Cellular and subcellular distributions of beta1- and beta2-adrenoceptors in the CA1 and CA3 regions of the rat hippocampus

Effect of propranolol on temporomandibular joint pain in repeatedly stressed rats

Stress substantially increases the risk of developing painful temporomandibular disorders (TMDs) by influencing the release of endogenous catecholamines. Propranolol, an antagonist of β-adrenergic receptors, has shown potential in alleviating TMD-associated pain, particularly when the level of catecholamines is elevated. The aim of this study was to explore whether intra-articular propranolol administration is effective in diminishing temporomandibular joint (TMJ) pain during repeated stress situations. Additionally, we investigated the effect of repeated stress on the expression of genes encoding β-adrenoceptors in the trigeminal ganglion. In the present study, rats were exposed to a stress protocol induced by sound, then to the administration of formalin in the TMJ (to elicit a nociceptive response), followed immediately afterward by different doses of propranolol, after which the analgesic response to propranolol was evaluated. We also assessed the levels of beta-1 and beta-2 adrenergic receptor mRNAs (Adrb1 and Adrb2, respectively) using reverse transcription-quantitative PCR (RT-qPCR). Our findings revealed that propranolol administration reduces formalin-induced TMJ nociception more effectively in stressed rats than in non-stressed rats. Furthermore, repeated stress decreases the expression of the Adrb2 gene within the trigeminal ganglion. The findings of this study are noteworthy as they suggest that individuals with a chronic stress history might find potential benefits from β-blockers in TMD treatment.

Adrenoceptors: A Focus on Psychiatric Disorders and Their Treatments

Research into the involvement of adrenoceptor subtypes in the cause(s) of psychiatric disorders is particularly challenging. This is partly because of difficulties in developing animal models that recapitulate the human condition but also because no evidence for any causal links has emerged from studies of patients. These, and other obstacles, are outlined in this chapter. Nevertheless, many drugs that are used to treat psychiatric disorders bind to adrenoceptors to some extent. Direct or indirect modulation of the function of specific adrenoceptor subtypes mediates all or part of the therapeutic actions of drugs in various psychiatric disorders. On the other hand, interactions with central or peripheral adrenoceptors can also explain their side effects. This chapter discusses both aspects of the field, focusing on disorders that are prevalent: depression, schizophrenia, anxiety, attention-deficit hyperactivity disorder, binge-eating disorder, and substance use disorder. In so doing, we highlight some unanswered questions that need to be resolved before it will be feasible to explain how changes in the function of any adrenoceptor subtype affect mood and behavior in humans and other animals.

Noradrenergic neuromodulation in ageing and disease

The locus coeruleus (LC) is a small brainstem structure located in the lower pons and is the main source of noradrenaline (NA) in the brain. Via its phasic and tonic firing, it modulates cognition and autonomic functions and is involved in the brain's immune response. The extent of degeneration to the LC in healthy ageing remains unclear, however, noradrenergic dysfunction may contribute to the pathogenesis of Alzheimer's (AD) and Parkinson's disease (PD). Despite their differences in progression at later disease stages, the early involvement of the LC may lead to comparable behavioural symptoms such as preclinical sleep problems and neuropsychiatric symptoms as a result of AD and PD pathology. In this review, we draw attention to the mechanisms that underlie LC degeneration in ageing, AD and PD. We aim to motivate future research to investigate how early degeneration of the noradrenergic system may play a pivotal role in the pathogenesis of AD and PD which may also be relevant to other neurodegenerative diseases.

A comprehensive pharmacological analysis of fenoterol and its derivatives to unravel the role of β2-adrenergic receptor in zebrafish

β-adrenergic receptors (βARs) belong to a key molecular targets that regulate the most important processes occurring in the human organism. Although over the last decades a zebrafish model has been developed as a model complementary to rodents in biomedical research, the role of β₂AR in regulation of pathological and toxicological effects remains to elucidate. Therefore, the study aimed to clarify the role of β₂AR with a particular emphasis on the distinct role of subtypes A and B of zebrafish β₂AR. As model compounds selective β₂AR agonists - (R,R)-fenoterol ((R,R)-Fen) and its new derivatives: (R,R)-4'-methoxyfenoterol ((R,R)-MFen) and (R,R)-4'-methoxy-1-naphtylfenoterol ((R,R)-MNFen) - were tested. We described dose-dependent changes observed after fenoterols exposure in terms of general toxicity, cardiotoxicity and neurobehavioural responses. Subsequently, to better characterise the role of β₂-adrenergic stimulation in zebrafish, we have performed a series of molecular docking simulations. Our results indicate that (R,R)-Fen displays the highest affinity for subtype A of zebrafish β₂AR and β_2AAR might be involved in pigment depletion. (R,R)-MFen shows the lowest affinity for zebrafish β₂ARs out of the tested fenoterols and this might be associated with its cardiotoxic and anxiogenic effects. (R,R)-MNFen displays the highest affinity for subtype B of zebrafish β₂AR and modulation of this receptor might be associated with the development of malformations, increases locomotor activity and induces a negative chronotropic effect. Taken together, the presented data offer insights into the functional responses of the zebrafish β₂ARs confirming their intraspecies conservation, and support the translation of the zebrafish model in pharmacological and toxicological research.

The β-adrenergic hypothesis of synaptic and microglial impairment in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease originating partly from amyloid β protein-induced synaptic failure. As damaging of noradrenergic neurons in the locus coeruleus (LC) occurs at the prodromal stage of AD, activation of adrenergic receptors could serve as the first line of defense against the onset of the disease. Activation of β₂ -ARs strengthens long-term potentiation (LTP) and synaptic activity, thus improving learning and memory. Physical stimulation of animals exposed to an enriched environment (EE) leads to the activation of β₂ -ARs and prevents synaptic dysfunction. EE also suppresses neuroinflammation, suggesting that β₂ -AR agonists may play a neuroprotective role. The β₂ -AR agonists used for respiratory diseases have been shown to have an anti-inflammatory effect. Epidemiological studies further support the beneficial effects of β₂ -AR agonists on several neurodegenerative diseases. Thus, I propose that β₂ -AR agonists may provide therapeutic value in combination with novel treatments for AD.

