Norepinephrine Stores Research Articles

Neurotensin releases norepinephrine differentially from perfused hypothalamus of sated and fasted rat.

The central injection of neurotensin (NT) has been reported to attenuate the intake of food in the fasted animal. To determine whether endogenous norepinephrine (NE) is involved in the satiating effect of NT, the in vivo activity of NE in circumscribed sites in the hypothalamus of the unanesthetized rat was examined. Bilateral guide tubes for push-pull perfusion were implanted stereotaxically to rest permanently above one of several intended sites of perfusion, which included the paraventricular nucleus (PVN), ventromedial nucleus (VMN), and the lateral hypothalamic (LH) area. After endogenous stores of NE at a specific hypothalamic locus were radiolabeled by microinjection of 0.02-0.5 mu Ci of [3H]NE, an artificial cerebrospinal fluid was perfused at the site at a rate of 20 microliter/min over successive intervals of 5.0 min. When 0.05 or 0.1 micrograms/microliter NT (0.03-0.6 mM) was added to the perfusate, the peptide served either to enhance or reduce the local release of NE at 50% of the sites of perfusion. In these experiments, the circumscribed effect of NT on the characteristics of catecholamine efflux depended entirely on the state of hunger or satiety of the rat. That is, when NT was perfused in the fully satiated rat, NE release was augmented within the PVN or VMN; conversely, NE release was inhibited in the LH. In the animal fasted for 18-22 h, NT exerted an opposite effect on the activity of NE within the same anatomical loci in that the efflux of NE was enhanced in the LH but attenuated or unaffected in the PVN or VMN.(ABSTRACT TRUNCATED AT 250 WORDS)

Voluntary wheel running exercise and monoamine levels in brain, heart and adrenal glands of aging mice

The goals of this study were to examine the effects of three months of voluntary wheel-running exercise on life span, whole body and brain, heart and adrenal weights and biogenic amine content (norepinephrine, dopamine, epinephrine and serotonin) in three age groups of male mice. The three groups consisted of mature (9 months), middle-aged (19 months), and old (27–29 months) mice. No significant differences in weight were found between control and exercise or age. The oldest mice had a survival rate of 69% for the exercise group and 43% for the age matched controls when the exercise phase was completed. Locomotor activity was significantly reduced for the old mice compared to the middle-age and mature mice. Only the mature (12 months of age at sacrifice) exercised mice showed a cardiac and adrenal hypertrophy (about 10%). There was a moderate increase in norepinephrine content in the ventral hypothalamus of the brain with exercise (significant at 12 months of age). Biogenic amine content in other regions of the brain (brain stem and forebrain minus hypothalamus) was not affected by age and/or exercise. There was a significant decrease in heart norepinephrine content with exercise in old mice (30–32 months). Adrenal gland norepinephrine content was significantly increased by exercise at 12 months of age and decreased at 22 months of age. Our results suggest that an increase in norepinephrine content in the hypothalamus might be a manifestation of an adaptation to the increased demands upon hypothalamic noradrenergic terminals imposed by prolonged exercise. It is also apparent that aging and exercise alters the amounts of sympathetic transmitter of the heart and adrenal glands. Such alteration may be beneficial to the aging brain by retaining norepinephrine stores that normally decline with age.

Down-regulation of serotonin 2 but not of beta-adrenergic receptors during chronic treatment with amitriptyline is independent of stimulation of serotonin 2 and beta-adrenergic receptors

