Absence Of Sympathetic Innervation Research Articles

Parasympathetic reflex vasodilation in the cerebral hemodynamics of rats

We investigated the role of parasympathetic reflex vasodilation in the regulation of the cerebral hemodynamics, and whether GABAA receptors modulate the response. We examined the effects of activation of the parasympathetic fibers through trigeminal afferent inputs on blood flow in the internal carotid artery (ICABF) and the cerebral blood vessels (rCBF) in parietal cortex in urethane-anesthetized rats. Electrical stimulation of the central cut end of the lingual nerve (LN) elicited intensity- and frequency-dependent increases in ICABF that were independent of changes in external carotid artery blood flow. Increases in ICABF were elicited by LN stimulation regardless of the presence or absence of sympathetic innervation. The ICABF increases evoked by LN stimulation were almost abolished by the intravenous administration of hexamethonium (10 mg kg(-1)) and were reduced significantly by atropine administration (0.1 mg kg(-1)). Although the LN stimulation alone had no significant effect on rCBF, LN stimulation in combination with a blocker of the GABAA receptor pentylenetetrazole increased the rCBF markedly. This increase in rCBF was reduced significantly by the administration of hexamethonium and atropine. These observations indicate that the increases in both ICABF and rCBF are evoked by parasympathetic activation via the trigeminal-mediated reflex. The rCBF increase evoked by LN stimulation is thought to be limited by the GABAA receptors in the central nervous system. These results suggest that the parasympathetic reflex vasodilation and its modulation mediated by GABA receptors within synaptic transmission in the brainstem are involved in the regulation of the cerebral hemodynamics during trigeminal afferent inputs.

Neuroendocrine properties of intrinsic cardiac adrenergic cells in fetal rat heart.

Intrinsic cardiac adrenergic (ICA) cells in developing rat heart constitute a novel adrenergic signaling system involved in cardiac regulation. Regulatory mechanisms of ICA cells remain to be defined. Immunohistochemical study of fetal rat hearts demonstrated ICA cells with catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). The mRNA of TH and PNMP was also detected in fetal rat hearts before sympathetic innervation. Immunoreactivity of norepinephrine transporter (NET) was localized to ICA cells in rat heart tissue and primary cell culture. For the functional study, the activity of intracellular Ca2+ concentration ([Ca2+]i) transients was quantified by a ratio fluorescent spectrometer in cultured ICA cells and myocytes. ICA cells generated spontaneous [Ca2+]i transients that were eliminated by tetrodotoxin or Ca(2+)-free solutions and showed greatly reduced amplitude with the addition of L-type Ca2+ channel blocker nifedipine. [3H]norepinephrine studies demonstrate release and uptake of norepinephrine. Functional interaction between catecholamines produced by the ICA cells and cocultured myocytes was evident by the effect of the beta-adrenergic blocker atenolol eliciting a dose-dependent reduction in the amplitude and frequency of [Ca2+]i transients of beating myocytes. Hypoxia inhibited [Ca2+]i transient activity of ICA cells, which subsequently produced a reoxygenation-mediated rebound augmentation of [Ca2+]i transients. We conclude that ICA cells are capable of catecholamine synthesis, release, and uptake. They generate spontaneous [Ca2+]i transient activity that can be regulated by oxygen tension. ICA cells may provide an alternative adrenergic supply to maintain cardiac contractile and pacemaker function at rest and during stress in the absence of sympathetic innervation.

Sympathectomy potentiates the vasoconstrictor response to nitric oxide synthase inhibition in humans.

