Synergism between two BLA-to-BNST pathways for appropriate expression of anxiety-like behaviors in male mice.

Understanding how distinct functional circuits are coordinated to fine-tune mood and behavior is of fundamental importance. Here, we observe that within the dense projections from basolateral amygdala (BLA) to bed nucleus of stria terminalis (BNST), there are two functionally opposing pathways orchestrated to enable contextually appropriate expression of anxiety-like behaviors in male mice. Specifically, the anterior BLA neurons predominantly innervate the anterodorsal BNST (adBNST), while their posterior counterparts send massive fibers to oval BNST (ovBNST) with moderate to adBNST. Optogenetic activation of the anterior and posterior BLA inputs oppositely regulated the activity of adBNST neurons and anxiety-like behaviors, via disengaging and engaging the inhibitory ovBNST-to-adBNST microcircuit, respectively. Importantly, the two pathways exhibited synchronized but opposite responses to both anxiolytic and anxiogenic stimuli, partially due to their mutual inhibition within BLA and the different inputs they receive. These findings reveal synergistic interactions between two BLA-to-BNST pathways for appropriate anxiety expression with ongoing environmental demands.

Spatial transcriptomics reveal neuron-astrocyte synergy in long-term memory.

Memory encodes past experiences, thereby enabling future plans. The basolateral amygdala is a centre of salience networks that underlie emotional experiences and thus has a key role in long-term fear memory formation1. Here we used spatial and single-cell transcriptomics to illuminate the cellular and molecular architecture of the role of the basolateral amygdala in long-term memory. We identified transcriptional signatures in subpopulations of neurons and astrocytes that were memory-specific and persisted for weeks. These transcriptional signatures implicate neuropeptide and BDNF signalling, MAPK and CREB activation, ubiquitination pathways, and synaptic connectivity as key components of long-term memory. Notably, upon long-term memory formation, a neuronal subpopulation defined by increased Penk and decreased Tac expression constituted the most prominent component of the memory engram of the basolateral amygdala. These transcriptional changes were observed both with single-cell RNA sequencing and with single-molecule spatial transcriptomics in intact slices, thereby providing a rich spatial map of a memory engram. The spatial data enabled us to determine that this neuronal subpopulation interacts with adjacent astrocytes, and functional experiments show that neurons require interactions with astrocytes to encode long-term memory.

Overexpression of EphB2 in the basolateral amygdala is crucial for inducing visceral pain sensitization in rats subjected to water avoidance stress.

AIMS: Basolateral amygdala (BLA), as a center for stress responses and emotional regulation, is involved in visceral hypersensitivity of irritable bowel syndrome (IBS) induced by stress. In the present study, we aimed to investigate the role of EphB2 receptor (EphB2) in BLA and explore the underlying mechanisms in this process. METHODS: Visceral hypersensitivity was induced by water avoidance stress (WAS). Elevated plus maze test, forced swimming test, and sucrose preference test were applied to assess anxiety- and depression-like behaviors. Ibotenic acid or lentivirus was used to inactivate BLA in either the induction or maintenance stage of visceral hypersensitivity. The expression of protein was determined by quantitative PCR, immunofluorescence, and western blot. RESULTS: EphB2 expression was increased in BLA in WAS rats. Inactivation of BLA or downregulation of EphB2 in BLA failed to induce visceral hypersensitivity as well as anxiety-like behaviors. However, during the maintenance stage of visceral pain, visceral hypersensitivity was only partially relieved but anxiety-like behaviors were abolished by inactivation of BLA or downregulation of EphB2 in BLA. Chronic WAS increased the expression of EphB2, N-methyl-D-aspartate receptors (NMDARs), and postsynaptic density protein (PSD95) in BLA. Downregulation of EphB2 in BLA reduced NMDARs and PSD95 expression in WAS rats. However, activation of NMDARs after the knockdown of EphB2 expression still triggered visceral hypersensitivity and anxiety-like behaviors. CONCLUSIONS: Taken together, the results suggest that EphB2 in BLA plays an essential role in inducing visceral hypersensitivity. In the maintenance stage, the involvement of EphB2 is crucial but not sufficient. The increase in EphB2 induced by WAS may enhance synaptic plasticity in BLA through upregulating NMDARs, which results in IBS-like symptoms. These findings may give insight into the treatment of IBS and related psychological distress.