Antidepressant drugs down-regulate beta-adrenergic, alpha 2-adrenergic and serotonergic 5-HT 2 receptors with a time course that parallels their clinical efficacy, i.e. chronic administration is required (Crews and Smith, 1978; Svensson and Usdin, 1978; Banerjee, Kung, Riggi and Chanda, 1979; Bergstrom and Keller, 1979; Peroutka and Snyder, 1980). In the present study, it was found that the 5-HT 2 receptor antagonist, nefazadone (50 mg/kg per day) did not prevent the downregulation of 5-HT 2 receptors in the cerebral cortex produced by amitriptyline (10 mg/kg per day), when administered for 3 weeks. Moreover, treatment with nefazadone (50 mg/kg per day) alone for 3 weeks decreased binding to 5-HT 2 receptors in cerebral cortex. In contrast, administration of propranolol, the beta receptor antagonist, (10 mg/kg per day) with amitriptyline (10 mg/kg per day) for 3 weeks prevented the down-regulation of beta receptors, but did not alter the decrease in binding to 5-HT 2 receptors. In addition, the depletion of central stores of norepinephrine and serotonin by a 4-day treatment with reserpine (5 mg/kg per day) increased binding to beta receptors in the cerebral cortex and hippocampus, but did not affect binding to 5-HT 2 receptors in either region. These results suggest that the 5-HT 2 receptor is not down-regulated by direct stimulation by serotonin agonists and that the down-regulation of 5-HT 2 receptors by amitriptyline is independent of down-regulation of beta-adrenergic receptors.

Experimental diabetic diarrhea in rats: Intestinal mucosal denervation hypersensitivity and treatment with clonidine

Diarrhea in streptozocin-induced chronically diabetic rats is caused by an impaired adrenergic regulation of intestinal fluid and electrolyte transport. Stimulation of α2-adrenergic receptors on enterocytes normally promotes NaCl absorption and inhibits HCO3 secretion. The purpose of this study was to determine (a) if adrenergic denervation of intestinal mucosa in chronically diabetic rats alters postsynaptic receptor response, and (b) if the α2-adrenergic agonist clonidine could correct observed fluid malabsorption. Mucosal norepinephrine stores, a measure of adrenergic tone, were markedly reduced in diabetic rats compared with nondiabetic littermates. In vitro, short-circuit current changes to exogenously added l-epinephrine were significantly greater in diabetics, suggesting that denervation hypersensitivity was due to increased numbers of postsynaptic α2-adrenergic receptors. In vivo loop studies demonstrated net fluid secretion in the ileum and colon of diabetics. In diabetics, clonidine reversed the secretion to absorption, but it had no effect on fluid absorption in controls. We conclude that diabetic diarrhea in streptozocin-induced chronically diabetic rats is (a) due to impaired adrenergic regulation of mucosal ion transport, (b) accompanied by a postsynaptic denervation hypersensitivity that can be reversed by clonidine, and (c) accompanied by net intestinal fluid secretion that can be effectively reversed with clonidine.

Differential effects of sino-aortic denervations on cardiac noradrenaline stores, turnover and neuronal re-uptake in normotensive and renal hypertensive rabbits.

The effects of sino-aortic denervation (SAD) on cardiac noradrenaline stores, turnover and neuronal re-uptake were examined in normotensive rabbits and rabbits with two-kidney, two wrapped hypertension. Ten to 12 days after SAD, left ventricular (LV) noradrenaline stores were reduced in renal hypertensives to 43% of that of the sham-operated rabbits, although there was no overt evidence of heart failure. This did not occur after SAD of normotensive rabbits. The reduction in noradrenaline content was accompanied by a reduction in [3H]-noradrenaline turnover time (4.4 h) compared with renal hypertensive (7.4 h) and the normotensive subgroups (9.3 h). Noradrenaline turnover rates were elevated by 25% in hypertensive compared with normotensive rabbits. Left ventricular tyrosine hydroxylase, dopamine-beta-hydroxylase and type A monoamine oxidase activities were similar in normotensive and hypertensive rabbits and were unaffected by SAD. Following SAD of hypertensive rabbits cardiac neuronal uptake for alpha-methylnoradrenaline was reduced by 33% compared with either the hypertensive or the normotensive rabbits. Sino-aortic denervation did not affect neuronal uptake in normotensives. These results suggest that following SAD of hypertensive rabbits, cardiac noradrenaline stores are depleted by enhanced cardiac sympathetic activity (reduction in [3H]-noradrenaline turnover time) and a reduction in neuronal re-uptake. It appears that the hypertensive hypertrophied heart is less able to tolerate chronic sympathetic overactivity and/or liability in coronary oxygen supply brought about by SAD.