Nitric oxide exerts its cardiovascular actions at least in part by modulation of the sympathetic vasoconstrictor tone. There is increasing evidence that nitric oxide inhibits central neural sympathetic outflow, and preliminary evidence suggests that it may also modulate peripheral sympathetic vasoconstrictor tone. To test this latter concept, in six subjects having undergone thoracic sympathectomy for hyperhydrosis, we compared the vascular responses to systemic L-NMMA infusion (1 mg/kg/min over 10 min) in the innervated and the denervated limb. We also studied vascular responses to the infusion of the non-nitric-oxide-dependent vasoconstrictor phenylephrine. L-NMMA infusion evoked a roughly 3-fold larger increase in vascular resistance in the denervated forearm than in the innervated calf. In the denervated forearm, vascular resistance increased by 58 +/- 10 percent (mean +/- SE), whereas in the innervated calf it increased only by 21 +/- 6 percent (P < 0.01, forearm vs. calf). This augmented vasoconstrictor response was specific for L-NMMA, and not related to augmented non-specific vasoconstrictor responsiveness secondary to sympathectomy, because phenylephrine infusion increased vascular resistance similarly in the denervated forearm and the innervated calf (by 24 +/- 7, and 29 +/- 8 percent, respectively). The augmented vasoconstrictor response was related specifically to denervation, because in control subjects, the vasoconstrictor responses to L-NMMA were comparable in the forearm and the calf. These findings indicate that in the absence of sympathetic innervation, the vasoconstrictor responses to nitric oxide synthase inhibition are augmented.

Restoration of the transient outward potassium current by noradrenaline in chagasic canine epicardium.

1. The transient outward potassium current (Ito) is reduced in canine epicardial myocytes during the acute stage of infection with Trypanosoma cruzi (Chagas' disease). Sympathetic nerve terminals are also destroyed during the acute stage of this disease. To test whether the reduction of Ito is related to the absence of sympathetic innervation, acutely infected isolated epicardial myocytes were exposed in vitro to the sympathetic neurotransmitter noradrenaline (NA) and the effects of NA exposure on Ito were determined. 2. Continuous exposure to NA (1.0 microM) for 0-6 h had no effect on Ito density, whereas exposure to NA for 24 h significantly increased Ito density. Ito was also restored 24 h after a 1 h exposure to NA. Cell capacitance was not significantly affected by NA. 3. The alpha1-adrenergic receptor antagonist prazosin (0.1 microM) blocked the effects of NA on Ito, but the beta-adrenergic receptor antagonist propranolol (20 microM) did not. The beta-adrenergic receptor agonist isoprenaline (1 microM) had no effect on Ito. 4. Restoration of Ito by NA was prevented by pretreatment with neomycin (100 microM), a phospholipase C inhibitor, but not by pretreatment with 100-400 ng ml(-1) pertussis toxin (PTX). 5. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (0.1 microM) mimicked the effect of NA on Ito, whereas the inactive analogue 4alpha-phorbol (20 microM) had no effect on Ito. Pretreatment with bisindolylmaleimide (0.1 microM), a specific PKC inhibitor, completely blocked the effect of NA on Ito. 6. Thus, NA restores Ito in chagasic canine epicardial myocytes. The induction of Ito by NA appears to result from alpha1-adrenergic stimulation of PKC via a PTX-insensitive signalling cascade. These results suggest that the reduction of Ito in chagasic myocytes during the acute stage of Chagas' disease may reflect the lack of the trophic effects of sympathetic innervation.

Congenital Horner's syndrome does not alter Lisch nodule formation

A 21-year-old woman with neurofibromatosis type 1 (NF-1) had a unilateral congenital Horner's syndrome with resultant hypopigmentation of the affected iris. Lisch nodules, which are melanocytic hamartomas, were similar in number, size, and pigmentation in both eyes. The present findings suggest that the formation of Lisch nodules is not influenced by the presence or absence of sympathetic innervation of the iris.

Interaction between cerebrovascular sympathetic, parasympathetic and sensory nerves in blood flow regulation.

Morphological and pharmacological findings support that different cerebrovascular nerve types have close relationships in the vessel wall and that interactions may contribute to the control of vascular tone. This study in rat investigates whether interaction in blood flow regulation occurs between sympathetic, parasympathetic and sensory nerves in the cerebral vessels. Cortical blood flow (CBF) was measured with a laser-Doppler flowmeter during electrical stimulation of one of the nerves, with or without prior denervation of one or two of the other nerves. Unilateral sympathetic stimulation significantly decreased CBF ipsilaterally. The response was unaffected in magnitude and time course by parasympathetic or sensory denervation. Sensory nerve stimulation did not significantly affect CBF, even after sympathetic denervation. Parasympathetic nerve stimulation caused a marked increase in CBF, which was similar in magnitude in the presence or absence of sympathetic innervation. However, the return to the basal CBF level after parasympathetic stimulation was prolonged after sympathetic denervation. Thus, activation of the sympathetic nerves may contribute to a rapid normalization of the enhanced CBF during parasympathetic nerve stimulation, whereas the reverse phenomenon, parasympathetic normalization of the sympathetically induced CBF reduction, does not occur.