Lateralization of the 5-HT1A receptors in the basolateral amygdala in metabolic and anxiety responses to chronic restraint stress.

Behavioral and functional studies describe hemispheric asymmetry in anxiety and metabolic behaviors in responses to stress. However, no study has reported serotonergic receptor (the 5-HT1A receptor) lateralization in the basolateral amygdala (BLA) in vivo on anxiety and metabolic behaviors under stress. In the present study, the effect of unilateral and bilateral suppression of the 5-HT1A receptor in the BLA on anxiety, and metabolic responses to chronic restraint stress was assessed. Male Wistar rats 7 days after cannulation into the BLA received chronic restraint stress for 14 consecutive days. 20 minutes before induction of stress, WAY-100-635 (selective 5-HT1A antagonist) or sterile saline (vehicle) was administered either uni- or bi-laterally into the BLA. Behavioral (elevated plus maze; EPM, and open field test), and metabolic parameter studies were performed. Results showed that stress causes a significant increase in weight gain compared to control. In the non-stress condition, the left and bilaterally, and in the stress condition the right, left, and both sides, inhibition of 5-HT1A in the BLA reduced weight gain. In the restraint stress condition, only inhibition of the 5-HT1A receptor in the left BLA led to decreased food intake compared to the control group. In stress conditions, inhibition of the 5-HT1A receptor on the right, left, and bilateral BLA increased water intake compared to the stress group. Inhibition of the 5-HT1A receptor on the left side of the BLA by WAY-100-635 induced anxiety-like behaviors in stressed rats. Similarly, WAY-100-635 on the left BLA effectively caused anxiety-like behaviors in both EPM and open field tests in the control animals. In conclusion, it seems that 5-HT1A receptors in the left BLA are more responsible for anxiety-like behaviors and metabolic changes in responses to stress.

Leptin excites basolateral amygdala principal neurons and reduces food intake by LepRb-JAK2-PI3K-dependent depression of GIRK channels.

Leptin is an adipocyte-derived hormone that modulates food intake, energy balance, neuroendocrine status, thermogenesis, and cognition. Whereas a high density of leptin receptors has been detected in the basolateral amygdala (BLA) neurons, the physiological functions of leptin in the BLA have not been determined yet. We found that application of leptin excited BLA principal neurons by activation of the long form leptin receptor, LepRb. The LepRb-elicited excitation of BLA neurons was mediated by depression of the G protein-activated inwardly rectifying potassium (GIRK) channels. Janus Kinase 2 (JAK2) and phosphoinositide 3-kinase (PI3K) were required for leptin-induced excitation of BLA neurons and depression of GIRK channels. Microinjection of leptin into the BLA reduced food intake via activation of LepRb, JAK2, and PI3K. Our results may provide a cellular and molecular mechanism to explain the physiological roles of leptin in vivo.

Basolateral amygdala neuropeptide Y system modulates binge ethanol consumption.