Effects of chloride ion substitution on the frequency dependence and alpha-autoinhibition of [3H]noradrenaline secretion in guinea-pig vas deferens.

Guinea-pig isolated vas deferens, in which the stores of noradrenaline (NA) had been labelled by preincubation with [3H]NA, was used to study the effects of substitution of chloride with other anions, on transmitter secretion evoked by electrical stimulation of postganglionic sympathetic nerves. Chloride was omitted from the Tyrode's solution and substituted with acetate, nitrate, methylsulphate, sulphate or HEPES. All substituents increased both the spontaneous and the stimulus-evoked fractional secretion of [3H]NA under control conditions. The effect was essentially the same at all frequencies of stimulation (1-8 Hz). In the presence of the alpha-adrenoceptor blocker phentolamine, which enhanced the secretion of [3H]NA in all media, the secretion was not further enhanced by chloride substitution. Chloride substitution reduced the depressing effect of exogenous NA on the secretory response. In conclusion, chloride ions may be required for full expression of alpha-adrenoceptor-mediated inhibition of [3H]NA secretion, but do not markedly influence facilitation by increased frequency of stimulation.

Neural regulation of adrenal chromaffin cell function in the mouse: fate and distribution of [ 3H]dopamine in denervated adrenal medulla

The distribution and time course of appearance and decline of radioactivity in denervated adrenal medulla of mice injected with [ 3H]dopamine was examined by autoradiography. Radioactivity irradiated from [ 3H]dopamine was increased from 7.5 min to 30 min, then decreased rapidly in both adrenaline-storing (A) cells and noradrenaline-storing (NA) cells of either intact or denervated adrenals. In subcortical A cells, the incorporation of radioactivity was increased by denervation while in NA cells and in A cells in the center of the medulla, the increment was not significant. In the denervated adrenals, the decline of [ 3H]dopamine-derived radioactivity was slower than that in the intact gland. The denervation increased the gradient in radioactivity from the surface to the center of the medulla. The present results suggest that the sensitivity to neuronal suppression of dopamine uptake in subcortical A cells is different from that in A and NA cells in the rest of the gland. The results also indicate a functional heterogenity within a single type of chromaffin cells.

Biochemical evidence for norepinephrine stores outside the sympathetic nerves in rat carotid body

Adult rats were submitted to pharmacological or surgical sympathectomy. The chronic administration of guanethidine caused tremendous reductions in the norepinephrine stores in heart and superior cervical ganggion due to the destruction of the sympathetic nerve fibers and cell bodies. Guanethidine-sympathectomy resulted in a 70% loss of norepinephrine in the carotid body, whereas the dopamine and DOPAC contents were unaltered. The surgical sympathectomy induced by removing the superior cervical ganglion led to similar results. The present data indicate that a considerable part of norepinephrine in the rat carotid body is stored in the sympathetic nerves. In addition, a significant part of norepinephrine resides outside the sympathetic nerves, probably within the glomus cells.

Alterations in the noradrenergic projection to the cerebellum of the dystonic ( dt) rat

The genetically dystonic rat ( dt) has elevated resting levels of cerebellar norepinephrine (NE) in comparison with phenotypically normal littermates. This difference is not secondary to cerebellar hypoplasia. Increased NE is observed as early as postnatal day 12, when clinical symptoms have become evident. The elevation in cerebellar NE levels in the dt rat involves all cerebellar areas, but is not generalized to all terminal fields of the locus coeruleus. Elevations in cerebellar NE are followed developmentally by a reduction in sensitivity to the NE-depleting effects of reserpine, a change which is also confined to the cerebellum. The effects of amphetamine and the tyrosine hydroxylase inhibitor alpha-methyl- para-tyrosine were similar in normal and dt rats. Levels of the major cerebellar metabolite of NE, 3-methoxy-4-hydroxyphenylglycol, did not differ between mutant and normal animals. Nor were any changes noted in the number or affinity of beta-adrenergic receptors. These data indicate that there is a regional alteration in NE storage. Cerebellar morphology appears normal in the dt rat, except for a decrease in Purkinje cell size. This change and other evidence of biochemical abnormalities in the Purkinje cells suggest that the alterations in cerebellar NE in the dt mutant may be a secondary response to a functional change in the target neuron for this system, the Purkinje cell.

