Activation of Extracellular Signal-Regulated Kinases (ERK 1/2) in the Locus Coeruleus Contributes to Pain-Related Anxiety in Arthritic Male Rats

Anxiety disorders: Treatments, models, and circuitry mechanisms

Anxiety disorders are one of the most prevalent mental health conditions worldwide, imposing a significant burden on individuals affected by them and society in general. Current research endeavors aim to enhance the effectiveness of existing anxiolytic drugs and reduce their side effects through optimization or the development of new treatments. Several anxiolytic novel drugs have been produced as a result of discovery-focused research. However, many drug candidates that show promise in preclinical rodent model studies fail to offer any substantive clinical benefits to patients. This review provides an overview of the diagnosis and classification of anxiety disorders together with a systematic review of anxiolytic drugs with a focus on their targets, therapeutic applications, and side effects. It also provides a concise overview of the constraints and disadvantages associated with frequently administered anxiolytic drugs. Additionally, the study comprehensively reviews animal models used in anxiety studies and their associated molecular mechanisms, while also summarizing the brain circuitry related to anxiety. In conclusion, this article provides a valuable foundation for future anxiolytic drug discovery efforts.

Contextual memory engrams, and the neuromodulatory influence of the locus coeruleus

Here, we review the basis of contextual memory at a conceptual and cellular level. We begin with an overview of the philosophical foundations of traversing space, followed by theories covering the material bases of contextual representations in the hippocampus (engrams), exploring functional characteristics of the cells and subfields within. Next, we explore various methodological approaches for investigating contextual memory engrams, emphasizing plasticity mechanisms. This leads us to discuss the role of neuromodulatory inputs in governing these dynamic changes. We then outline a recent hypothesis involving noradrenergic and dopaminergic projections from the locus coeruleus (LC) to different subregions of the hippocampus, in sculpting contextual representations, giving a brief description of the neuroanatomical and physiological properties of the LC. Finally, we examine how activity in the LC influences contextual memory processes through synaptic plasticity mechanisms to alter hippocampal engrams. Overall, we find that phasic activation of the LC plays an important role in promoting new learning and altering mnemonic processes at the behavioral and cellular level through the neuromodulatory influence of NE/DA in the hippocampus. These findings may provide insight into mechanisms of hippocampal remapping and memory updating, memory processes that are potentially dysregulated in certain psychiatric and neurodegenerative disorders.

Glycemic Challenge Is Associated with the Rapid Cellular Activation of the Locus Ceruleus and Nucleus of Solitary Tract: Circumscribed Spatial Analysis of Phosphorylated MAP Kinase Immunoreactivity

Rodent studies indicate that impaired glucose utilization or hypoglycemia is associated with the cellular activation of neurons in the medulla (Winslow, 1733) (MY), believed to control feeding behavior and glucose counterregulation. However, such activation has been tracked primarily within hours of the challenge, rather than sooner, and has been poorly mapped within standardized brain atlases. Here, we report that, within 15 min of receiving 2-deoxy-d-glucose (2-DG; 250 mg/kg, i.v.), which can trigger glucoprivic feeding behavior, marked elevations were observed in the numbers of rhombic brain (His, 1893) (RB) neuronal cell profiles immunoreactive for the cellular activation marker(s), phosphorylated p44/42 MAP kinases (phospho-ERK1/2), and that some of these profiles were also catecholaminergic. We mapped their distributions within an open-access rat brain atlas and found that 2-DG-treated rats (compared to their saline-treated controls) displayed greater numbers of phospho-ERK1/2+ neurons in the locus ceruleus (Wenzel and Wenzel, 1812) (LC) and the nucleus of solitary tract (>1840) (NTS). Thus, the 2-DG-activation of certain RB neurons is more rapid than perhaps previously realized, engaging neurons that serve multiple functional systems and which are of varying cellular phenotypes. Mapping these populations within standardized brain atlas maps streamlines their targeting and/or comparable mapping in preclinical rodent models of disease.

