Basolateral Amygdala Neurons Research Articles

The ethanol inhibition of basolateral amygdala neuron spiking is mediated by a γ-aminobutyric acid type A-mediated tonic current.

The basolateral nucleus of the amygdala (BLA) plays an important role in the development of fear and anxiety-related behaviors. The BLA receives inputs from all sensory stimuli. After processing those stimuli, BLA neurons signal neurons within the central amygdala and other brain regions, including the ventral and dorsal striatum and frontal cortex. Studies suggest that the BLA is involved in drug dependence and in the reinforcing actions of ethanol. For example, acute exposure to ethanol reduces anxiety, while withdrawal from chronic ethanol exposure alters BLA synaptic transmission, which increases anxiety, a common underlying cause of relapse. Exposure to and withdrawal from chronic alcohol also disrupts many brain areas that connect with the BLA. Despite these important findings, the acute actions of alcohol on the intrinsic excitability of BLA neurons have not been fully characterized. Brain slices containing the BLA were prepared from adult C57BL/6J male mice. Whole-cell and sharp electrode electrophysiological recordings were performed to characterize the effects of acute ethanol on BLA neuronal and astrocyte function, respectively. Ethanol inhibited action potential (AP) firing of BLA neurons but had no effect on BLA astrocyte resting membrane potential. The ethanol-induced inhibition of firing was concentration-dependent (11 to 66 mM) and accompanied by a reduction in the input resistance and an increase in the rheobase of BLA neurons. The inhibitory effect of ethanol was suppressed by picrotoxin, which blocks both γ-aminobutyric acid type A (GABAA ) and glycine receptors, but not by the selective glycine receptor antagonist strychnine, which suggests an involvement of GABAA receptors. Ethanol did not affect spontaneous inhibitory postsynaptic currents suggesting that the inhibition of BLA neuronal excitability by ethanol was not due to an increase in GABAA -mediated synaptic transmission. However, acute ethanol enhanced the amplitude of the holding current of BLA neurons, an effect that was prevented by picrotoxin, which by itself reduced the holding current. These results suggest that BLA neurons express a GABA-mediated tonic current that is enhanced by acute ethanol, which leads to reduced excitability of BLA neurons.

Neurotensin orchestrates valence assignment in the amygdala.

The ability to associate temporally segregated information and assign positive or negative valence to environmental cues is paramount for survival. Studies have shown that different projections from the basolateral amygdala (BLA) are potentiated following reward or punishment learning1-7. However, we do not yet understand how valence-specific information is routed to the BLA neurons with the appropriate downstream projections, nor do we understand how to reconcile the sub-second timescales of synaptic plasticity8-11 with the longer timescales separating the predictive cues from their outcomes. Here we demonstrate that neurotensin (NT)-expressing neurons in the paraventricular nucleus of the thalamus (PVT) projecting to the BLA (PVT-BLA:NT) mediate valence assignment by exerting NT concentration-dependent modulation in BLA during associative learning. We found that optogenetic activation of the PVT-BLA:NT projection promotes reward learning, whereas PVT-BLA projection-specific knockout of the NT gene (Nts) augments punishment learning. Using genetically encoded calcium and NT sensors, we further revealed that both calcium dynamics within the PVT-BLA:NT projection and NT concentrations in the BLA are enhanced after reward learning and reduced after punishment learning. Finally, we showed that CRISPR-mediated knockout of the Nts gene in the PVT-BLA pathway blunts BLA neural dynamics and attenuates the preference for active behavioural strategies to reward and punishment predictive cues. In sum, we have identified NT as a neuropeptide that signals valence in the BLA, and showed that NT is a critical neuromodulator that orchestrates positive and negative valence assignment in amygdala neurons by extending valence-specific plasticity to behaviourally relevant timescales.

Representation of ethological events by basolateral amygdala neurons.

The accurate interpretation of ethologically relevant stimuli is crucial for survival. While basolateral amygdala (BLA) neuronal responses during fear conditioning are well studied, little is known about how BLA neurons respond during naturalistic events. We recorded from the rat BLA during interaction with ethological stimuli: male or female rats, a moving toy, and rice. Forty-two percent of the cells reliably respond to at least one stimulus, with over half of these exclusively identifying one of the four stimulus classes. In addition to activation during interaction with their preferred stimulus, these cells signal micro-behavioral interactions like social contact. After stimulus removal, firing activity persists in 30% of responsive cells for several minutes. At the micro-circuit level, information flows from highly tuned event-specific neurons to less specific neurons, and connection strength increases after the event. We propose that individual BLA neurons identify specific ethological events, with event-specific neurons driving circuit-wide activity during and after salient events.

