Multiple Nicotinic Acetylcholine Receptor Subtypes in the Mouse Amygdala Regulate Affective Behaviors and Response to Social Stress

A global overview of shared genetic architecture between smoking behaviors and major depressive disorder in European and East Asian ancestry

BACKGROUND

The co-occurrence of smoking behaviors and major depressive disorder (MDD) has been widely documented in populations. However, the underlying mechanism of this association remains unclear.

METHODS

Genome-wide association studies of smoking behaviors and MDD, combined with multi-omics datasets, were used to characterise genetic correlations, identify shared loci and genes, and explore underlying biological mechanisms. Mendelian randomization (MR) analyses were conducted to infer causal relationships between smoking behaviors and MDD. Druggability analyses were performed to identify potential drugs with both antidepressant and smoking cessation effects.

RESULTS

Extensive overall genetic correlations were found between smoking behaviors and MDD. Furthermore, eighteen local regions showed significant genetic correlations, which could be partly explained by gene co-expression patterns. We identified 24 shared loci and 120 genes, which were enriched in limbic system, GABAergic and dopaminergic neurons, as well as in synaptic pathways. Through integrating with tissue specific information, seven key genes (ANKK1, NEGR1, USP4, TCTA, SORCS5, SPPL3, and USP28) were pinpointed. Notably, druggability analyses supported ANKK1 as a potential drug target for the treatment of MDD and tobacco dependence. MR analyses suggested a bidirectional causal relationship between smoking initiation and MDD. Although findings in East Asian ancestry were limited, the shared locus (chr15:47613403-47,685,504) identified in European ancestry remained significant in East Asian ancestry.

CONCLUSIONS

Our findings suggest the extensive genetic overlap between smoking behaviors and MDD, support the role of limbic system and synapse involved in shared mechanisms, and implicate for prevention, intervention and treatment.

Modulation of neural activity and gene expression by arecoline

Arecoline, a biologically active alkaloid extracted from the areca nut, serves as the primary psychoactive ingredient in betel quid, one of the most widely consumed psychoactive substances worldwide. Despite its extensive use, the central nervous system (CNS) effects of arecoline remain inadequately understood. This study aims to investigate the central actions of arecoline through a comprehensive, multi-dimensional approach that integrates behavioral assays, neuroimaging techniques, calcium signaling analysis, and transcriptomic profiling. Our findings demonstrate dose-dependent addictive properties of arecoline, alongside distinct behavioral alterations that highlight its potential for addiction. Neuroimaging and calcium signaling data revealed region-specific alterations in neural activity, particularly in areas associated with learning, memory, and reward processing. Furthermore, transcriptomic analysis identified significant changes in gene expression, particularly in pathways related to synaptic plasticity, calcium signaling, and metal ion transport. These results provide valuable insights into the addictive potential of arecoline and its underlying neurobiological mechanisms, offering crucial information for understanding its broader impact on CNS function. The study's findings hold significant implications for informing public health strategies aimed at addressing arecoline misuse and its potential role in addiction-related disorders.

A phase 2, placebo-controlled study to evaluate the efficacy and safety of BNC210, an alpha-7 nicotinic receptor negative allosteric modulator, for acute, as-needed treatment of social anxiety disorder (SAD) - The PREVAIL study

Social anxiety disorder (SAD) is a chronic, debilitating, and prevalent neuropsychiatric condition for which an acute, as-needed therapy is an unmet medical need. This Phase 2 study evaluated a potential novel, fast-acting, anxiolytic, BNC210, in SAD patients (NCT05193409). PREVAIL was a placebo-controlled, acute dose study of 225 mg and 675 mg BNC210 in 151 adult participants with SAD. Anxiety was evaluated by self-report efficacy scales during the anticipation and performance phases of a simulated public speaking challenge. Safety data were collected. Least squares mean ± standard error (SE) differences compared to placebo for the Subjective Units of Distress Scale (SUDS) scores for the change from baseline to the average of the performance phase were -6.6 ± 4.75 for 225 mg BNC210 and -4.8 ± 4.73 for 675 mg BNC210 (not significant). A post hoc analysis of SUDS scores evaluating combined BNC210 doses and speaking challenge phases (anticipation and performance) revealed a nominally statistically significant reduction compared to placebo (p = 0.044; effect size 0.36). Both dose levels of BNC210 demonstrated a favorable safety profile. PREVAIL supported further testing of 225 mg BNC210 as a potential safe and effective anxiolytic for acute, as-needed treatment of SAD. A Phase 3 trial is ongoing.

Abnormal response to chronic social defeat stress and fear extinction in a mouse model of Lynx2-based cholinergic dysregulation

Nicotinic receptor signaling is influential in modulating appropriate responses to salient stimuli within a complex environment. The cholinergic neurotransmitter system drives attention to salient stimuli such as stressors, and aids in orchestrating the proper neural and behavioral responses. Dysregulation of this system, however, has been implicated in altered anxiety regulation and mood disorders. Among the multiple layers of regulation are protein modulators such as Lynx2/Lypd1, which provides negative nicotinic acetylcholine receptor regulation within anxiety-related circuits, such as the amygdala and medial prefrontal cortex, among other brain regions. Mice null for Lynx2/Lypd1 (Lynx2 KO) show elevated basal anxiety-like behavior in tests such as elevated plus maze, light-dark box and social interaction assays. Here, we queried how a line predisposed to basal anxiety-like behavior would respond to specific stressors, using validated models of experiential-based affective disorders such as fear extinction, acute and chronic social defeat stress assays. We discovered that Lynx2 KO mice demonstrate an inability to extinguish learned fear during fear extinction tests even during milder stress conditions. In social defeat studies, contrary to our predictions, the Lynx2 KO mice switched from a socially avoidant phenotype (which could be considered susceptible) before defeat to a social approach/resilient phenotype after defeat. Consistent with reports of the inverse relationship between resilience and BDNF levels, we observed reduced BDNF levels in the VTA of Lynx2 KO mice. Furthermore, we provide evidence for the functional role of α7 nicotinic receptor subtypes by phenotypic rescue of fear extinction and social defeat phenotypes by MLA antagonism of α7 nicotinic acetylcholine receptors, or by crossing with α7 nicotinic acetylcholine receptor null mutant mice. A stable physical interaction between LYNX2 and α7 nAChRs was observed by co-immunoprecipitation of complexes from mouse amygdalae extracts. Together, these data indicate that responses to specific stressors can become aberrant when baseline genetic factors predispose animals to anxiety dysregulation. These studies underscore the critical nature of well-regulated nicotinic receptor function in the adaptive response to environmental stressors.

Rapid changes in plasma corticosterone and medial amygdala transcriptome profiles during social status change reveal molecular pathways associated with a major life history transition in mouse dominance hierarchies

Social hierarchies are a common form of social organization across species. Although hierarchies are largely stable across time, animals may socially ascend or descend within hierarchies depending on environmental and social challenges. Here, we develop a novel paradigm to study social ascent and descent within male CD-1 mouse social hierarchies. We show that mice of all social ranks rapidly establish new stable social hierarchies when placed in novel social groups with animals of equivalent social status. Seventy minutes following social hierarchy formation, males that were socially dominant prior to being placed into new social hierarchies exhibit higher increases in plasma corticosterone and vastly greater transcriptional changes in the medial amygdala (MeA), which is central to the regulation of social behavior, compared to males who were socially subordinate prior to being placed into a new hierarchy. Specifically, the loss of social status in a new hierarchy (social descent) is associated with reductions in MeA expression of myelination and oligodendrocyte differentiation genes. Maintaining high social status is associated with high expression of genes related to cholinergic signaling in the MeA. Conversely, gaining social status in a new hierarchy (social ascent) is related to relatively few unique rapid changes in the MeA. We also identify novel genes associated with social transition that show common changes in expression when animals undergo either social descent or social ascent compared to maintaining their status. Two genes, Myosin binding protein C1 (Mybpc1) and μ-Crystallin (Crym), associated with vasoactive intestinal polypeptide (VIP) and thyroid hormone pathways respectively, are highly upregulated in socially transitioning individuals. Further, increases in genes associated with synaptic plasticity, excitatory glutamatergic signaling and learning and memory pathways were observed in transitioning animals suggesting that these processes may support rapid social status changes.