Norepinephrine, beyond the Synapse: Coordinating Epigenetic Codes for Memory

The noradrenergic system is implicated in neuropathologies contributing to major disorders of the memory, including post-traumatic stress disorder and Alzheimer’s disease. Determining the impact of norepinephrine on cellular function and plasticity is thus essential for making inroads into our understanding of these brain conditions, while expanding our capacity for treating them. Norepinephrine is a neuromodulator within the mammalian central nervous system which plays important roles in cognition and associated synaptic plasticity. Specifically, norepinephrine regulates the formation of memory through the stimulation of β-ARs, increasing the dynamic range of synaptic modifiability. The mechanisms through which NE influences neural circuit function have been extended to the level of the epigenome. This review focuses on recent insights into how the noradrenergic recruitment of epigenetic modifications, including DNA methylation and post-translational modification of histones, contribute to homo- and heterosynaptic plasticity. These advances will be placed in the context of synaptic changes associated with memory formation and linked to brain disorders and neurotherapeutic applications.

Propranolol Administration Modulates Neural Activity in the Hippocampal Hilus During Fear Retrieval

Altered fear learning is a strong behavioral component of anxiety disorders such as post-traumatic stress disorder (PTSD). Recent efforts have attempted to combine exposure therapies with drugs that target fear memory retrieval and memory reconsolidation, in order to improve treatment efficacy. The noradrenergic (NA) signaling system is of particular interest, due to its role in regulating the stress response and its involvement in fear and learning processes. Importantly, propranolol (P), a non-selective β-adrenergic antagonist, has shown the potential in decreasing exaggerated fear in both humans and animal models. In a previous study, we utilized an activity-dependent tagging murine model to determine the neural mechanisms by which propranolol attenuates learned fear. We found that propranolol acutely decreased memory trace reactivation specifically in the dorsal dentate gyrus (dDG), but not in CA3 or CA1. Here, we extended our previous study by investigating whether propranolol additionally altered activity in the hilus, a polymorphic layer that consists of neurons, mossy cells, and GABAergic interneurons. We found that propranolol acutely reduced overall hilar activity in both the dorsal and ventral hilus. Moreover, we report that propranolol significantly altered the activity of parvalbumin (PV)⁺ cells in the ventral (vDG), but not dorsal DG (dDG). Together, these results suggest that a β-adrenergic blockade may affect the activity of excitatory and inhibitory cell types in the hilar layer of the DG, and that these alterations may contribute to manipulating fear memory traces.

Noradrenergic Profile of Hippocampal Formation Theta Rhythm in Anaesthetized Rats

The present study was undertaken to identify the noradrenergic receptors underlying the production of hippocampal formation (HPC) type 2 theta rhythm. The experiments were performed on urethanized rats wherein type 2 theta is the only rhythm present. In three independent stages of experiments, the effects of noradrenaline (NE) and selective noradrenergic α and β agonists and antagonists were tested. We indicate that the selective activation of three HPC noradrenergic receptors, α1, α2 and β1, induced a similar effect (i.e., inhibition) on type 2 theta rhythm. The remaining HPC β2 and β3 noradrenergic receptors do not seem to be directly involved in the pharmacological mechanism responsible for the suppression of theta rhythm in anaesthetized rats. Obtained results provide evidence for the suppressant effect of exogenous NE on HPC type 2 theta rhythm and show the crucial role of α1, α2 and β1 noradrenergic receptors in the modulation of HPC mechanisms of oscillations and synchrony. This finding is in contrast to the effects of endogenous NE produced by electrical stimulation of the locus coeruleus (LC) and procaine injection into the LC (Broncel et al., 2020).

Propranolol Decreases Fear Expression by Modulating Fear Memory Traces

BACKGROUND

Posttraumatic stress disorder can develop after a traumatic event and results in heightened, inappropriate fear and anxiety. Although approximately 8% of the U.S. population is affected by posttraumatic stress disorder, only two drugs have been approved by the Food and Drug Administration to treat it, both with limited efficacy. Propranolol, a nonselective β-adrenergic antagonist, has shown efficacy in decreasing exaggerated fear, and there has been renewed interest in using it to treat fear disorders.

METHODS

Here, we sought to determine the mechanisms by which propranolol attenuates fear by utilizing an activity-dependent tagging system, ArcCreERT2 x eYFP mice. 129S6/SvEv mice were administered a 4-shock contextual fear conditioning paradigm followed by immediate or delayed context reexposures. Saline or propranolol was administered either before or after the first context reexposure. To quantify hippocampal, prefrontal, and amygdalar memory traces, ArcCreERT2 x eYFP mice were administered a delayed context reexposure with either a saline or propranolol injection before context reexposure.

RESULTS

Propranolol decreased fear expression only when administered before a delayed context reexposure. Fear memory traces were affected in the dorsal dentate gyrus and basolateral amygdala after propranolol administration in the ArcCreERT2 x eYFP mice. Propranolol acutely altered functional connectivity between the hippocampal, cortical, and amygdalar regions.

CONCLUSIONS

These data indicate that propranolol may decrease fear expression by altering network-correlated activity and by weakening the reactivation of the initial traumatic memory trace. This work contributes to the understanding of noradrenergic drugs as therapeutic aids for patients with posttraumatic stress disorder.

