Adrenergic Synapses Research Articles

Physiology of cholinergic and adrenergic synapses. Role in pharmacology and practical significance

The transmission of signals between cholinergic neurons and from neurons to muscle cells (neuro-neuronal and neuromuscular transduction) occurs through synapses. They are formed by the membranes of two contacting cells, presynaptic and postsynaptic, which are separated by a narrow synaptic gap. The review article provides up-to-date information about the physiological processes in cholinergic and adrenergic synapses. The role of these synapses in pharmacology and their practical significance are presented. The transmission of excitation in cholinergic synapses occurs with the help of acetylcholine. The stages of synthesis, storage and release of acetylcholine are the same in all cholinergic neurons. The specific effects of acetylcholine mediated through cholinergic synapses depend mainly on the type of synaptic cholinergic receptors. In the system of efferent innervation, adrenergic synapses are formed by the endings of postganglionic sympathetic (adrenergic) fibers and cells of effector organs.

MRNA and microRNA Profiles in the Amygdala Are Relevant to Susceptibility and Resilience to Psychological Stress Induced in Mice.

Severe or prolonged stress increases the risk for developing psychopathological disorders. An individual's perception of stress exposure varies greatly, as do its consequences. Numerous individuals demonstrate resilience to psychological stress. The mRNA and microRNA profiles of stress susceptibility and resilience to induced psychological stress in the amygdala remain to be elucidated. In this work, psychological stress was induced in an observer mouse by witnessing a similar individual under attack by an aggressor. After 5 days of psychological stress, the degree of fear memory and anxiety in mice was measured by a social interaction test and elevated plus-maze (EPM) test. mRNA and microRNA profiles were quantified by high-throughput sequencing in amygdala tissue harvested from Control, Susceptible and Resilient mice. In the amygdala of Susceptible versus Resilient mice, the upregulation of peptide, thyrotropin-releasing hormone, ECM receptors, glutamatergic synapse, cytokine-cytokine receptor interaction, long-term depression, PI3K-Akt, oxytocin, GnRH, HIF-1, estrogen, and calcium signaling pathways may be related to psychological stress-induced susceptibility, and their downregulation may be related to resilience. The downregulation of adrenergic synapse, adherens junction, Wnt, sphingolipid, B cell receptor, cAMP, Rap1, and Toll-like receptor signaling pathways may be related to psychological stress-induced susceptibility, and the upregulation may be related to resilience. Results by sequencing of mRNA and microRNA profiles are consistent, in which some are validated by qRT-PCR and dual-luciferase reporter assay. Susceptibility and resilience induced by psychological stresses are caused by the imbalanced regulation of different synapses and signaling pathways in the amygdala.

Merkel Cells Activate Sensory Neural Pathways through Adrenergic Synapses

Epithelial-neuronal signaling is essential for sensory encoding in touch, itch, and nociception; however, little is known about the release mechanisms and neurotransmitter receptors through which skin cells govern neuronal excitability. Merkel cells are mechanosensory epidermal cells that have long been proposed to activate neuronal afferents through chemical synaptic transmission. We employed a set of classical criteria for chemical neurotransmission as a framework to test this hypothesis. RNA sequencing of adult mouse Merkel cells demonstrated that they express presynaptic molecules and biosynthetic machinery for adrenergic transmission. Moreover, live-cell imaging directly demonstrated that Merkel cells mediate activity- and VMAT-dependent release of fluorescent catecholamine neurotransmitter analogs. Touch-evoked firing in Merkel-cell afferents was inhibited either by pre-synaptic silencing of SNARE-mediated vesicle release from Merkel cells or by neuronal deletion of β2-adrenergic receptors. Together, these results identify both pre- and postsynaptic mechanisms through which Merkel cells excite mechanosensory afferents to encode gentle touch. VIDEO ABSTRACT.

