Recent progress in alpha1-adrenergic receptor research

Evolution and divergence of teleost adrenergic receptors: why sometimes 'the drugs don't work' in fish

Adrenaline and noradrenaline, released as hormones and/or neurotransmitters, exert diverse physiological functions in vertebrates, and teleost fishes are widely used as model organisms to study adrenergic regulation; however, such investigations often rely on receptor subtype-specific pharmacological agents (agonists and antagonists; see Glossary) developed and validated in mammals. Meanwhile, evolutionary (phylogenetic and comparative genomic) studies have begun to unravel the diversification of adrenergic receptors (ARs) and reveal that whole-genome duplications and pseudogenization events in fishes results in notable distinctions from mammals in their genomic repertoire of ARs, while lineage-specific gene losses within teleosts have generated significant interspecific variability. In this Review, we visit the evolutionary history of ARs (including α1-, α2- and β-ARs) to highlight the prominent interspecific differences in teleosts, as well as between teleosts and other vertebrates. We also show that structural modelling of teleost ARs predicts differences in ligand binding affinity compared with mammalian orthologs. To emphasize the difficulty of studying the roles of different AR subtypes in fish, we collate examples from the literature of fish ARs behaving atypically compared with standard mammalian pharmacology. Thereafter, we focus on specific case studies of the liver, heart and red blood cells, where our understanding of AR expression has benefited from combining pharmacological approaches with molecular genetics. Finally, we briefly discuss the ongoing advances in 'omics' technologies that, alongside classical pharmacology, will provide abundant opportunities to further explore adrenergic signalling in teleosts.

Sympathetic Nervous System and Atherosclerosis

Atherosclerosis is characterized by the narrowing of the arterial lumen due to subendothelial lipid accumulation, with hypercholesterolemia being a major risk factor. Despite the recent advances in effective lipid-lowering therapies, atherosclerosis remains the leading cause of mortality globally, highlighting the need for additional therapeutic strategies. Accumulating evidence suggests that the sympathetic nervous system plays an important role in atherosclerosis. In this article, we reviewed the sympathetic innervation in the vasculature, norepinephrine synthesis and metabolism, sympathetic activity measurement, and common signaling pathways of sympathetic activation. The focus of this paper was to review the effectiveness of pharmacological antagonists or agonists of adrenoceptors (α1, α2, β1, β2, and β3) and renal denervation on atherosclerosis. All five types of adrenoceptors are present in arterial blood vessels. α1 blockers inhibit atherosclerosis but increase the risk of heart failure while α2 agonism may protect against atherosclerosis and newer generations of β blockers and β3 agonists are promising therapies against atherosclerosis; however, new randomized controlled trials are warranted to investigate the effectiveness of these therapies in atherosclerosis inhibition and cardiovascular risk reduction in the future. The role of renal denervation in atherosclerosis inhibition in humans is yet to be established.

Understanding How Physical Exercise Improves Alzheimer’s Disease: Cholinergic and Monoaminergic Systems

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, characterized by the accumulation of proteinaceous aggregates and neurofibrillary lesions composed of β-amyloid (Aβ) peptide and hyperphosphorylated microtubule-associated protein tau, respectively. It has long been known that dysregulation of cholinergic and monoaminergic (i.e., dopaminergic, serotoninergic, and noradrenergic) systems is involved in the pathogenesis of AD. Abnormalities in neuronal activity, neurotransmitter signaling input, and receptor function exaggerate Aβ deposition and tau hyperphosphorylation. Maintenance of normal neurotransmission is essential to halt AD progression. Most neurotransmitters and neurotransmitter-related drugs modulate the pathology of AD and improve cognitive function through G protein-coupled receptors (GPCRs). Exercise therapies provide an important alternative or adjunctive intervention for AD. Cumulative evidence indicates that exercise can prevent multiple pathological features found in AD and improve cognitive function through delaying the degeneration of cholinergic and monoaminergic neurons; increasing levels of acetylcholine, norepinephrine, serotonin, and dopamine; and modulating the activity of certain neurotransmitter-related GPCRs. Emerging insights into the mechanistic links among exercise, the neurotransmitter system, and AD highlight the potential of this intervention as a therapeutic approach for AD.

A Concise and Useful Guide to Understand How Alpha1 Adrenoceptor Antagonists Work

Adrenoceptors are the receptors for the catecholamines, adrenaline and noradrenaline. They are divided in α (α1 and α2) and β (β1, β2 and β3). α1-Adrenoceptors are subdivided in α1A, α1B and α1D. Most tissues express mixtures of α1-adrenoceptors subtypes, which appear to coexist in different densities and ratios, and in most cases their responses are probably due to the activation of more than one type. The three subtypes of α1-adrenoceptors are G-protein-coupled receptors (GPCR), specifically coupled to Gq/11. Additionally, the activation of these receptors may activate other signaling pathways or different components of these pathways, which leads to a great variety of possible cellular effects. The first clinically used α1 antagonist was Prazosin, for Systemic Arterial Hypertension (SAH). It was followed by its congeners, Terazosin and Doxazosin. Nowadays, there are many classes of α-adrenergic antagonists with different selectivity profiles. In addition to SAH, the α1-adrenoceptors are used for the treatment of Benign Prostatic Hyperplasia (BPH) and urolithiasis. This antagonism may be part of the mechanism of action of tricyclic antidepressants. Moreover, the activation of these receptors may lead to adverse effects such as orthostatic hypotension, similar to what happens with the antidepressants and with some antipsychotic. Structure-activity relationships can explain, in part, how antagonists work and how selective they can be for each one of the subtypes. However, it is necessary to develop new molecules which antagonize the α1-adrenoceptors or make chemical modifications in these molecules to improve the selectivity, pharmacokinetic profile and/or reduce the adverse effects of known drugs.

Involvement of the Dorsal Vagal Complex in Alcohol-Related Behaviors

The neurobiological mechanisms that regulate the development and maintenance of alcohol use disorder (AUD) are complex and involve a wide variety of within and between systems neuroadaptations. While classic reward, preoccupation, and withdrawal neurocircuits have been heavily studied in terms of AUD, viable treatment targets from this established literature have not proven clinically effective as of yet. Therefore, examination of additional neurocircuitries not classically studied in the context of AUD may provide novel therapeutic targets. Recent studies demonstrate that various neuropeptides systems are important modulators of alcohol reward, seeking, and intake behaviors. This includes neurocircuitry within the dorsal vagal complex (DVC), which is involved in the control of the autonomic nervous system, control of intake of natural rewards like food, and acts as a relay of interoceptive sensory information via interactions of numerous gut-brain peptides and neurotransmitter systems with DVC projections to central and peripheral targets. DVC neuron subtypes produce a variety of neuropeptides and transmitters and project to target brain regions critical for reward such as the mesolimbic dopamine system as well as other limbic areas important for the negative reinforcing and aversive properties of alcohol withdrawal such as the extended amygdala. This suggests the DVC may play a role in the modulation of various aspects of AUD. This review summarizes the current literature on neurotransmitters and neuropeptides systems in the DVC (e.g., norepinephrine, glucagon-like peptide 1, neurotensin, cholecystokinin, thyrotropin-releasing hormone), and their potential relevance to alcohol-related behaviors in humans and rodent models for AUD research. A better understanding of the role of the DVC in modulating alcohol related behaviors may lead to the elucidation of novel therapeutic targets for drug development in AUD.

Interdisciplinary Approach to Biological and Health Implications in Selected Professional Competences

Everyday life’s hygiene and professional realities, especially in economically developed countries, indicate the need to modify the standards of pro-health programs as well as modern hygiene and work ergonomics programs. These observations are based on the problem of premature death caused by civilization diseases. The biological mechanisms associated with financial risk susceptibility are well described, but there is little data explaining the biological basis of neuroaccounting. Therefore, the aim of the study was to present relationships between personality traits, cognitive competences and biological factors shaping behavioral conditions in a multidisciplinary aspect. This critical review paper is an attempt to compile biological and psychological factors influencing the development of professional competences, especially decent in the area of accounting and finance. We analyzed existing literature from wide range of scientific disciplines (including economics, psychology, behavioral genetics) to create background to pursuit multidisciplinary research models in the field of neuroaccounting. This would help in pointing the best genetically based behavioral profile of future successful financial and accounting specialists.