Amylin regulates testosterone levels via steroidogenesis-related enzymes in the central nervous system of male mice

Amylin is a peripheral satiation signal polypeptide co-secreted with insulin by pancreatic β-cells in response to nutrient ingestion. Amylin participates in the eating-inhibitory effect and regulates energy metabolism by acting on the central nervous system (CNS). However, the role of amylin in regulating the biosynthesis of steroid hormones, such as testosterone, through the hypothalamic-pituitary-gonadal axis (HPG) remains unexplored. However, only limited evidence is available on the involvement of amylin in steroid synthesis, we hypothesize that amylin regulates testosterone levels via steroidogenesis-related enzymes in the CNS. In this study, we elucidated the effect of intraperitoneal injection of amylin on the protein expression of steroidogenesis-related enzymes, including 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17A1 (CYP17A1), and steroidogenic acute regulatory protein (StAR), and phospho-extracellular signal-regulated kinase (pERK). Additionally, the effect of amylin on testosterone levels in male mice was examined. Our results suggested that 3β-HSD and CYP17A1 neurons were widely expressed in the CNS of male mice, whereas StAR neurons were mainly expressed in the zona incerta (ZI) and locus coeruleus (LC) regions. Intraperitoneal injection of amylin significantly reduced (p < 0.01) the expression of 3β-HSD, CYP17A1, and StAR in ZI and other areas near the third ventricle (3 V) but increased (p < 0.01) pERK expression, brain testosterone levels, serum FSH, serum LH, and decreased (p < 0.01) serum testosterone levels in mice. In conclusion, amylin regulates testosterone levels via steroidogenesis-related enzymes in the central nervous system of male mice.

Automated Mouse Pupil Size Measurement System to Assess Locus Coeruleus Activity with a Deep Learning-Based Approach

Strong evidence from studies on primates and rodents shows that changes in pupil diameter may reflect neural activity in the locus coeruleus (LC). Pupillometry is the only available non-invasive technique that could be used as a reliable and easily accessible real-time biomarker of changes in the in vivo activity of the LC. However, the application of pupillometry to preclinical research in rodents is not yet fully standardized. A lack of consensus on the technical specifications of some of the components used for image recording or positioning of the animal and cameras have been recorded in recent scientific literature. In this study, a novel pupillometry system to indirectly assess, in real-time, the function of the LC in anesthetized rodents is presented. The system comprises a deep learning SOLOv2 instance-based fast segmentation framework and a platform designed to place the experimental subject, the video cameras for data acquisition, and the light source. The performance of the proposed setup was assessed and compared to other baseline methods using a validation and an external test set. In the latter, the calculated intersection over the union was 0.93 and the mean absolute percentage error was 1.89% for the selected method. The Bland–Altman analysis depicted an excellent agreement. The results confirmed a high accuracy that makes the system suitable for real-time pupil size tracking, regardless of the pupil’s size, light intensity, or any features typical of the recording process in sedated mice. The framework could be used in any neurophysiological study with sedated or fixed-head animals.

Inhibition of Elevated Ras-MAPK Signaling Normalizes Enhanced Motor Learning and Excessive Clustered Dendritic Spine Stabilization in the MECP2-Duplication Syndrome Mouse Model of Autism

The inflexible repetitive behaviors and "insistence on sameness" seen in autism imply a defect in neural processes controlling the balance between stability and plasticity of synaptic connections in the brain. It has been proposed that abnormalities in the Ras-ERK/MAPK pathway, a key plasticity-related cell signaling pathway known to drive consolidation of clustered synaptic connections, underlie altered learning phenotypes in autism. However, a link between altered Ras-ERK signaling and clustered dendritic spine plasticity has yet to be explored in an autism animal model in vivo The formation and stabilization of dendritic spine clusters is abnormally increased in the MECP2-duplication syndrome mouse model of syndromic autism, suggesting that ERK signaling may be increased. Here, we show that the Ras-ERK pathway is indeed hyperactive following motor training in MECP2-duplication mouse motor cortex. Pharmacological inhibition of ERK signaling normalizes the excessive clustered spine stabilization and enhanced motor learning behavior in MECP2-duplication mice. We conclude that hyperactive ERK signaling may contribute to abnormal clustered dendritic spine consolidation and motor learning in this model of syndromic autism.