Involvement of GABAergic and Adrenergic Neurotransmissions on Paraventricular Nucleus of Hypothalamus in the Control of Cardiac Function

Sympathetic premotor neurons of the paraventricular hypothalamus (PVN) play a role in hemodynamics adjustments during changes in body fluid homeostasis. However, PVN contribution to the tonic control of cardiac function remains to be systematically studied. In this study, we assessed whether GABAergic and adrenergic synapses, known for being active in the PVN, are involved in the control of cardiac function. Adult male Wistar rats (250–350 g; n = 27) were anesthetized with urethane (1.2–1.4 g/kg i.p.) and underwent catheterization of femoral artery to record blood pressure and heart rate. The femoral vein was used to inject the vasoactive agents phenylephrine (10 μg/kg) and sodium nitroprusside (10 μg/kg) and to supplement anesthesia. The cardiac left ventricle was catheterized to record left ventricular pressure and its derivative. Craniotomy allowed for injections (100 nL) into the PVN of: muscimol (20 mM), bicuculline methiodide (0.4 mM), propranolol (10 mM), isoproterenol (100 μM), phentolamine (13 mM), phenylephrine (30 nM). We found that: (i) inhibition of PVN by muscimol, reduced arterial pressure, cardiac chronotropy and inotropy; (ii) disinhibition of PVN neurons by bicuculline evoked positive chronotropy and inotropy, and increase blood pressure; (iii) PVN alpha adrenergic receptors control cardiac chronotropy and inotropy; (iv) beta adrenergic receptors of the PVN do not influence cardiac function; (v) afterload does not contribute to the PVN-evoked inotropy. Our results indicate that the modulation of the activity of PVN neurons exerted by GABAergic and adrenergic mechanisms contribute to the control of cardiac function.

Excess Nitric Oxide (NO) Blunts Presynaptic Adrenergic Transduction in Orthostatic Intolerance (OI)

NO is a fundamental signaling molecule during postural blood redistribution. NO can centrally modulate sympathetic vasoconstriction by reducing sympathetic outflow, and can peripherally reduce sympathetic transduction at pre- and post-junctional sites of the adrenergic synapse. Prior data suggest blunted adrenergic vasoconstriction as a fundamental mechanism in orthostatic intolerance. We hypothesized that the production of NO in OI is enhanced resulting in reduced sympathetic noradrenergic neurotransmission which may be at pre- or post-junctional sites. To investigate this we predilated cutaneous arteries using adenosine as a [mostly] NO-independent vasodilator and local heat as a[mostly] NO-dependent vasodilator. We investigated the dose response to pre-synaptic vasoconstriction with tyramine and post-synaptic vasoconstriction with norepinephrine with or without NOS inhibition using nitro-L-arginine (NLA). The dose-responses of 8 OI (19 ± 3 yrs) patients were compared with 11 healthy controls (21 ±3 yrs). Data from OI and control subjects with and without NLA were compared by repeated measures ANOVA. OI subjects exhibited blunted vasoconstriction responses (P<0.001) to tyramine following adenosine pre-dilation which were similar to control with NLA. Tyramine dose-response following heat pre-dilation were blunted in both OI and controls. Norepinephrine dose-response was similar for OI and controls with and without NLA. The data confirm that NO modulates cutaneous sympathetic nerve transduction both pre- and post-synaptically in OI and controls. However, excessive endogenous NO blunts pre-synaptic adrenergic transduction in OI which may account, in part, for impaired sympathetic vasoconstriction.

3,4 Diaminopyridine - A Promising Novel Treatment Approach to Orthostatic Hypotension (P05.204)