Stress-Induced Enhanced Long-Term Potentiation and Reduced Threshold for N-Methyl-D-Aspartate Receptor- and β-Adrenergic Receptor-Mediated Synaptic Plasticity in Rodent Ventral Subiculum

Stress is a biologically relevant signal and can modulate hippocampal synaptic plasticity. The subiculum is the major output station of the hippocampus and serves as a critical hub in the stress response network. However, stress-associated synaptic plasticity in the ventral subiculum has not been adequately addressed. Therefore, we investigated the impact of a single exposure to an inherently stressful two-way active avoidance conditioning on the induction of long-term potentiation (LTP) at CA1-subiculum synapses in ventral hippocampal slices from young adult rats 1 day after stressor exposure. We found that acute stress enhanced LTP and lowered the induction threshold for a late-onset LTP at excitatory CA1 to subicular burst-spiking neuron synapses. This late-onset LTP was dependent on the activation of β-adrenergic and glutamatergic N-methyl-D-aspartate receptors and independent of D1/D5 dopamine receptor activation. Thereby, we present a cellular mechanism that might contribute to behavioral stress adaptation after acute stressor exposure.

Rapid eye movement sleep deprivation impairs neuronal plasticity and reduces hippocampal neuronal arborization in male albino rats: Noradrenaline is involved in the process

Rapid eye movement sleep (REMS) favors brain development and memory, while it is decreased in neurodegenerative diseases. REMS deprivation (REMSD) affects several physiological processes including memory consolidation; however, its detailed mechanism(s) of action was unknown. REMS reduces, while REMSD elevates noradrenaline (NA) level in the brain; the latter induces several deficiencies and disorders, including changes in neuronal cytomorphology and apoptosis. Therefore, we proposed that REMS- and REMSD-associated modulation of NA level might affect neuronal plasticity and affect brain functions. Male albino rats were REMS deprived by flower-pot method for 6 days, and its effects were compared with home cage and large platform controls as well as post-REMSD recovered and REMS-deprived prazosin (α1-adrenoceptor antagonist)-treated rats. We observed that REMSD reduced CA1 and CA3 neuronal dendritic length, branching, arborization, and spine density, while length of active zone and expressions of pre- as well as post-synaptic proteins were increased as compared to controls; interestingly, prazosin prevented most of the effects in vivo. Studies on primary culture of neurons from chick embryo brain confirmed that NA at lower concentration(s) induced neuronal branching and arborization, while higher doses were destructive. The findings support our contention that REMSD adversely affects neuronal plasticity, branching, and synaptic scaffold, which explain the underlying cytoarchitectural basis of REMSD-associated patho-physio-behavioral changes. Consolidation of findings of this study along with that of our previous reports suggest that the neuronal disintegration could be due to either withdrawal of direct protective and proliferative role of low dose of NA or indirect effect of high dose of NA or both.

Noradrenaline Release from Locus Coeruleus Terminals in the Hippocampus Enhances Excitation-Spike Coupling in CA1 Pyramidal Neurons Via β-Adrenoceptors

Release of the neuromodulator noradrenaline signals salience during wakefulness, flagging novel or important experiences to reconfigure information processing and memory representations in the hippocampus. Noradrenaline is therefore expected to enhance hippocampal responses to synaptic input; however, noradrenergic agonists have been found to have mixed and sometimes contradictory effects on Schaffer collateral synapses and the resulting CA1 output. Here, we examine the effects of endogenous, optogenetically driven noradrenaline release on synaptic transmission and spike output in mouse hippocampal CA1 pyramidal neurons. We show that endogenous noradrenaline release enhances the probability of CA1 pyramidal neuron spiking without altering feedforward excitatory or inhibitory synaptic inputs in the Schaffer collateral pathway. β-adrenoceptors mediate this enhancement of excitation-spike coupling by reducing the charge required to initiate action potentials, consistent with noradrenergic modulation of voltage-gated potassium channels. Furthermore, we find the likely effective concentration of endogenously released noradrenaline is sub-micromolar. Surprisingly, although comparable concentrations of exogenous noradrenaline cause robust depression of slow afterhyperpolarization currents, endogenous release of noradrenaline does not, indicating that endogenous noradrenaline release is targeted to specific cellular locations. These findings provide a mechanism by which targeted endogenous release of noradrenaline can enhance information transfer in the hippocampus in response to salient events.

β3-Adrenergic receptor-dependent modulation of the medium afterhyperpolarization in rat hippocampal CA1 pyramidal neurons

Action potential firing in hippocampal pyramidal neurons is regulated by generation of an afterhyperpolarization (AHP). Three phases of AHP are recognized, with the fast AHP regulating action potential firing at the onset of a burst and the medium and slow AHPs supressing action potential firing over hundreds of milliseconds and seconds, respectively. Activation of β-adrenergic receptors suppresses the slow AHP by a protein kinase A-dependent pathway. However, little is known regarding modulation of the medium AHP. Application of the selective β-adrenergic receptor agonist isoproterenol suppressed both the medium and slow AHPs evoked in rat CA1 hippocampal pyramidal neurons recorded from slices maintained in organotypic culture. Suppression of the slow AHP was mimicked by intracellular application of cAMP, with the suppression of the medium AHP by isoproterenol still being evident in cAMP-dialyzed cells. Suppression of both the medium and slow AHPs was antagonized by the β-adrenergic receptor antagonist propranolol. The effect of isoproterenol to suppress the medium AHP was mimicked by two β₃-adrenergic receptor agonists, BRL37344 and SR58611A. The medium AHP was mediated by activation of small-conductance calcium-activated K⁺ channels and deactivation of H channels at the resting membrane potential. Suppression of the medium AHP by isoproterenol was reduced by pretreating cells with the H-channel blocker ZD7288. These data suggest that activation of β₃-adrenergic receptors inhibits H channels, which suppresses the medium AHP in CA1 hippocampal neurons by utilizing a pathway that is independent of a rise in intracellular cAMP. This finding highlights a potential new target in modulating H-channel activity and thereby neuronal excitability. NEW & NOTEWORTHY The noradrenergic input into the hippocampus is involved in modulating long-term synaptic plasticity and is implicated in learning and memory. We demonstrate that activation of functional β₃-adrenergic receptors suppresses the medium afterhyperpolarization in hippocampal pyramidal neurons. This finding provides an additional mechanism to increase action potential firing frequency, where neuronal excitability is likely to be crucial in cognition and memory.