Medial prefrontal cortex acetylcholine signaling mediates the ability to learn an active avoidance response following learned helplessness training

Increased brain levels of acetylcholine (ACh) have been observed in patients with depression, and increasing ACh levels pharmacologically can precipitate stress-related behaviors in humans and animals. Conversely, optimal ACh levels are required for cognition and memory. We hypothesize that excessive ACh signaling results in strengthening of negative encoding in which memory formation is aberrantly strengthened for stressful events. The medial prefrontal cortex (mPFC) is critical for both top-down control of stress-related circuits, and for encoding of sensory experiences. We therefore evaluated the role of ACh signaling in the mPFC in a learned helplessness task in which mice were exposed to repeated inescapable stressors followed by an active avoidance task. Using fiber photometry with a genetically-encoded ACh sensor, we found that ACh levels in the mPFC during exposure to inescapable stressors were positively correlated with later escape deficits in an active avoidance test in males, but not females. Consistent with these measurements, we found that both pharmacologically- and chemogenetically-induced increases in mPFC ACh levels resulted in escape deficits in both male and female mice, whereas chemogenetic inhibition of ACh neurons projecting to the mPFC improved escape performance in males, but impaired escape performance in females. These results highlight the adaptive role of ACh release in stress response, but also support the idea that sustained elevation of ACh contributes to maladaptive behaviors. Furthermore, mPFC ACh signaling may contribute to stress-based learning differentially in males and females.

Distinct cholinergic circuits underlie discrete effects of reward on attention

Attention and reward are functions that are critical for the control of behavior, and massive multi-region neural systems have evolved to support the discrete computations associated with each. Previous research has also identified that attention and reward interact, though our understanding of the neural mechanisms that mediate this interplay is incomplete. Here, we review the basic neuroanatomy of attention, reward, and cholinergic systems. We then examine specific contexts in which attention and reward computations interact. Building on this work, we propose two discrete neural circuits whereby acetylcholine, released from cell groups located in different parts of the brain, mediates the impact of stimulus-reward associations as well as motivation on attentional control. We conclude by examining these circuits as a potential shared loci of dysfunction across diseases states associated with deficits in attention and reward.

BNC210, a negative allosteric modulator of the alpha 7 nicotinic acetylcholine receptor, demonstrates anxiolytic- and antidepressant-like effects in rodents

This work describes the characterization of BNC210 (6-[(2,3-dihydro-1H-inden-2-yl)amino]-1-ethyl-3-(4-morpholinylcarbonyl)-1,8-naphthyridin-4(1H)-one), a selective, small molecule, negative allosteric modulator (NAM) of α7 nicotinic acetylcholine receptors (α7 nAChR). With the aim to discover a non-sedating, anxiolytic compound, BNC210 was identified during phenotypic screening of a focused medicinal chemistry library using the mouse Light Dark (LD) box to evaluate anxiolytic-like activity and the mouse Open Field (OF) (dark) test to detect sedative and/or motor effects. BNC210 exhibited anxiolytic-like activity with no measurable sedative or motor effects. Electrophysiology showed that BNC210 did not induce α7 nAChR currents by itself but inhibited EC80 agonist-evoked currents in recombinant GH4C1 cell lines stably expressing the rat or human α7 nAChR. BNC210 was not active when tested on cell lines expressing other members of the cys-loop ligand-gated ion channel family. Screening over 400 other targets did not reveal any activity for BNC210 confirming its selectivity for α7 nAChR. Oral administration of BNC210 to male mice and rats in several tests of behavior related to anxiety- and stress- related disorders, demonstrated significant reduction of these behaviors over a broad therapeutic range up to 500 times the minimum effective dose. Further testing for potential adverse effects in suitable rat and mouse tests showed that BNC210 did not produce sedation, memory and motor impairment or physical dependence, symptoms associated with current anxiolytic therapeutics. These data suggest that allosteric inhibition of α7 nAChR function may represent a differentiated approach to treating anxiety- and stress- related disorders with an improved safety profile compared to current treatments.

Functional neuroanatomy of basal forebrain projections to the basolateral amygdala: Transmitters, receptors, and neuronal subpopulations

The projections of the basal forebrain (BF) to the hippocampus and neocortex have been extensively studied and shown to be important for higher cognitive functions, including attention, learning, and memory. Much less is known about the BF projections to the basolateral nuclear complex of the amygdala (BNC), although the cholinergic innervation of this region by the BF is actually far more robust than that of cortical areas. This review will focus on light and electron microscopic tract-tracing and immunohistochemical (IHC) studies, many of which were published in the last decade, that have analyzed the relationship of BF inputs and their receptors to specific neuronal subtypes in the BNC in order to better understand the anatomical substrates of BF-BNC circuitry. The results indicate that BF inputs to the BNC mainly target the basolateral nucleus of the BNC (BL) and arise from cholinergic, GABAergic, and perhaps glutamatergic BF neurons. Cholinergic inputs mainly target dendrites and spines of pyramidal neurons (PNs) that express muscarinic receptors (MRs). MRs are also expressed by cholinergic axons, as well as cortical and thalamic axons that synapse with PN dendrites and spines. BF GABAergic axons to the BL also express MRs and mainly target BL interneurons that contain parvalbumin. It is suggested that BF-BL circuitry could be very important for generating rhythmic oscillations known to be critical for emotional learning. BF cholinergic inputs to the BNC might also contribute to memory formation by activating M1 receptors located on PN dendritic shafts and spines that also express NMDA receptors.

Associations Between the Wisconsin Inventory of Smoking Dependence Motives and Regional Brain Volumes in Adult Smokers

INTRODUCTION

The Wisconsin Inventory of Smoking Dependence Motives (WISDM-68) is a 68-item questionnaire to assess nicotine dependence as a multifactorial construct based on 13 theoretically derived smoking motives. Chronic smoking is associated with structural changes in brain regions implicated in the maintenance of smoking behavior; however, associations between brain morphometry and the various reinforcing components of smoking behavior remain unexamined. The present study investigated the potential association between smoking dependence motives and regional brain volumes in a cohort of 254 adult smokers.

AIMS AND METHODS

The WISDM-68 was administered to participants at the baseline session. Structural magnetic resonance brain imaging (MRI) data from 254 adult smokers (Mage = 42.7 ± 11.4) with moderate to severe nicotine dependence (MFTND = 5.4 ± 2.0) smoking for at least 2 years (Myears = 24.3 ± 11.8) were collected and analyzed with Freesurfer.

RESULTS

Vertex-wise cluster analysis revealed that high scores on the WISDM-68 composite, secondary dependence motives (SDM) composite, and multiple SDM subscales were associated with lower cortical volume in the right lateral prefrontal cortex (cluster-wise p's < .035). Analysis of subcortical volumes (ie, nucleus accumbens, amygdala, caudate, and pallidum) revealed several significant associations with WISDM-68 subscales, dependence severity (Fagerström Test for Nicotine Dependence), and overall exposure (pack-years). No significant associations between cortical volume and other nicotine dependence measures or pack-years were observed.

CONCLUSIONS

Results suggest that smoking motives may play a larger role in cortical abnormalities than addiction severity and smoking exposure per se, whereas subcortical volumes are associated with smoking motives, addiction severity, and smoking exposure.

IMPLICATIONS

The present study reports novel associations between the various reinforcing components of smoking behavior assessed by the WISDM-68 and regional brain volumes. Results suggest that the underlying emotional, cognitive, and sensory processes that drive non-compulsive smoking behaviors may play a larger role in gray matter abnormalities of smokers than smoking exposure or addiction severity.

Acetylcholine signaling in the medial prefrontal cortex mediates the ability to learn an active avoidance response following learned helplessness training

Increased brain levels of acetylcholine (ACh) are observed in subsets of patients with depression and increasing ACh levels chronically can precipitate stress-related behaviors in humans and animals. Conversely, optimal ACh levels are required for cognition and memory. We hypothesize that ACh signaling is important for encoding both appetitive and stress-relevant memories, but that excessive increases in ACh result in a negative encoding bias in which memory formation of a stressful event is aberrantly strengthened, potentially contributing to the excessive focus on negative experience that could lead to depressive symptoms. The medial prefrontal cortex (mPFC) is critical to control the limbic system to filter exteroceptive cues and stress-related circuits. We therefore evaluated the role of ACh signaling in the mPFC in a learned helplessness task in which mice were exposed to repeated inescapable stressors followed by an active avoidance task. Using fiber photometry with a genetically-encoded ACh sensor, we found that ACh levels in the mPFC during exposure to inescapable stressors were positively correlated with later escape deficits in an active avoidance test in males, but not females. Consistent with these measurements, we found that both pharmacologically- and chemogenetically-induced increases in mPFC ACh levels resulted in escape deficits in both male and female mice, whereas chemogenetic inhibition of ACh neurons projecting to the mPFC improved escape performance in males, but impaired escape performance in females. These results highlight the adaptive role of ACh release in stress response, but also support the idea that sustained elevated ACh levels contribute to maladaptive behaviors. Furthermore, mPFC ACh signaling may contribute to depressive symptomology differentially in males and females.