Developmental expression of muscarinic cholinergic receptors and coupling to phospholipase C in rat sweat glands are independent of innervation

During development, the innervation of rat sweat glands undergoes a striking change from noradrenergic to cholinergic function. The acquisition of secretory responsiveness by the glands is temporally correlated with the appearance of cholinergic properties. In addition, responsiveness fails to appear in the absence of innervation. To investigate the basis of the onset of functional transmission and secretory responsiveness and its possible relationship to innervation, we analyzed the development of muscarinic cholinergic receptors in sweat glands, examined their expression in the glands of adult rats sympathectomized at birth, and assayed the ability of muscarinic agonists to increase phosphoinositide (PI) turnover. Autoradiographic and in situ hybridization analysis revealed that muscarinic ligand binding sites were first detectable as glands begin to form on postnatal day 4 (P4). Between P4 and P14, receptor concentration increased in parallel with mRNA for the m3 receptor subtype. On P14, the concentration of ligand binding sites approached adult levels, although only a small proportion of glands at this age secrete in response to nerve stimulation or cholinergic agonists. When the pharmacological properties of muscarinic receptors in sweat glands of adult rats sympathectomized at birth were compared to those of normal glands, the concentration and affinity determined with [N-methyl-3H]-scopolamine and the Ki values determined with the subtype-selective muscarinic antagonists 4-DAMP, pirenzepine, and AF DX-116 were similar. In addition, the molecular subtype was unchanged as was the level of m3 message. Studies of PI turnover in response to muscarinic stimulation indicated that the receptors expressed in sweat glands isolated from sympathectomized and acutely denervated, as well as control, rats were functionally coupled to phospholipase C. The absence of sympathetic innervation therefore does not appear to influence either the development of muscarinic receptors or their coupling to PI turnover. Our results suggest that functional sympathetic cholinergic innervation plays a central role in the development and maintenance of secretory function at a step distal to signal transduction across the cell membrane.

Sympathetic neural and alpha-adrenergic modulation of arrhythmias.

alpha 1-Adrenergic stimulation of the neonatal heart may induce either an increase or a decrease in ventricular automaticity, with the latter response predominating as age increases. We used isolated tissues from the hearts of neonatal and adult dogs and rats, as well as rat myocytes in tissue culture alone or in coculture with sympathetic nerves, to study the role of sympathetic innervation in modulating the alpha-adrenergic response. In the absence of sympathetic innervation, alpha-adrenergic stimulation uniformly increases automaticity. As the myocyte is innervated, an increased quantity of a GTP regulatory protein is detectable. That this protein is an essential transducer of alpha-adrenergic inhibition of automaticity is evidenced by the conversion of the alpha response from excitatory to inhibitory as the protein develops. ADP-ribosylation of the protein with pertussis toxin causes the alpha response to revert to excitation in both adult canine hearts and innervated myocytes in tissue culture. Hence, we have evidence for sympathetic modulation of cardiac rhythm via a regulatory protein whose function depends on normal neuronal development. Abnormal development of innervation may predispose to arrhythmogenesis via persistence of a primitive response to alpha stimulation.

Development of interscapular brown adipose tissue in the hamster. II - Differentiation of transplants in the anterior chamber of the eye: role of the sympathetic innervation.