Acupuncture Prevents the Impairment of Hippocampal LTP Through β1-AR in Vascular Dementia Rats

It is widely accepted that the synaptic dysfunction and synapse loss contribute to the cognitive deficits of vascular dementia (VD) patients. We have previously reported that acupuncture improved cognitive function in rats with VD. However, the mechanisms involved in acupuncture improving cognitive ability remain to be elucidated. The present study aims to investigate the pathways and molecules involved in the neuroprotective effect of acupuncture. We assessed the effects of acupuncture on hippocampal long-term potentiation (LTP), the most prominent cellular model of memory formation. Acupuncture enhanced LTP and norepinephrine (NE) levels in the hippocampus. Inhibition of the β-adrenergic receptor (AR), but not the α-AR, was able to block the effects of acupuncture on hippocampal LTP. Furthermore, inhibition of β1-AR, not β2-AR, abolished the enhanced LTP induced by acupuncture. The expression analysis revealed a significant upregulation of β1-AR and unchanged β2-AR with acupuncture, which supported the above findings. Specifically, increased β1-ARs in the dentate gyrus were expressed on neurons exclusively. Taken together, the present data supports a beneficial role of acupuncture in synaptic plasticity challenged with VD. A likely mechanism is the increase of NE and activation of β1-AR in the hippocampus.

Regulation on Toll-like Receptor 4 and Cell Barrier Function by Rab26 siRNA-loaded DNA Nanovector in Pulmonary Microvascular Endothelial Cells

The small GTPase Rab26 is involved in multiple processes, such as vesicle-mediated secretion and autophagy. However, the mechanisms and functions of Rab26 in the human pulmonary microvascular endothelial cells (HPMVECs) are not clear. In this study, we thoroughly investigated the role and novel mechanism of Rab26 in permeability and apoptosis of HPMVECs using a self-assembled Rab26 siRNA loaded DNA Y-motif nanoparticle (siRab26-DYM) and Rab26 adenovirus. We found that siRab26-DYM could be efficiently transfected into HPMVECs in a time- and dose-dependent manner. Importantly, the siRab26-DYM nanovector markedly aggravated the LPS-induced apoptosis and hyper-permeability of HPMVECs by promoting the nuclear translocation of Foxo1, and subsequent activation of Toll-like receptor 4 (TLR4) signal pathway. Overexpression of Rab26 by Rab26 adenoviruses partially inactivated LPS-induced TLR4 signaling pathway, suppressed the cell apoptosis and attenuated the hyperpermeability of HPMVECs. These results suggest that the permeability and apoptosis of HPMVECs can be modulated by manipulating Rab26 derived TLR4 signaling pathway, and that Rab26 can be potential therapeutic target for the treatment of vascular diseases related to endothelial barrier functions.

Neuromodulation of the Feedforward Dentate Gyrus-CA3 Microcircuit

The feedforward dentate gyrus-CA3 microcircuit in the hippocampus is thought to activate ensembles of CA3 pyramidal cells and interneurons to encode and retrieve episodic memories. The creation of these CA3 ensembles depends on neuromodulatory input and synaptic plasticity within this microcircuit. Here we review the mechanisms by which the neuromodulators aceylcholine, noradrenaline, dopamine, and serotonin reconfigure this microcircuit and thereby infer the net effect of these modulators on the processes of episodic memory encoding and retrieval.

Neuritin Up-regulates Kv4.2 α-Subunit of Potassium Channel Expression and Affects Neuronal Excitability by Regulating the Calcium-Calcineurin-NFATc4 Signaling Pathway

Neuritin is an important neurotrophin that regulates neural development, synaptic plasticity, and neuronal survival. Elucidating the downstream molecular signaling is important for potential therapeutic applications of neuritin in neuronal dysfunctions. We previously showed that neuritin up-regulates transient potassium outward current (IA) subunit Kv4.2 expression and increases IA densities, in part by activating the insulin receptor signaling pathway. Molecular mechanisms of neuritin-induced Kv4.2 expression remain elusive. Here, we report that the Ca(2+)/calcineurin (CaN)/nuclear factor of activated T-cells (NFAT) c4 axis is required for neuritin-induced Kv4.2 transcriptional expression and potentiation of IA densities in cerebellum granule neurons. We found that neuritin elevates intracellular Ca(2+) and increases Kv4.2 expression and IA densities; this effect was sensitive to CaN inhibition and was eliminated in Nfatc4(-/-) mice but not in Nfatc2(-/-) mice. Stimulation with neuritin significantly increased nuclear accumulation of NFATc4 in cerebellum granule cells and HeLa cells, which expressed IR. Furthermore, NFATc4 was recruited to the Kv4.2 gene promoter loci detected by luciferase reporter and chromatin immunoprecipitation assays. More importantly, data obtained from cortical neurons following adeno-associated virus-mediated overexpression of neuritin indicated that reduced neuronal excitability and increased formation of dendritic spines were abrogated in the Nfatc4(-/-) mice. Together, these data demonstrate an indispensable role for the CaN/NFATc4 signaling pathway in neuritin-regulated neuronal functions.