Chemogenetic Activation of Astrocytes in the Basolateral Amygdala Contributes to Fear Memory Formation by Modulating the Amygdala-Prefrontal Cortex Communication.

The basolateral amygdala (BLA) is one of the key brain areas involved in aversive learning, especially fear memory formation. Studies of aversive learning in the BLA have largely focused on neuronal function, while the role of BLA astrocytes in aversive learning remains largely unknown. In this study, we manipulated the BLA astrocytes by expressing the Gq-coupled receptor hM3q and discovered that astrocytic Gq modulation during fear conditioning promoted auditorily cued fear memory but did not affect less stressful memory tasks or induce anxiety-like behavior. Moreover, chemogenetic activation of BLA astrocytes during memory retrieval had no effect on fear memory expression. In addition, astrocytic Gq activation increased c-Fos expression in the BLA and the medial prefrontal cortex (mPFC) during fear conditioning, but not in the home cage. Combining these results with retrograde virus tracing, we found that the activity of mPFC-projecting BLA neurons showed significant enhancement after astrocytic Gq activation during fear conditioning. Electrophysiology recordings showed that activating astrocytic Gq in the BLA promoted spike-field coherence and phase locking percentage, not only within the BLA but also between the BLA and the mPFC. Finally, direct chemogenetic activation of mPFC-projecting BLA neurons during fear conditioning enhanced cued fear memory. Taken together, our data suggest that astrocytes in the BLA may contribute to aversive learning by modulating amygdala–mPFC communication.

MDMA treatment paired with a trauma-cue promotes adaptive stress responses in a translational model of PTSD in rats

MDMA (3,4-methylenedioxymethamphetamine), a synthetic ring-substituted amphetamine, combined with psychotherapy has demonstrated efficacy for the treatment of chronic posttraumatic stress disorder (PTSD) patients. This controlled prospective study aimed to assess the bio-behavioral underpinnings of MDMA in a translational model of PTSD. Rats exposed to predator-scent stress (PSS) were subjected to a trauma-cue at day 7 shortly after single-dose MDMA injection (5 mg/kg). The elevated plus maze and acoustic startle response tests were assessed on day 14 and served for classification into behavioral response groups. Freezing response to a further trauma-reminder was assessed on Day 15. The morphological characteristics of the dentate gyrus (DG) and basolateral amygdala (BLA) were subsequently examined. Hypothalamic–pituitary–adrenal axis and 5-hydroxytryptamine involvement were evaluated using: (1) corticosterone measurements at 2 h and 4 h after MDMA treatment, (2) Lewis strain rats with blunted HPA-response and (3) pharmacological receptor-blockade. MDMA treatment was effective in attenuating stress behavioral responses only when paired with memory reactivation by a trauma-cue. The effects of the treatment on behavior were associated with a commensurate normalization of the dendritic cytoarchitecture of DG and BLA neurons. Pretreatment with RU486, Ketanserin, or Pindolol prevented the above improvement in anxiety-like behavioral responses. MDMA treatment paired with memory reactivation reduced the prevalence rate of PTSD-phenotype 14 days later and normalized the cytoarchitecture changes induced by PSS (in dendritic complexities) compared to saline control. MDMA treatment paired with a trauma-cue may modify or update the original traumatic memory trace through reconsolidation processes. These anxiolytic-like effects seem to involve the HPA axis and 5-HT systems.