Objective: To prove the hypothesis that 3,4-diaminopyridine (3,4-DAP) effectively improves blood pressure (BP) and symptoms in orthostatic hypotension (OH) with predominant effects in the upright position. Background Treatment options for OH are limited and often associated with aggravation of supine hypertension. We could recently demonstrate that acetylcholinesterase inhibition is efficacious in OH without worsening of supine hypertension, but with modest efficacy. We now hypothesized that the potassium channel blocker 3,4-DAP has similar but greater beneficial effects in patients with OH, as it should not only enhance adrenergic ganglionic neurotransmission but also neurotransmission at the adrenergic endorgan synapse, resulting in serially linked and therefore potentiated effects. Design/Methods: We studied 11 patients with neurogenic OH in a placebo-controlled patient-blinded protocol. Following a 20 minute period of supine rest, BP and heart rate (HR) were continuously monitored for 10 minutes in the supine position, followed by 5 minutes of 70 degree head-up tilt, 1 hour following administration of placebo and 1 hour after 20mg of 3,4-DAP. Cardiovascular parameters, orthostatic symptoms, QTc interval, and side effects were compared between treatment status in this pilot trial. Results: Orthostatic BP was significantly improved after administration of 3,4-DAP compared to placebo (systolic BP 111.9±6.2 vs. 88.7±6.3mmHg, diastolic BP 77.9±3.8 vs. 63.3±3.8, both p Conclusions: 3,4-DAP is safe and well tolerated, and dramatically improves OH and orthostatic symptoms. The improvement is much more pronounced than that seen with pyridostigmine, consistent with the hypothesis of potentiated, serially linked effects. A large double-blind, placebo-controlled trial is now planned to further confirm these findings. Supported by: Ronald F. Kinney Executive Dean for Research Career Development Award, NIH (BIRCWH 5K12HD065987-02 and NS 44233), and Mayo CTSA (RR00585). Disclosure: Dr. Singer has nothing to disclose. Dr. Gehrking has nothing to disclose. Dr. Gehrking has nothing to disclose. Dr. Sletten has nothing to disclose. Dr. Figueroa has nothing to disclose. Dr. Sandroni has nothing to disclose. Dr. Low has received personal compensation for activities with Chelsea, Pfizer, and WR Medical Inc. as a consultant.Dr. Low has received personal compensation in an editorial capacity for Autonomic Neuroscience.

Role of neuronal potassium M-channels in sympathetic regulation of cardiac function

Role of neuronal potassium M-channels in sympathetic regulation of cardiac function

Presynaptic changes promoted by alloxan diabetes in the cat isolated heart.

Adrenergic presynaptic functions were evaluated in the cat isolated perfused heart preparation. The sympathetic nerve endings were labelled with [3H]noradrenaline ([3H]NA) and the effect of electric neural stimulation was determined in the presence of drugs which inhibit neuronal or extraneuronal uptake, or which antagonize alpha-adrenoceptors. [3H]NA overflow was measured in control and diabetic cats and was significantly increased by electric neural stimulation on both conditions. Perfusion with 0.1 microM phentolamine increased transmitter overflow in control hearts but failed to do so on organs obtained from alloxan-treated cats. The data provide evidence that in alloxan diabetic cats there is an abnormality of the adrenergic synapse.

Fetal Meconium Peritonitis Associated with Prenatal Methamphetamine Exposure

In roughly 50% of all patients with meconium peritonitis, there is no evidence of primary obstruction of the bowel. We report a case of maternal methamphetamine and heroin abuse complicated by fetal meconium pseudocyst without a definite intestinal obstructive lesion. We discuss the correlation between the presence of meconium peritonitis and prenatal exposure to methamphetamine. A 19-year-old, gravida 2, para 0, abortus 1, woman had abused illegal drugs, including methamphetamine and intravenous heroin. Suffering from withdrawal symptoms, she was taken to a shelter where she was diagnosed with a pregnancy of 26 weeks' gestation. The patient underwent cesarean section at 34 weeks due to preterm labor and fetal malpresentation. A boy weighing 2,474 g was born, but had to be intubated and admitted to the intensive care unit because of a distended abdomen and respiratory distress. A laparotomy performed on the second day of life revealed a large calcified pseudocyst associated with two perforations of the distal jejunum. A segmental resection of the jejunum with primary anastomosis was performed. The infant recovered well after the operation and was discharged 65 days after birth. Since methamphetamine is a powerful α-adrenergic stimulant and induces the release of catecholamines from adrenergic synapses, it can cause powerful vessel constriction. Prenatal exposure to methamphetamine can cause disruption of mesenteric blood flow with transmural necrosis of the bowel, resulting in bowel perforation and meconium peritonitis.