β-Adrenergic Control of Hippocampal Function: Subserving the Choreography of Synaptic Information Storage and Memory

Noradrenaline (NA) is a key neuromodulator for the regulation of behavioral state and cognition. It supports learning by increasing arousal and vigilance, whereby new experiences are “earmarked” for encoding. Within the hippocampus, experience-dependent information storage occurs by means of synaptic plasticity. Furthermore, novel spatial, contextual, or associative learning drives changes in synaptic strength, reflected by the strengthening of long-term potentiation (LTP) or long-term depression (LTD). NA acting on β-adrenergic receptors (β-AR) is a key determinant as to whether new experiences result in persistent hippocampal synaptic plasticity. This can even dictate the direction of change of synaptic strength.

The different hippocampal subfields play different roles in encoding components of a spatial representation through LTP and LTD. Strikingly, the sensitivity of synaptic plasticity in these subfields to β-adrenergic control is very distinct (dentate gyrus > CA3 > CA1). Moreover, NA released from the locus coeruleus that acts on β-AR leads to hippocampal LTD and an enhancement of LTD-related memory processing. We propose that NA acting on hippocampal β-AR, that is graded according to the novelty or saliency of the experience, determines the content and persistency of synaptic information storage in the hippocampal subfields and therefore of spatial memories.

Norepinephrine triggers metaplasticity of LTP by increasing translation of specific mRNAs

Norepinephrine (NE) is a key modulator of synaptic plasticity in the hippocampus, a brain structure crucially involved in memory formation. NE boosts synaptic plasticity mostly through initiation of signaling cascades downstream from beta (β)-adrenergic receptors (β-ARs). Previous studies demonstrated that a β-adrenergic receptor agonist, isoproterenol, can modify the threshold for long-term potentiation (LTP), a putative cellular mechanism for learning and memory, in a process known as “metaplasticity.” Metaplasticity is the ability of synaptic plasticity to be modified by prior experience. We asked whether NE itself could engage metaplastic mechanisms in area CA1 of mouse hippocampal slices. Using extracellular field potential recording and stimulation, we show that application of NE (10 µM), which did not alter basal synaptic strength, enhances the future maintenance of LTP elicited by subthreshold, high-frequency stimulation (HFS: 1 × 100 Hz, 1 sec). HFS applied 30 min after NE washout induced long-lasting (>4 h) LTP, which was significantly extended in duration relative to HFS alone. This NE-induced metaplasticity required β1-AR activation, as coapplication of the β1-receptor antagonist CGP-20712A (1 µM) attenuated maintenance of LTP. We also found that NE-mediated metaplasticity was translation- and transcription-dependent. Polysomal profiles of CA1 revealed increased translation rates for specific mRNAs during NE-induced metaplasticity. Thus, activation of β-ARs by NE primes synapses for future long-lasting plasticity on time scales extending beyond fast synaptic transmission; this may facilitate neural information processing and the subsequent formation of lasting memories.

β-Adrenergic receptor signaling and modulation of long-term potentiation in the mammalian hippocampus

Encoding new information in the brain requires changes in synaptic strength. Neuromodulatory transmitters can facilitate synaptic plasticity by modifying the actions and expression of specific signaling cascades, transmitter receptors and their associated signaling complexes, genes, and effector proteins. One critical neuromodulator in the mammalian brain is norepinephrine (NE), which regulates multiple brain functions such as attention, perception, arousal, sleep, learning, and memory. The mammalian hippocampus receives noradrenergic innervation and hippocampal neurons express β-adrenergic receptors, which are known to play important roles in gating the induction of long-lasting forms of synaptic potentiation. These forms of long-term potentiation (LTP) are believed to importantly contribute to long-term storage of spatial and contextual memories in the brain. In this review, we highlight the contributions of noradrenergic signaling in general and β-adrenergic receptors in particular, toward modulating hippocampal LTP. We focus on the roles of NE and β-adrenergic receptors in altering the efficacies of specific signaling molecules such as NMDA and AMPA receptors, protein phosphatases, and translation initiation factors. Also, the roles of β-adrenergic receptors in regulating synaptic "tagging" and "capture" of LTP within synaptic networks of the hippocampus are reviewed. Understanding the molecular and cellular bases of noradrenergic signaling will enrich our grasp of how the brain makes new, enduring memories, and may shed light on credible strategies for improving mental health through treatment of specific disorders linked to perturbed memory processing and dysfunctional noradrenergic synaptic transmission.

Hippocampal long-term potentiation that is elicited by perforant path stimulation or that occurs in conjunction with spatial learning is tightly controlled by beta-adrenoreceptors and the locus coeruleus

The noradrenergic system, driven by locus coeruleus (LC) activation, plays a key role in the regulating and directing of changes in hippocampal synaptic efficacy. The LC releases noradrenaline in response to novel experience and LC activation leads to an enhancement of hippocampus‐based learning, and facilitates synaptic plasticity in the form of long‐term depression (LTD) and long‐term potentiation (LTP) that occur in association with spatial learning. The predominant receptor for mediating these effects is the β‐adrenoreceptor. Interestingly, the dependency of synaptic plasticity on this receptor is different in the hippocampal subfields whereby in the CA1 in vivo, LTP, but not LTD requires β‐adrenoreceptor activation, whereas in the mossy fiber synapse LTP and LTD do not depend on this receptor. By contrast, synaptic plasticity that is facilitated by spatial learning is highly dependent on β‐adrenoreceptor activation in both hippocampal subfields. Here, we explored whether LTP induced by perforant‐path (pp) stimulation in vivo or that is facilitated by spatial learning depends on β‐adrenoreceptors. We found that under both LTP conditions, antagonising the receptors disabled the persistence of LTP. β‐adrenoreceptor‐antagonism also prevented spatial learning. Strikingly, activation of the LC before high‐frequency stimulation (HFS) of the pp prevented short‐term potentiation but not LTP, and LC stimulation after pp‐HFS‐induced depotentiation of LTP. This depotentiation was prevented by β‐adrenoreceptor‐antagonism. These data suggest that β‐adrenoreceptor‐activation, resulting from noradrenaline release from the LC during enhanced arousal and learning, comprises a mechanism whereby the duration and degree of LTP is regulated and fine tuned. This may serve to optimize the creation of a spatial memory engram by means of LTP and LTD. This process can be expected to support the special role of the dentate gyrus as a crucial subregional locus for detecting and processing novelty within the hippocampus. © 2015 The Authors Hippocampus Published by Wiley Periodicals, Inc.