The relationship between brown adipose tissue (BAT) and its sympathetic innervation during development was investigated by transplantation of undifferentiated (white fat-like) hamster BAT into the anterior eye chamber of adult hamsters. Such transplants are known to be revascularized and reinnervated by the vessels and the nerves of the host iris. The morphology of the BAT transplants was analysed during the post-operative weeks by light and electron microscopy, and the ingrowth of sympathetic nerve fibres from the iris was followed by radioautography. BAT appeared to differentiate in oculo, i.e. presented increasing amounts of adipocytes with multilocular fat deposits and abundant, well-developed mitochondria, but only after a delay of approx. 10 days, and remained much fatter than in situ. The establishment of the sympathetic innervation was not synchronous with the revascularization process. It occurred simultaneously with the morphological differentiation of the BAT transplants, and the nerve fibre density remained low. In the absence of sympathetic innervation, i.e. when the host irides were sympathectomized prior to transplantation, BAT still differentiated, but the process was further delayed and the proportion of differentiated brown adipocytes after 20 days in oculo was clearly lower than in control transplants. It is concluded that the sympathetic innervation in BAT is involved in the regulation of differentiating activity in the tissue, but is not obligatory for differentiation to occur.

Effect of sympathetic input on ontogeny of β-adrenergic receptors in rat pineal gland

The ontogeny of beta-adrenergic receptors was investigated in the pineal glands of rats 1–64 days of age. The density of beta-receptors increased about 3-fold between 1 and 16 days of age and decreased slightly by 64 days, correlating temporally with the development of the sensitivity of adenylate cyclase to norepinephrine in pineal gland. Preventing adrenergic innervation of the pineal gland by neonatal ganglionectomy or decentralization failed to prevent the development of beta-adrenergic receptors in pineal gland. Bilateral adrenal demedullation alone or in combination with ganglionectomy also failed to prevent the normal developmental increase of betareceptors in the gland. These results, showing that the ontogeny of pineal beta-receptors correlates temporally with that of the responsiveness of adenylate cyclase to adrenergic neurohormones, support the hypothesis that the responsiveness of tissues to beta-agonists is dependent on the development of the beta-receptor. In addition, these experiments show that the beta-adrenergic receptor can develop even in the absence of sympathetic innervation or circulating catecholamines produced by the adrenal medullae.

In vitro and in vivo activities of anticholinergics on the cholinoceptors of the cardiac pacemaker cells

The tachycardia-inducing effects of atropine, N-methylscopolammonium and N-butylscopolammonium were studied in the conscious dog, both in the presence and absence of sympathetic innervation. These effects were atria. The order of potency for inhibition of the effects of acetylcholine on the isolated atria was N-methylscopolammonium > atropine > N-butylscopolammonium. This order was the same for the tachycardia-inducing potencies. Maximal tachycardia with these three drugs was less marked in the absence of sympathetic innervation than in its presence. However, the doses of atropine and of N-butylscopolammonium required to block the effects of vagal influence were greater. Sympathectomy had no effect on the vagolytic potency of N-methylscopolammonium. In the case of atropine and N-methyl-scopolammonium there was good correlation between antocholinergic and tachycardia-inducing potencies. The tachycardiac effects of these compounds can be explained by their anticholinergic effect. The tachycardia-inducing potency of N-butylscopolammonium was greater than its anticholinergic potency.

Localized and disseminated forms of neuronal intestinal dysplasia mimicking Hirschsprung's disease

Neuronal intestinal dysplasia is characterized by structural changes consisting of hyperplasia of the myenteric plexus, an increase of the acetyl cholinesterase activity and the formation of giant ganglia. The condition gives rise to signs and symptoms similar to Hirschsprung's disease. Neuronal intestinal dysplasia can occur as a clinical entity itself in a localized or disseminated form. It may also accompany Hirschsprung's disease either as a localized defect or as a disseminated disorder of the entire intestinal tract. In localized forms, resection of the entire diseased segment is curative. Disseminated forms often have a fetal outcome despite ileostomy and colectomy. It is conceivable that differences in the severity of symptoms depend upon the development or absence of sympathetic innervation.

Influence of autonomic innervation on the foetal rat pancreas in vitro.