Neuropeptide Y (NPY) signaling regulation of corticolimbic communication is known to modulate binge-like ethanol consumption in rodents. In this work we sought to assess the impact of intra-BLA NPY system modulation on binge-like ethanol intake and to assess the role of the NPY1R+ projection from the BLA to the mPFC in this behavior. We used "drinking-in-the-dark" (DID) procedures in C57BL6J mice to address these questions. First, the impact of intra-BLA administration of NPY on binge-like ethanol intake was assessed. Next, the impact of repeated cycles of DID intake on NPY1R expression in the BLA was assessed with use of immunohistochemistry (IHC). Finally, chemogenetic inhibition of BLA→mPFC NPY1R+ projections was assessed to determine if limbic communication with the mPFC was specifically involved in binge-like ethanol intake. Importantly, as both the BLA and NPY system are sexually dimorphic, both sexes were assessed in these studies. Intra-BLA NPY dose-dependently decreased binge-like ethanol intake in males only. Repeated DID reduced NPY1R expression in the BLA of both sexes. Silencing of BLA→mPFC NPY1R+ neurons significantly reduced binge-like ethanol intake in both sexes in a dose-dependent manner. We provide novel evidence that (1) intra-BLA NPY reduces binge-like ethanol intake in males; (2) binge-like ethanol intake reduces NPY1R levels in the BLA; and (3) chemogenetic inhibition of BLA→mPFC NPY1R+ neurons blunts binge-like drinking in male and female mice. These observations provide the first direct evidence that NPY signaling in the BLA, and specifically BLA communication with the mPFC, modulates binge-like ethanol consumption.

Stimulating oxytocin receptors in the basolateral amygdala enhances stimulus processing: Differential and consistent effects for stimuli paired with fear versus sucrose in extinction and reversal learning.

Oxytocin (OT) influences a range of social behaviors by enhancing the salience of social cues and regulating the expression of specific social behaviors (e.g., maternal care versus defensive aggression). We previously showed that stimulating OT receptors in the basolateral amygdala of rats also enhanced the salience of fear conditioned stimuli: relative to rats given vehicle infusions, rats infused with [Thr4,Gly7]-oxytocin (TGOT), a selective OT receptor agonist, showed greater discrimination between a cue predictive of danger, and one that signaled safety. In the present series of experiments using male rats, the effects of OT receptor activation in the basolateral amygdala on stimulus processing were examined further using conditioning protocols that consist of changes in stimulus-outcome contingencies (i.e., extinction and reversal), and with stimuli paired with aversive (i.e., foot shock) and appetitive (i.e., sucrose) outcomes. It was revealed that the effects of OTR stimulation diverge for aversive and appetitive learning - enhancing the former but not the latter. However, across both types of learning, OTR stimulation enhanced the detection of conditioned stimuli. Overall, these results are consistent with an emerging view of OT's effects on stimulus salience; facilitating the detection of meaningful stimuli while reducing responding to those that are irrelevant.

The delta opioid receptor agonist KNT-127 relieves innate anxiety-like behavior in mice by suppressing transmission from the prelimbic cortex to basolateral amygdala.

AIM: Excitatory projections from the prelimbic cortex (PL) to the basolateral nucleus of the amygdala (BLA) are implicated in the regulation of anxiety-like behaviors, and we previously demonstrated that anxiolytic-like effects of the selective delta-opioid receptor (DOP) agonist KNT-127 is involved in suppressing glutamate neurotransmission in the PL. Here, we investigated the mechanisms underlying the anxiolytic-like effect of KNT-127 in mice by combining optogenetic stimulation of the PL-BLA pathway with behavioral analyses. METHODS: Four-week-old male C57BL/6J mice received bilateral administration of adeno-associated virus (AAV)2-CaMKIIa-hChR2(H134R)-enhanced yellow fluorescent protein (EYFP) into the PL to induce expression of the light-activated excitatory ionic channel ChR2. Subsequently, an optic fiber cannula connected to a wireless photo-stimulator was implanted into the BLA for optogenetic PL-BLA pathway stimulation. We evaluated innate anxiety using the elevated plus maze (EPM) and open field (OF) tests as well as learned anxiety using the contextual fear conditioning (CFC) test. RESULTS: Optogenetic activation of the PL-BLA pathway enhanced anxiety-like behaviors in the EPM and OF, while prior subcutaneous administration of KNT-127 (10 mg/kg) reduced this anxiogenic effect. In contrast, optogenetic activation of the PL-BLA pathway had no significant effect on conditioned fear. CONCLUSION: Our findings indicate that the PL-BLA circuit contributes to innate anxiety and that the anxiolytic-like effects of KNT-127 are mediated at least in part by suppression of PL-BLA transmission. The PL delta-opioid receptor may thus be an effective therapeutic target for anxiety disorders.