Expression and functions of β1- and β2-adrenergic receptors on the bulbospinal neurons in the rostral ventrolateral medulla

The expression and effects of β-adrenergic receptors (β-ARs) on the neurons of the bulbospinal rostral ventrolateral medulla (RVLM) have been limitedly examined to date. The objective of this study was to examine the expression of β1- and β2-ARs on the bulbospinal RVLM neurons electrophysiologically and histologically. To directly investigate whether RVLM neurons display sensitivity to metoprolol (a β1-AR antagonist), dobutamine (a β1-AR agonist), butoxamine (a β2-AR antagonist), and salbutamol (a β2-AR agonist), we examined changes in the membrane potentials of the bulbospinal RVLM neurons using the whole-cell patch-clamp technique during superfusion of these drugs. During metoprolol superfusion, 16 of the 20 RVLM neurons were hyperpolarized, and 5 of the 6 RVLM neurons were depolarized during dobutamine superfusion. During butoxamine superfusion, 11 of the 16 RVLM neurons were depolarized, and all of the 8 RVLM neurons were hyperpolarized during salbutamol superfusion. These results suggest the expression of β1- and β2-ARs on the RVLM neurons. To determine the presence of β1- and β2-ARs histologically, immunofluorescence examination was performed. Five metoprolol-hyperpolarized neurons were examined for β1-AR and tyrosine hydroxylase (TH) immunoreactivity. All of the neurons displayed β1-AR immunoreactivity, whereas three of the neurons displayed TH immunoreactivity. All of the five RVLM neurons that became depolarized during metoprolol superfusion and hyperpolarized during butoxamine superfusion displayed β1- and β2-AR immunoreactivity. Our findings suggest that β1-AR antagonists or β2-AR agonists may decrease blood pressure through decreasing the activity of the bulbospinal RVLM neurons.

Expression of β1- and β2-adrenoceptors in different subtypes of interneurons in the medial prefrontal cortex of mice

Noradrenaline acting via β-adrenoceptors (β-ARs) in the CNS plays an important role in learning/memory and cognitive functions. β-ARs have been shown to be expressed in cortical pyramidal and subcortical principal cells. However, little is known about β-AR expression in different subtypes of GABAergic neurons. Here, we report that both β1- and β2-ARs are expressed in a majority of GABAergic interneurons in the medial prefrontal cortex of mice, including parvalbumin (PV)-, calretinin (CR)-, calbindin D-28k (CB)-, somatostatin (SST)- and Reelin-immunoreactive (ir) interneurons. Relative to PV-, CB-, SST- and Reelin-ir interneurons, CR-ir interneurons are less likely to express β1- and β2-ARs. SST-ir interneurons are more likely to express β2-AR compared with the other subtypes of interneurons. The present results are of significance for understanding the role of β-ARs in prefrontal cortical functions.

Functional neuroanatomy of the central noradrenergic system

The central noradrenergic neurone, like the peripheral sympathetic neurone, is characterized by a diffusely arborizing terminal axonal network. The central neurones aggregate in distinct brainstem nuclei, of which the locus coeruleus (LC) is the most prominent. LC neurones project widely to most areas of the neuraxis, where they mediate dual effects: neuronal excitation by α₁-adrenoceptors and inhibition by α₂-adrenoceptors. The LC plays an important role in physiological regulatory networks. In the sleep/arousal network the LC promotes wakefulness, via excitatory projections to the cerebral cortex and other wakefulness-promoting nuclei, and inhibitory projections to sleep-promoting nuclei. The LC, together with other pontine noradrenergic nuclei, modulates autonomic functions by excitatory projections to preganglionic sympathetic, and inhibitory projections to preganglionic parasympathetic neurones. The LC also modulates the acute effects of light on physiological functions ('photomodulation'): stimulation of arousal and sympathetic activity by light via the LC opposes the inhibitory effects of light mediated by the ventrolateral preoptic nucleus on arousal and by the paraventricular nucleus on sympathetic activity. Photostimulation of arousal by light via the LC may enable diurnal animals to function during daytime. LC neurones degenerate early and progressively in Parkinson's disease and Alzheimer's disease, leading to cognitive impairment, depression and sleep disturbance.

Prenatal stress alters noradrenergic modulation of LTP in hippocampal slices

Long-term effects of stress during pregnancy on brain and behavior have been analyzed extensively in recent years. These effects include changes in emotional behavior, a reduction in learning capacity, and ability to generate long-term potentiation (LTP) in the offspring. In earlier studies, we and others have described a difference in ability to express LTP in dorsal and ventral sectors of the hippocampus (DH and VH, respectively) and its modification by prior stress. We now found that norepinephrine (NE) facilitated conversion of short-term potentiation to LTP in the normal DH but not in VH. Prenatal stress (PS) switched the locus of the facilitating action of NE from the DH to the VH. The effects of NE are likely to be mediated by activation of calcium stores. PS also facilitated ( S)-3,5-dihydroxyphenylglycine hydrate (DHPG)-induced LTD in the VH, assumed to be mediated by release of calcium from stores. These observations have important implications for the role of the hippocampus in cognitive and emotional memories.