The presynaptic activity of huwentoxin-I, a neurotoxin from the venom of the Chinese bird spider Selenocosmia huwena

Three different types of isolated nerve–synapse preparations, guinea pig ileum, rat vas deferens and toad heart, were used to investigate the physiological activity of Huwentoxin-I, a neurotoxin from the venom of the spider Selenocosmia huwena. The twitch response of isolated guinea pig ileum induced by electrical stimulus can be inhibited by HWTX-I. After blockage, contraction of the ileum can be induced by exogenously applied acetylcholine. HWTX-I caused the inhibition of the twitch response to electrical nerve stimulation in the rat vas deferens. After the twitch was completely inhibited, noradrenaline triggered rhythmic contraction of the vas deferens. The inhibitory effect on heart of toad induced by stimulating sympathetic-vagus nerve can be reversed by HWTX-I, although exogenously applied acetylcholine still acts as an effective inhibitor. All of these results support the conclusion that HWTX-I has the presynaptic activity that effects the release of neurotransmitter from the nerve endings of both the cholinergic synapse and the adrenergic synapse.

Spontaneous synaptogenesis in ex vivo sympathetic ganglion and the blockade by serum treatment

Central denervation for more than 1 month has been shown to cause an increase in the number of adrenergic synapses in sympathetic ganglia in vivo. Here, we report several lines of evidence that adrenergic synapses may be generated de novo in ex vivo superior cervical ganglion (SCG) of adult rats only several hours after the isolation. Structures immunoreactive for synaptophysin, a marker of presynaptic elements, were drastically decreased 6 days after the preganglionic denervation. A significant increase in number of synaptophysin positive boutons was observed over 3-8 hours in the denervated SCGs maintained ex vivo at 36 degrees C in oxygenated physiologic saline, and this increase was blocked by adding normal serum in the saline. Electron microscopic analysis confirmed that the number of adrenergic synapses specifically labeled with 5-hydroxydopamine was increased by several-fold under the same condition. Intracellular labeling of SCG neurons revealed an increase in the incidence (from 8 to 50%) of neurons having dendritic plexus after the in vitro incubation. No evidence of axonal sprouting within the ganglion was observed. Intracellular recordings from single neurons of denervated SCGs revealed that maximum amplitudes of inhibitory postsynaptic potentials, which were completely blocked by yohimbine, an alpha2-adrenoceptor antagonist, in response to focal stimulation were increased over the several hours. These results suggest that dendrites of SCG neurons rapidly develop and exhibit local efferent characteristics that underlie the inhibitory synaptic transmission once they are subjected to serum deprivation.

Adverse effects of polluted continental water bodies in Chile on frog adrenergic synapse.

Adverse effects of polluted continental water bodies in Chile on frog adrenergic synapse.

The adrenergic innervation of the rat central amygdaloid nucleus: a light and electron microscopic immunocytochemical study using phenylethanolamine N-methyltransferase as a marker.

Using immunocytochemistry of phenylethanolamine N-methyltransferase for light and electron microscopy, investigations were carried out to document the morphology of adrenergic afferents innervating the rat central amygdaloid nucleus and to analyse the manner in which contacts with neurons of the nucleus are formed. With the light microscope, dense terminal plexus of phenylethanolamine N-methyltransferase-immunoreactive axons with typical large boutons (diameter > 1 micron) were found in the medial central nucleus, extending into its ventral subdivision and the adjacent intra-amygdaloid portion of the bed nucleus of the stria terminalis. Electron microscopy of the medial central nucleus showed phenylethanolamine N-methyltransferase-immunoreaction product in the cytoplasm of intervaricose axons and boutons. Large adrenergic boutons contained numerous small clear vesicles and, occasionally, large dense-cored vesicles. In serial sections, most boutons formed synaptic contacts. Synapses of immunoreactive terminals were mainly of the asymmetric type and localized preferentially on medium sized to small dendrites and dendritic spines. Structures postsynaptic to adrenergic boutons were often additionally contacted by non-labelled terminals. The study gives evidence that adrenergic afferents exert a direct synaptic influence on medial central nucleus neurons. The peripheral localization of the majority of adrenergic synapses, their asymmetric configuration, and the presence of non-adrenergic synapsing terminals in their immediate vicinity indicate that the major component of the adrenergic input is of an excitatory nature, and is integrated with innervation from other sources.