ADRENERGIC MECHANISMS IN CONGESTIVE HEART FAILURE

The normal control of cardiovascular function exerted by the sympathetic nervous system is disturbed in congestive heart failure. The failing pump function of the heart evokes an increase in sympathetic activity which may be reflected in increased levels of plasma noradrenaline. However, these levels are generally below the concentrations needed to activate the adrenergic effector systems, indicating that the cardiovascular consequences of the increased sympathetic activity is not mediated by circulating noradrenaline. In the failing human heart there is a decrease in beta-adrenoceptor density which is related to decreasing ventricular function. This finding suggests that the myocardium is exposed to high concentrations of noradrenaline, inducing downregulation of the receptor number, despite the fact that in the failing heart the noradrenaline stores are reduced. In heart failure the plasma noradrenaline concentration was found to be directly related to mortality and was suggested to provide a better guide to prognosis than other commonly measured indexes of cardiac performance.

Partial depletion of neuropeptide Y from noradrenergic perivascular and cardiac axons by 6-hydroxydopamine and reserpine

The effects of 6-hydroxydopamine (6-OHDA) and reserpine on the storage of neuropeptide Y (NPY) in noradrenergic cardiovascular nerves were examined with both immunohistochemistry and radioimmunoassay (RIA). Immunohistochemical double-labelling techniques demonstrated that NPY was located only in noradrenergic axons in the guinea-pig carotid artery, mitral valve, thoracic inferior vena cava, thoracic aorta, superior mesenteric artery and small saphenous vein. Treatment with 6-OHDA in vivo eliminated noradrenergic, NPY-containing axon terminals from all tissues, but preterminal axons were still prominent in the superior mesenteric artery. The greatest depletion of NPY detected by RIA after 6-OHDA treatment was found in tissues with a predominance of terminal noradrenergic axons, such as the small saphenous vein, whereas NPY accumulating in preterminal axons masked the loss of NPY from terminal axons in the superior mesenteric artery. After treatment with doses of reserpine that led to a rapid depletion of noradrenaline (NA) from perivascular nerves, NPY was still detected histochemically at all times although levels sometimes appeared to be reduced. RIA demonstrated that the partial depletion of NPY after reserpine consisted of a rapid phase seen in the vena cava and saphenous vein after the highest doses, and a slower phase of NPY depletion from all tissues after all doses of reserpine. The greatest depletion of NPY from terminal axons by reserpine (in small saphenous vein) was 85–90%. These results demonstrate that some NPY can be stored in noradrenergic perivascular axons in the absence of noradrenaline, but that partial depletion of NPY from axon terminals results when NA stores are depleted by reserpine. The variation in extent of NPY depletion between tissues after drug treatments can be explained by variation in the ratio of preterminal to terminal axons.

Neuropharmacological modification of central catecholamines: effects on pinealectomy-induced convulsions.

Removal of the pineal gland produces stereotyped tonic convulsions in parathyroidectomized rats. Inasmuch as central levels of norepinephrine (NE) are decreased in these animals, the purpose of this study was to investigate the effects of alterations in central catecholamine function on convulsions produced by pinealectomy in parathyroidectomized rats. The treatment of rats with alpha-methyl-p-tyrosine or FLA-63 produced large reductions in forebrain levels of both NE and dopamine or NE alone, respectively, which were not associated with facilitation of convulsions. However, the incidence of convulsions was increased by FLA-63 in rats pretreated with the catecholamine precursor L-dihydroxyphenylalanine. Reserpine, a monoamine depleter, had no effect on either the incidence or severity of convulsions. An acute injection of desipramine, an inhibitor of the reuptake of NE, however, significantly lowered the incidence of convulsions. Timolol, a beta-adrenergic receptor antagonist, reduced, in a dose-dependent manner, the average latency to onset of convulsions and increased the average number of convulsions each rat experienced. Clonidine, an alpha 2-adrenergic agonist, did not significantly alter convulsions. Thus presynaptic mechanisms such as synthesis and storage of both NE and DA appear to have little, if any, effect on pinealectomy-induced convulsions, whereas enhancing synaptic levels of NE by blocking its reuptake into adrenergic axons had an anticonvulsant effect. Further evidence suggesting a role for NE in modulating these convulsions is provided by the proconvulsant effect of blocking central beta-adrenergic receptors.