Selective increase in the association of the β2 adrenergic receptor, β Arrestin-1 and p53 with Mdm2 in the ventral hippocampus one month after underwater trauma

Chronic infusion of mice with a β2 adrenergic receptor (β2AR) analog was shown to cause long-term DNA damage in a pathway which involves β Arresin-1-mediated activation of Mdm2 and subsequent degradation of the tumor suppressor protein p53. The objective of the present study was to test whether a single acute stress, which manifests long lasting changes in behavior, affects the interaction of Mdm2 with p53, β2AR, and β Arrestin-1 in the dorsal and ventral hippocampal CA1. Adult rats were subject to underwater trauma, a brief forceful submersion under water and tested a month later for behavioral and biochemical changes. Elevated plus maze tests confirmed that animals that experienced the threat of drowning present heightened levels of anxiety one month after trauma. An examination of the CA1 hippocampal areas of the same rats showed that underwater trauma caused a significant increase in the association of Mdm2 with β2AR, β Arrestin-1, and p53 in the ventral but not dorsal CA1. Our results provide support for the idea that stress-related events may result in biochemical changes restricted to the ventral 'emotion-related' parts of the hippocampus.

Stress stimulates production of catecholamines in rat adipocytes

The sympathoadrenal system is the main source of catecholamines (CAs) in adipose tissues and therefore plays the key role in the regulation of adipose tissue metabolism. We recently reported existence of an alternative CA-producing system directly in adipose tissue cells, and here we investigated effect of various stressors-physical (cold) and emotional stress (immobilization) on dynamics of this system. Acute or chronic cold exposure increased intracellular norepinephrine (NE) and epinephrine (EPI) concentration in isolated rat mesenteric adipocytes. Gene expression of CA biosynthetic enzymes did not change in adipocytes but was increased in stromal vascular fraction (SVF) after 28 day cold. Exposure of rats to a single IMO stress caused increases in NE and EPI levels, and also gene expression of CA biosynthetic enzymes in adipocytes. In SVF changes were similar but more pronounced. Animals adapted to a long-term cold exposure (28 days, 4°C) did not show those responses found after a single IMO stress either in adipocytes or SVF. Our data indicate that gene machinery accommodated in adipocytes, which is able to synthesize NE and EPI de novo, is significantly activated by stress. Cold-adapted animals keep their adaptation even after an exposure to a novel stressor. These findings suggest the functionality of CAs produced endogenously in adipocytes. Taken together, the newly discovered CA synthesizing system in adipocytes is activated in stress situations and might significantly contribute to regulation of lipolysis and other metabolic or thermogenetic processes.

Proteomic profiling of rapid non-genomic and concomitant genomic effects of acute restraint stress on rat thymocytes

In order to investigate rapid non-genomic effects of acute stress, rats were restrained for 15 min which was sufficient to activate the hypothalamus-pituitary-adrenal (HPA) axis but too short to induce massive genomic effects of cortisol. Subcellular fractions of thymocytes (cytosol, nucleus, membrane) were investigated using quantitative 2D DIGE with MALDI-TOF/TOF mass spectrometry. In total, 108 proteins with differential subcellular localizations were identified. The specificity of the changes induced by psychological stress was reflected by the prominent modulation of proteins involved in the HPA and sympathoadrenal medullar (SAM) axis such as HMGB1 and NHERF1. Intracellular trafficking was characterized by a dominant protein exodus from the cytosol. Real translocation was observed for 9 proteins with 6 that shuttled from the cytosol to the nucleus (HYOU1, HNRPF, HNRPC, STRAP, PSA1, PPA1) and 3 from the nucleus to the cytosol (HMGB1, NHERF1, PSMA1). Proteins showing subcellular reshuffling were largely involved in transcription and translation processes (39 of 108) with a significant enrichment of RNA splicing factors. Bioinformatics analysis revealed significant enrichment for protein kinase A and 14-3-3 signaling, probably reflecting real non-genomic effects. This is the first study investigating rapid effects of stress-induced HPA activation in vivo at the proteome level.

Acute stress differently modulates β1, β2 and β3 adrenoceptors in T cells, but not in B cells, from the rat spleen

OBJECTIVES

Stress-induced rise in circulating catecholamines (CAs), followed by modulation of β-adrenergic receptors (adrenoceptors, ARs), is one of the pathways involved in the stress-mediated effects of immune functions. The spleen is an organ with a high number of lymphocytes and provides a unique microenvironment in which they reside. Thus, lymphocytes may respond differently to CAs in the spleen than in the circulation. No reports exist concerning the involvement of β-ARs in stress-mediated effects on T and B cells isolated from the spleen. Therefore, our aim was to investigate the effect of single stress exposure on gene expression and cellular localization of β-adrenoceptor subtypes in splenic T and B cells. We tried to correlate changes in adrenoceptors with the expression of apoptotic proteins.

METHODS

Immobilization (IMMO) was used as a stress model. T and B cells were isolated from rat spleen using magnetically labeled antibodies. The gene expression of individual adrenoceptors and apoptotic proteins was evaluated by real-time PCR. Immunofluorescence was used to evaluate localization and adrenoceptor expression.

RESULTS

We have found T cells to be more vulnerable to stress compared to B cells, because of increased β₁-, β₂- and β₃-ARs after a single IMMO. Moreover, β₂-ARs translocated from the nucleus to the plasma membrane in T cells after IMMO. The rise in β-ARs most probably led to the rise of Bax mRNA and Bax to Bcl-2 mRNA ratio. This might suggest the induction of an apoptotic process in T cells.

CONCLUSION

Higher susceptibility of T cells to stress via modulation of β-ARs and apoptotic proteins might shift the immune responsiveness in the spleen.