Regulation of anxiety-like behaviors by S-palmitoylation and S-nitrosylation in basolateral amygdala.

Protein posttranslational modification regulates synaptic protein stability, sorting and trafficking, and is involved in emotional disorders. Yet the molecular mechanisms regulating emotional disorders remain unelucidated. Here we report unknown roles of protein palmitoylation/nitrosylation crosstalk in regulating anxiety-like behaviors in rats. According to the percentages of open arm duration in the elevated plus maze test, the rats were divided into high-, intermediate- and low-anxiety groups. The palmitoylation and nitrosylation levels were detected by acyl-biotin exchange assay, and we found low palmitoylation and high nitrosylation levels in the basolateral amygdala (BLA) of high-anxiety rats. Furthermore, we observed that 2-bromopalmitate (2-BP), a palmitoylation inhibitor, induced anxiety-like behaviors, accompanied with decreased amplitude and frequency of mEPSCs and mIPSCs in the BLA. Additionally, we also found that inhibiting nNOS activity with 7-nitroindazole (7-NI) in the BLA caused anxiolytic effects and reduced the synaptic transmission. Interestingly, diazepam (DZP) rapidly elevated the protein palmitoylation level and attenuated the protein nitrosylation level in the BLA. Specifically, similar to DZP, the voluntary wheel running exerted DZP-like anxiolytic action, and induced high palmitoylation and low nitrosylation levels in the BLA. Lastly, blocking the protein palmitoylation with 2-BP induced an increase in protein nitrosylation level, and attenuating the nNOS activity by 7-NI elevated the protein palmitoylation level. Collectively, these results show a critical role of protein palmitoylation/nitrosylation crosstalk in orchestrating anxiety behavior in rats, and it may serve as a potential target for anxiolytic intervention.

Basolateral amygdala corticotropin releasing factor receptor 2 interacts with nonmuscle myosin II to destabilize memory in males.

Preclinical studies show that inhibiting the actin motor ATPase nonmuscle myosin II (NMII) with blebbistatin (Blebb) in the basolateral amgydala (BLA) depolymerizes actin, resulting in an immediate, retrieval-independent disruption of methamphetamine (METH)-associated memory in male and female adult and adolescent rodents. The effect is highly selective, as NMII inhibition has no effect in other relevant brain regions (e.g., dorsal hippocampus [dPHC], nucleus accumbens [NAc]), nor does it interfere with associations for other aversive or appetitive stimuli, including cocaine (COC). To understand the mechanisms responsible for drug specific selectivity we began by investigating, in male mice, the pharmacokinetic differences in METH and COC brain exposure . Replicating METH's longer half-life with COC did not render the COC association susceptible to disruption by NMII inhibition. Therefore, we next assessed transcriptional differences. Comparative RNA-seq profiling in the BLA, dHPC and NAc following METH or COC conditioning identified crhr2, which encodes the corticotropin releasing factor receptor 2 (CRF2), as uniquely upregulated by METH in the BLA. CRF2 antagonism with Astressin-2B (AS2B) had no effect on METH-associated memory after consolidation, allowing for determination of CRF2 influences on NMII-based susceptibility. Pretreatment with AS2B prevented the ability of Blebb to disrupt an established METH-associated memory. Alternatively, combining CRF2 overexpression and agonist treatment, urocortin 3 (UCN3), in the BLA during conditioning rendered COC-associated memory susceptible to disruption by NMII inhibition, mimicking the Blebb-induced, retrieval-independent memory disruption seen with METH. These results suggest that BLA CRF2 receptor activation during memory formation in male mice can prevent stabilization of the actin-myosin cytoskeleton supporting the memory, rendering it vulnerable to disruption by NMII inhibition. CRF2 represents an interesting target for BLA-dependent memory destabilization via downstream effects on NMII.

Acute Ethanol Modulates Synaptic Inhibition in the Basolateral Amygdala via Rapid NLRP3 Inflammasome Activation and Regulates Anxiety-Like Behavior in Rats.