Characterization of a Nociceptive Neural Ensemble in the Nucleus Accumbens Shell

The experience of pain encompasses both nociceptive sensory and negative affective dimensions. A key first step to understand the affective dimension is to functionally and genetically identify nociceptive neurons connected across affective-motivational neural circuits in acute and chronic pain states. We recently identified a nociceptive subpopulation of negative valence basolateral amygdala (BLA) neurons essential for pain aversion. Here, we characterize a downstream target of BLA nociceptive neurons—the nucleus accumbens Shell (NAcSh). Broadly, aberrant activity of the NAcSh has been linked to motivational deficits in chronic pain, yet much remains unknown regarding specific NAcSh nociceptive cell-types or their modulation by BLA nociceptive neurons. Here, we used targeted recombination in active populations (TRAP) mice to genetically capture nociceptive NAcSh neurons (nociTRAP) with combined immunohistochemistry, fluorescent in situ hybridization (FISH), and viral tract tracing. We identified a previously unreported posterior medial NAcSh subregion—anatomically encompassed by the Islands of Cajella granule cell clusters—that contains numerous nociTRAP neurons. This region, which we termed the "NAcre" (named after the inner shell layer of mollusks), receives projections from nociceptive BLA neurons. Importantly, the majority of acute nociTRAP NAcre neurons also display increased immediate early gene FOS expression to light touch following a peripheral nerve injury, revealing consistent activation across pain states independent of stimulus sensory modality. Finally, using multiplexed FISH, we found that nociTRAP NAcre neurons, while molecularly heterogeneous, were primarily medium spiny neurons expressing dopamine receptor 2 and kappa opioid receptor mRNA. In total, the NAcre is a highly nociceptive subregion of the posterior medial NAcSh that receives nociceptive transmissions from the BLA and may be involved in pain-related kappa opioid aversion processes. Further work will determine the necessity and sufficiency of this neural population for affective-motivational behaviors in acute and chronic pain states. Grant support from 5R00DA043609-04 - Deconstructing the network mechanisms of chronic pain and reward in the amygdala (Independent Phase).

Repeated Restraint Stress Alters Small Conductance Calcium‐activated Potassium Channel (SK) Expression in Rat Basolateral Amygdala Neurons in Sex‐dependent Manner

Mood disorders disproportionally affect women more than men. The basolateral amygdala (BLA) is critical for the expression of fear and anxiety‐like behaviors and is hyperactive in mood disorders. Our prior work has shown greater spontaneous BLA activity in naïve females compared to males, but the mechanisms by which this occurs remain unknown. BLA activity is regulated, in part, by small conductance calcium‐activated potassium (SK) channels (SK1‐4), which mediate afterhyperpolarizations (AHPs) and reduce neuronal firing. Activation of the SK2 channel inhibits BLA neuronal firing in males, but the role of SK2 in females is relatively unexplored. We hypothesized that SK2 expression would be lower in females resulting in higher spontaneous firing rate of BLA neurons compared to males. In order to test this hypothesis, we utilized qPCR and Western blot analysis to determine the relative expression of SK channels in the BLA of adult naïve male and female rats. We found BLA SK2 mRNA levels are similar between the sexes, but BLA SK2 protein levels are lower in females compared to males. We found no differences in other SK channels. To examine whether lower SK2 expression in females corresponds with reduced SK2 channel activity, we performed in vivo single‐unit electrophysiological recordings of BLA neuronal activity following local injections of a SK2 channel inhibitor (apamin; 1uM) or saline. Preliminary results revealed spontaneous BLA activity increased following apamin injections in both sexes, but to a greater degree in males. This suggests that the reduced SK2 protein expression in females coincides with greater spontaneous activity in BLA and a diminished effect of apamin compared to males. Since it is known that stress is a leading factor in the development of mood disorders and BLA activity following stress also varies between the sexes; we also sought to determine whether sex differences exist in SK2 expression and function in rats following repeated restraint stress (20 min/day for 7 out of 9 days), compared to control‐handled rats. Previous research from our lab has found that repeated restraint stress leads to an increase in BLA spontaneous activity in males, but a reduction in activity in females. Therefore, we hypothesized that the expression and activity of SK2 channels will be reduced in males following stress, but increased in females. Our initial findings suggest that repeated restraint stress increases spontaneous BLA activity in males and this activity is less sensitive to apamin injection compared to control‐handled rats. In contrast, repeated restraint stress appears to reduce spontaneous BLA activity in females, but like the males, females have reduced sensitivity to apamin. These electrophysiological findings correspond to a reduction in SK2 protein expression in BLA from males, but a slight increase in SK2 expression in BLA from females. A more thorough understanding of sex differences in SK2 channel expression and activity following stress may contribute to a better understanding of the sex disparities observed in mood disorders.