miRNA-132/212 Deficiency Disrupts Selective Corticosterone Modulation of Dorsal vs. Ventral Hippocampal Metaplasticity

Cortisol is a potent human steroid hormone that plays key roles in the central nervous system, influencing processes such as brain neuronal synaptic plasticity and regulating the expression of emotional and behavioral responses. The relevance of cortisol stands out in the disease, as its dysregulation is associated with debilitating conditions such as Alzheimer's Disease, chronic stress, anxiety and depression. Among other brain regions, cortisol importantly influences the function of the hippocampus, a structure central for memory and emotional information processing. The mechanisms fine-tuning the different synaptic responses of the hippocampus to steroid hormone signaling remain, however, poorly understood. Using ex vivo electrophysiology and wild type (WT) and miR-132/miR-212 microRNAs knockout (miRNA-132/212-/-) mice, we examined the effects of corticosterone (the rodent's equivalent to cortisol in humans) on the synaptic properties of the dorsal and ventral hippocampus. In WT mice, corticosterone predominantly inhibited metaplasticity in the dorsal WT hippocampi, whereas it significantly dysregulated both synaptic transmission and metaplasticity at dorsal and ventral regions of miR-132/212-/- hippocampi. Western blotting further revealed significantly augmented levels of endogenous CREB and a significant CREB reduction in response to corticosterone only in miR-132/212-/- hippocampi. Sirt1 levels were also endogenously enhanced in the miR-132/212-/- hippocampi but unaltered by corticosterone, whereas the levels of phospo-MSK1 were only reduced by corticosterone in WT, not in miR-132/212-/- hippocampi. In behavioral studies using the elevated plus maze, miRNA-132/212-/- mice further showed reduced anxiety-like behavior. These observations propose miRNA-132/212 as potential region-selective regulators of the effects of steroid hormones on hippocampal functions, thus likely fine-tuning hippocampus-dependent memory and emotional processing.

Plasticity in ventral pallidal cholinergic neuron-derived circuits contributes to comorbid chronic pain-like and depression-like behaviour in male mice

Nucleus- and cell-specific interrogation of individual basal forebrain (BF) cholinergic circuits is crucial for refining targets to treat comorbid chronic pain-like and depression-like behaviour. As the ventral pallidum (VP) in the BF regulates pain perception and emotions, we aim to address the role of VP-derived cholinergic circuits in hyperalgesia and depression-like behaviour in chronic pain mouse model. In male mice, VP cholinergic neurons innervate local non-cholinergic neurons and modulate downstream basolateral amygdala (BLA) neurons through nicotinic acetylcholine receptors. These cholinergic circuits are mobilized by pain-like stimuli and become hyperactive during persistent pain. Acute stimulation of VP cholinergic neurons and the VP-BLA cholinergic projection reduces pain threshold in naïve mice whereas inhibition of the circuits elevated pain threshold in pain-like states. Multi-day repetitive modulation of the VP-BLA cholinergic pathway regulates depression-like behaviour in persistent pain. Therefore, VP-derived cholinergic circuits are implicated in comorbid hyperalgesia and depression-like behaviour in chronic pain mouse model.

Pathophysiology of nAChRs: limbic circuits and related disorders

Human epidemiological studies have identified links between nicotine intake and stress disorders, including anxiety, depression and PTSD. Here we review the clinical evidence for activation and desensitization of nicotinic acetylcholine receptors (nAChRs) relevant to affective disorders. We go on to describe clinical and preclinical pharmacological studies suggesting that nAChR function may be involved in the etiology of anxiety and depressive disorders, may be relevant targets for medication development, and may contribute to the antidepressant efficacy of non-nicotinic therapeutics. We then review what is known about nAChR function in a subset of limbic system areas (amygdala, hippocampus and prefrontal cortex), and how this contributes to stress-relevant behaviors in preclinical models that may be relevant to human affective disorders. Taken together, the preclinical and clinical literature point to a clear role for ACh signaling through nAChRs in regulation of behavioral responses to stress. Disruption of nAChR homeostasis is likely to contribute to the psychopathology observed in anxiety and depressive disorders. Targeting specific nAChRs may therefore be a strategy for medication development to treat these disorders or to augment the efficacy of current therapeutics.

BNC210: an investigational α7-nicotinic acetylcholine receptor modulator for the treatment of anxiety disorders

INTRODUCTION

Anxiety disorders are common, disabling psychiatric conditions associated with excessive worry, irritability, and physiological symptoms of stress. Following insufficient response to psychological therapies, first-line pharmacological treatments for anxiety disorders suffer from inconsistent efficacy, addiction, and intolerable side-effect profiles (e.g. sedation), especially when used inappropriately or contrary to evidence-based guidelines. Developing anxiolytics acting via cholinergic modulation may provide novel options for the treatment of anxiety disorders, without the drawbacks of existing anxiolytics.

AREAS COVERED

We review pharmacological treatment of anxiety disorders and proposed mechanisms of action in relation to the associated neural circuitry. We then consider the mechanism of action, pharmacodynamics, and pharmacokinetics of the negative-allosteric modulator of the alpha7 nicotinic receptor BNC210, an investigational anxiolytic so far employed in studies of those with social anxiety disorder, post-traumatic stress disorder, and agitation in hospitalized elderly. Lastly, we consider the environment of competitor compounds for this indication, and BNC210's place within it, in both the present and near-future.

EXPERT OPINION

: There is a relative paucity of data regarding BNC210, albeit the small amount of mostly non-peer reviewed data indicate it is a well-tolerated, effective anxiolytic. Phase III trials are required for proper appraisal of its utility.

Alleviating anxiety and taming trauma: Novel pharmacotherapeutics for anxiety disorders and posttraumatic stress disorder

Psychiatric disorders associated with psychological trauma, stress and anxiety are a highly prevalent and increasing cause of morbidity worldwide. Current therapeutic approaches, including medication, are effective in alleviating symptoms of anxiety disorders and posttraumatic stress disorder (PTSD), at least in some individuals, but have unwanted side-effects and do not resolve underlying pathophysiology. After a period of stagnation, there is renewed enthusiasm from public, academic and commercial parties in designing and developing drug treatments for these disorders. Here, we aim to provide a snapshot of the current state of this field that is written for neuropharmacologists, but also practicing clinicians and the interested lay-reader. After introducing currently available drug treatments, we summarize recent/ongoing clinical assessment of novel medicines for anxiety and PTSD, grouped according to primary neurochemical targets and their potential to produce acute and/or enduring therapeutic effects. The evaluation of putative treatments targeting monoamine (including psychedelics), GABA, glutamate, cannabinoid, cholinergic and neuropeptide systems, amongst others, are discussed. We emphasize the importance of designing and clinically assessing new medications based on a firm understanding of the underlying neurobiology stemming from the rapid advances being made in neuroscience. This includes harnessing neuroplasticity to bring about lasting beneficial changes in the brain rather than - as many current medications do - produce a transient attenuation of symptoms, as exemplified by combining psychotropic/cognitive enhancing drugs with psychotherapeutic approaches. We conclude by noting some of the other emerging trends in this promising new phase of drug development.