Physiological and transcriptomic changes of zebrafish (Danio rerio) embryos-larvae in response to 2-MIB exposure

2-Methylisoborneol (2-MIB), a natural odorous substance, is widely distributed in water environment, but there is a paucity of information concerning its systemic toxicity. Herein, we investigated the effects of 2-MIB exposure on developmental parameters, locomotive behavior, oxidative stress, apoptosis and transcriptome of zebrafish. Zebrafish embryos exposed to different concentrations (0, 0.5, 5 and 42.8 μg/L) of 2-MIB showed no changes in mortality, hatchability, and malformation rate, but the body length of zebrafish larvae was significantly increased in a dose-dependent manner, and accompanied by the changes of growth hormone/insulin-like growth factor (GH/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis genes. Moreover, the swimming activity of zebrafish larvae increased, which may be due to the increase of acetylcholinesterase (AChE) activity. Meanwhile, 2-MIB caused oxidative stress and apoptosis in zebrafish larvae by altering the NF-E2-related factor 2 (Nrf2) and mitochondrial signaling pathways, respectively. Transcriptome sequencing assay showed that the phototransduction signaling pathway was significantly enriched, and most of the genes in this pathway exhibited enhanced expression after exposure to 2-MIB. These findings provide an important reference for risk assessment and early warning to 2-MIB exposure.

Effects of different vasopressors on the contraction of the superior mesenteric artery and uterine artery in rats during late pregnancy

Background

Hypotension after neuraxial anaesthesia is one of the most common complications during caesarean section. Vasopressors are the most effective method to improve hypotension, but which of these drugs is best for caesarean section is not clear. We assessed the effects of vasopressors on the contractile response of uterine arteries and superior mesenteric arteries in pregnant rats to identify a drug that increases the blood pressure of the systemic circulation while minimally affecting the uterine and placental circulation.

Methods

Isolated ring segments from the uterine and superior mesenteric arteries of pregnant rats were mounted in organ baths, and the contractile responses to several vasopressor agents were studied. Concentration-response curves for norepinephrine, phenylephrine, metaraminol and vasopressin were constructed.

Results

The contractile response of the mesenteric artery to norepinephrine, as measured by the pEC50 of the drug, was stronger than the uterine artery (5.617 ± 0.11 vs. 4.493 ± 1.35, p = 0.009), and the contractile response of the uterine artery to metaraminol was stronger than the mesenteric artery (pEC50: 5.084 ± 0.17 vs. 4.92 ± 0.10, p = 0.007). There was no statistically significant difference in the pEC50 of phenylephrine or vasopressin between the two blood vessels.

Conclusions

In vitro experiments showed that norepinephrine contracts peripheral blood vessels more strongly and had the least effect on uterine artery contraction. These findings support the use of norepinephrine in mothers between the time of neuraxial anaesthesia and the delivery of the foetus.

A Study to Decipher the Potential Effects of Butylphthalide against Central Nervous System Diseases Based on Network Pharmacology and Molecular Docking Integration Strategy

Background

Butylphthalide (NBP), approved by the China National Medical Products Administration (NMPA) for the treatment of ischemic stroke (IS), showed pleiotropic potentials against central nervous system (CNS) diseases, including neuroprotection and cognitive deficits improvement. However, the effects and corresponding modes of action were not fully explored. This study was designed to investigate the potential of NBP against IS-associated CNS diseases based on network pharmacology (NP) and molecular docking (MD).

Methods

IS was inputted as the index disease to retrieve the “associated diseases” in DisGeNET. Three-database-based IS genes were obtained and integrated (DisGeNET, Malacards, and OMIM). Then, IS-associated genes were identified by combining these genes. Meanwhile, PubMed references and online databases were applied to identify NBP target genes. The IS-related disease-disease association (DDA) network and NBP-disease regulation network were constructed and analyzed in Cytoscape. In silico MD and references were used to validate the binding affinity of NBP with critical targets and the potential of NBP against certain IS-related CNS disease regulation.

Results

175 NBP target genes were obtained, while 312 IS-related disease genes were identified. 36 NBP target genes were predicted to be associated with IS-related CNS diseases, including Alzheimer's disease (AD), epilepsy, major depressive disorder (MDD), amyotrophic lateral sclerosis (ALS), and dementia. Six target genes (i.e., GRIN1, PTGIS, PTGES, ADRA1A, CDK5, and SULT1E1) indicating disease specificity index (DSI) >0.5 showed certain to good degree binding affinity with NBP, ranging from −9.2 to −6.7 kcal/mol. And the binding modes may be mainly related to hydrogen bonds and hydrophobic “bonds.” Further literature validations inferred that these critical NBP targets had a tight association with AD, epilepsy, ALS, and depression.

Conclusions

Our study proposed a drug-target-disease integrated method to predict the drug repurposing potentials to associated diseases by application of NP and MD, which could be an attractive alternative to facilitate the development of CNS disease therapies. NBP may be promising and showed potentials to be repurposed for treatments for AD, epilepsy, ALS, and depression, and further investigations are warranted to be carefully designed and conducted.

Photoinduced Electron Transfer-Based Fluorescent Agonists for α1-Adrenergic Receptors Imaging

The novel fluorescent agonists were discovered herein for α₁-adrenergic receptors (α₁-ARs) based on photoinduced electron transfer (PeT) off-on switch by conjugating the fluorophore 7-(diethylamino)coumarin-3-carboxylic acid with phenylephrine. After careful evaluation, these probes exhibited efficient binding affinity with α₁-ARs and could be applied to selectively imaging α₁-ARs or successfully tracing the dynamic process of α₁-AR internalization in living cells. Meanwhile, a bioluminescence resonance energy transfer binding assay with these new probes has been well-established and applied. Therefore, these PeT-based on-off agonists may serve as powerful tools for the α₁-AR-associated study during drug discovery.

The Role of Adrenoceptors in the Retina

The retina is a part of the central nervous system, a thin multilayer with neuronal lamination, responsible for detecting, preprocessing, and sending visual information to the brain. Many retinal diseases are characterized by hemodynamic perturbations and neurodegeneration leading to vision loss and reduced quality of life. Since catecholamines and respective bindings sites have been characterized in the retina, we systematically reviewed the literature with regard to retinal expression, distribution and function of alpha₁ (α₁)-, alpha₂ (α₂)-, and beta (β)-adrenoceptors (ARs). Moreover, we discuss the role of the individual adrenoceptors as targets for the treatment of retinal diseases.

Adrenaline induces calcium signal in astrocytes and vasoconstriction via activation of monoamine oxidase

Adrenaline or epinephrine is a hormone playing an important role in physiology. It is produced de-novo in the brain in very small amounts compared to other catecholamines, including noradrenaline. Although the effects of adrenaline on neurons have been extensively studied, much less is known about the action of this hormone on astrocytes. Here, we studied the effects of adrenaline on astrocytes in primary co-culture of neurons and astrocytes. Application of adrenaline induced calcium signal in both neurons and astrocytes, but only in neurons this effect was dependent on α- and β-receptor antagonists. The effects of adrenaline on astrocytes were less dependent on adrenoreceptors: the antagonist carvedilol had only moderate effect on the calcium signal and the agonist of adrenoreceptors methoxamine induced a signal only in small proportion of the cells. We found that adrenaline in astrocytes activates phospholipase C and subsequent release of calcium from the endoplasmic reticulum. Calcium signal in astrocytes is initiated by the metabolism of adrenaline by the monoamine oxidase (MAO), which activates reactive oxygen species production and induces lipid peroxidation. Inhibitor of MAO selegiline inhibited both adrenaline-induced calcium signal in astrocytes and the vasoconstriction that indicates an important role for monoamine oxidase in adrenaline-induced signalling and function.