Chronic alcohol exposure leads to a neuroinflammatory response involving activation of the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome and proinflammatory cytokine production. Acute ethanol (EtOH) exposure activates GABAergic synapses in the central and basolateral amygdala (BLA) ex vivo, but whether this rapid modulation of synaptic inhibition is because of an acute inflammatory response and alters anxiety-like behavior in male and female animals is not known. Here, we tested the hypotheses that acute EtOH facilitates inhibitory synaptic transmission in the BLA by activating the NLRP3 inflammasome-dependent acute inflammatory response, that the alcohol-induced increase in inhibition is cell type and sex dependent, and that acute EtOH in the BLA reduces anxiety-like behavior. Acute EtOH application at a binge-like concentration (22-44 mm) stimulated synaptic GABA release from putative parvalbumin (PV) interneurons onto BLA principal neurons in ex vivo brain slices from male, but not female, rats. The EtOH facilitation of synaptic inhibition was blocked by antagonists of the Toll-like receptor 4 (TLR4), the NLRP3 inflammasome, and interleukin-1 receptors, suggesting it was mediated by a rapid local neuroinflammatory response in the BLA. In vivo, bilateral injection of EtOH directly into the BLA produced an acute concentration-dependent reduction in anxiety-like behavior in male but not female rats. These findings demonstrate that acute EtOH in the BLA regulates anxiety-like behavior in a sex-dependent manner and suggest that this effect is associated with presynaptic facilitation of parvalbumin-expressing interneuron inputs to BLA principal neurons via a local NLRP3 inflammasome-dependent neuroimmune response.SIGNIFICANCE STATEMENT Chronic alcohol exposure produces a neuroinflammatory response, which contributes to alcohol-associated pathologies. Acute alcohol administration increases inhibitory synaptic signaling in the brain, but the mechanism for the rapid alcohol facilitation of inhibitory circuits is unknown. We found that acute ethanol at binge-like concentrations in the basolateral amygdala (BLA) facilitates GABA release from parvalbumin-expressing (PV) interneuron synapses onto principal neurons in ex vivo brain slices from male rats and that intra-BLA ethanol reduces anxiety-like behavior in vivo in male rats, but not female rats. The ethanol (EtOH) facilitation of inhibition in the BLA is mediated by Toll-like receptor 4 (TLR4) and nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome activation and proinflammatory IL-1ß signaling, which suggests a rapid NLRP3 inflammasome-dependent neuroimmune cascade that plays a critical role in acute alcohol intoxication.

Endocannabinoid release at ventral hippocampal-amygdala synapses regulates stress-induced behavioral adaptation.

The endocannabinoid (eCB) system is a key modulator of glutamate release within limbic neurocircuitry and thus heavily modulates stress responsivity and adaptation. The ventral hippocampus (vHPC)-basolateral amygdala (BLA) circuit has been implicated in the expression of negative affective states following stress exposure and is modulated by retrograde eCB signaling. However, the mechanisms governing eCB release and the causal relationship between vHPC-BLA eCB signaling and stress-induced behavioral adaptations are not known. Here, we utilized in vivo optogenetic- and biosensor-based approaches to determine the temporal dynamics of activity-dependent and stress-induced eCB release at vHPC-BLA synapses. Furthermore, we demonstrate that genetic deletion of cannabinoid type-1 receptors selectively at vHPC-BLA synapses decreases active stress coping and exacerbates stress-induced avoidance and anhedonia phenotypes. These data establish the in vivo determinants of eCB release at limbic synapses and demonstrate that eCB signaling within vHPC-BLA circuitry serves to counteract adverse behavioral consequences of stress.

Corticosterone injection into the basolateral amygdala before and after memory reactivation impairs the subsequent expression of fear memory in rats: An interaction of glucocorticoids and ß-adrenoceptors.