Differential Regulation of Prelimbic and Thalamic Transmission to the Basolateral Amygdala by Acetylcholine Receptors

The amygdalar anterior basolateral nucleus (BLa) plays a vital role in emotional behaviors. This region receives dense cholinergic projections from basal forebrain which are critical in regulating neuronal activity in BLa. Cholinergic signaling in BLa has also been shown to modulate afferent glutamatergic inputs to this region. However, these studies, which have used cholinergic agonists or prolonged optogenetic stimulation of cholinergic fibers, may not reflect the effect of physiological acetylcholine release in the BLa. To better understand these effects of acetylcholine, we have used electrophysiology and optogenetics in male and female mouse brain slices to examine cholinergic regulation of afferent BLa input from cortex and midline thalamic nuclei. Phasic ACh release evoked by single pulse stimulation of cholinergic terminals had a biphasic effect on transmission at cortical input, producing rapid nicotinic receptor-mediated facilitation followed by slower mAChR-mediated depression. In contrast, at this same input, sustained ACh elevation through application of the cholinesterase inhibitor physostigmine suppressed glutamatergic transmission through mAChRs only. This suppression was not observed at midline thalamic nuclei inputs to BLa. In agreement with this pathway specificity, the mAChR agonist, muscarine more potently suppressed transmission at inputs from prelimbic cortex than thalamus. Muscarinic inhibition at prelimbic cortex input required presynaptic M4 mAChRs, while at thalamic input it depended on M3 mAChR-mediated stimulation of retrograde endocannabinoid signaling. Muscarinic inhibition at both pathways was frequency-dependent, allowing only high-frequency activity to pass. These findings demonstrate complex cholinergic regulation of afferent input to BLa that is pathway-specific and frequency-dependent.SIGNIFICANCE STATEMENT Cholinergic modulation of the basolateral amygdala regulates formation of emotional memories, but the underlying mechanisms are not well understood. Here, we show, using mouse brain slices, that ACh differentially regulates afferent transmission to the BLa from cortex and midline thalamic nuclei. Fast, phasic ACh release from a single optical stimulation biphasically regulates glutamatergic transmission at cortical inputs through nicotinic and muscarinic receptors, suggesting that cholinergic neuromodulation can serve precise, computational roles in the BLa. In contrast, sustained ACh elevation regulates cortical input through muscarinic receptors only. This muscarinic regulation is pathway-specific with cortical input inhibited more strongly than midline thalamic nuclei input. Specific targeting of these cholinergic receptors may thus provide a therapeutic strategy to bias amygdalar processing and regulate emotional memory.

Why Are Some People with Lower Urinary Tract Symptoms (LUTS) Depressed? New Evidence That Peripheral Inflammation in the Bladder Causes Central Inflammation and Mood Disorders

Anecdotal evidence has long suggested that patients with lower urinary tract symptoms (LUTS) develop mood disorders, such as depression and anxiety, at a higher rate than the general population and recent prospective studies have confirmed this link. Breakthroughs in our understanding of the diseases underlying LUTS have shown that many have a substantial inflammatory component and great strides have been made recently in our understanding of how this inflammation is triggered. Meanwhile, studies on mood disorders have found that many are associated with central neuroinflammation, most notably in the hippocampus. Excitingly, work on other diseases characterized by peripheral inflammation has shown that they can trigger central neuroinflammation and mood disorders. In this review, we discuss the current evidence tying LUTS to mood disorders, its possible bidirectionally, and inflammation as a common mechanism. We also review modern theories of inflammation and depression. Finally, we discuss exciting new animal studies that directly tie two bladder conditions characterized by extensive bladder inflammation (cyclophosphamide-induced hemorrhagic cystitis and bladder outlet obstruction) to neuroinflammation and depression. We conclude with a discussion of possible mechanisms by which peripheral inflammation is translated into central neuroinflammation with the resulting psychiatric concerns.

Abnormal response to chronic social defeat stress and fear extinction in a mouse model of cholinergic dysregulation

Cholinergic signaling is critical for an individual to react appropriately and adaptably to salient stimuli while navigating a complex environment. The cholinergic neurotransmitter system drives attention to salient stimuli, such as stressors, and aids in orchestrating the proper neural and behavioral response. Fine-tuned regulation of the cholinergic system has been linked to appropriate stress responses and subsequent mood regulation while dysregulation has been implicated in mood disorders. Among the multiple layers of regulation are cholinergic protein modulators. Here, we use validated models of experiential-based affective disorders to investigate differences in responses to stress in a genetic mouse model of cholinergic dysregulation based on the loss of protein modulator. The lynx2 nicotinic receptor modulatory protein provides negative cholinergic regulation within the amygdala, medial prefrontal cortex, and other brain regions. We discovered here that lynx2 knockout (KO) mice demonstrate an inability to update behavior with an inability to extinguish learned fear during a fear extinction test. We also observed, under an increased stress load following exposure to chronic social defeat stress (CSDS) paradigm, there was a unified resilience phenotype in lynx2KO mice, as opposed to the wild-type cohort which was split between resilience and susceptible phenotypes. Furthermore, we provide evidence for the functional role of α7 nicotinic receptor subtypes by phenotypic rescue with MLA or crossing with an α7 null mutant mouse (e.g. lynx2/α7 double KO mice). We demonstrate a direct physical interaction between lynx2 and α7 nAChR by co-immunoprecipitation of complexes from mouse BLA extracts. The genetic predisposition to heightened basal anxiety-like behavior and altered cholinergic signaling impairs individual behavior responses stressors. Together, these data indicate that the effects of social stress can be influenced by baseline genetic factors involved in anxiety regulation.

Dopaminergic and cholinergic modulation of the amygdala is altered in female mice with oestrogen receptor β deprivation

The amygdala is modulated by dopaminergic and cholinergic neurotransmission, and this modulation is altered in mood disorders. Therefore, this study was designed to evaluate the presence/absence of quantitative alterations in the expression of main dopaminergic and cholinergic markers in the amygdala of mice with oestrogen receptor β (ERβ) knock-out which exhibit increased anxiety, using immunohistochemistry and quantitative methods. Such alterations could either contribute to increased anxiety or be a compensatory mechanism for reducing anxiety. The results show that among dopaminergic markers, the expression of tyrosine hydroxylase (TH), dopamine transporter (DAT) and dopamine D₂-like receptor (DA₂) is significantly elevated in the amygdala of mice with ERβ deprivation when compared to matched controls, whereas the content of dopamine D₁-like receptor (DA₁) is not altered by ERβ knock-out. In the case of cholinergic markers, muscarinic acetylcholine type 1 receptor (AChR_M1) and alpha-7 nicotinic acetylcholine receptor (AChR_α7) display overexpression while the content of acetylcholinesterase (AChE) and vesicular acetylcholine transporter (VAChT) remains unchanged. In conclusion, in the amygdala of ERβ knock-out female the dopaminergic and cholinergic signalling is altered, however, to determine the exact role of ERβ in the anxiety-related behaviour further studies are required.

ACh signaling modulates activity of the GABAergic signaling network in the basolateral amygdala and behavior in stress-relevant paradigms

The balance between excitatory and inhibitory (E/I) signaling is important for maintaining homeostatic function in the brain. Indeed, dysregulation of inhibitory GABA interneurons in the amygdala has been implicated in human mood disorders. We hypothesized that acetylcholine (ACh) signaling in the basolateral amygdala (BLA) might alter E/I balance resulting in changes in stress-sensitive behaviors. We therefore measured ACh release as well as activity of calmodulin-dependent protein kinase II (CAMKII)-, parvalbumin (PV)-, somatostatin (SOM)- and vasoactive intestinal protein (VIP)-expressing neurons in the BLA of awake, behaving male mice. ACh levels and activity of both excitatory and inhibitory BLA neurons increased when animals were actively coping, and decreased during passive coping, in the light-dark box, tail suspension and social defeat. Changes in neuronal activity preceded behavioral state transitions, suggesting that BLA activity may drive the shift in coping strategy. In contrast to exposure to escapable stressors, prolonging ACh signaling with a cholinesterase antagonist changed the balance of activity among BLA cell types, significantly increasing activity of VIP neurons and decreasing activity of SOM cells, with little effect on CaMKII or PV neurons. Knockdown of α7 or β2-containing nAChR subtypes in PV and SOM, but not CaMKII or VIP, BLA neurons altered behavioral responses to stressors, suggesting that ACh signaling through nAChRs on GABA neuron subtypes contributes to stress-induced changes in behavior. These studies show that ACh modulates the GABAergic signaling network in the BLA, shifting the balance between SOM, PV, VIP and CaMKII neurons, which are normally activated coordinately during active coping in response to stress. Thus, prolonging ACh signaling, as occurs in response to chronic stress, may contribute to maladaptive behaviors by shifting the balance of inhibitory signaling in the BLA.

Potential of Heterogeneous Compounds as Antidepressants: A Narrative Review

Depression is a globally widespread disorder caused by a complicated interplay of social, psychological, and biological factors. Approximately 280 million people are suffering from depression worldwide. Traditional frontline antidepressants targeting monoamine neurotransmitters show unsatisfactory effects. The development and application of novel antidepressants for dissimilar targets are on the agenda. This review characterizes the antidepressant effects of multiple endogenous compounds and/or their targets to provide new insight into the working mechanism of antidepressants. We also discuss perspectives and challenges for the generation of novel antidepressants.