PET Radiotracers for CNS-Adrenergic Receptors: Developments and Perspectives

Epinephrine (E) and norepinephrine (NE) play diverse roles in our body’s physiology. In addition to their role in the peripheral nervous system (PNS), E/NE systems including their receptors are critical to the central nervous system (CNS) and to mental health. Various antipsychotics, antidepressants, and psychostimulants exert their influence partially through different subtypes of adrenergic receptors (ARs). Despite the potential of pharmacological applications and long history of research related to E/NE systems, research efforts to identify the roles of ARs in the human brain taking advantage of imaging have been limited by the lack of subtype specific ligands for ARs and brain penetrability issues. This review provides an overview of the development of positron emission tomography (PET) radiotracers for in vivo imaging of AR system in the brain.

Oláh A, Fésüs L, Mádi A. Transglutaminase 2 Has Metabolic and Vascular Regulatory Functions Revealed by In Vivo Activation of Alpha1-Adrenergic Receptor

The multifunctional tissue transglutaminase has been demonstrated to act as α1-adrenergic receptor-coupled G protein with GTPase activity in several cell types. To explore further the pathophysiological significance of this function we investigated the in vivo effects of the α1-adrenergic receptor agonist phenylephrine comparing responses in wild type and TG2-/- mice. Injection of phenylephrine, but not a beta3-adrenergic agonist (CL-316,243), resulted in the long-term decline of the respiratory exchange ratio and lower lactate concentration in TG2-/- mice indicating they preferred to utilize fatty acids instead of glucose as fuels. Measurement of tail blood pressure revealed that the vasoconstrictive effect of phenylephrine was milder in TG2-/- mice leading to lower levels of lactate dehydrogenase (LDH) isoenzymes in blood. LDH isoenzyme patterns indicated more damage in lung, liver, kidney, skeletal, and cardiac muscle of wild type mice; the latter was confirmed by a higher level of heart-specific CK-MB. Our data suggest that TG2 as an α1-adrenergic receptor-coupled G protein has important regulatory functions in alpha1-adrenergic receptor-mediated metabolic processes and vascular functions.

Activation of alpha-1 adrenergic receptors increases cytosolic calcium in neurones of the paraventricular nucleus of the hypothalamus

Norepinephrine (NE) activates adrenergic receptors (ARs) in the hypothalamic paraventricular nucleus (PVN) to increase excitatory currents, depolarise neurones and, ultimately, augment neuro-sympathetic and endocrine output. Such cellular events are known to potentiate intracellular calcium ([Ca²⁺ ]_i ); however, the role of NE with respect to modulating [Ca²⁺ ]_i in PVN neurones and the mechanisms by which this may occur remain unclear. We evaluated the effects of NE on [Ca²⁺ ]_i of acutely isolated PVN neurones using Fura-2 imaging. NE induced a slow increase in [Ca²⁺ ]_i compared to artificial cerebrospinal fluid vehicle. NE-induced Ca²⁺ elevations were mimicked by the α₁ -AR agonist phenylephrine (PE) but not by α₂ -AR agonist clonidine (CLON). NE and PE but not CLON also increased the overall number of neurones that increase [Ca²⁺ ]_i (ie, responders). Elimination of extracellular Ca²⁺ or intracellular endoplasmic reticulum Ca²⁺ stores abolished the increase in [Ca²⁺ ]_i and reduced responders. Blockade of voltage-dependent Ca²⁺ channels abolished the α₁ -AR induced increase in [Ca²⁺ ]_i and number of responders, as did inhibition of phospholipase C inhibitor, protein kinase C and inositol triphosphate receptors. Spontaneous phasic Ca²⁺ events, however, were not altered by NE, PE or CLON. Repeated K⁺ -induced membrane depolarisation produced repetitive [Ca²⁺ ]_i elevations. NE and PE increased baseline Ca²⁺ , whereas NE decreased the peak amplitude. CLON also decreased peak amplitude but did not affect baseline [Ca²⁺ ]_i . Taken together, these data suggest receptor-specific influence of α₁ and α₂ receptors on the various modes of calcium entry in PVN neurones. They further suggest Ca²⁺ increase via α₁ -ARs is co-dependent on extracellular Ca²⁺ influx and intracellular Ca²⁺ release, possibly via a phospholipase C inhibitor-mediated signalling cascade.

Impaired diaphragm resistance vessel vasodilation with prolonged mechanical ventilation

Mechanical ventilation (MV) is a life-saving intervention, yet with prolonged MV (i.e., ≥6 h) there are time-dependent reductions in diaphragm blood flow and an impaired hyperemic response of unknown origin. Female Sprague-Dawley rats (4-8 mo, n = 118) were randomized into two groups; spontaneous breathing (SB) and 6-h (prolonged) MV. After MV or SB, vasodilation (flow-induced, endothelium-dependent and -independent agonists) and constriction (myogenic and α-adrenergic) responses were measured in first-order (1A) diaphragm resistance arterioles in vitro, and endothelial nitric oxide synthase (eNOS) mRNA expression was quantified. Following prolonged MV, there was a significant reduction in diaphragm arteriolar flow-induced (SB, 34.7 ± 3.8% vs. MV, 22.6 ± 2.0%; P ≤ 0.05), endothelium-dependent (via acetylcholine; SB, 64.3  ± 2.1% vs. MV, 36.4 ± 2.3%; P ≤ 0.05) and -independent (via sodium nitroprusside; SB, 65.0 ± 3.1% vs. MV, 46.0 ± 4.6%; P ≤ 0.05) vasodilation. Compared with SB, there was reduced eNOS mRNA expression (P ≤ 0.05). Prolonged MV diminished phenylephrine-induced vasoconstriction (SB, 37.3 ± 6.7% vs. MV, 19.0 ± 1.9%; P ≤ 0.05) but did not alter myogenic or passive pressure responses. The severe reductions in diaphragmatic blood flow at rest and during contractions, with prolonged MV, are associated with diaphragm vascular dysfunction which occurs through both endothelium-dependent and endothelium-independent mechanisms.NEW & NOTEWORTHY Following prolonged mechanical ventilation, vascular alterations occur through both endothelium-dependent and -independent pathways. This is the first study, to our knowledge, demonstrating that diaphragm arteriolar dysfunction occurs consequent to prolonged mechanical ventilation and likely contributes to the severe reductions in diaphragmatic blood flow and weaning difficulties.

Complex noradrenergic dysfunction in Alzheimer's disease: Low norepinephrine input is not always to blame

The locus coeruleus-noradrenergic (LC-NA) system supplies the cerebral cortex with norepinephrine, a key modulator of cognition. Neurodegeneration of the LC is an early hallmark of Alzheimer's disease (AD). In this article, we analyze current literature to understand whether NA degeneration in AD simply leads to a loss of norepinephrine input to the cortex. With reported adaptive changes in the LC-NA system at the anatomical, cellular, and molecular levels in AD, existing evidence support a seemingly sustained level of extracellular NE in the cortex, at least at early stages of the long course of AD. We postulate that loss of the integrity of the NA system, rather than mere loss of NE input, is a key contributor to AD pathogenesis. A thorough understanding of NA dysfunction in AD has a large impact on both our comprehension and treatment of this devastating disease.

Endocannabinoids modulate Gq/11 protein-coupled receptor agonist-induced vasoconstriction via a negative feedback mechanism

OBJECTIVES

The endocannabinoid (eCB) system centrally and peripherally regulates cardiovascular parameters, including blood pressure, in health and disease. The relationship between G_q/11 protein-coupled receptor activation, regulation of eCBs release (mainly 2-arachidonoylglycerol) and subsequent CB₁ receptor activation was initially observed in the central nervous system. Here, we review the latest findings from systemic physiological studies which include for the first time data from pulmonary arteries. We present evidence for direct CB₁ -dependent cannabinoid ligand-induced vasorelaxation, vascular expression of eCBs along with their degradation enzymes, and indicate the location of the described interaction.