Modelling of the enteric nervous network: 3. Adrenergic neuron

A mathematical model is developed to investigate the coupled electrochemical processes of nerve-pulse transmission via adrenergic synapse. Based on pharmacological and morphophysiological data, the model describes the dynamics of the propagation of the electric signal along the unmyelinated geometrically non-uniform axon of the neuron and the chemical mechanisms of the transformation of the electrical signal in the synaptic zone into the post-synaptic output. The combined nonlinear system of partial and ordinary differential equations has been obtained and solved numerically. The results of computer simulation of the function of the idealized adrenergic neuron quantitatively and qualitatively describe the dynamics of Ca 2+ ion influx into the terminal, noradrenaline release from the free ‘releasable’ store, its diffusion into the synaptic cleft, binding with the adrenoceptors on the pre- and post-synaptic structures with the generation of the inhibitory post-synaptic potential, and utilization of noradrenaline by neuronal and non-neuronal capture mechanisms.

A hypothetical model of processes involved in the release of norepinephrine in the adrenergic synapse

A hypothetical, conceptual model of mechanisms involved in the release of norepinephrine in the adrenergic synapse is presented. An illustrative, mathematical equivalent of the model was constructed to enable computer simulation of the considered processes in varying cytophysiological conditions. The mathematical model has the form of a set of equations that make it possible to compute the state of the system at the moment t + Δt on the basis of the state at the moment t.

Studies on the presynaptic mechanisms involved in the adrenergic synapse function in the myenteric plexus

Studies on the presynaptic mechanisms involved in the adrenergic synapse function in the myenteric plexus

Stereoselective delivery and actions of beta receptor antagonists

These studies have revealed that the delivery and actions of beta receptor antagonist drugs are controlled by a cascade of stereoselective processes involving multiple enzymes, transport proteins and receptors. In essence, the free concentration of the pharmacologically active (−)-enantiomer species of these drugs presented to cell surface beta receptors appears to be a function of the stereoselective clearance by hepatic cytochrome P-450 isoenzymes, enantiomer selective binding to α 1-acid glycoprotein and albumin and perhaps predominantly by stereoselective sequestration (and release) by the vesicular amine transport protein within adrenergic neurons. Stereoselectivity in the clearance of beta blocking drugs, which can favor either the (+)- or (−)- enantiomer, only appears to be important for the lipophilic drugs which are cleared by hepatic metabolism. Such Stereoselectivity is due to differential stereochemical substrate requirements of individual hepatic cytochrome P-450 isoenzymes. Interindividual variations in the Stereoselectivity can occur as a result of differences in the amount and expression of cytochrome P-450 isoenzymes due to genetic predisposition or other factors. In the same context, we have observed a significant correlation between the extent and Stereoselectivity of binding of beta blocking drugs to plasma proteins. This is another finding which suggests that variability in the expression of individual proteins involved in the beta blocking drug-protein cascade determines the free concentration of the pharmacologically active enantiomer. However, since most observations have been made in young normal subjects, the extent of Stereoselectivity in metabolism, binding and other processes is unknown in the general population where steady-state plasma concentrations can vary widely due to multiple biological factors. The observations from neural studies support the concept that adrenergic nerve endings provide a depot for the stereoselective storage and release of the active enantiomer of beta receptor antagonists. The mechanism of this release appears to involve exocytotic secretion of drug that has been stereoselectively accumulated by the neurotransmitter storage vesicles. In terms of this idea, beta receptor antagonists released during nerve stimulation may achieve concentrations of the (−)-enantiomer within the adrenergic synapse greatly in excess of those found in plasma. Such a mechanism could significantly influence both the intensity and duration of beta receptor blockade in the heart, blood vessels, brain and other target tissues. Indeed, persistence of the cardiovascular effects of beta receptor antagonists after plasma levels of drug have apparently declined below effective concentrations could be explained in part by this phenomenon. In any event, it seems clear that stereoselective storage and secretion by nerve endings provides an additional mechanism for modulating the delivery and concentration of the active enantiomer of beta receptor blocking drugs at sites of action within the adrenergic synapse. In conclusion, multiple enzymes, transport proteins and other proteins, each with specific stereochemical requirements, determine the delivery and therapeutic actions of beta receptor antagonist drugs.