Chronic Intermittent Ethanol Exposure Dysregulates Nucleus Basalis Magnocellularis Afferents in the Basolateral Amygdala

Nucleus basalis magnocellularis (NBM) cholinergic projections to the basolateral amygdala (BLA) regulate the acquisition and consolidation of fear-like and anxiety-like behaviors. However, it is unclear whether the alterations in the NBM-BLA circuit promote negative affect during ethanol withdrawal (WD). Therefore, we performed ex vivo whole-cell patch-clamp electrophysiology in both the NBM and the BLA of male Sprague Dawley rats following 10 d of chronic intermittent ethanol (CIE) exposure and 24 h of WD. We found that CIE exposure and withdrawal enhanced the neuronal excitability of NBM putative "cholinergic" neurons. We subsequently used optogenetics to directly manipulate NBM terminal activity within the BLA and measure cholinergic modulation of glutamatergic afferents and BLA pyramidal neurons. Our findings indicate that CIE and withdrawal upregulate NBM cholinergic facilitation of glutamate release via activation of presynaptic nicotinic acetylcholine receptors (AChRs). Ethanol withdrawal-induced increases in NBM terminal activity also enhance BLA pyramidal neuron firing. Collectively, our results provide a novel characterization of the NBM-BLA circuit and suggest that CIE-dependent modifications to NBM afferents enhance BLA pyramidal neuron activity during ethanol withdrawal.

Discrimination of motor and sensorimotor effects of phencyclidine and MK-801: Involvement of GluN2C-containing NMDA receptors in psychosis-like models

Non-competitive NMDA receptor (NMDA-R) antagonists like ketamine, phencyclidine (PCP) and MK-801 are routinely used as pharmacological models of schizophrenia. However, the NMDA-R subtypes, neuronal types (e.g., GABA vs. glutamatergic neurons) and brain regions involved in psychotomimetic actions are not fully understood. PCP activates thalamo-cortical circuits after NMDA-R blockade in reticular thalamic GABAergic neurons. GluN2C subunits are densely expressed in thalamus and cerebellum. Therefore, we examined their involvement in the behavioral and functional effects elicited by PCP and MK-801 using GluN2C knockout (GluN2CKO) and wild-type mice, under the working hypothesis that psychotomimetic effects should be attenuated in mutant mice. PCP and MK-801 induced a disorganized and meandered hyperlocomotion in both genotypes. Interestingly, stereotyped behaviors like circling/rotation, rearings and ataxia signs were dramatically reduced in GluN2CKO mice, indicating a better motor coordination in absence of GluN2C subunits. In contrast, other motor or sensorimotor (pre-pulse inhibition of the startle response) aspects of the behavioral syndrome remained unaltered by GluN2C deletion. PCP and MK-801 evoked a general pattern of c-fos activation in mouse brain (including thalamo-cortical networks) but not in the cerebellum, where they markedly reduced c-fos expression, with significant genotype differences paralleling those in motor coordination. Finally, resting-state fMRI showed an enhanced cortico-thalamic-cerebellar connectivity in GluN2CKO mice, less affected by MK-801 than controls. Hence, the GluN2C subunit allows the dissection of the behavioral alterations induced by PCP and MK-801, showing that some motor effects (in particular, motor incoordination), but not deficits in sensorimotor gating, likely depend on GluN2C-containing NMDA-R blockade in cerebellar circuits.

Differentiating the Neuropharmacological Properties of Nicotinic Acetylcholine Receptor-Activating Alkaloids

Alkaloids that target nicotinic acetylcholine receptors (nAChR) are of great interest because of the critical role they play in mood and anxiety. However, understanding of the neuropharmacological effects of nicotinic alkaloids, such as cotinine and anatabine, is very limited. In this study, we investigated the neuropharmacological effects of three naturally occurring alkaloids-nicotine, cotinine, and anatabine-in vitro and in vivo. A single injection of nicotine induced anxiolytic-like behavioral features in mice by using the SmartCube® behavioral profiling system, while cotinine and anatabine had no detectable effect. The results were corroborated by using the zebrafish novel tank test (NTT), which showed a profound anxiolytic-like effect induced by multiple doses of nicotine after a single 20-min treatment. When the regulation of dopamine and norepinephrine release-the neurotransmitter systems relevant for anxiety-were examined in vitro, we found that nicotine stimulated the release of both norepinephrine and dopamine, while cotinine and anatabine mainly stimulated the dopamine release. The molecular targets of nicotine were confirmed to be nAChRs with its most potent activities against α4β2 and α6/3β2β3 subtypes in vitro. Anatabine was a weaker agonist for these receptors than nicotine. Cotinine was the least potent nAChR compound, only being able to activate α4β2 and α6/3β2β3 subtypes at high doses and no detectable activities against α3β4 and α7 subtypes at the concentrations tested. The observed effects were unlikely due to the off-target effect, because these alkaloids did not bind or regulate >160 other molecular targets in vitro. Thus, the present results suggest that natural nicotinic alkaloids can induce an anxiolytic-like behavior in nonclinical animal models, potency of which may depend on the activation of various nAChRs and regulation of various neurotransmitter systems. Further investigations would help understand their effects on humans, because non-clinical studies should not be taken as a direct indication for human behavior and nicotine is not risk free.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

Age-Dependent and Pathway-Specific Bimodal Action of Nicotine on Synaptic Plasticity in the Hippocampus of Mice Lacking the miR-132/212 Genes

Nicotine addiction develops predominantly during human adolescence through smoking. Self-administration experiments in rodents verify this biological preponderance to adolescence, suggesting evolutionary-conserved and age-defined mechanisms which influence the susceptibility to nicotine addiction. The hippocampus, a brain region linked to drug-related memory storage, undergoes major morpho-functional restructuring during adolescence and is strongly affected by nicotine stimulation. However, the signaling mechanisms shaping the effects of nicotine in young vs. adult brains remain unclear. MicroRNAs (miRNAs) emerged recently as modulators of brain neuroplasticity, learning and memory, and addiction. Nevertheless, the age-dependent interplay between miRNAs regulation and hippocampal nicotinergic signaling remains poorly explored. We here combined biophysical and pharmacological methods to examine the impact of miRNA-132/212 gene-deletion (miRNA-132/212-/-) and nicotine stimulation on synaptic functions in adolescent and mature adult mice at two hippocampal synaptic circuits: the medial perforant pathway (MPP) to dentate yrus (DG) synapses (MPP-DG) and CA3 Schaffer collaterals to CA1 synapses (CA3-CA1). Basal synaptic transmission and short-term (paired-pulse-induced) synaptic plasticity was unaltered in adolescent and adult miRNA-132/212-/- mice hippocampi, compared with wild-type controls. However, nicotine stimulation promoted CA3-CA1 synaptic potentiation in mature adult (not adolescent) wild-type and suppressed MPP-DG synaptic potentiation in miRNA-132/212-/- mice. Altered levels of CREB, Phospho-CREB, and acetylcholinesterase (AChE) expression were further detected in adult miRNA-132/212-/- mice hippocampi. These observations propose miRNAs as age-sensitive bimodal regulators of hippocampal nicotinergic signaling and, given the relevance of the hippocampus for drug-related memory storage, encourage further research on the influence of miRNAs 132 and 212 in nicotine addiction in the young and the adult brain.

A circuit of COCH neurons encodes social-stress-induced anxiety via MTF1 activation of Cacna1h

The hippocampus is a temporal lobe structure critical for cognition, such as learning, memory, and attention, as well as emotional responses. Hippocampal dysfunction can lead to persistent anxiety and/or depression. However, how millions of neurons in the hippocampus are molecularly and structurally organized to engage their divergent functions remains unknown. Here, we genetically target a subset of neurons expressing the coagulation factor c homolog (COCH) gene. COCH-expressing neurons or COCH neurons are topographically segregated in the distal region of the ventral CA3 hippocampus and express Mtf1 and Cacna1h. MTF1 activation of Cacna1h transcription in COCH neurons encodes the ability of COCH neurons to burst action potentials and cause social-stress-induced anxiety-like behaviors by synapsing directly with a subset of GABAergic inhibitory neurons in the lateral septum. Together, this study provides a molecular and circuitry-based framework for understanding how COCH neurons in the hippocampus are assembled to engage social behavior.

