normal density function. The maximum gain and the "range of change" were found to be greater for the vagal than for the sympathetic and arterial pressure responses. The sinus pressure values derived from "response curves" and "reflex gain curves" for vagal and sympathetic nerve responses were close to each other, while these values and those obtained from arterial pressure responses were considerably apart. It was concluded that: (1) The cardiac vagal neurons are more sensitive to the baroreceptor input than the sympathetic neurons; (2) The similar type of baroreceptor afferent inputs reach the cardiac vagal and the sympathetic structures which are controlling the autonomic outflows.

Changes in renal sympathetic nerve activity, heart rate and arterial blood pressure associated with eating in cats

1. Renal sympathetic nerve activity, heart rate and arterial blood pressure were simultaneously measured in thirteen awake cats before, during and after eating which was evoked by presenting food for a period of 10-15 s. 2. With food presentation, eating behaviour occurred in 93% (191) of 205 trials, and renal sympathetic nerve activity significantly increased in 65% of the 191 trials. On the other hand, in many of food presentation trials when no eating occurred, or with presentation of an empty food box, renal sympathetic nerve activity did not change significantly. 3. Eating started 1-8 s after the food presentation. The increase in renal sympathetic nerve activity was closely related to the beginning of eating but not to the onset of food presentation. Renal sympathetic nerve activity and heart rate increased with a slight time lag of 0.5-1.5 s from the onset of eating, whereas an increase in arterial blood pressure followed the onset of eating by 5.5 s. After the beginning of eating, renal sympathetic nerve activity, heart rate and arterial blood pressure increased at a maximum of 61 +/- 18% (mean +/- S.E. of mean), 26 +/- 4.0 beats/min, and 17 +/- 4.9 mmHg from the control values at 1.0, 5.5 and 11.5 s, respectively. 4. Cardiac-related grouped discharges of renal sympathetic nerve activity, which were observed at rest, increased during eating. 5. When arterial blood pressure was elevated by noradrenaline (2-5 micrograms/kg I.V.), renal sympathetic nerve activity during resting was almost completely inhibited and the increase in renal sympathetic nerve activity during eating was not induced. 6. We conclude that renal sympathetic nerve activity increases in association with eating behaviour but not as firmly with the food presentation, and that the increase in renal sympathetic nerve activity is initiated by descending input from the higher central nervous system rather than either by the viscero-autonomic reflex due to food intake or by the baroreflex due to a decrease in arterial blood pressure.

Conditioning of inhibition of sympathetic nerve discharge to stimulation of A- and C-fibres in the aortic nerve

Stimulation of either A- or C-fibres in the aortic nerve inhibits sympathetic nerve discharge (SND) recorded from the renal nerve in rabbits anaesthetized with urethane. When the test inhibition of SND to stimulation of A-fibres is preceded by conditioning stimulation of the same afferents, the test response is depressed at shorter and facilitated at longer testing intervals. Facilitation of the inhibition of SND reaches 120% of control at a testing interval of 10 s. The recovery curve of inhibition of SND to activation of A-fibres has a time course of 17 s. Following conditioning activation only depression of the test inhibition of SND to stimulation of C-fibres is seen. It reaches 46% of control at an interval of 2 s and the recovery curve of inhibition of SND to stimulation of C-fibres has a time course of about 30 s. In other series of experiments the duration of the conditioning stimulation was varied while the testing intervals were fixed. At a testing interval of 2 s the reductions of the test responses are deeper and the durations of conditioning at which plateaus of depression are reached are longer with stimulation of C- than of A-fibres. Taken together with a longer recovery curve these findings suggest a more effective control of the test inhibition of SND by C-fibres. Opposite changes in the patterns of inhibition of SND to activation of either A- or C-fibres are explained by frequency-dependent post-tetanic effects of the conditioning stimulation.

The renal sympathetic baroreflex in the rabbit. Arterial and cardiac baroreceptor influences, resetting, and effect of anesthesia