KEY FINDINGS

Endocannabinoids (mainly 2-arachidonoylglycerol), acting via CB₁ receptors, evoke vasodilatory effects and may modulate responses of vasoconstrictors for G_q/11 protein-coupled receptors including angiotensin II, thromboxane A₂ , phenylephrine, noradrenaline in systemic or pulmonary arteries. However, the role of the endothelium in this interaction is not well-established, and the precise vascular location of eCB system components remains unclear, which contributes to discrepancies in the interpretation of results when describing the above-mentioned relationship.

SUMMARY

Endocannabinoid's negative feedback is responsible for diminishing agonist-induced vasoconstriction, which may be clinically important in the treatment of arterial and pulmonary hypertension. Further research is required to establish the importance of the eCB system and its downstream signalling pathways.

Factors influencing biased agonism in recombinant cells expressing the human α1A -adrenoceptor

BACKGROUND AND PURPOSE

Agonists acting at GPCRs promote biased signalling via Gα or Gβγ subunits, GPCR kinases and β-arrestins. Since the demonstration of biased agonism has implications for drug discovery, it is essential to consider confounding factors contributing to bias. We have examined bias at human α_1A -adrenoceptors stably expressed at low levels in CHO-K1 cells, identifying off-target effects at endogenous receptors that contribute to ERK1/2 phosphorylation in response to the agonist oxymetazoline.

EXPERIMENTAL APPROACH

Intracellular Ca²⁺ mobilization was monitored in a Flexstation® using Fluo 4-AM. The accumulation of cAMP and ERK1/2 phosphorylation were measured using AlphaScreen® proximity assays, and mRNA expression was measured by RT-qPCR. Ligand bias was determined using the operational model of agonism.

KEY RESULTS

Noradrenaline, phenylephrine, methoxamine and A61603 increased Ca²⁺ mobilization, cAMP accumulation and ERK1/2 phosphorylation. However, oxymetazoline showed low efficacy for Ca⁺² mobilization, no effect on cAMP generation and high efficacy for ERK1/2 phosphorylation. The apparent functional selectivity of oxymetazoline towards ERK1/2 was related to off-target effects at 5-HT_1B receptors endogenously expressed in CHO-K1 cells. Phenylephrine and methoxamine showed genuine bias towards ERK1/2 phosphorylation compared to Ca²⁺ and cAMP pathways, whereas A61603 displayed bias towards cAMP accumulation compared to ERK1/2 phosphorylation.

CONCLUSION AND IMPLICATIONS

We have shown that while adrenergic agonists display bias at human α_1A -adrenoceptors, the marked bias of oxymetazoline for ERK1/2 phosphorylation originates from off-target effects. Commonly used cell lines express a repertoire of endogenous GPCRs that may confound studies on biased agonism at recombinant receptors.

Redistribution of Cerebral Blood Flow during Severe Hypovolemia and Reperfusion in a Sheep Model: Critical Role of α1-Adrenergic Signaling

Background: Maintenance of brain circulation during shock is sufficient to prevent subcortical injury but the cerebral cortex is not spared. This suggests area-specific regulation of cerebral blood flow (CBF) during hemorrhage. Methods: Cortical and subcortical CBF were continuously measured during blood loss (≤50%) and subsequent reperfusion using laser Doppler flowmetry. Blood gases, mean arterial blood pressure (MABP), heart rate and renal blood flow were also monitored. Urapidil was used for α1A-adrenergic receptor blockade in dosages, which did not modify the MABP-response to blood loss. Western blot and quantitative reverse transcription polymerase chain reactions were used to determine adrenergic receptor expression in brain arterioles. Results: During hypovolemia subcortical CBF was maintained at 81 ± 6% of baseline, whereas cortical CBF decreased to 40 ± 4% (p < 0.001). Reperfusion led to peak CBFs of about 70% above baseline in both brain regions. α1A-Adrenergic blockade massively reduced subcortical CBF during hemorrhage and reperfusion, and prevented hyperperfusion during reperfusion in the cortex. α1A-mRNA expression was significantly higher in the cortex, whereas α1D-mRNA expression was higher in the subcortex (p < 0.001). Conclusions: α1-Adrenergic receptors are critical for perfusion redistribution: activity of the α1A-receptor subtype is a prerequisite for redistribution of CBF, whereas the α1D-receptor subtype may determine the magnitude of redistribution responses.

Activation of CB1 receptors by 2-arachidonoylglycerol attenuates vasoconstriction induced by U46619 and angiotensin II in human and rat pulmonary arteries

Recent evidence suggests that endocannabinoids acting via cannabinoid CB₁ receptors may modulate vascular responses of various vasoconstrictors in the rodent systemic vasculature. The aim of the study was to investigate whether endocannabinoids modulate the contractile responses evoked by a thromboxane A₂ analog (U46619), angiotensin II (ANG II), serotonin (5-HT), and phenylephrine, which stimulate distinct G_q/11 protein-coupled receptors (thromboxane, ANG II type 1, 5-HT₂, and α₁-adrenergic receptors) in isolated endothelium-intact human and rat pulmonary arteries (hPAs and rPAs, respectively). The CB₁ receptor antagonist AM251 (1 μM) and diacylglycerol lipase (2-arachidonoylglycerol synthesis enzyme) inhibitor RHC80267 (40 μM) enhanced contractions induced by U46619 in hPAs and rPAs and by ANG II in rPAs in an endothelium-dependent manner. AM251 did not influence vasoconstrictions induced by 5-HT or phenylephrine in rPAs. The monoacylglycerol lipase (2-arachidonoylglycerol degradation enzyme) inhibitor JZL184 (1 μM), but not the fatty acid amide hydrolase (anandamide degradation enzyme) inhibitor URB597 (1 μM), attenuated contractions evoked by U46619 in hPAs and rPAs and ANG II in rPAs. 2-Arachidonoylglycerol concentration-dependently induced relaxation of hPAs, which was inhibited by endothelium denudation or AM251 and enhanced by JZL184. Expression of CB₁ receptors was confirmed in hPAs and rPAs using Western blotting and immunohistochemistry. The present study shows the protective interaction between the endocannabinoid system and vasoconstriction in response to U46619 and ANG II in the human and rat pulmonary circulation. U46619 and ANG II may stimulate rapid endothelial release of endocannabinoids (mainly 2-arachidonoylglycerol), leading to CB₁ receptor-dependent and/or CB₁ receptor-independent vasorelaxation, which in the negative feedback mechanism reduces later agonist-induced vasoconstriction.

Smooth Muscle Phenotypic Diversity: Effect on Vascular Function and Drug Responses

At its simplest resistance to blood flow is regulated by changes in the state of contraction of the vascular smooth muscle (VSM), a function of the competing activities of the myosin kinase and phosphatase determining the phosphorylation and activity of the myosin ATPase motor protein. In contrast, the vascular system of humans and other mammals is incredibly complex and highly regulated. Much of this complexity derives from phenotypic diversity within the smooth muscle, reflected in very differing power outputs and responses to signaling pathways that regulate vessel tone, presumably having evolved over the millennia to optimize vascular function and its control. The highly regulated nature of VSM tone, described as pharmacomechanical coupling, likely underlies the many classes of drugs in clinical use to alter vascular tone through activation or inhibition of these signaling pathways. This review will first describe the phenotypic diversity within VSM, followed by presentation of specific examples of how molecular diversity in signaling, myofilament, and calcium cycling proteins impacts arterial smooth muscle function and drug responses.