New synapses associated with the granule-containing cells of rat sympathetic ganglia.

The synapses of the rat superior cervical sympathetic ganglion were studied with both conventional and ultrastructural histochemical methods. Besides the cholinergic synapses polarized from preganglionic fibers to sympathetic ganglion neurons, two morphologically and functionally different types of synapses were observed in relation to the small granule-containing (catecholamine-containing) cells of the rat superior cervical ganglion. The first type is an efferent adrenergic synapse polarized from granule-containing cells to the dendrites of the sympathetic ganglion neurons. This type of synapse might mediate the inhibitory effects (slow inhibitory postsynaptic potentials) induced by catecholamines on the sympathetic neurons. The second type is a reciprocal type of synapse between the granule-containing cells and the cholinergic preganglionic fibers. Through such synapses, these cells could exert a modulating effect on the excitatory preganglionic fibers. Therefore, we propose that these cells, through their multiple synaptic connections, exhibit a local modulatory feedback system in the rat sympathetic ganglia and may serve as interneurons between the preganglionic and postganglionic sympathetic neurons.

Potentiation of sympathetic neurosecretion by forskolin and cyclic AMP in the rabbit iris-ciliary body.

Forskolin has been reported to stimulate cAMP formation and reduce intraocular pressure in rabbit and primate eyes. In view of recent evidence for the involvement of cAMP in modulation of transmitter release at adrenergic synapses, we have investigated the presynaptic effects of forskolin and other cAMP activators on field-stimulated secretion of 3H-norepinephrine (3H-NE) in the isolated, perfused rabbit iris-ciliary body. Forskolin (10(-7)-10(-5) M) was found to markedly enhance stimulation-evoked 3H-NE release without affecting basal (spontaneous) release. The response to forskolin was potentiated by the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX; 0.5 mM) and was mimicked by the cell-permeant cyclic nucleotide analog 8-bromo-cAMP. 8-bromo-cGMP also produce a small enhancement of stimulus-evoked 3H-NE secretion, whereas IBMX alone had little effect on either stimulated or basal secretion. These results suggest that cAMP may play an important neuromodulatory role in regulation of norepinephrine release at intraocular synapses, and raise the possibility that the ocular hypotensive response to forskolin in rabbit eyes may be mediated, in part, by enhanced adrenergic neurosecretion.

Possible control mechanisms of feather follicle movement in the pectoral tract of the chicken.

Feather follicle movement control was studied on feathers of the pectoral tract in the anaesthetized chicken. Dissection of nerves leading to the follicles showed that their origin was at least partially in the sympathetic ganglia. Reflectoric ruffling of feathers could be obtained after adequate stimulation. Intravenous injections of drugs in doses which influenced the circulation gave the following results: Adrenaline caused erection of feathers which was abolished by phentolamine. Noradrenaline caused up and down movements after injection only at high doses. Similar results were obtained by placing of skin pieces in saline containing the drugs. The reaction to drugs was typical always for a given group of feathers. Killing of birds and anaesthesia caused general erection of feathers which was not abolished by phentolamine. The findings suggest that adrenergic synapses are involved in feather follicle movement control, but at least another mechanism (CNS) regulates feather follicle movement.