Glucocorticoid administration, before or after fear memory reactivation, impairs subsequent fear memory expression, but the underlying mechanisms are not well understood. The present study examined the role of basolateral amygdala (BLA) ß-adrenoceptors in the effects of intra-BLA corticosterone injection on fear memory in rats. Bilateral cannulae were implanted in the BLA of Wistar male rats. The rats were trained and tested using an inhibitory avoidance task (1 mA footshock for 3 s). Forty-eight hours after training, corticosterone (CORT, 5, 10, or 20 ng/0.5 µl/side) and the ß2-adrenoceptor agonist clenbuterol (CLEN, 10 or 20 ng/0.5 µl/side) or the ß-adrenoceptor antagonist propranolol (PROP, 250 or 500 ng/0.5 µl/side) were injected into the BLA before or right after memory reactivation (retrieval, Test 1). We performed subsequent tests 2 (Test 2), 5 (Test 3), 7 (Test 4), and 9 (Test 5) days after Test 1. The results demonstrated that CORT injection before Test 1 disrupted memory retrieval and reduced fear expression in Tests 2-5, possibly due to enhanced extinction or impaired reconsolidation. CORT injection after Test 1 also impaired reconsolidation and reduced fear expression in Tests 2-5. CLEN prevented, but PROP exacerbated, the effects of CORT on fear expression. The reminder shock did not recover fear memory in CORT-treated animals, suggesting that reconsolidation, not extinction, was affected. These results indicate that glucocorticoids and ß-adrenoceptors in the BLA jointly modulate fear memory reconsolidation and expression. Comprehending the neurobiology of stress and the impact of glucocorticoids on fear memory may lead to new treatments for stress and trauma-induced disorders such as PTSD.

Treadmill exercise modulates the medial prefrontal-amygdala neural circuit to improve the resilience against chronic restraint stress.

Aerobic exercise effectively ameliorates mental disorders including anxiety and depression. Current findings mainly attribute its neural mechanism to the improvement of adult neurogenesis, while leaving the possible circuitry mechanism unclear. In the current study, we identify the overexcitation of the medial prefrontal cortex (mPFC) to basolateral amygdala (BLA) pathway under chronic restraint stress (CRS), and 14-day treadmill exercise selectively reverses such abnormalities. Using chemogenetic approaches, we find that the mPFC-BLA circuit is necessary for preventing anxiety-like behaviors in CRS mice. These results collectively suggest a neural circuitry mechanism by which exercise training improves the resilience against environmental stress.

Harmine exerts anxiolytic effects by regulating neuroinflammation and neuronal plasticity in the basolateral amygdala.

Increasing evidence indicates that an altered immune system is closely linked to the pathophysiology of anxiety disorders, and inhibition of neuroinflammation may represent an effective therapeutic strategy to treat anxiety disorders. Harmine, a beta-carboline alkaloid in various medicinal plants, has been widely reported to display anti-inflammatory and potentially anxiolytic effects. However, the exact underlying mechanisms are not fully understood. Our recent study has demonstrated that dysregulation of neuroplasticity in the basolateral amygdala (BLA) contributes to the pathological processes of inflammation-related anxiety. In this study, using a mouse model of anxiety challenged with Escherichia coli lipopolysaccharide (LPS), we found that harmine alleviated LPS-induced anxiety-like behaviors in mice. Mechanistically, harmine significantly prevented LPS-induced neuroinflammation by suppressing the expression of pro-inflammatory cytokines including IL-1ß and TNF-α. Meanwhile, ex vivo whole-cell slice electrophysiology combined with optogenetics showed that LPS-induced increase of medial prefrontal cortex (mPFC)-driven excitatory but not inhibitory synaptic transmission onto BLA projection neurons, thereby alleviating LPS-induced shift of excitatory/inhibitory balance towards excitation. In addition, harmine attenuated the increased intrinsic neuronal excitability of BLA PNs by reducing the medium after-hyperpolarization. In conclusion, our findings provide new evidence that harmine may exert its anxiolytic effect by downregulating LPS-induced neuroinflammation and restoring the changes in neuronal plasticity in BLA PNs.