Antidiuretic and antinatriuretic response to high salt load in normotensive Wistar-Kyoto rats: Role of alpha-1A-adrenoreceptors

Altered renal adrenergic responses have been recognized as pathophysiological responses to high salt intake. This study aims to investigate the influence of 6 weeks of high salt diet on α_1A -adrenoceptor regulation of renal tubular antinatriuretic and antidiuretic response in normal Wistar Kyoto rats. To achieve the above objective, antinatriuretic and antidiuretic response to phenylephrine was measured in the absence and presence of 5-methylurapidil (5-MeU) using the inulin clearance method. Systemic mean arterial blood pressure and renal haemodynamics were also measured simultaneously. Six weeks of high salt intake in Wistar-Kyoto (WKY) rats did not bring any significant increase in mean arterial blood pressure. WKY rat on high salt diet (WKYHNa) showed an exaggerated increase in absolute and fractional sodium excretion. There was a significant involvement of α_1A -adrenoceptor in carrying out renal tubular antinatriuretic and antidiuretic response in Wistar Kyoto rats on normal sodium diet (WKYNNa). However, α_1A -adrenoceptor played a minimal role in handling the tubular reabsorptive response in WKY rats on high salt diet.

Homobivalent Conjugation Increases the Allosteric Effect of 9-aminoacridine at the α1-Adrenergic Receptors

The α₁-adrenergic receptors are targets for a number of cardiovascular and central nervous system conditions, but the current drugs for these receptors lack specificity to be of optimal clinical value. Allosteric modulators offer an alternative mechanism of action to traditional α₁-adrenergic ligands, yet there is little information describing this drug class at the α₁-adrenergic receptors. We have identified a series of 9-aminoacridine compounds that demonstrate allosteric modulation of the α_1A- and α_1B-adrenergic receptors. The 9-aminoacridines increase the rate of [³H]prazosin dissociation from the α_1A- and α_1B-adrenergic receptors and noncompetitively inhibit receptor activation by the endogenous agonist norepinephrine. The structurally similar compound, tacrine, which is a known allosteric modulator of the muscarinic receptors, is also shown to be a modulator of the α₁-adrenergic receptors, which suggests a general lack of selectivity for allosteric binding sites across aminergic G protein-coupled receptor. Conjugation of two 9-aminoacridine pharmacophores, using linkers of varying length, increases the potency and efficacy of the allosteric effects of this ligand, likely through optimization of bitopic engagement of the allosteric and orthosteric binding sites of the receptor. Such a bivalent approach may provide a mechanism for fine tuning the efficacy of allosteric compounds in future drug design efforts.

A targeted genome association study examining transient receptor potential ion channels, acetylcholine receptors, and adrenergic receptors in Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Background

Chronic Fatigue Syndrome, also known as Myalgic Encephalomyelitis (CFS/ME) is a debilitating condition of unknown aetiology. It is characterized by a range of physiological effects including neurological, sensory and motor disturbances. This study examined candidate genes for the above clinical manifestations to identify single nucleotide polymorphism (SNP) alleles associated with CFS/ME compared with healthy controls.

Methods

DNA was extracted and whole genome genotyping was performed using the HumanOmniExpress BeadChip array. Gene families for transient receptor potential ion channels, acetylcholine receptors, and adrenergic receptors, and acetylcholinesterase were targeted. The frequency of each SNP and their association between CFS/ME and healthy controls was examined using Fisher’s exact test, and to adjust for multiple testing, False Detection Rate (FDR) and Bonferroni corrections were applied (p < 0.05).

Results

The study included 172 participants, consisting of 95 Fukuda defined CFS/ME patients (45.8 ± 8.9; 69 % female) and 77 healthy controls (42.3 ± 10.3; 63 % female). A total of 950 SNPs were included for analysis. 60 significant SNPs were associated with CFS/ME compared with healthy controls. After applying FDR and Bonferroni corrections, SNP rs2322333 in adrenergic receptor α1 (ADRA1A) was higher in CFS/ME compared with healthy controls (45.3 % vs. 23.4 %; p = 0.059). The genotype class that was homozygous minor (AA) was substantially lower in CFS/ME compared with healthy controls (4.2 % vs. 24.7 %).

Conclusions

This study reports for the first time the identification of ADRA1A and a possible association between CFS/ME and genotype classes. Further examination of the functional role of this class of adrenergic receptors may elucidate the cause of particular clinical manifestations observed in CFS/ME.

A high-throughput in vitro ring assay for vasoactivity using magnetic 3D bioprinting

Vasoactive liabilities are typically assayed using wire myography, which is limited by its high cost and low throughput. To meet the demand for higher throughput in vitro alternatives, this study introduces a magnetic 3D bioprinting-based vasoactivity assay. The principle behind this assay is the magnetic printing of vascular smooth muscle cells into 3D rings that functionally represent blood vessel segments, whose contraction can be altered by vasodilators and vasoconstrictors. A cost-effective imaging modality employing a mobile device is used to capture contraction with high throughput. The goal of this study was to validate ring contraction as a measure of vasoactivity, using a small panel of known vasoactive drugs. In vitro responses of the rings matched outcomes predicted by in vivo pharmacology, and were supported by immunohistochemistry. Altogether, this ring assay robustly models vasoactivity, which could meet the need for higher throughput in vitro alternatives.

Mechanisms Underlying Activation of α₁-Adrenergic Receptor-Induced Trafficking of AQP5 in Rat Parotid Acinar Cells under Isotonic or Hypotonic Conditions

Defective cellular trafficking of aquaporin-5 (AQP5) to the apical plasma membrane (APM) in salivary glands is associated with the loss of salivary fluid secretion. To examine mechanisms of α₁-adrenoceptor (AR)-induced trafficking of AQP5, immunoconfocal microscopy and Western blot analysis were used to analyze AQP5 localization in parotid tissues stimulated with phenylephrine under different osmolality. Phenylephrine-induced trafficking of AQP5 to the APM and lateral plasma membrane (LPM) was mediated via the α_1A-AR subtype, but not the α_1B- and α_1D-AR subtypes. Phenylephrine-induced trafficking of AQP5 was inhibited by ODQ and KT5823, inhibitors of nitric oxide (NO)-stimulated guanylcyclase (GC) and protein kinase (PK) G, respectively, indicating the involvement of the NO/ soluble (c) GC/PKG signaling pathway. Under isotonic conditions, phenylephrine-induced trafficking was inhibited by La³⁺, implying the participation of store-operated Ca²⁺ channel. Under hypotonic conditions, phenylephrine-induced trafficking of AQP5 to the APM was higher than that under isotonic conditions. Under non-stimulated conditions, hypotonicity-induced trafficking of AQP5 to the APM was inhibited by ruthenium red and La³⁺, suggesting the involvement of extracellular Ca²⁺ entry. Thus, α_1A-AR activation induced the trafficking of AQP5 to the APM and LPM via the Ca²⁺/ cyclic guanosine monophosphate (cGMP)/PKG signaling pathway, which is associated with store-operated Ca²⁺ entry.

Alpha1a-Adrenoceptor Genetic Variant Triggers Vascular Smooth Muscle Cell Hyperproliferation and Agonist Induced Hypertrophy via EGFR Transactivation Pathway

α_1a Adrenergic receptors (α_1aARs) are the predominant AR subtype in human vascular smooth muscle cells (SMCs). α_1aARs in resistance vessels are crucial in the control of blood pressure, yet the impact of naturally occurring human α_1aAR genetic variants in cardiovascular disorders remains poorly understood. To this end, we present novel findings demonstrating that 3D cultures of vascular SMCs expressing human α_1aAR-247R (247R) genetic variant demonstrate significantly increased SMC contractility compared with cells expressing the α_1aAR-WT (WT) receptor. Stable expression of 247R genetic variant also triggers MMP/EGFR-transactivation dependent serum- and agonist-independent (constitutive) hyperproliferation and agonist-dependent hypertrophy of SMCs. Agonist stimulation reduces contractility Using pathway-specific inhibitors we determined that the observed hyperproliferation of 247R-expressing cells is triggered via β-arrestin1/Src/MMP-2/EGFR/ERK-dependent mechanism. MMP-2-specific siRNA inhibited 247R-triggered hyperproliferation indicating MMP-2 involvement in 247R-triggered hyperproliferation in SMCs. β-arrestin1-specific shRNA also inhibited 247R-triggered hyperproliferation but did not affect hypertrophy in 247R-expressing SMCs, indicating that agonist-dependent hypertrophy is independent of β-arrestin1. Our data reveal that in different cardiovascular cells the same human receptor genetic variant can activate alternative modulators of the same signaling pathway. Thus, our findings in SMCs demonstrate that depending on the type of cells expressing the same receptor (or receptor variant), different target-specific inhibitors could be used to modulate aberrant hyperproliferative or hypertrophic pathways in order to restore normal phenotype.