Brain Adaptation to Acute Stress: Effect of Time, Social Buffering, and Nicotinic Cholinergic System

Both social behavior and stress responses rely on the activity of the prefrontal cortex (PFC) and basolateral nucleus of the amygdala (BLA) and on cholinergic transmission. We previously showed in adult C57BL/6J (B6) mice that social interaction has a buffering effect on stress-related prefrontal activity, depending on the β2-/- cholinergic nicotinic receptors (nAChRs, β2-/- mice). The latency for this buffer to emerge being short, we question here whether the associated brain plasticity, as reflected by regional c-fos protein quantification and PFC-BLA functional connectivity, is modulated by time. Overall, we show that time normalized the stress-induced PFC hyperactivation in B6 mice and PFC hypo-activation in β2-/- mice, with no effect on BLA. It also triggered a multitude of functional links between PFC subareas, and between PFC and BLA in B6 mice but not β2-/- mice, showing a central role of nAChRs in this plasticity. Coupled with social interaction and time, stress led to novel and drastic diminution of functional connectivity within the PFC in both genotypes. Thus, time, emotional state, and social behavior induced dissociated effects on PFC and BLA activity and important cortico-cortical reorganizations. Both activity and plasticity were under the control of the β2-nAChRs.

Role of the Cholinergic Anti-Inflammatory Reflex in Central Nervous System Diseases

In several central nervous system diseases, it has been reported that inflammation may be related to the etiologic process, therefore, therapeutic strategies are being implemented to control inflammation. As the nervous system and the immune system maintain close bidirectional communication in physiological and pathological conditions, the modulation of inflammation through the cholinergic anti-inflammatory reflex has been proposed. In this review, we summarized the evidence supporting chemical stimulation with cholinergic agonists and vagus nerve stimulation as therapeutic strategies in the treatment of various central nervous system pathologies, and their effect on inflammation.

Effects of nicotinic acetylcholine receptor-activating alkaloids on anxiety-like behavior in zebrafish

Alkaloids are a structurally complex group of natural products that have a diverse range of biological activities and significant therapeutic applications. In this study, we examined the acute, anxiolytic-like effects of nicotinic acetylcholine receptor (nAChR)-activating alkaloids with reported neuropharmacological effects but whose effects on anxiety are less well understood. Because α4β2 nAChRs can regulate anxiety, we first demonstrated the functional activities of alkaloids on these receptors in vitro. Their effects on anxiety-like behavior in zebrafish were then examined using the zebrafish novel tank test (NTT). The NTT is a relatively high-throughput behavioral paradigm that takes advantage of the natural tendency of fish to dive down when stressed or anxious. We report for the first time that cotinine, anatabine, and methylanatabine may suppress this anxiety-driven zebrafish behavior after a single 20-min treatment. Effective concentrations of these alkaloids were well above the concentrations naturally found in plants and the concentrations needed to induce anxiolytic-like effect by nicotine. These alkaloids showed good receptor interactions at the α4β2 nAChR agonist site as demonstrated by in vitro binding and in silico docking model, although somewhat weaker than that for nicotine. Minimal or no significant effect of other compounds may have been due to low bioavailability of these compounds in the brain, which is supported by the in silico prediction of blood-brain barrier permeability. Taken together, our findings indicate that nicotine, although not risk-free, is the most potent anxiolytic-like alkaloid tested in this study, and other natural alkaloids may regulate anxiety as well.

Nicotine inhibits the VTA-to-amygdala dopamine pathway to promote anxiety

Nicotine stimulates dopamine (DA) neurons of the ventral tegmental area (VTA) to establish and maintain reinforcement. Nicotine also induces anxiety through an as yet unknown circuitry. We found that nicotine injection drives opposite functional responses of two distinct populations of VTA DA neurons with anatomically segregated projections: it activates neurons that project to the nucleus accumbens (NAc), whereas it inhibits neurons that project to the amygdala nuclei (Amg). We further show that nicotine mediates anxiety-like behavior by acting on β2-subunit-containing nicotinic acetylcholine receptors of the VTA. Finally, using optogenetics, we bidirectionally manipulate the VTA-NAc and VTA-Amg pathways to dissociate their contributions to anxiety-like behavior. We show that inhibition of VTA-Amg DA neurons mediates anxiety-like behavior, while their activation prevents the anxiogenic effects of nicotine. These distinct subpopulations of VTA DA neurons with opposite responses to nicotine may differentially drive the anxiogenic and the reinforcing effects of nicotine.

Subchronic effects of plant alkaloids on anxiety-like behavior in zebrafish

Zebrafish provide a valuable emerging complementary model for neurobehavioral research. They offer a powerful way to screen for the potential therapeutic effects of neuroactive drugs. A variety of behavioral tests for zebrafish have been developed and validated for assessing neurobehavioral function. The novel tank diving test is a straightforward, reproducible way of measuring anxiety-like behavior in zebrafish. When introduced into a novel tank, zebrafish normally dive to the bottom of the tank and then gradually explore the higher levels of the water column as time progresses. Buspirone is an effective anxiolytic drug in humans, which has been found, with acute administration, to reduce this anxiety-like response in zebrafish. The current study used the zebrafish model to evaluate the potential anxiolytic effects of alkaloids, commonly found in Solanaceae plants, with known neuropharmacology relevant to mood regulation. In line with previous findings, acute treatment with anxiolytic positive controls buspirone and the plant alkaloid nicotine reduced the anxiety-like diving response in the zebrafish novel tank diving test. Further, both buspirone and nicotine continued to produce anxiolytic-like effects in zebrafish after 5 days of exposure. In the same treatment paradigm, the effects of five other alkaloids-cotinine, anatabine, anabasine, harmane, and norharmane-were investigated. Cotinine, the major metabolite of nicotine, also caused anxiolytic-like effects, albeit at a dose higher than the effective dose of nicotine. Nicotine's anxiolytic-like effect was not shared by the other nicotinic alkaloids, anabasine and anatabine, or by the naturally present monoamine oxidase inhibitors harmane and norharmane. We conclude that nicotine uniquely induces anxiolytic-like effects after acute and subchronic treatment in zebrafish. The zebrafish model with the novel tank diving test could be a useful complement to rodent models for screening candidate compounds for anxiolytic effects in nonclinical studies.

Mechanisms of Nicotine Addiction

Tobacco smoking results in more than five million deaths each year and accounts for ∼90% of all deaths from lung cancer.³ Nicotine, the major reinforcing component of tobacco smoke, acts in the brain through the neuronal nicotinic acetylcholine receptors (nAChRs). The nAChRs are allosterically regulated, ligand-gated ion channels consisting of five membrane-spanning subunits. Twelve mammalian α subunits (α2-α10) and three β subunits (β2-β4) have been cloned. The predominant nAChR subtypes in mammalian brain are those containing α4 and β2 subunits (denoted as α4β2* nAChRs). The α4β2* nAChRs mediate many behaviors related to nicotine addiction and are the primary targets for currently approved smoking cessation agents. Considering the large number of nAChR subunits in the brain, it is likely that nAChRs containing subunits in addition to α4 and β2 also play a role in tobacco smoking. Indeed, genetic variation in the CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nAChR subunits, respectively, has been shown to increase vulnerability to tobacco dependence and smoking-associated diseases including lung cancer. Moreover, mice, in which expression of α5 or β4 subunits has been genetically modified, have profoundly altered patterns of nicotine consumption. In addition to the reinforcing properties of nicotine, the effects of nicotine on appetite, attention, and mood are also thought to contribute to establishment and maintenance of the tobacco smoking habit. Here, we review recent insights into the behavioral actions of nicotine, and the nAChR subtypes involved, which likely contribute to the development of tobacco dependence in smokers.

Long-term consumption of Moringa oleifera-supplemented diet enhanced neurocognition, suppressed oxidative stress, acetylcholinesterase activity and neuronal degeneration in rat's hippocampus

OBJECTIVES

This study investigates protection against oxidative stress and memory enhancing potential of long-term consumption of Moringa oleifera leaves.

METHODS

Male Wistar rat were fed with mixture of M. oleifera-supplemented diets (MOSD) partitioned in 1, 5, 10, and 20% continuously for 12 weeks. Object recognition test (ORT) and Morris water maze (MWM) was used for assessing neurocognition. Changes in body weight, Lipid peroxidation (MDA), Glutathione (GSH), Catalase (CAT) and Acetylcholinesterase (AChE) activity was assayed in the brain tissue. Histomorphometric of the hippocampus was also examined.

RESULTS

The diets progressively increase the body weigh after the 12 weeks, improved spatial (MWM) and non-spatial (ORT) memory performance, protect against oxidative stress, inhibit AChE activity and suppresses neuronal degeneration in the hippocampus when stained with Cresyl violent stain.

CONCLUSIONS

Conclusively, long-term consumption of MOSD shows strong protection against oxidative stress and hippocampal degeneration and improves neurocognition with dose dependent effect.

Long-term consumption of Moringa oleifera-supplemented diet enhanced neurocognition, suppressed oxidative stress, acetylcholinesterase activity and neuronal degeneration in rat's hippocampus

OBJECTIVES

This study investigates protection against oxidative stress and memory enhancing potential of long-term consumption of Moringa oleifera leaves.