5-HT1B receptors in the basolateral amygdaloid nucleus regulate anxiety-like behaviors through AC-PKA signal pathway in a rat model of Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is commonly accompanied with anxiety, multiple studies indicate that the basolateral amygdaloid nucleus (BLA) is closely related to modulation of anxiety and expresses serotonin1B (5-HT1B) receptors, however, effects of BLA 5-HT1B receptors on anxiety-like behaviors are unclear, particularly in PD-related anxiety. METHODS: The open-field and elevated plus maze tests were used to examine anxiety-like behaviors. In vivo electrophysiology and microdialysis were performed to observe the firing activity of BLA neurons and GABA, glutamate, dopamine (DA) and 5-HT release in the BLA, respectively. Western blotting was used to analyze protein expression of 5-HT1B receptors, adenylate cyclase (AC) and phosphorylated protein kinase A at threonine 197 site (p-PKA-Thr197) in the BLA. RESULTS: Intra-BLA injection of 5-HT1B receptor agonist CP93129 produced anxiety-like effects and antagonist SB216641 induced anxiolytic-like responses in sham-operated and 6-hydroxydopamine-lesioned rats. Further, pretreatment with AC inhibitor SQ22536 and PKA inhibitor KT5720 blocked the behavioral effects of CP93129, respectively. Intra-BLA injection of CP93129 increased the firing rate of BLA glutamate neurons and decreased GABA/glutamate ratio and DA and 5-HT levels in the BLA of sham-operated and the lesioned rats, while SB216641 induced the opposite effects. Compared with sham-operated rats, effects of CP93129 and SB216641 on behaviors, electrophysiology and microdialysis were decreased in the lesioned rats, which were associated with decreased expression of 5-HT1B receptors, AC and p-PKA-Thr197 in the BLA. CONCLUSION: These findings suggest that 5-HT1B receptor-AC-PKA signal pathway in the BLA is involved in the regulation of PD-related anxiety.

Functional neuroanatomy of monoaminergic systems in the basolateral nuclear complex of the amygdala: Neuronal targets, receptors, and circuits.

This review discusses neuroanatomical aspects of the three main monoaminergic systems innervating the basolateral nuclear complex (BNC) of the amygdala (serotonergic, noradrenergic, and dopaminergic systems). It mainly focuses on immunohistochemical (IHC) and in situ hybridization (ISH) studies that have analyzed the relationship of specific monoaminergic inputs and their receptors to specific neuronal subtypes in the BNC in order to better understand the anatomical substrates of the monoaminergic modulation of BNC circuitry. First, light and electron microscopic IHC investigations identifying the main BNC neuronal subpopulations and characterizing their local circuitry, including connections with discrete PN compartments and other INs, are reviewed. Then, the relationships of each of the three monoaminergic systems to distinct PN and IN cell types, are examined in detail. For each system, the neuronal targets and their receptor expression are discussed. In addition, pertinent electrophysiological investigations are discussed. The last section of the review compares and contrasts various aspects of each of the three monoaminergic systems. It is concluded that the large number of different receptors, each with a distinct mode of action, expressed by distinct cell types with different connections and functions, should offer innumerable ways to subtlety regulate the activity of the BNC by therapeutic drugs in psychiatric diseases in which there are alterations of BNC monoaminergic modulatory systems, such as in anxiety disorders, depression, and drug addiction. It is suggested that an important area for future studies is to investigate how the three systems interact in concert at the neuronal and neuronal network levels.

Gastric vagal afferent signaling to the basolateral amygdala mediates anxiety-like behaviors in experimental colitis mice.

