Tone of sympathetic nerves and regulation of heart activity

Tone of sympathetic nerves to the heart was studied in rats and guinea pigs. Experiments with pharmacological blockade of the sympathetic nervous system and vagotomy confirmed the general notion on the absence of tonic effects of sympathetic nerves on the heart. Reduction of the heart rate reported previously probably attests to various experimental designs (type and depth of anesthesia, possible hypothermia, duration of observations, and pharmacological preparations). As differentiated from the vascular tone, the heart rate under rest conditions depends on the vagal tone and circulating humoral substances. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 130, No. 10, pp. 370–373, October, 2000     

Reflex responses evoked in the adrenal sympathetic nerve to electrical stimulation of somatic afferent nerves in the rat

The present study was initiated to determine the role of somatic A (myelinated) and C (unmyelinated) afferent fibers in both responses of increases and decreases in adrenal sympathetic nerve activities during repetitive mechanical pinching and brushing stimulations of the skin in anesthetized rats with central nervous system (CNS) intact. Accordingly, changes in adrenal sympathetic nerve activity resulting from repetitive and single shock electrical stimulation of various spinal afferent nerves, especially the 13th thoracic (Th13) spinal nerve and the sural nerve, were examined in urethane/chloralose-anesthetized rats. Repetitive electrical stimulation of A afferent fibers in Th13 spinal or sural nerve decreased the adrenal nerve activity similarly as brushing stimulation of skin of the lower chest or hindlimb did, while repetitive stimulation of A plus C afferent fibers of those nerves increased the adrenal nerve activity as pinching stimulation of those skins did. Single shock stimulation of spinal afferent nerves evoked various reflex components in the adrenal nerve: an initial depression of spontaneous activity (the early depression); the following reflex discharge due to activation of A afferent fibers (the A-reflex); a subsequent reflex discharge due to activation of C afferent fibers (the C-reflex); and following post-excitatory depressions. These reflexes seem to be mediated mainly via supraspinal pathways since they were abolished by spinal transection at the C1-2 level. Although the supraspinal A- and C-reflexes could be elicited from stimulation of a wide variety of spinal segmental afferent levels, the early depression was more prominent when afferents at spinal segments closer to the level of adrenal nerve outflow were excited. It is suggested that the decreased responses of the adrenal nerve during repetitive electrical stimulation of A afferent nerve fibers are attributable to summation of both the early depression and post-excitatory depression evoked by single shock stimulation, while the increased responses during repetitive stimulation of A plus C afferent fibers are attributable to summation of the C-reflex after single shock stimulation. In spinalized rats, repetitive stimulation of Th13 always increased the adrenal nerve activities regardless of whether A fibers alone or A plus C fibers were stimulated, just as brushing and pinching of the lower chest skin always increased them. The increased responses in spinal animals seem to be related to the fact that single electrical stimuli of Th13 produced A- and C-reflexes of spinal origin without clear depressions.     

Identification of sympathetic and parasympathetic nerves function in cardiovascular regulation using ANFIS approximation

Objective

In this paper a new nonlinear system identification approach is developed for dynamical quantification of cardiovascular regulation. This approach is specifically focused on the identification of the heart rate (HR) baroreflex mechanism. The principal objective of this paper is to improve the model accuracy in the estimation of HR by proposing a modified nonlinear model.

Methods and material

The proposed HR baroreflex model is based on inherent features of the autonomic nervous system for which we develop an adaptive neuro-fuzzy inference system (ANFIS) structure. This method allows incorporation of physiological understandings about the sympathetic and parasympathetic nerves through the selection of appropriate membership functions in the ANFIS structure. The required data for system modeling are collected from the publicly available PhysioNet database.

Results

The results agree with the natural characteristics and physiological understanding of the cardiovascular regulatory system, such as delay in the parasympathetic function, durability in the function of sympathetic nerves and the correlation between the HR and the ABP signals. They also show significant improvements in HR prediction in terms of the normalized root mean square error (NRMSE) in comparison with other reported methods. We achieved to 0.191 in mean NRMSE in prediction of HR in this paper which is about 20% better than the best reported result in other researches.

Conclusion

We have shown that for cardiovascular system regulation, our proposed nonlinear model is more accurate than other recently developed methods. Accurate HR baroreflex modeling enables clinicians to have more reliable information for their patients.     

Participation of the parasympathetic and sympathetic nerves in regulation of gallbladder motility in the dog

The participation of the parasympathetic and sympathetic nerves in the canine gallbladder motility was examined. Efferent stimulation of the parasympathetic (vagus) and sympathetic (celiac) nerves caused contraction or inhibition of the neck, body and fundus of the gallbladder. The contractile response induced by vagus nerve stimulation was reduced by subthreshold efferent stimulation of the celiac nerve, while the inhibitory response was neither reduced nor enhanced by subthreshold efferent stimulation of the celiac nerve. The contractile and inhibitory response induced by celiac nerve stimulation was not reduced in the neck, body and fundus by subthreshold efferent stimulation of the vagus nerve. The contractile response to vagus nerve stimulation was reversed to a relaxant response by atropine administration, which was reduced or abolished by hexamethonium. It is suggested that the vagus nerve-induced contractile response in the canine gallbladder is modulated by sympathetic nerves presynaptically at the vagus nerve endings in the enteric ganglion, but the vagus nerve-induced relaxant response, which probably was induced by non-adrenergic non-cholinergic inhibitory neurons, is not modulated by the sympathetic nerves.     