β₁-adrenergic receptor up-regulation induced by nadolol is mediated via signal transduction pathway coupled to α₁-adrenergic receptors

Although up-regulation of β-adrenergic receptors (β-ARs) occurs after long-term use of their antagonists in various tissues, the available data are little on mechanisms of β-AR up-regulation induced by their continuous blockade. The present study attempted to clarify mechanisms of β-AR up-regulation using mouse cerebral cortical neurons continuously exposed to nadolol (10 nM), a non-selective β-AR antagonist, for 24 h. Nadolol dose-dependently induced both subtypes of β-ARs, β₁- and β₂-ARs, which were not suppressed by protein A kinase inhibition with KT5720. On the other hand, blockade of α₁-ARs, which are immunohistochemically confirmed to be co-localized with β-ARs in the same neurons, significantly inhibited only β₁-AR up-regulation and the expression of β₂-ARs did not alter. In addition, phenylephrine, an agonist specific to α₁-ARs up-regulated β₁-ARs, but not β₂-ARs. Under the conditions with β-AR up-regulation, the level of phosphorylated protein kinase Cα (pPKCα) increased, which is significantly suppressed by prazosin, an α1-AR antagonist. Furthermore, nadolol decreased the degradation of mRNA of β₁-ARs, but not β₂-ARs. These results indicate that the nadolol-induced β₁-AR up-regulation is mediated via PKC-relating pathway via α₁-AR activation with stabilizing β₁-AR mRNA and that the increased expression of β₂-ARs is regulated by pathways different from those for β₁-AR expression.

Regional distribution and cellular localization of beta2-adrenoceptors in the adult zebrafish brain (Danio rerio)

The beta(2)-adrenergic receptors (ARs) are G-protein-coupled receptors that mediate the physiological responses to adrenaline and noradrenaline. The present study aimed to determine the regional distribution of beta(2)-ARs in the adult zebrafish (Danio rerio) brain by means of in vitro autoradiographic and immunohistochemical methods. The immunohistochemical localization of beta(2)-ARs, in agreement with the quantitative beta-adrenoceptor autoradiography, showed a wide distribution of beta(2)-ARs in the adult zebrafish brain. The cerebellum and the dorsal zone of periventricular hypothalamus exhibited the highest density of [(3)H]CGP-12177 binding sites and beta(2)-AR immunoreactivity. Neuronal cells strongly stained for beta(2)-ARs were found in the periventricular ventral telencephalic area, magnocellular and parvocellular superficial pretectal nuclei (PSm, PSp), occulomotor nucleus (NIII), locus coeruleus (LC), medial octavolateral nucleus (MON), magnocellular octaval nucleus (MaON) reticular formation (SRF, IMRF, IRF), and ganglionic cell layer of cerebellum. Interestingly, in most cases (NIII, LC, MON, MaON, SRF, IMRF, ganglionic cerebellar layer) beta(2)-ARs were colocalized with alpha(2A)-ARs in the same neuron, suggesting their interaction for mediating the physiological functions of nor/adrenaline. Moderate to low labeling of beta(2)-ARs was found in neurons in dorsal telencephalic area, optic tectum (TeO), torus semicircularis (TS), and periventricular gray zone of optic tectum (PGZ). In addition to neuronal, glial expression of beta(2)-ARs was found in astrocytic fibers located in the central gray and dorsal rhombencephalic midline, in close relation to the ventricle. The autoradiographic and immunohistochemical distribution pattern of beta(2)-ARs in the adult zebrafish brain further support the conserved profile of adrenergic/noradrenergic system through vertebrate brain evolution.

Zebrafish beta-adrenergic receptor mRNA expression and control of pigmentation

Beta adrenergic receptors (beta-ARs) are members of the G-protein-coupled receptor superfamily and mediate various physiological processes in many species. The expression patterns and functions of beta-ARs in zebrafish are, however, largely unknown. We have identified zebrafish beta-AR orthologs, which we have designated as adrb1, adrb2a, adrb2b, adrb3a and adrb3b. adrb1 was found to be expressed in the heart and brain. Expression of adrb2a predominated in the brain and skin, whereas adrb2b was found to be highly expressed in muscle, pancreas and liver. Both adrb3a and adrb3b were exclusively expressed in blood. Knock-down of these beta-ARs by morpholino oligonucleotides revealed a functional importance of adrb2a in pigmentation. Expression of atp5a1 and atp5b, genes that encode subunits of F1F0-ATPase, which is known to be involved in pigmentation, was significantly increased by knock-down of adrb2a. Our data suggest that adrb2a may regulate pigmentation, partly by modulating F1F0-ATPase.

Altered hippocampal long-term potentiation after peripheral nerve injury in mice

It has been clinically reported that patients with chronic pain often have accompanying cognitive deficiency, which hampers efficient medical treatment. In the present study, we investigated whether hippocampal synaptic plasticity, which has been considered to be a cellular model of learning and memory, could be influenced by chronic pain conditions using a murine model of neuropathic pain prepared by partial ligation of the sciatic nerve (the Seltzer model). In slices obtained from neuropathic animals, tetanus-induced long-term potentiation of CA1 hippocampal synaptic transmission was impaired, whereas long-term depression induced by low-frequency stimulation was similar in neuropathic and sham-treated (control) animals. Bath application of the beta-adrenoceptor agonist isoproterenol or the beta-adrenoceptor antagonist propranolol diminished the difference of synaptic plasticity between neuropathic and control mice. In the presence of isoproterenol, long-term potentiation was successfully induced in neuropathic mice. By contrast, long-term potentiation in sham-treated mice was impaired by propranolol which did not alter the already impaired long-term potentiation after peripheral nerve injury. These results suggest that beta-adrenergic functions are changed in chronic pain conditions, which may underlie the deficiency of long-term potentiation.