METHODS

Male Wistar rat were fed with mixture of M. oleifera-supplemented diets (MOSD) partitioned in 1, 5, 10, and 20% continuously for 12 weeks. Object recognition test (ORT) and Morris water maze (MWM) was used for assessing neurocognition. Changes in body weight, Lipid peroxidation (MDA), Glutathione (GSH), Catalase (CAT) and Acetylcholinesterase (AChE) activity was assayed in the brain tissue. Histomorphometric of the hippocampus was also examined.

RESULTS

The diets progressively increase the body weigh after the 12 weeks, improved spatial (MWM) and non-spatial (ORT) memory performance, protect against oxidative stress, inhibit AChE activity and suppresses neuronal degeneration in the hippocampus when stained with Cresyl violent stain.

CONCLUSIONS

Conclusively, long-term consumption of MOSD shows strong protection against oxidative stress and hippocampal degeneration and improves neurocognition with dose dependent effect.

Repurposing Cholinesterase Inhibitors as Antidepressants? Dose and Stress-Sensitivity May Be Critical to Opening Possibilities

When stress becomes chronic it can trigger lasting brain and behavioral changes including Major Depressive Disorder (MDD). There is conflicting evidence regarding whether acetylcholinesterase inhibitors (AChEIs) may have antidepressant properties. In a recent publication, we demonstrated a strong dose-dependency of the effect of AChEIs on antidepressant-related behavior in the mouse forced swim test: whereas the AChEI donepezil indeed promotes depression-like behavior at a high dose, it has antidepressant-like properties at lower doses in the same experiment. Our data therefore suggest a Janus-faced dose-response curve for donepezil in depression-related behavior. In this review, we investigate the mood-related properties of AChEIs in greater detail, focusing on both human and rodent studies. In fact, while there have been many studies showing pro-depressant activity by AChEIs and this is a major concept in the field, a variety of other studies in both humans and rodents show antidepressant effects. Our study was one of the first to systematically vary dose to include very low concentrations while measuring behavioral effects, potentially explaining the apparent disparate findings in the field. The possibility of antidepressant roles for AChEIs in rodents may provide hope for new depression treatments. Importantly, MDD is a psychosocial stress-linked disorder, and in rodents, stress is a major experimental manipulation for studying depression mechanisms, so an important future direction will be to determine the extent to which these depression-related effects are stress-sensitive. In sum, gaining a greater understanding of the potentially therapeutic mood-related effects of low dose AChEIs, both in rodent models and in human subjects, should be a prioritized topic in ongoing translational research.

The role of acetylcholine in negative encoding bias: Too much of a good thing?

Optimal acetylcholine (ACh) signaling is important for sustained attention and facilitates learning and memory. At the same time, human and animal studies have demonstrated increased levels of ACh in the brain during depressive episodes and increased symptoms of anxiety, depression, and reactivity to stress when ACh breakdown is impaired. While it is possible that the neuromodulatory roles of ACh in cognitive and affective processes are distinct, one possibility is that homeostatic levels of ACh signaling are necessary for appropriate learning, but overly high levels of cholinergic signaling promote encoding of stressful events, leading to the negative encoding bias that is a core symptom of depression. In this review, we outline this hypothesis and suggest potential neural pathways and underlying mechanisms that may support a role for ACh signaling in negative encoding bias.

Chronic Ethanol Exposure Potentiates Cholinergic Neurotransmission in the Basolateral Amygdala

Chronic intermittent ethanol (CIE) exposure dysregulates glutamatergic and GABAergic neurotransmission, facilitating basolateral amygdala (BLA) pyramidal neuron hyperexcitability and the expression of anxiety during withdrawal. It is unknown whether ethanol-induced alterations in nucleus basalis magnocellularis (NBM) cholinergic projections to the BLA mediate anxiety-related behaviors through direct modulation of GABA and glutamate afferents. Following 10 days of CIE exposure and 24 h of withdrawal, we recorded GABAergic and glutamatergic synaptic responses in BLA pyramidal neurons with electrophysiology, assessed total protein expression of cholinergic markers, and quantified acetylcholine and choline concentrations using a colorimetric assay. We measured α₇ nicotinic acetylcholine receptor (nAChR) dependent modulation of presynaptic function at distinct inputs in AIR- and CIE-exposed BLA coronal slices as a functional read-out of cholinergic neurotransmission. CIE/withdrawal upregulates the endogenous activity of α₇ nAChRs, facilitating release at both GABAergic' local' interneuron and glutamatergic synaptic responses to stria terminalis (ST) stimulation, with no effect at GABAergic lateral paracapsular cells (LPCs). CIE caused a three-fold increase in BLA acetylcholine concentration, with no changes in α₇ nAChR or cholinergic marker expression. These data illustrate that α₇ nAChR-dependent changes in presynaptic function serve as a proxy for CIE-dependent alterations in synaptic acetylcholine levels. Thus, cholinergic projections appear to mediate CIE-induced alterations at GABA/glutamate inputs.

Cumulative Effects of Social Stress on Reward-Guided Actions and Prefrontal Cortical Activity

BACKGROUND

When exposed to chronic social stress, animals display behavioral changes that are relevant to depressive-like phenotypes. However, the cascading relationship between incremental stress exposure and neural dysfunctions over time remains incompletely understood.

METHODS

We characterized the longitudinal effect of social defeat on goal-directed actions and prefrontal cortical activity in mice using a novel head-fixed sucrose preference task and two-photon calcium imaging.

RESULTS

Behaviorally, stress-induced loss of reward sensitivity intensifies over days. Motivational anhedonia, the failure to translate positive reinforcements into future actions, requires multiple sessions of stress exposure to become fully established. For neural activity, individual layer 2/3 pyramidal neurons in the cingulate and medial secondary motor subregions of the medial prefrontal cortex have heterogeneous responses to stress. Changes in ensemble activity differ significantly between susceptible and resilient mice after the first defeat session and continue to diverge following successive stress episodes before reaching persistent abnormal levels.

CONCLUSIONS

Collectively, these results demonstrate that the cumulative impact of an ethologically relevant stress can be observed at the level of cellular activity of individual prefrontal neurons. The distinct neural responses associated with resilience versus susceptibility suggests the hypothesis that the negative impact of social stress is neutralized in resilient animals, in part through an adaptive reorganization of prefrontal cortical activity.

Associations of serum chromogranin A with depressive symptoms in men with unipolar depressive disorder

OBJECTIVE

The aim of the present study was to determine the changes of serum chromogranin A (CgA) levels upon depression by investigating the relationship between serum CgA levels and the depressive symptoms assessed by 24-item Hamilton Rating Scale for Depression (HRSD-24).

METHOD

Serum CgA levels were measured by enzyme-linked immunosorbent assay in 133 male patients with major depressive disorder (MDD) and were compared with those of 47 healthy controls. Then generalized linear regression, logistic regression and restricted cubic spline models were performed to examine the association between serum CgA levels and depressive symptoms.

RESULTS

Serum CgA levels were lower in MDD patients than in controls (P < 0.001) and were inversely associated with scores on HRSD-24 in unadjusted, age, smoking, alcohol consumption, traumatic life events and family history of depression-adjusted and fully adjusted linear regression model. The fully adjusted regression coefficient with 95% confidence intervals was -0.028 (-0.045, -0.010) for serum CgA levels and HRSD-24 score. Serum CgA levels were inversely associated with depressive symptoms (HRSD ≥20) in each logistic regression model.

CONCLUSION

Serum CgA decrease was noted in male patients of MDD and may be inversely associated with depressive symptoms.

Molecular, histological and behavioral evidences for neuroprotective effects of minocycline against nicotine-induced neurodegeneration and cognition impairment: Possible role of CREB-BDNF signaling pathway

AIM

Neurodegeneration is one of the serious adverse effects of stimulant agents such as nicotine. Minocycline possess established neuroprotective properties. The role of CREB-BDNF signaling pathway in mediating the neuroprotective effects of minocycline against nicotine-induced neurodegeneration in rats was evaluated in current study.