Adrenergic signaling in teleost fish liver, a challenging path

Adrenergic receptors or adrenoceptors (ARs) belong to the huge family of G-protein coupled receptors (GPCRs) that have been well characterized in mammals primarily because of their importance as therapeutic drug targets. ARs are found across vertebrates and this review examines the path to identify and characterize these receptors in fish with emphasis on hepatic metabolism. The absence of reliable and specific pharmacological agents led investigators to define the fish hepatic AR system as relying solely on a β2-AR, cAMP-dependent signaling transduction pathway. The use of calcium-radiometric imaging, purified membranes for ligand-binding studies, and perifused rather than static cultured fish hepatocytes, unequivocally demonstrated that both α1- and β2-AR signaling systems existed in the fish liver consistent with studies in mammals. Additionally, the use of molecular tools and phylogenetic analysis clearly demonstrated the existence of multiple AR-types and -subtypes in hepatic and other tissues of a number of fish species. This review also examines the use of β-blockers as pharmaceuticals and how these drugs that are now in the aquatic environment may be impacting aquatic species including fish and some invertebrates. Clearly there is a large conservation of structure and function within the AR system of vertebrates but there remain a number of key questions that need to be addressed before a clear understanding of these systems can be resolved.

Ultrastructural evidence for synaptic contacts between cortical noradrenergic afferents and endocannabinoid-synthesizing post-synaptic neurons

Endocannabinoids (eCBs) are involved in a myriad of physiological processes that are mediated through the activation of cannabinoid receptors, which are ubiquitously distributed within the nervous system. One neurochemical target at which cannabinoids interact to have global effects on behavior is brain noradrenergic circuitry. We, and others, have previously shown that CB type 1 receptors (CB1r) are positioned to pre-synaptically modulate norepinephrine (NE) release in the rat frontal cortex (FC). Diacylglycerol lipase (DGL) is a key enzyme in the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG). While DGL-α is expressed in the FC in the rat brain, it is not known whether noradrenergic afferents target neurons expressing synthesizing enzymes for the endocannabinoid, 2-AG. In the present study, we employed high-resolution neuroanatomical approaches to better define cellular sites for interactions between noradrenergic afferents and FC neurons expressing DGL-α. Immunofluorescence microscopy showed close appositions between processes containing the norepinephrine transporter (NET) or dopamine-β-hydroxylase (DβH) and cortical neurons expressing DGL-α-immunoreactivity. Ultrastructural analysis using immunogold-silver labeling for DGL-α and immunoperoxidase labeling for NET or DβH confirmed that NET-labeled axon terminals were directly apposed to FC somata and dendritic processes that exhibited DGL-α-immunoreactivity. Finally, tissue sections were processed for immunohistochemical detection of DGL-α, CB1r and DβH. Triple label immunofluorescence revealed that CB1r and DβH were co-localized in common cellular profiles and these were in close association with DGL-α. Taken together, these data provide anatomical evidence for direct synaptic associations between noradrenergic afferents and cortical neurons exhibiting endocannabinoid synthesizing machinery.

Noradrenergic dysfunction in Alzheimer's disease

The brain noradrenergic system supplies the neurotransmitter norepinephrine throughout the brain via widespread efferent projections, and plays a pivotal role in modulating cognitive activities in the cortex. Profound noradrenergic degeneration in Alzheimer's disease (AD) patients has been observed for decades, with recent research suggesting that the locus coeruleus (where noradrenergic neurons are mainly located) is a predominant site where AD-related pathology begins. Mounting evidence indicates that the loss of noradrenergic innervation greatly exacerbates AD pathogenesis and progression, although the precise roles of noradrenergic components in AD pathogenesis remain unclear. The aim of this review is to summarize current findings on noradrenergic dysfunction in AD, as well as to point out deficiencies in our knowledge where more research is needed.

The α₁B -adrenoceptor subtype mediates adrenergic vasoconstriction in mouse retinal arterioles with damaged endothelium

BACKGROUND AND PURPOSE

The α₁-adrenoceptor family plays a critical role in regulating ocular perfusion by mediating responses to catecholamines. The purpose of the present study was to determine the contribution of individual α₁-adrenoceptor subtypes to adrenergic vasoconstriction of retinal arterioles using gene-targeted mice deficient in one of the three adrenoceptor subtypes (α₁A-AR(-/-), α₁B-AR(-/-) and α₁D-AR(-/-) respectively).

EXPERIMENTAL APPROACH

Using real-time PCR, mRNA expression for individual α₁-adrenoceptor subtypes was determined in murine retinal arterioles. To assess the functional relevance of the three α₁-adrenoceptor subtypes for mediating vascular responses, retinal vascular preparations from wild-type mice and mice deficient in individual α₁-adrenoceptor subtypes were studied in vitro using video microscopy.

KEY RESULTS

Retinal arterioles expressed mRNA for all three α₁-adrenoceptor subtypes. In functional studies, arterioles from wild-type mice with intact endothelium responded only negligibly to the α₁-adrenoceptor agonist phenylephrine. In endothelium-damaged arterioles from wild-type mice, phenylephrine evoked concentration-dependent constriction that was attenuated by the α₁-adrenoceptor blocker prazosin. Strikingly, phenylephrine only minimally constricted endothelium-damaged retinal arterioles from α₁B-AR(-/-) mice, whereas arterioles from α₁A -AR(-/-) and α₁D-AR(-/-) mice constricted similarly to arterioles from wild-type mice. Constriction to U46619 was similar in endothelium-damaged retinal arterioles from all four mouse genotypes.

CONCLUSIONS AND IMPLICATIONS

The present study is the first to demonstrate that α₁-adrenoceptor-mediated vasoconstriction in murine retinal arterioles is buffered by the endothelium. When the endothelium is damaged, a vasoconstricting role of the α₁B-adrenoceptor subtype is unveiled. Hence, the α₁B-adrenoceptor may represent a target to selectively modulate retinal blood flow in ocular diseases associated with endothelial dysfunction.

Invertebrate specific D1-like dopamine receptor in control of salivary glands in the black-legged tick Ixodes scapularis

The control of tick salivary secretion, which plays a crucial role in compromising the host immune system, involves complex neural mechanisms. Dopamine is known to be the most potent activator of salivary secretion, as a paracrine/autocrine factor. We describe the invertebrate-specific D1-like dopamine receptor (InvD1L), which is highly expressed in tick salivary glands. The InvD1L phylogenic clade was found only in invertebrates, suggesting that this receptor was lost in vertebrates during evolution. InvD1L expressed in Chinese hamster ovary (CHO)-K1 cells was activated by dopamine with a median effective dose (EC50 ) of 1.34 μM. Immunohistochemistry using the antibody raised against InvD1L revealed two different types of immunoreactivities: basally located axon terminals that are colocalized with myoinhibitory peptide (MIP) and SIFamide neuropeptides, and longer axon-like processes that are positive only for the InvD1L antibody and extended to the apical parts of the acini. Both structures were closely associated with the myoepithelial cell, as visualized by beta-tubulin antibody, lining the acinar lumen in a web-like fashion. Subcellular localizations of InvD1L in the salivary gland suggest that InvD1L modulates the neuronal activities including MIP/SIFamide varicosities, and leads the contraction of myoepithelial cells and/or of the acinar valve to control the efflux of the luminal content. Combining the previously described D1 receptor with its putative function for activating an influx of fluid through the epithelial cells of acini, we propose that complex control of the tick salivary glands is mediated through two different dopamine receptors, D1 and InvD1L, for different downstream responses of the acinar cells.