Diazepam and SL-327 synergistically attenuate anxiety-like behaviours in mice - Possible hippocampal MAPKs specificity

Intracellular signalling pathways have been extensively studied as therapeutic targets for the treatment of mental diseases. Our attention has been caught by two kinases potentially involved in anxiety, ERK1/2 and CaMKII. The study aimed to examine changes in the activation of ERK1/2 and CaMKII concerning anxiolytic-like behaviours in mice. To evaluate anxiety-related response in mice, we used the open field test and the elevated plus maze test. Behavioural studies were complemented with the immunoblotting analysis to identify proteins of interest in the cortex, hippocampus, and striatum. We analysed the phosphorylation status of ERK1/2 and CaMKII in mice treated with a well-known anxiolytic drug - diazepam. Next, the blockade of ERK1/2 pathway by SL-327, a selective MEK1/2 inhibitor, was checked for anxiolytic action. Finally, the co-administration of subeffective doses of diazepam and SL-327 was investigated for a potential synergistic anxiolytic effect. Anxiolytic effects of acute diazepam are accompanied by decreased p-ERK1/2 and upregulation of p-CaMKII. Subchronic treatment with SL-327 leads to the manifestation of anxiolytic-like behaviours and changes in the phosphorylation status of both kinases in a diazepam-like manner. Co-administration of subeffective doses of SL-327 and diazepam induces anxiolysis, which is CaMKII-independent and correlates to selectively decreased phosphoactive ERK1/2 in the hippocampus. The MEK-ERK pathway is significantly involved in anxiolytic action of diazepam and its prolonged inhibition produces anxiolytic-like phenotype in mice. ERK inhibition could be used to manage anxiety symptoms in a benzodiazepine-sparing regimen for treatment of anxiety.

Pain in neuropsychiatry: Insights from animal models

Pain is the most common symptom reported in clinical practice, meaning that it is associated with many pathologies as either the origin or a consequence of other illnesses. Furthermore, pain is a complex emotional and sensorial experience, as the correspondence between pain and body damage varies considerably. While these issues are widely acknowledged in clinical pain research, until recently they have not been extensively considered when exploring animal models, important tools for understanding pain pathophysiology. Interestingly, chronic pain is currently considered a risk factor to suffer psychiatric disorders, mainly stress-related disorders like anxiety and depression. Conversely, pain appears to be altered in many psychiatric disorders, such as depression, anxiety and schizophrenia. Thus, pain and psychiatric disorders have been linked in epidemiological and clinical terms, although the neurobiological mechanisms involved in this pathological bidirectional relationship remain unclear. Here we review the evidence obtained from animal models about the co-morbidity of pain and psychiatric disorders, placing special emphasis on the different dimensions of pain.

Effects of amylin on food intake and body weight via sympathetic innervation of the interscapular brown adipose tissue

Objective: Amylin acts on the lateral dorsal tegmental nucleus (LDT), resulting in anorexic and weight-loss effects and activates thermogenesis in the interscapular brown adipose tissue (IBAT). In addition, it induces neuronal nitric oxide synthase (nNOS) and choline acetyltransferase (ChAT)-mediated feeding. However, the influence of the intact sympathetic nervous system (SNS) in mediating amylin's effects has not been fully characterised. We investigated whether extracellular signal-regulated kinase (ERK), nNOS, and ChAT activities in the LDT are responsible for amylin's anorexigenic effects and whether this requires an intact SNS.Methods: C57BL/6J mice [wild-type (WT), sham, and sympathetic denervation of IBAT] were used. Food consumption, body weight, and distribution of pERK, nNOS, and ChAT positive neurons in the brain were examined following acute and chronic amylin administration.Results: Food intake was significantly decreased in WT and sham animals following acute amylin injection, but not in the denervated mice. Chronic amylin reduced body weight and serum glucose levels after 6 weeks, but increased insulin levels; no changes were observed in the denervated mice. Acute amylin increased the expression of nNOS, ChAT, and uncoupling protein-1 in the IBAT of WT and sham mice, while no changes were observed in the denervated mice and pERK from the above effect.Conclusions: Intact SNS of IBAT influences amylin-induced suppression of food intake and body weight, thus affecting nNOS and ChAT signalling in the LDT and locus coeruleus.