Medianosomes as integrative units in the external layer of the median eminence. Studies on grf/catecholamine and somatostatin/catecholamine interactions in the hypothalamus of the male rat☆

Somatostatin/catecholamine as well as growth hormone releasing factor/catecholamine interactions have been characterized in the hypothalamus and the preoptic area using morphometrical and quantitative histofluorimetrical analyses. The combined results of the present and previous studies have led us to put forward the medianosome concept. The medianosome is defined as an integrative unit, which consists of well defined aggregates of transmitter identified nerve terminals interacting with one another in the external layer of the median eminence. Our present data indicate the existence of putative medianosomes consisting predominantly of growth hormone releasing factor nerve terminals costoring dopamine as well as of somatostatin and dopamine nerve terminals, which interact locally to control growth hormone secretion. A complementary control of growth hormone secretion may be exerted by noradrenaline mechanisms in the subependymal layer, in the ventral zone and/or in the suprachiasmatic preoptic nucleus. However, further analyses in view of the differential effects seen with the present doses of rat hypothalamic and human pancreatic growth hormone releasing factor have to be done. The results also indicate the possible existence of growth hormone releasing factor receptors in the median eminence which may participate in the feedback control of the growth hormone releasing factor immunoreactive neurons in the ventral zone of the hypothalamus.

The effect of reserpine treatment on choline acetyltransferase activity in rat submaxillary glands

Rats were treated daily with a low dose of reserpine (0.1 mg kg-1) injected subcutaneously for 3 weeks. In the submaxillary glands the noradrenaline content was reduced by about 95%. The total activity of the acetylcholine-synthesizing enzyme choline acetyltransferase remained unchanged. However, the activity of this enzyme was found to be increased when the reserpine treatment was followed by surgical sympathetic denervation and the glands were analysed 3 weeks post-operatively. The enzyme activity also increased in the glands when the surgical sympathetic denervation was performed on the day of the start of the reserpine treatment. The lack of effect of reserpine on choline acetyltransferase activity in the glands seems to exclude the possibility that it is the depletion of neuronal noradrenaline stores that initiates the events giving rise to increases in choline acetyltransferase activity after sympathetic denervation.

Differential effects of sino-aortic denervation on cardiac noradrenaline stores, turnover and neuronal re-uptake in normotensive and renal hypertensive rabbits

Differential effects of sino-aortic denervation on cardiac noradrenaline stores, turnover and neuronal re-uptake in normotensive and renal hypertensive rabbits

Correlation between total catecholamine content and redistribution of myosin isoenzymes in pressure loaded ventricular myocardium of the spontaneously hypertensive rat.

In the spontaneously hypertensive rat (SHR) with established hypertension left ventricular mass closely correlated with the proportion of ventricular myosin (VM)-3. A 60% VM-3 content was reached corresponding, under the present housing conditions, to an average age of 40 weeks without any significant change in total noradrenaline content. However, all 72-week-old SHR showed marked reduction in total noradrenaline content which corresponded to noradrenaline depletion. At this stage, the proportion of VM-3 varied greatly; some of the SHR exhibited a higher proportion of VM-3 than would be expected from their ventricular weight. The excessive redistribution in the direction of VM-3 might, therefore, be considered as a reaction secondary to noradrenaline depletion. Total dopamine content was also reduced in 72-week-old SHR. In younger SHR, a positive correlation was found for dopamine content and left ventricular weight. It is concluded that a redistribution of the myosin isoenzymes up to 60% VM-3 in SHR is not associated with deterioration of ventricular performance to the extent that an excessive neurohumoral drive ensues. However, in the late stage of haemodynamic overload, a functional state is reached which is prone to noradrenaline depletion. A causative factor involved in this process could be the extreme redistribution of the myosin isoenzyme population, besides other factors such as fibrosis and dilatation. Which functional determinants or structural elements are finally decisive for the transition into a myocardium with depleted noradrenaline stores requires further investigation.