Expression and regulation of intercellular adhesion molecule-1 on airway parasympathetic nerves

BACKGROUND: Eosinophils cluster along airway nerves in patients with asthma and release eosinophil major basic protein, an antagonist of inhibitory M2 muscarinic receptors on nerves. Blocking M2 function increases bronchoconstriction, leading to airway hyperreactivity. Intercellular adhesion molecule-1 (ICAM-1) mediates eosinophil adhesion to nerves. OBJECTIVE: We investigated mechanisms of ICAM-1 expression by parasympathetic nerves. METHODS: ICAM-1 expression was examined by immunocytochemistry of lung sections from ovalbumin-sensitized and challenged guinea pigs. ICAM-1 was measured in parasympathetic nerves isolated from subjects and guinea pigs and in human neuroblastoma cells by real-time RT-PCR, immunocytochemistry, and Western blot. RESULTS: ICAM-1 was not detected in control airway parasympatheric nerves in vivo or in cultured cells. ICAM-1 was expressed throughout antigen-challenged guinea pig lung tissue and was selectively decreased by dexamethasone only in nerves. ICAM-1 was induced in human and guinea pig parasympathetic nerves by TNF-alpha and IFN-gamma and was inhibited by dexamethasone and by an inhibitor of nuclear factor-kappaB (NF-kappaB). In neuroblastoma cell lines TNF-alpha and IFN-gamma-induced ICAM-1 was blocked by an inhibitor of NF-kappaB but not by inhibitors of mitogen-activated protein kinases. Dexamethasone did not inhibit ICAM-1 expression in neuroblastoma cells. CONCLUSIONS: ICAM-1 induced in nerves by antigen challenge and proinflammatory cytokines is sensitive to dexamethasone. ICAM-1 expression is also sensitive to inhibitors of NF-kappaB. Neuroblastoma cells mimic many, but not all, characteristics of ICAM-1 expression in parasympathetic nerves. CLINICAL IMPLICATIONS: Dexamethasone and NF-kappaB inhibitors could prevent eosinophils from adhering to nerves by blocking ICAM-1 expression on parasympathetic nerves, thus protecting inhibitory M2 muscarinic receptors and making this pathway a potential target for asthma treatment.     

Reflex sympathetic changes in aortic diastolic pressure-diameter relationship.

In anesthetized vagotomized cats with the chest opened and artificially ventilated, aortic blood pressure (AP) and external diameter (AD; ultrasound technique) were measured in the proximal third of the descending thoracic aorta. Slow sinusoidal oscillations (0.2-0.3 Hz in aortic volume were produced by a piston pump connected to a femoral artery. Diastolic pressure-diameter relationship (PDR) curves were obtained during control conditions and during stimulation of either the cut central end of the left inferior cardiac nerve (ICN) or the decentralized thoracic sympathetic chain (SC). In six cats with both carotid arteries occluded ICN stimulation reflexly shifted the PDR curves to lower diameters for any given pressure (mean deltaAD 3.2% at control AP). A smaller response to ICN stimulation was obtained in five cats with one patent carotid artery (mean deltaAD 2.3% at control AP). Stimulation of sympathetic efferents to the aorta (SC) caused similar responses in five animals (mean deltaAD 3.4% at control AP). This reflex control of the thoracic aorta may be involved in cardioaortic coupling and may influence the sensitivity of aortic mechanoreceptors.     

Reflex regulation of capacity for work

Summary The stability of changes of the muscular working capacity under the effect of various analysors was investigated in this work. This study was conducted on the background of decreased, working ability of the right arm.The results of these observations showed that increase of working capacity caused by stimulation of the cutaneous temperature and olfactory analysors disappears following repetition of these experiments 2 or 3 times. They are components of reaction of orientation. Increase of the working capacity under the effect of additional stimulation of the motor analysor is very stable under conditions of these experiments. Evidently, excitation of certain centers plays an important part in creation of stability of this effect. This excitation appears as an unconditioned reflex as a result of stimulation of the proprioceptors.Presented by Academician K. M. Bykov     

Substance P-like immunoreactivity in nerves associated with the vascular system of guinea-pigs

Substance P-like immunoreactivity was localized by an indirect immunohistochemical technique in whole mounts and sections of blood vessels from the guinea-pig. There was a widespread association of nerve fibres that had substance P-like immunoreactivity with blood vessels, extending into all vascular beds. The relative densities of supply of different vessels were assessed visually and a rating scale used to compare them. Large elastic arteries close to the heart had dense networks of immunoreactive nerves associated with them. The density decreased as more peripheral beds were approached, except that there was a particularly dense network of nerves with arteries of the splanchnic beds. Arteries to myocardial, central nervous system, renal, reproductive and skeletal muscle beds all had substance P-immunoreactive nerves associated with them to varying extents. The venae cavae near the heart were densely supplied, but there were few fibres with their more peripheral extensions. Some large veins (e.g. pulmonary, hepatic portal and superior mesenteric) had a few fibres with them, but veins of peripheral vascular beds had very few or no immunoreactive nerve fibres. Substance P-like immunoreactivity in vascular nerves was markedly reduced in guinea-pigs that were injected with capsaicin but was unaffected by the injection of 6-hydroxydopamine. It is concluded that the vascular substance P-immunoreactive nerves are likely to be of sensory origin.