Curves relating renal sympathetic nerve activity and mean arterial pressure were derived in conscious rabbits during ramp changes in mean arterial pressure, elicited by perivascular balloon inflation. The renal sympathetic nerve activity-mean arterial pressure relationship consisted of a high-gain sigmoidal region about resting, where renal sympathetic nerve activity rose or fell in response to moderate falls and rises of mean arterial pressure. With larger pressure rises, renal sympathetic nerve activity first fell to a lower plateau and then reversed at even higher mean arterial pressure. When mean arterial pressure was lowered below resting, renal sympathetic nerve activity rose to an upper plateau and then reversed abruptly toward resting at low mean arterial pressure. Both arterial and cardiac baroreceptors exerted substantial inhibitory influences on renal sympathetic nerve activity at all pressure levels. These effects appeared additive over the central high gain region of the curve, but beyond this region there were non-additive interactions. The latter were affected considerably by alfathesin anesthesia. In other experiments, we studied the effects of sustained alterations in resting mean arterial pressure induced by infusing nitroprusside and phenylephrine, which produced rapid resetting of the renal baroreflex. The latter could be accounted for, in part, by resetting of the threshold of the arterial baroreceptors and in part by contributions from other afferents, probably the cardiac receptors. During resetting associated with nitroprusside-induced falls in resting blood pressure, high-gain reflex adjustments in renal sympathetic nerve activity to moderate changes in mean arterial pressure were preserved, but during resetting associated with phenylephrine-induced rises in resting mean mean arterial pressure, the resting renal sympathetic nerve activity lay on the lower curve plateau, resulting in reduction in the apparent gain of the reflex renal sympathetic nerve activity response to moderate changes in mean arterial pressure.

Efferent discharges of sympathetic and parasympathetic nerve fibers during increased intracranial pressure in anesthetized cats in the absence and presence of pressor response

Efferent discharges of the cervical sympathetic cardiovascular and vagal type 1 fibers in response to increased intracranial pressure (ICP) were simultaneously recorded in cats anesthetized with pentobarbitone and ventilated artificially. Sympathetic outflow of renal nerve fibers was also recorded in some animals. The type 1 fibers were assumed to be cardiac vagal fibers, from the response behavior such a pulse-synchronicity to respiratory and heart rhythm, reflex activation from arterial baroreceptors and reciprocal relationship of the activity to sympathetic ones during slower fluctuations of hemodynamic changes, and which occur spontaneously during Mayer waves. The vagal type 1 discharges increased to various amplitudes with increase in ICP and in the absence and the presence of pressor response. Efferent outflow of the renal and cervical sympathetic fibers frequently decreased with a moderate increase in ICP. There was a slight decrease or no apparent change in the blood pressure, and a higher elevation of ICP ensued. Heart rates decreased with increase in ICP, while the rate frequently increased with levels of ICP over about 120 mm Hg. Changes in the vagal and sympathetic discharges always began at a time before the initiation of cardiovascular response to the elevated ICP. However, when ICP was repeatedly increased, the increase in vagal discharges progressively decayed and was accompanied by vigorous sympathetic firings and a marked pressor response. The sympathetic outflow also decayed following the decrease in vagal activities. The present findings of changes in the vagal type 1 discharges demonstrate clear participation of parasympathetic as well as sympathetic nerve activity in the occurrence of cardiovascular responses to increased ICP. Changes in both these autonomic nerve responses may explain the initial fall in arterial blood pressure and pressor responses associated with bradycardia or tachycardia, at different levels of elevated ICP.

Segmental distribution and central projections of renal afferent fibers in the cat studied by transganglionic transport of horseradish peroxidase

The segmental and central distributions of renal nerve afferents in adults cats and kittens were studied by using retrograde and transganglionic transport of horseradish peroxidase (HRP). Transport of HRP from the central cut ends of the left renal nerves labelled afferent axons in the ipsilateral minor splanchnic nerves and sensory perikarya in the dorsal root ganglia from T12 to L4. The majority of labeled cells (85%) were located between L1 and L3. A few neurons in the contralateral dorsal root ganglia were also labeled. Labeled cells were not confined to any particular region within a dorsal root ganglion. Some examples of bifurcation of the peripheral and central processes within the ganglion were noted. A small number of preganglionic neurons, concentrated in the intermediolateral nucleus, were also identified in some experiments. In addition, many sympathetic postganglionic neurons were labeled in the renal nerve ganglia, the superior mesenteric ganglion, and the ipsilateral paravertebral ganglia from T12 to L3. Transganglionic transport of HRP labeled renal afferent projections to the spinal cord of kittens from T11 to L6, with the greatest concentrations between L1 and L3. These afferents extended rostrocaudally in Lissauer's tract and sent collaterals into lamina I. In the transverse plane, a major lateral projection and a minor medial projection were observed along the outer and inner margins of the dorsal horn, respectively. From the lateral projection many fibers extended medially in laminae V and VI forming dorsal and ventral bundles around Clarke's nucleus. The dorsal bundle was joined by collaterals from the medial afferent projection and crossed to the contralateral side. The ventral bundle extended into lamina VII along the lateroventral border of Clarke's nucleus. Some afferents in the lateral projection could be followed ventrally into the dorsolateral portion of lamina VII in the vicinity of the intermediolateral nucleus. In the contralateral spinal cord, labeled afferent fibers were mainly seen in laminae V and VI. These results provide the first anatomical evidence for sites of central termination of renal afferent axons. Renal inputs to regions (laminae I, V, and VI) containing spinoreticular and spinothalamic tract neurons may be important in the mediation of supraspinal cardiovascular reflexes as well as in the transmission of activity from nociceptors in the kidney. In addition, the identification of a bilateral renal afferent projection in close proximity to the thoracolumbar autonomic nuclei is consistent with the demonstration in physiological experiments of a spinal pathway for the renorenal sympathetic reflexes.