Inflammatory bowel disease (IBD) is a relapsing-remitting disorder characterized by chronic inflammation of the gastrointestinal (GI) tract. Anxiety symptoms are commonly observed in patients with IBD, but the mechanistic link between IBD and anxiety remains elusive. Here, we sought to characterize gut-to-brain signaling and brain circuitry responsible for the pathological expression of anxiety-like behaviors in male dextran sulfate sodium-induced (DSS-induced) experimental colitis mice. We found that DSS-treated mice displayed increased anxiety-like behaviors, which were prevented by bilateral GI vagal afferent ablation. The locus coeruleus (LC) is a relay center connecting the nucleus tractus solitarius to the basolateral amygdala (BLA) in controlling anxiety-like behaviors. Chemogenetic silencing of noradrenergic LC projections to the BLA reduced anxiety-like behaviors in DSS-treated mice. This work expands our understanding of the neural mechanisms by which IBD leads to comorbid anxiety and emphasizes a critical role of gastric vagal afferent signaling in gut-to-brain regulation of emotional states.

miR-483-5p offsets functional and behavioural effects of stress in male mice through synapse-targeted repression of Pgap2 in the basolateral amygdala.

Severe psychological trauma triggers genetic, biochemical and morphological changes in amygdala neurons, which underpin the development of stress-induced behavioural abnormalities, such as high levels of anxiety. miRNAs are small, non-coding RNA fragments that orchestrate complex neuronal responses by simultaneous transcriptional/translational repression of multiple target genes. Here we show that miR-483-5p in the amygdala of male mice counterbalances the structural, functional and behavioural consequences of stress to promote a reduction in anxiety-like behaviour. Upon stress, miR-483-5p is upregulated in the synaptic compartment of amygdala neurons and directly represses three stress-associated genes: Pgap2, Gpx3 and Macf1. Upregulation of miR-483-5p leads to selective contraction of distal parts of the dendritic arbour and conversion of immature filopodia into mature, mushroom-like dendritic spines. Consistent with its role in reducing the stress response, upregulation of miR-483-5p in the basolateral amygdala produces a reduction in anxiety-like behaviour. Stress-induced neuromorphological and behavioural effects of miR-483-5p can be recapitulated by shRNA mediated suppression of Pgap2 and prevented by simultaneous overexpression of miR-483-5p-resistant Pgap2. Our results demonstrate that miR-483-5p is sufficient to confer a reduction in anxiety-like behaviour and point to miR-483-5p-mediated repression of Pgap2 as a critical cellular event offsetting the functional and behavioural consequences of psychological stress.

Alpha-linolenic acid enhances the facilitation of GABAergic neurotransmission in the BLA and CA1.

Hyperexcitability is a major mechanism implicated in several neuropsychiatric disorders, such as organophosphate-induced status epilepticus (SE), primary epilepsy, stroke, spinal cord injury, traumatic brain injury, schizophrenia, and autism spectrum disorders. Underlying mechanisms are diverse, but a functional impairment and loss of GABAergic inhibitory neurons are common features in many of these disorders. While novel therapies abound to correct for the loss of GABAergic inhibitory neurons, it has been difficult at best to improve the activities of daily living for the majority of patients. Alpha-linolenic acid (ALA) is an essential omega-3 polyunsaturated fatty acid found in plants. ALA exerts pleiotropic effects in the brain that attenuate injury in chronic and acute brain disease models. However, the effect of ALA on GABAergic neurotransmission in hyperexcitable brain regions involved in neuropsychiatric disorders, such as the basolateral amygdala (BLA) and CA1 subfield of the hippocampus, is unknown. Administration of a single dose of ALA (1500 nmol/kg) subcutaneously increased the charge transfer of inhibitory postsynaptic potential currents mediated by GABAA receptors in pyramidal neurons by 52% in the BLA and by 92% in the CA1 compared to vehicle animals a day later. Similar results were obtained in pyramidal neurons from the BLA and CA1 when ALA was bath-applied in slices from naïve animals. Importantly, pretreatment with the high-affinity, selective TrkB inhibitor, k252, completely abolished the ALA-induced increase in GABAergic neurotransmission in the BLA and CA1, suggesting a brain-derived neurotrophic factor (BDNF)-mediated mechanism. Addition of mature BDNF (20 ng/mL) significantly increased GABAA receptor inhibitory activity in the BLA and CA1 pyramidal neurons similar to the results obtained with ALA. ALA may be an effective treatment for neuropsychiatric disorders where hyperexcitability is a major feature.