METHODS

Seventy adult male rats were divided randomly into seven groups. Group 1 and 2, received 0.7 ml/rat of normal saline (i.p) and nicotine (10 mg/kg, s.c) respectively. Groups 3, 4, 5 and 6, treated concurrently with nicotine (10 mg/kg) and minocycline (10, 20, 30 and 40 mg/kg, i.p, respectively) for 21 days. Group 7 received minocycline alone (40 mg/kg, i.p) for 21 days. From 17th to 21 st days of experiment, Morris water maze (MWM) was used to evaluate learning and spatial memory in rats treated in different groups. According to the critical role of hippocampus in cognitive behavior, hippocampal neurodegenerative parameters (oxidative stress and inflammatory biomarkers) and also cyclic AMP response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF) levels were evaluated in isolated hippocampus in day 22 of experiment and after drug treatment. Also hippocampal cell density and tissue changes were evaluated by hematoxylin and eosin staining.

RESULT

Nicotine administration impaired the learning and spatial memory in rats and simultaneous treatment with various doses of minocycline attenuated the nicotine-induced cognition disturbances. In addition, nicotine treatment increased lipid peroxidation and the levels of oxidized form of glutathione (GSSG), interleukin 1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), and Bax protein, while decreasing reduced form of glutathione (GSH), Bcl-2 protein, P-CREB and BDNF levels in the hippocampus of experimental animals. Nicotine also reduced the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) in the hippocampus. Minocycline attenuated nicotine-induced neurodegeneration and elevating CREB (both forms) and BDNF levels. Also minocycline treatment alone increases the cognitive activity and increased CREB (both forms) and BDNF levels and decreased oxidative stress, inflammation and apoptotic biomarkers. Minocycline at high doses cause inhibition of nicotine induced cell density and changes in both area of dentate gyrus (DG) and CA1 in hippocampus.

CONCLUSION

It can be concluded that minocycline, probably through activation of P-CREB/BDNF signaling pathway, confers neuroprotection against nicotine-induced neurodegeneration in rat hippocampus.

Cholinergic Modulation of Disorder-Relevant Neural Circuits in Generalized Anxiety Disorder

BACKGROUND

Generalized anxiety disorder is associated with hyperactivity in the amygdala-prefrontal networks, and normalization of this aberrant function is thought to be critical for successful treatment. Preclinical evidence implicates cholinergic neurotransmission in the function of these systems and suggests that cholinergic modulation may have anxiolytic effects. However, the effects of cholinergic modulators on the function of anxiety-related networks in humans have not been investigated.

METHODS

We administered a novel α7 nicotinic acetylcholine receptor-negative allosteric modulator, BNC210, to 24 individuals (3 male subjects) with generalized anxiety disorder and assessed its effects on neural responses to fearful face stimuli.

RESULTS

BNC210 reduced amygdala reactivity to fearful faces relative to placebo and similarly to lorazepam and also reduced connectivity between the amygdala and the anterior cingulate cortex, a network involved in regulating anxious responses to aversive stimuli.

CONCLUSIONS

These results demonstrate for the first time that the function of disorder-relevant neural circuits in generalized anxiety disorder can be beneficially altered through modulation of cholinergic neurotransmission and suggest potential for this system as a novel target for anxiolytic pharmacotherapy.

α7 nicotinic receptor full agonist reverse basolateral amygdala hyperactivity and attenuation of dopaminergic neuron activity in rats exposed to chronic mild stress

Neuroimaging and preclinical studies showing that nicotinic receptors (nAChR) may play a role in mood control has increased interest in targeting the cholinergic system for treatment of major depressive disorder. Indeed, modulation of nAChRs in the basolateral amygdala (BLA) are sufficient to produce an anti-immobility effect in the mouse tail suspension test. However, how α7 nAChR modulation impacts BLA neuronal activity in vivo as well as the downstream mechanisms involved in its mood-related effects are not understood. In this work, we used the unpredictable chronic mild stress (CMS) model to investigate the mechanisms underlying the antidepressant-like effect of an α7 nAChR full agonist on BLA-induced changes in dopaminergic neurotransmission. Male adult Sprague-Dawley rats were exposed to four weeks of CMS. Behavioral and electrophysiological experiments were performed within one week following stress. CMS exposure increased rats' immobility time in the forced swimming test, decreased the number of spontaneously active dopamine neurons in the ventral tegmental area and increased the firing rate of putative projection neurons in the BLA. Stress-induced behavioral and electrophysiological changes were reversed by a single systemic administration of PNU282987. In summary, our findings corroborate previous descriptions of a potential rapid antidepressant effect for the α7 nAChR full agonist. This effect appears to involve a mechanism distinct from those of classic antidepressants: normalization of BLA hyperactivity and, consequently, of DA hypofunction. These observations corroborate the role of α7 nAChR as a potential target for novel antidepressant drug development.

Nicotine and alcohol: the role of midbrain dopaminergic neurons in drug reinforcement

Nicotine and alcohol addiction are leading causes of preventable death worldwide and continue to constitute a huge socio-economic burden. Both nicotine and alcohol perturb the brain's mesocorticolimbic system. Dopamine (DA) neurons projecting from the ventral tegmental area (VTA) to multiple downstream structures, including the nucleus accumbens, prefrontal cortex, and amygdala, are highly involved in the maintenance of healthy brain function. VTA DA neurons play a crucial role in associative learning and reinforcement. Nicotine and alcohol usurp these functions, promoting reinforcement of drug taking behaviors. In this review, we will first describe how nicotine and alcohol individually affect VTA DA neurons by examining how drug exposure alters the heterogeneous VTA microcircuit and network-wide projections. We will also examine how coadministration or previous exposure to nicotine or alcohol may augment the reinforcing effects of the other. Additionally, this review briefly summarizes the role of VTA DA neurons in nicotine, alcohol, and their synergistic effects in reinforcement and also addresses the remaining questions related to the circuit-function specificity of the dopaminergic system in mediating nicotine/alcohol reinforcement and comorbidity.

Induction of reversible bidirectional social approach bias by olfactory conditioning in male mice

Social avoidance is a common component of neuropsychiatric disorders that confers substantial functional impairment. An unbiased approach to identify brain regions and neuronal circuits that regulate social avoidance might enable development of novel therapeutics. However, most paradigms that alter social avoidance are irreversible and accompanied by multiple behavioral confounds. Here we report a straightforward behavioral paradigm in male mice enabling the reversible induction of social avoidance or approach with temporal control. C57BL/6J mice repeatedly participated in both negative and positive social experiences. Negative social experience was induced by brief social defeat by an aggressive male CD-1 mouse, while positive social experience was induced by exposure to a female mouse, each conducted daily for five days. Each social experience valence was conducted in a specific odorant context (i.e. negative experience in odorant A, positive experience in odorant B). Odorants were equally preferred pre-conditioning. However, after conditioning, mice sniffed positive experience-paired odorants more than negative experience-paired odorants. Furthermore, positive- or negative-conditioned odorant contexts increased or decreased, respectively, the approach behavior of conditioned mice toward conspecifics. Because individual mice undergo both positive and negative conditioning, this paradigm may be useful to examine neural representations of social approach or avoidance within the same subject.

Cholinergic Receptor Blockade in the VTA Attenuates Cue-Induced Cocaine-Seeking and Reverses the Anxiogenic Effects of Forced Abstinence

Drug relapse after periods of abstinence is a common feature of substance abuse. Moreover, anxiety and other mood disorders are often co-morbid with substance abuse. Cholinergic receptors in the ventral tegmental area (VTA) are known to mediate drug-seeking and anxiety-related behavior in rodent models. However, it is unclear if overlapping VTA cholinergic mechanisms mediate drug relapse and anxiety-related behaviors associated with drug abstinence. We examined the effects of VTA cholinergic receptor blockade on cue-induced cocaine seeking and anxiety during cocaine abstinence. Male Sprague-Dawley rats were trained to self-administer intravenous cocaine (~0.5 mg/kg/infusion, FR1 schedule) for 10 days, followed by 14 days of forced abstinence. VTA infusion of the non-selective nicotinic acetylcholine receptor antagonist mecamylamine (0, 10, and 30 μg/side) or the non-selective muscarinic receptor antagonist scopolamine (0, 2.4 and 24 μg /side) significantly decreased cue-induced cocaine seeking. In cocaine naïve rats, VTA mecamylamine or scopolamine also led to dose-dependent increases in open arm time in the elevated plus maze (EPM). In contrast, rats that received I.V. cocaine, compared to received I.V. saline rats, displayed an anxiogenic response on day 14 of abstinence as reflected by decreased open arm time in the EPM. Furthermore, low doses of VTA mecamylamine (10 μg /side) or scopolamine (2.4 μg /side), that did not alter EPM behavior in cocaine naive rats, were sufficient to reverse the anxiogenic effects of cocaine abstinence. Together, these data point to an overlapping role of VTA cholinergic mechanisms to regulate relapse and mood disorder-related responses during cocaine abstinence.