Essential hypertension: abnormal renal vascular and endocrine responses to a mild psychological stimulus

We have assessed the influence of a mild emotional stimulus on arterial blood pressure, heart rate, renal blood flow, plasma renin activity (PRA), and plasma aldosterone concentration in 24 normal subjects, eight of who had a parent with hypertension, and in 15 patients with essential hypertension. A nonverbal IQ test, Raven's Progressive Matrices, was employed as the stimulus. In 11 of the 15 hypertensives, arterial blood pressure rose transiently by 7 mm Hg or more, but in only three of 16 normal subjects (x2 = 7.23, p less than 0.01). Transient moderate increases in heart rate were also more common in the hypertensives (p less than 0.01). Renal blood flow rose in 11 of 16 normal subjects and fell in each of the 15 patients with essential hypertension (x2 = 15.1; p less than 0.005). As opposed to the transient changes in arterial pressure and heart rate, the fall in renal perfusion was sustained. The PRA fell in 10 of the 16 normal subjects with a negative family history and rose in 14 of 15 patients with essential hypertension (p less than 0.005). Changes in plasma angiotensin II concentration and in plasma aldosterone were in accord with the changes in PRA, but plasma cortisol did not change. Both the renal vascular response and the change in PRA were intermediate in normal subjects in whom family history was positive for hypertension. For the entire group of 39 subjects there was statistically significant agreement between the direction of the renal vascular response and the directional change in PRA: renal blood flow rose when PRA fell and fell when PRA rose (p less than 0.005). We conclude that there is an abnormality in the control of both the renal circulation and of renin release in patients with essential hypertension in response to psychological provocation, and that a similar process is present in some normotensive subjects whose parents have hypertension.

Effects of baroreceptor activation on spontaneous activity in the sweat glands and nictitating membrane of the cat

(1) In chloralose-anesthetized cats, elevation of carotid sinus pressure caused blood pressure, sweat gland potentials and nictitating membrane tension to decrease. (2) The onset and recovery of the sweat gland and nictitating membrane responses usually preceded the respective phases of the blood pressure (depressor) response; the latencies of the sweat gland and nictitating membrane responses agreed with the latencies predicted for neural reflex pathways. (3) The sweat gland and nictitating membrane responses were evoked less consistently than the depressor response. (4) In experiments where only the sweat gland potentials and blood pressure were studied: (a) the sinus pressure threshold for inhibition of sweat gland activity was similar to the threshold for the depressor response; (b) cutting the sinus nerves, or blocking the efferent neural activity to the sweat glands, eliminated the effects of sinus pressure elevation on the sweat gland potentials; (c) with carotid sinus pressure held constant, decreases in blood pressure, produced by stimulating the peripheral end of the vagus nerve, did not affect the sweat gland potentials. (5) These results indicate that baroreceptors can reflexly modulate activity in sympathetic neurons whose target organs are not fundamentally involved in blood pressure regulation.

Sympathetic hyperactivity during hypothalamic stimulation in spontaneously hypertensive rats

To determine whether sympathetic hyperactivity of hypothalamic origin contributes to keep blood pressures high in spontaneous hypertension, aortic pressures and sympathetic nerve spike potentials were recorded during electrical stimulation of the posterior hypothalamus in urethane-anesthetized normotensive or hypertensive rats. Basal sympathetic nerve activity was higher in spontaneously hypertensive rats than in either normotensive or deoxycorticosterone acetate-salt hypertensive ones even before stimulation began. Blood pressure elevations produced by hypothalamic stimulation were always preceded by substantial increases in amplitude and rate of neural firing. Changes in amplitude could not be quantified, but rates of neural firing accelerated much more in spontaneous hypertensives than in normotensives during stimulation with 50- and 100-muA currents. Similar differences between deoxycorticosterone acetate-salt hypertensives and either normotensives or spontaneous hypertensives were not statistically significant. Nerve activity invariably became quiescent immediately after hypothalamic stimulation was discontinued, and recovery from this poststimulatory inhibition was faster in spontaneously hypertensive than in normotensive rats. Although spontaneous hypertensives generally also had stronger pressor responses to various sympathomimetic stimuli, responses to hypothalamic stimulation were enhanced to a greater extent than those to either norepinephrine or sympathetic nerve stimulation. Because this selectivity indicates participation of mechanisms other than augmented cardiovascular reactivity, further enhancement of responsiveness to hypothalamic stimuli was attributed to the associated increase in sympathetic nerve firing. These results are in accord with the hypothesis that the blood pressure elevation in rats with established spontaneous hypertension is a result, at least in part, of sympathetic hyperactivity emanating from the posterior hypothalamus.