Attenuation of the Diffuse Noxious Inhibitory Controls in Chronic Joint Inflammatory Pain Is Accompanied by Anxiodepressive-Like Behaviors and Impairment of the Descending Noradrenergic Modulation

The noradrenergic system is paramount for controlling pain and emotions. We aimed at understanding the descending noradrenergic modulatory mechanisms in joint inflammatory pain and its correlation with the diffuse noxious inhibitory controls (DNICs) and with the onset of anxiodepressive behaviours. In the complete Freund's adjuvant rat model of Monoarthritis, nociceptive behaviors, DNICs, and anxiodepressive-like behaviors were evaluated. Spinal alpha2-adrenergic receptors (a2-AR), dopamine beta-hydroxylase (DBH), and noradrenaline were quantified concomitantly with a2-AR pharmacologic studies. The phosphorylated extracellular signal-regulated kinases 1 and 2 (pERK1/2) were quantified in the Locus coeruleus (LC), amygdala, and anterior cingulate cortex (ACC). DNIC was attenuated at 42 days of monoarthritis while present on days 7 and 28. On day 42, in contrast to day 28, noradrenaline was reduced and DBH labelling was increased. Moreover, spinal a2-AR were potentiated and no changes in a2-AR levels were observed. Additionally, at 42 days, the activation of ERKs1/2 was increased in the LC, ACC, and basolateral amygdala. This was accompanied by anxiety- and depressive-like behaviors, while at 28 days, only anxiety-like behaviors were observed. The data suggest DNIC is attenuated in prolonged chronic joint inflammatory pain, and this is accompanied by impairment of the descending noradrenergic modulation and anxiodepressive-like behaviors.

Chemogenetic Silencing of the Locus Coeruleus-Basolateral Amygdala Pathway Abolishes Pain-Induced Anxiety and Enhanced Aversive Learning in Rats

BACKGROUND

Pain affects both sensory and emotional aversive responses, often provoking anxiety-related diseases when chronic. However, the neural mechanisms underlying the interactions between anxiety and chronic pain remain unclear.

METHODS

We characterized the sensory, emotional, and cognitive consequences of neuropathic pain (chronic constriction injury) in a rat model. Moreover, we determined the role of the locus coeruleus (LC) neurons that project to the basolateral amygdala (BLA) using a DREADD (designer receptor exclusively activated by designer drugs).

RESULTS

Chronic constriction injury led to sensorial hypersensitivity in both the short term and long term. Otherwise, long-term pain led to an anxiety-like profile (in the elevated zero maze and open field tests), as well as increased responses to learn aversive situations (in the passive avoidance and fear conditioning tests) and an impairment of nonemotional cognitive tasks (in the novel object recognition and object pattern of separation tests). Chemogenetic blockade of the LC-BLA pathway and intra-BLA or systemic antagonism of beta-adrenergic receptors abolished both long-term pain-induced anxiety and enhanced fear learning. By contrast, chemogenetic activation of this pathway induced anxiety-like behaviors and enhanced the aversive learning and memory index in sham animals, although it had little effect on short- and long-term chronic constriction injury animals. Interestingly, modulation of LC-BLA activity did not modify sensorial perception or episodic memory.

CONCLUSIONS

Our results indicate that dimensions associated with pain are processed by independent pathways and that there is an overactivation of the LC-BLA pathway when anxiety and chronic pain are comorbid, which involves the activity of beta-adrenergic receptors.

The Effects of Cobalt Protoporphyrin IX and Tricarbonyldichlororuthenium (II) Dimer Treatments and Its Interaction with Nitric Oxide in the Locus Coeruleus of Mice with Peripheral Inflammation