Comments on the mechanisms of action of radiation protective agents: basis components and their polyvalence

Purpose

These comments suggest a division of radiation protective agents on the grounds of their mechanism of action that increase the radio resistance of an organism.

Conclusion

Given below is the division of radiation protective agents on the basis of their mechanism of action into 3 groups: 1) Radiation protective agents, with the implementation of radiation protective action taking place at the cellular level in the course of rapidly proceeding radiation-chemical reactions. At the same time, when the ionizing radiation energy is absorbed, these agents partially neutralize the “oxygen effect” as a radiobiological phenomenon, especially in the radiolysis of DNA; 2) Radiation protective agents that exert their effect at the system level by accelerating the post-radiation recovery of radiosensitive tissues through activation of a number of pro-inflammatory signaling pathways and an increase in the secretion of hematopoietic growth factors, including their use as mitigators in the early period after irradiation prior to the clinical development of acute radiation syndrome (ARS). 3) Radiomodulators including drugs and nutritional supplements that can elevate the resistance of the organism to adverse environmental factors, including exposure to ionization by means of modulating the gene expression through a hormetic effect of small doses of stressors and a “substrate” maintenance of adaptive changes, resulting in an increased antioxidant protection of the organism. Radiation protective agents having polyvalence in implementation of their action may simultaneously induce radioprotective effect by various routes with a prevalence of basis mechanisms of the action.

Nonredundant function of two highly homologous octopamine receptors in food-deprivation-mediated signaling in Caenorhabditis elegans

It is common for neurotransmitters to possess multiple receptors that couple to the same intracellular signaling molecules. This study analyzes two highly homologous G-protein-coupled octopamine receptors using the model animal Caenorhabditis elegans. In C. elegans, the amine neurotransmitter octopamine induces activation of cAMP response element-binding protein (CREB) in the cholinergic SIA neurons in the absence of food through activation of the Gq-coupled octopamine receptor SER-3 in these neurons. We also analyzed another Gq-coupled octopamine receptor, SER-6, that is highly homologous to SER-3. As seen in ser-3 deletion mutants, octopamine- and food-deprivation-mediated CREB activation was decreased in ser-6 deletion mutants compared with wild-type animals, suggesting that both SER-3 and SER-6 are required for signal transduction. Cell-specific expression of SER-6 in the SIA neurons was sufficient to restore CREB activation in the ser-6 mutants, indicating that SER-6, like SER-3, functions in these neurons. Taken together, these results demonstrate that two similar G-protein-coupled receptors, SER-3 and SER-6, function in the same cells in a nonredundant manner.

Effect of Block of α1-adrenoceptors on Overall Motor Activity but not on Spatial Cognition in the Object-Position Recognition Task

Prazosin, an α1-adrenoceptor antagonist, is well known for its depressant effect on motivation and motor activity, while it has no effect on retention of spatial behavior in several tasks, e.g. in the Morris water maze and radial arm maze. The role of α1-adrenoceptors in operant tasks with stimulus-controlled behavior has not yet been tested. The present study investigated the effect of prazosin on the modulation of overall motor activity and on cognitive performance in a spatial operant task called object-position recognition task, where operant behavior (lever pressing) was controlled by spatial stimuli displayed on a computer screen. This task has been previously showed to be hippocampal-dependent. Pre-test injection of prazosin at the dose of 3 mg/kg decreased the responding rate, while it did not affect the recognition of object’s position. In conclusion, we validated the new cognitive test with a drug with known pharmacological effects on behavior and confirmed the depressant effect of prazosin on motor activity and no effect on retrieval of spatial memory in the hippocampal-dependent operant task.

A drug repositioning approach identifies tricyclic antidepressants as inhibitors of small cell lung cancer and other neuroendocrine tumors

Small cell lung cancer (SCLC) is an aggressive neuroendocrine subtype of lung cancer with high mortality. We used a systematic drug repositioning bioinformatics approach querying a large compendium of gene expression profiles to identify candidate U.S. Food and Drug Administration (FDA)-approved drugs to treat SCLC. We found that tricyclic antidepressants and related molecules potently induce apoptosis in both chemonaïve and chemoresistant SCLC cells in culture, in mouse and human SCLC tumors transplanted into immunocompromised mice, and in endogenous tumors from a mouse model for human SCLC. The candidate drugs activate stress pathways and induce cell death in SCLC cells, at least in part by disrupting autocrine survival signals involving neurotransmitters and their G protein-coupled receptors. The candidate drugs inhibit the growth of other neuroendocrine tumors, including pancreatic neuroendocrine tumors and Merkel cell carcinoma. These experiments identify novel targeted strategies that can be rapidly evaluated in patients with neuroendocrine tumors through the repurposing of approved drugs.

SIGNIFICANCE

Our work shows the power of bioinformatics-based drug approaches to rapidly repurpose FDA-approved drugs and identifies a novel class of molecules to treat patients with SCLC, a cancer for which no effective novel systemic treatments have been identified in several decades. In addition, our experiments highlight the importance of novel autocrine mechanisms in promoting the growth of neuroendocrine tumor cells.

The role of intracellular calcium stores in synaptic plasticity and memory consolidation

Memory processing requires tightly controlled signalling cascades, many of which are dependent upon intracellular calcium (Ca(2+)). Despite this, most work investigating calcium signalling in memory formation has focused on plasma membrane channels and extracellular sources of Ca(2+). The intracellular Ca(2+) release channels, ryanodine receptors (RyRs) and inositol (1,4,5)-trisphosphate receptors (IP3Rs) have a significant capacity to regulate intracellular Ca(2+) signalling. Evidence at both cellular and behavioural levels implicates both RyRs and IP3Rs in synaptic plasticity and memory formation. Pharmacobehavioural experiments using young chicks trained on a single-trial discrimination avoidance task have been particularly useful by demonstrating that RyRs and IP3Rs have distinct roles in memory formation. RyR-dependent Ca(2+) release appears to aid the consolidation of labile memory into a persistent long-term memory trace. In contrast, IP3Rs are required during long-term memory. This review discusses various functions for RyRs and IP3Rs in memory processing, including neuro- and glio-transmitter release, dendritic spine remodelling, facilitating vasodilation, and the regulation of gene transcription and dendritic excitability. Altered Ca(2+) release from intracellular stores also has significant implications for neurodegenerative conditions.

Differential phosphorylation, desensitization, and internalization of α1A-adrenoceptors activated by norepinephrine and oxymetazoline

Loss of response on repetitive drug exposure (i.e., tachyphylaxis) is a particular problem for the vasoconstrictor effects of medications containing oxymetazoline (OXY), an α1-adrenoceptor (AR) agonist of the imidazoline class. One cause of tachyphylaxis is receptor desensitization, usually accompanied by phosphorylation and internalization. It is well established that α1A-ARs are less phosphorylated, desensitized, and internalized on exposure to the phenethylamines norepinephrine (NE), epinephrine, or phenylephrine (PE) than are the α1B and α1D subtypes. However, here we show in human embryonic kidney-293 cells that the low-efficacy agonist OXY induces G protein-coupled receptor kinase 2-dependent α1A-AR phosphorylation, followed by rapid desensitization and internalization (∼40% internalization after 5 minutes of stimulation), whereas phosphorylation of α1A-ARs exposed to NE depends to a large extent on protein kinase C activity and is not followed by desensitization, and the receptors undergo delayed internalization (∼35% after 60 minutes of stimulation). Native α1A-ARs from rat tail artery and vas deferens are also desensitized by OXY, but not by NE or PE, indicating that this property of OXY is not limited to recombinant receptors expressed in cell systems. The results of the present study are clearly indicative of agonist-directed α1A-AR regulation. OXY shows functional selectivity relative to NE and PE at α1A-ARs, leading to significant receptor desensitization and internalization, which is important in view of the therapeutic vasoconstrictor effects of this drug and the varied biologic process regulated by α1A-ARs.