Cardiac and respiratory rhythmicities in cutaneous and muscle vasoconstrictor neurones to the cat's hindlimb

Cardiac and respiratory rhythmicities have been investigated quantitatively in postganglionic vasoconstrictor neurones supplying skeletal muscle and skin of the hindlimb in chloralose anesthetized, immobilized cats. Both rhythmicities are largest in muscle vasoconstrictor neurones, smaller in vasoconstrictor neurones supplying hariy skin, and smallest in vasoconstrictor neurones supplying hairless skin. The magnitude of the cardiac rhythmicity in the vasoconstrictor neurones is positively correlated with the quantitative reaction to systemic hypoxia.

The renal circulation in hypertensive disease

The pivotal role of the kidney in sustaining hypertension from any source or etiology is becoming increasingly clear. The possibility that the renal vasculature participates not only in the pathogenesis of renal vascular hypertension, but also in that of essential hypertension, has been the subject of continuing interest for 40 years. Evidence that a functional abnormality resulting in increased renal vascular tone is present in about two-thirds of patients with uncomplicated essential hypertension is reviewed, along with more circumstantial evidence that sympathetic nervous system activity operating on the renal vasculature is responsible. Two additional groups of patients in whom a characteristic abnormality of the renal vasculature is present have also been identified. In one group there is severe hypertension which is resistant to most forms of antihypertensive therapy but which is especially responsive to propranolol. In these patients renal blood flow and glomerular filtration rate are reduced, renin secretion rate is increased and the renal vessels are resistant to vasodilators, suggesting the presence of advanced organic arteriolonephrosclerosis, as a complication of long-standing, severe hypertension. The renal lesion, in turn, contributes to the increasing severity of the process. In a second group of patients, generally young and with uncomplicated hypertension, renal blood flow is inappropriately increased. In these patients a number of observations on their renal vasculature, renin and aldosterone responses to a volume challenge suggest an abnormality in the perception of extracellular fluid volume. A perfectly normal renal arterial tree, free of organic abnormality or an increase in tone due to active vasoconstriction, is distinctly unusual in essential hypertension.

Arterial baroreceptor function in differential cardiovascular adjustments induced by central thermal stimulation

Dogs were anesthetized with sodium pentobarbital, relaxed with succinyl choline and were kept under artificial ventilation. Both carotid bifurcations were denervated and the Vagus nerves were cut in the neck. Regional blood flow in the skin and the intestine, cardiac output, heart rate and arterial pressure were determined before, during and after spinal cord heating and cooling. Further experiments were performed in which, in addition, sympathetic effects on the heart were excluded by exstirpation of the caudal cervical and stellate ganglia or by beta-receptor blockade. The cardiovascular responses were compared with those obtained in a preceding investigation from dogs with intact baroreceptors and vagus nerves. As in intact dogs, appropiate thermoregulatory adjustments of skin blood flow were induced by thermal stimulation of the spinal cord after baroreceptor denervation and vagotomy. However, blood pressure homeostasis was lost. The pattern of cardiovascular ajustments during heating consisted in cutaneous vasodilatation intestinal vasoconstriction and, due to sympathetic activation an increase of heart rate and cardiac output. This pattern was qualitatively identical with that intact animals. During spinal cord cooling the cardiovascular response pattern consisted in cutaneous vasoconstriction, intestinal vasoconstriction and, depending on cooling intensity, a reduced or unchanged sympathetic influence on the heart. This pattern differed considerably from what in intact animals but basic features were still present as indicated by opposite changes of cardiac and vascular sympathetic tone during cooling. It is concluded that the baroreceptor signals play no primary role in the generation of differential vasomotor responses under the present experimental conditions. This confirms assumptions made on the basis of observations in animals with intact baroreceptor input. However, baroreceptor signals contribute significantly to blood pressure homeostasis which is normally maintained during spinal thermal stimulation.