Foetal rat pancreatic rudiments, explanted on day 14 of gestation and grown for 7 days in organ culture, were highly sensitive to the stimulatory effect of glucose on insulin secretion. The autonomic innervation of the cultivated explant was investigated as a possible explanation of this phenomenon. No sign of sympathetic innervation was detected in the pancreas explanted on day 14; the uptake of alpha-methyl-noradrenaline was not detectable by fluorescence microscopy, the concentration of noradrenaline/pancreatic rudiment was less than 7 pg and no nerve-endings containing granular vesicles were visible by electron microscopy. It was concluded that sympathetic innervation of the pancreas occurs after day 14 of gestation. Sympathetic receptors developed independently of innervation since phentolamine, and, to a lesser extent, phenoxybenzamine, potentiated the glucose-induced insulin release from cultured explants. The beta-agonists isoproterenol or salbutamol were inactive alone, but in combination with phentolamine, they potentiated the effect of glucose. Alpha-antagonists reversed the inhibitory effect of adrenaline in a dose-dependent manner. Intrapancreatic neurones were demonstrated microscopically as cholinesterase-positive cells; parasympathetic receptors were shown to be present after potentiation of glucose-stimulated insulin release by carbamylcholine and its reversal by atropine. The preservation of parasympathetic innervation and the absence of sympathetic innervation in the cultured pancreatic rudiment may explain in part the high sensitivity of the tissue to the stimulatory effect of glucose on the release of insulin.

Effect of sympathetic denervation on the 5-hydroxytryptamine levels of the submaxillary glands of rats

Sympathetic denervation of submaxillary glands of rats by means of superior cervical ganglionectomy resulted in significant increases of the 5-hydroxytryptamine concentration and total 5-hydroxytryptamine content. Sympathetic denervation reduced significantly the weight of the glands but this decrease was less marked than the previously observed reduction in gland weight following immunosympathectomy. These observations indicated that absence of sympathetic innervation may be responsible for the previously observed increase of the 5-hydroxytryptamine levels in a number of peripheral tissues of rats following immunosympathectomy.

Nervous control of urinary bladder in cats. II. The expulsion phase.

AbstractEdvardsen, P. Nervous control of urinary bladder in, cats. II. The expulsion phase. Acta physiol. scand. 1968. 72. 172–182.The volume threshold for micturition is altered by transection of the brain stem at variousu levels and also by section of the sympathetic nerves to the bladder. The aim of the present experiments has been to investigate whether the supraspinal influences are brought about by means of changes in peripheral sympathetic mechanisms. Mostly male cats were investigated using the ‘direct cystometry’ method. Cystometrograms obtained preoperatively were compared with those obtained after peripheral sympathectomy and during the phase of increased motility following laparotomy. Then the effects of brain stem transection on the micturition threshold in the. presence and absence of sympathetic innervation were compared. The peripheral factor responsible for eliciting the micturition reflex was found to be the tension in the bladder wall as assessed from the intravesical pressure. The lower volume threshold found after sympathectomy is due to the hypertonicity of the bladder following this procedure. The tonic supraspinal influence on the micturition reflex, on the other hand, was not altered by interruption of the sympathetic nerve supply to the bladder. Thus, the expulsion of urine is controlled by two different mechanisms, namely a peripheral regulation of the tension in the bladder wall and a supraspinal regulation of the micturition reflex threshold.

Nervous Control of Urinary Bladder in Cats

AbstractThe volume threshold for micturition is altered by transection of the brain stem at various levels and also by section of the sympathetic nerves to the bladder. The aim of the present experiments has been to investigate whether the supraspinal influences are brought about by means of changes in peripheral sympathetic mechanisms. Mostly male cats were investigated using the ‘direct cystometry’ method. Cystometrograms obtained preoperatively were compared with those obtained after peripheral sympathectomy and during the phase of increased motility following laparotomy. Then the effects of brain stem transection on the micturition threshold in the presence and absence of sympathetic innervation were compared. The peripheral factor responsible for eliciting the micturition reflex was found to be the tension in the bladder wall as assessed from the intravesical pressure. The lower volume threshold found after sympathectomy is due to the hypertonicity of the bladder following this procedure. The tonic supraspinal influence on the micturition reflex, on the other hand, was not altered by interruption of the sympathetic nerve supply to the bladder. Thus, the expulsion of urine is controlled by two different mechanisms, namely a peripheral regulation of the tension in the bladder wall and a supraspinal regulation of the micturition reflex threshold.