Heme oxygenase 1 (HO-1) and carbon monoxide were shown to normalize oxidative stress and inflammatory reactions induced by neuropathic pain in the central nervous system, but their effects in the locus coeruleus (LC) of animals with peripheral inflammation and their interaction with nitric oxide are unknown. In wild-type (WT) and knockout mice for neuronal (NOS1-KO) or inducible (NOS2-KO) nitric oxide synthases with inflammatory pain induced by complete Freund’s adjuvant (CFA), we assessed: (1) antinociceptive actions of cobalt protoporphyrin IX (CoPP), an HO-1 inducer; (2) effects of CoPP and tricarbonyldichlororuthenium(II) dimer (CORM-2), a carbon monoxide-liberating compound, on the expression of HO-1, NOS1, NOS2, CD11b/c, GFAP, and mitogen-activated protein kinases (MAPK) in the LC. CoPP reduced inflammatory pain in different time-dependent manners in WT and KO mice. Peripheral inflammation activated astroglia in the LC of all genotypes and increased the levels of NOS1 and phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK 1/2) in WT mice. CoPP and CORM-2 enhanced HO-1 and inhibited astroglial activation in all genotypes. Both treatments blocked NOS1 overexpression, and CoPP normalized ERK 1/2 activation. This study reveals an interaction between HO-1 and NOS1/NOS2 during peripheral inflammation and shows that CoPP and CORM-2 improved HO-1 expression and modulated the inflammatory and/or plasticity changes caused by peripheral inflammation in the LC.

Tannins from Terminalia chebula fruits attenuates GABA antagonist-induced anxiety-like behaviour via modulation of neurotransmitters

Objectives

This article investigates the anxiolytic activity of Terminalia chebula tannin-rich extract against picrotoxin (PTX; GABA antagonist)-induced anxiety in mice model.

Methods

Anxiolytic activity was studied by elevated plus maze (EPM), open field test (OFT), light/dark box test (LDT) and Vogel's conflict test (VCT). Electroencephalogram (EEG) was performed to know the changes in brain activity instigated by GABA antagonist. 5-hydroxytryptamine (5-HT), dopamine and norepinephrine levels in brain tissues were estimated by HPLC. The mRNA (CREB, BDNF, GABA, and 5-HT1A) and protein expression (CREB, p-CREB, BDNF, ERK ½, p-ERK ½, GABAARα1, 5-HT1A and GAPDH) levels in brain tissue were determined by RT-PCR and Western blot analysis, respectively.

Key findings

Terminalia chebula tannin-rich extract (TCHE) supplementation increased locomotion in mice towards open arm (EPM), time spent in illuminated area (LDT), rearing frequency (OFT) and number of shocks (VCT) compared to PTX (P &lt; 0.05). Furthermore, TCHE down-regulated serum cortisol levels and showed increased levels of 5-HT, DA and NE. Gene expressions such as BDNF, CREB, GABAA and 5-HT1A were up-regulated by TCHE treatment compared to PTX.

Conclusions

Terminalia chebula tannin-rich extract showed significant anxiolytic activity against picrotoxin and could be used as natural therapy in neurodegenerative disorders.

The Effect of Electroacupuncture on PKMzeta in the ACC in Regulating Anxiety-Like Behaviors in Rats Experiencing Chronic Inflammatory Pain

Chronic inflammatory pain can induce emotional diseases. Electroacupuncture (EA) has effects on chronic pain and pain-related anxiety. Protein kinase Mzeta (PKMzeta) has been proposed to be essential for the maintenance of pain and may interact with GluR1 to maintain CNS plasticity in the anterior cingulate cortex (ACC). We hypothesized that the PKMzeta-GluR1 pathway in the ACC may be involved in anxiety-like behaviors of chronic inflammatory pain and that the mechanism of EA regulation of pain emotion may involve the PKMzeta pathway in the ACC. Our results showed that chronic inflammatory pain model decreased the paw withdrawal threshold (PWT) and increased anxiety-like behaviors. The protein expression of PKCzeta, p-PKCzeta (T560), PKMzeta, p-PKMzeta (T560), and GluR1 in the ACC of the model group were remarkably enhanced. EA increased PWT and alleviated anxiety-like behaviors. EA significantly inhibited the protein expression of p-PKMzeta (T560) in the ACC, and only a downward trend effect for other substances. Further, the microinjection of ZIP remarkably reversed PWT and anxiety-like behaviors. The present study provides direct evidence that the PKCzeta/PKMzeta-GluR1 pathway is related to pain and pain-induced anxiety-like behaviors. EA treatment both increases pain-related somatosensory behavior and decreases pain-induced anxiety-like behaviors by suppressing PKMzeta activity in the ACC.