Neurotransmitter synthesis, storage, and turnover in neonatally deafferented sympathetic neurons

In the superior cervical sympathetic ganglion (SCG) of the rat, a significant amount of morphological and biochemical maturation occurs in the first few postnatal weeks. The specific activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of norepinephrine (NE), increases during this time and is subject to transsynaptic regulation by the preganglionic inputs. In the present study, we examined the normal postnatal development of NE stores in sympathetic neurons and the transsynaptic regulation of this development. NE content undergoes an 8-fold increase from the time of birth, and stabilizes at adult levels at one month. Following neonatal deafferentation, there is a temporary stunting of NE accumulation in sympathetic neurons and a permanent reduction in the activity of TH, whether or not regeneration of the afferents occurs. When regeneration is prevented, the turnover of NE is significantly reduced, while NE levels rise to near normal levels. When regeneration is permitted, however, both the stored amount and turnover of NE attain normal levels. These data suggest that there is a critical period during the first two postnatal weeks when transsynaptic influences from afferents are necessary for the induction of TH in sympathetic neurons. Levels and turnover of transmitter do not have this critical period, but appear to depend solely on the functional integrity of the system.

Behavioral depression after intraventricular infusion of octopamine in rats

The behavioral and neurochemical effects of four intraventricular infusions of octopamine (3,200 μg), tryptophan (800 μg), and octopamine plus tryptophan delivered over 6 hours was studied in rats after performing a portacaval anastomosis or a sham operation. After each infusion, each animal was rated for neurologic depression with a 17 point test battery. Although overt coma was not induced, octopamine infusions severely depressed neurologic function. Concentrations of norepinephrine, dopamine, and serotonin in the brain were significantly decreased after the infusion of octopamine. Levels of norepinephrine in the brain were significantly correlated with neurologic status and greater depletion of norepinephrine was associated with greater neurologic depression. These studies demonstrate that infusing large amounts of the trace amine octopamine depresses behavior in the rat and this depression is most closely associated with depletion of stores of norepinephrine in the brain.

The effect of etidocaine on spontaneous and evoked release of norepinephrine from rat brain synaptosomes.

Local anesthetics have been shown to have an effect on neurotransmission. In this study we examined the effect of a local anesthetic, etidocaine, on the uptake, efflux, and release of norepinephrine (NE) from central nerve terminals. The studies were performed on synaptosomes and vesicles prepared from rat brains. Etidocaine 10(-4) M inhibited synaptosomal accumulation of [3H]NE and did not significantly effect vesicular accumulation of this neurotransmitter. This concentration of etidocaine also augmented efflux of norepinephrine from synaptosomal preparations. This augmented efflux was primarily due to an increase in the deaminated metabolite 3,4-dihydroxyphenylglycol (DOPEG). The presence of etidocaine did not significantly alter the release of NE from synaptosomes superfused with high potassium (40 mM), a calcium-dependent exocytotic release process. These results indicate that in the central nervous system, as previously demonstrated in the peripheral nervous system, high concentrations of etidocaine alter vesicular storage of NE, resulting in more NE leaking into the cytoplasm where it is metabolized to an inactive metabolite.

Moderate cooling depresses the accumulation and the release of newly synthesized catecholamines in isolated canine saphenous veins.

Moderate cooling (from 37 degrees to 24 degrees C) depressed the formation of 3H-dopamine and 3H-norepinephrine from 3H-tyrosine by isolated canine saphenous veins. Cooling reduced the evoked release of newly synthesized catecholamine to the same extent as that of stored norepinephrine. Hence the augmentation by cold of the contractile response to sympathetic nerve stimulation observed in earlier work is not accompanied by an augmented release of newly synthesized norepinephrine.