Effects of the noradrenergic neurotoxin DSP-4 on the expression of α1-adrenoceptor subtypes after antidepressant treatment

We have previously reported that chronic imipramine and electroconvulsive treatments increase the α(1A)-adrenoceptor (but not the α(1B) subtype) mRNA level and the receptor density in the rat cerebral cortex. Furthermore, we have also shown that chronic treatment with citalopram does not affect the expression of either the α(1A)- or the α(1B)-adrenoceptor, indicating that the previously observed up-regulation of α(1A)-adrenoceptor may depend on the noradrenergic component of the pharmacological mechanism of action of these antidepressants. Here, we report that previous noradrenergic depletion with DSP-4 (50 mg/kg) (a neurotoxin selective for the noradrenergic nerve terminals) significantly attenuated the increase of α(1A)-adrenoceptor mRNA induced by a 14-day treatment with imipramine (IMI, 20 mg/kg, ip) and abolished the effect of electroconvulsive shock (ECS, 150 mA, 0.5 s) in the prefrontal cortex of the rat brain. The changes in the receptor protein expression (as reflected by its density) that were induced by IMI and ECS treatments were differently modulated by DSP-4 lesioning, and only the ECS-induced increase in α(1A)-adrenoceptor level was abolished. This study provides further evidence corroborating our initial hypothesis that the noradrenergic component of the action of antidepressant agents plays an essential role in the modulation of α(1A)-adrenoceptor in the rat cerebral cortex.

Molecular mechanisms of fear learning and memory

Pavlovian fear conditioning is a particularly useful behavioral paradigm for exploring the molecular mechanisms of learning and memory because a well-defined response to a specific environmental stimulus is produced through associative learning processes. Synaptic plasticity in the lateral nucleus of the amygdala (LA) underlies this form of associative learning. Here, we summarize the molecular mechanisms that contribute to this synaptic plasticity in the context of auditory fear conditioning, the form of fear conditioning best understood at the molecular level. We discuss the neurotransmitter systems and signaling cascades that contribute to three phases of auditory fear conditioning: acquisition, consolidation, and reconsolidation. These studies suggest that multiple intracellular signaling pathways, including those triggered by activation of Hebbian processes and neuromodulatory receptors, interact to produce neural plasticity in the LA and behavioral fear conditioning. Collectively, this body of research illustrates the power of fear conditioning as a model system for characterizing the mechanisms of learning and memory in mammals and potentially for understanding fear-related disorders, such as PTSD and phobias.

The tricyclic antidepressants amitriptyline, nortriptyline and imipramine are weak antagonists of human and rat alpha1B-adrenoceptors

Although it is long known that the tricyclic antidepressants amitriptyline, nortriptyline and imipramine inhibit the noradrenaline transporter and alpha(1)-adrenoceptors with similar affinities, which may lead to self-cancelling actions, the selectivity of these drugs for alpha(1)-adrenoceptor subtypes is unknown. The present study investigates the selectivity of amitriptyline, nortriptyline and imipramine for human recombinant and rat native alpha(1)-adrenoceptor subtypes. The selectivity of amitriptyline, nortriptyline and imipramine was investigated in HEK-293 cells expressing each of the human alpha(1)-subtypes and in rat native receptors from the vas deferens (alpha(1A)), spleen (alpha(1B)) and aorta (alpha(1D)) through [(3)H]prazosin binding, and noradrenaline-induced intracellular Ca(2+) increases and contraction assays. Amitriptyline, nortriptyline and imipramine showed considerably higher affinities for alpha(1A)- (approximately 25- to 80-fold) and alpha(1D)-adrenoceptors (approximately 10- to 25-fold) than for alpha(1B)-adrenoceptors in both contraction and [(3)H]prazosin binding assays with rat native and human receptors, respectively. In addition, amitriptyline, nortriptyline and imipramine were substantially more potent in the inhibition of noradrenaline-induced intracellular Ca(2+) increases in HEK-293 cells expressing alpha(1A)- or a truncated version of alpha(1D)-adrenoceptors which traffics more efficiently towards the cell membrane than in cells expressing alpha(1B)-adrenoceptors. Amitriptyline, nortriptyline and imipramine are much weaker antagonists of rat and human alpha(1B)-adrenoceptors than of alpha(1A)- and alpha(1D)-adrenoceptors. The differential affinities for these receptors indicate that the alpha(1)-adrenoceptor subtype which activation is most increased by the augmented noradrenaline availability resultant from the blockade of neuronal reuptake is the alpha(1B)-adrenoceptor. This may be important for the behavioural effects of these drugs.

Influence of high dietary sodium intake on the functional subtypes of alpha-adrenoceptors in the renal cortical vasculature of Wistar-Kyoto rats

1 Increased renal vascular resistance is one renal functional abnormality that contributes to hypertension, and alpha(1)-adrenoceptors play a pivotal role in modulating this renal vascular resistance. This study investigates the functional contribution of alpha(1)-adrenoceptor subtypes in the renal cortical vasculature of Wistar-Kyoto rats on a normal sodium diet (WKYNNa) compared with those given saline to drink for 6 weeks (WKYHNa). 2 The renal cortical vascular responses to the adrenergic agonists noradrenaline (NA), methoxamine (ME) and phenylephrine (PE) were measured in WKYHNa and WKYNNa rats either in the absence (the control phase) or presence of chloroethylclonidine (CEC), an alpha(1B)-adrenoceptor antagonist, 5-methylurapidil (5-MeU), an alpha(1A) antagonist, or BMY7378, an alpha(1D) antagonist. 3 Results showed a greater renal cortical vascular sensitivity to NA, PE and ME in the WKYHNa compared with WKYNNa rats (P < 0.05). Moreover, 5-MeU and BMY7378 attenuated adrenergically induced renal cortical vasoconstriction in WKYHNa and WKYNNa rats; this response was largely blunted in CEC-treated WKYHNa rats (all P < 0.05) but not in CEC-treated WKYNNa rats. 4 The data suggest that irrespective of dietary sodium content, in Wistar-Kyoto rats alpha(1A)- and alpha(1D)-subtypes are the major alpha(1)-adrenoceptors in renal cortical vasculature; however, there appears to be a functional involvement of alpha(1B)-adrenoceptors in the WKYHNa rats.

Chronic treatment with losartan and carvedilol differentially modulates renal vascular responses to sympathomimetics compared to treatment with individual agents in normal Wistar Kyoto and spontaneously hypertensive rats

This study set out to investigate the impact of chronic cumulative blockade of angiotensin II and adrenoceptors in WKY and SHR and to explore how the renovascular responses to adrenergic and angiotensin II receptor agonists may be interdependent. Rats were treated with either losartan, carvedilol or losartan+carvedilol for 7 days and on day eight, animals were pentobarbitone anaesthetized and prepared for renal haemodynamic study. Dose-response relationships were determined in terms of reduction/elevation in the magnitude of renal blood flow in response to intrarenal arterial injection of dopamine, phenylephrine and isoprenaline. Renal vascular responses were blunted in WKY and SHR treated with either losartan or carvedilol as compared to their untreated counterparts (P<0.05). In the combined treated rats, the vascular responses to isoprenaline and phenylephrine were restored to levels observed in the untreated rats, but the renal vasoconstrictor responses to dopamine decreased (P<0.05) in both WKY and SHR. There was a reduction of (P<0.05) in the magnitude of the isoprenaline induced renal vasodilation in all SHR as compared to WKY groups. The data obtained showed that the renal vascular action of dopamine, phenylephrine and isoprenaline depended on an intact renin-angiotensin system (RAS) in WKY and SHR. Treatment with losartan or carvedilol blunted the renal vasoconstrictor/vasodilator responses to sympathomimetics which was attenuated with the combined treatment. These observations using chronic blockade of adrenergic and angiotensin receptors demonstrated that there was a long standing interdependency between the RAS and sympathetic nervous system (SNS) in determining the responsiveness of the renal vasculature of normal and hypertensive rats.