Chronic Alcohol Dysregulates Glutamatergic Function in the Basolateral Amygdala in a Projection-and Sex-Specific Manner.

Chronic intermittent ethanol and withdrawal (CIE/WD) produces alcohol dependence, facilitates anxiety-like behavior, and increases post-CIE alcohol intake. The basolateral amygdala (BLA) is one of several brain regions that regulates anxiety-like behavior and alcohol intake through downstream projections to the nucleus accumbens (NAC) and bed nucleus of the stria terminalis (BNST), respectively. Previous studies revealed that CIE/WD induces input- and sex-specific adaptations to glutamatergic function in the BLA. The BLA receives information from two distinct input pathways. Glutamatergic afferents from medial structures like the thalamus and prefrontal cortex enter the BLA through the stria terminalis whereas lateral cortical structures like the anterior insula cortex enter the BLA through the external capsule. CIE/WD increases presynaptic glutamatergic function at stria terminalis synapses and postsynaptic function at external capsule synapses. Previous studies sampled neurons throughout the BLA, but did not distinguish between projection-specific populations. The current study investigated BLA neurons that project to the NAC (BLA-NAC neurons) or the BNST (BLA-BNST neurons) as representative “reward” and “aversion” BLA neurons, and showed that CIE/WD alters glutamatergic function and excitability in a projection- and sex-specific manner. CIE/WD increases glutamate release from stria terminalis inputs only onto BLA-BNST neurons. At external capsule synapses, CIE/WD increases postsynaptic glutamatergic function in male BLA-NAC neurons and female BLA-BNST neurons. Subsequent experiments demonstrated that CIE/WD enhanced the excitability of male BLA-NAC neurons and BLA-BNST neurons in both sexes when glutamatergic but not GABAergic function was intact. Thus, CIE/WD-mediated increased glutamatergic function facilitates hyperexcitability in male BLA-NAC neurons and BLA-BNST neurons of both sexes.

Colocalization of M1 muscarinic cholinergic receptors and NMDA receptors in dendrites and spines of pyramidal neurons of the mouse basolateral amygdala: An ultrastructural analysis

The cholinergic innervation of the neocortex, hippocampus, and basolateral amygdala is critical for higher cognitive functions, including attention and memory. One action of ACh in the hippocampus is the potentiation of NMDA receptor (NMDAR) currents in pyramidal neurons (PNs) by M1 muscarinic receptors (M1Rs). The increase in these currents enhances long-term potentiation (LTP), an important mechanism for memory formation. Ultrastructural observations in the hippocampus revealed that M1Rs and NMDARs were colocalized in hippocampal PN dendrites, consistent with electrophysiological studies demonstrating M1R-NMDAR interactions. Similar to the hippocampus, activation of M1Rs have been shown to be critical for mnemonic functions in the anterior basolateral nucleus of the amygdala (BLa). In the present study dual-labeling immunoelectron microscopy was used to determine if there was colocalization of M1Rs and NMDARs in neurons of the mouse BLa. We found extensive colocalization of these receptors in dendrites and spines of BLa PNs, and most of the M1Rs were membrane-associated where they could be activated by released acetylcholine. These results suggest that M1Rs in BLa PNs could be targeted by M1R positive allosteric modulators (PAMs), resulting in amelioration of memory impairments in neuropsychiatric disorders, such as Alzheimer’s disease, by potentiating NMDAR currents in the amygdala.

Oxytocin Receptor-Expressing Neurons in the Paraventricular Thalamus Regulate Feeding Motivation through Excitatory Projections to the Nucleus Accumbens Core.

Oxytocin receptors (OTR) have been found in the paraventricular thalamus (PVT) for the regulation of feeding and maternal behaviors. However, the functional projections of OTR-expressing PVT neurons remain largely unknown. Here, we used chemogenetic and optogenetic tools to test the role of OTR-expressing PVT neurons and their projections in the regulation of food intake in both male and female OTR-Cre mice. We found chemogenetic activation of OTR-expressing PVT neurons promoted food seeking under trials with a progressive ratio schedule of reinforcement. Using Feeding Experimentation Devices for real-time meal measurements, we found chemogenetic activation of OTR-expressing PVT neurons increased meal frequency but not cumulative food intake because of a compensatory decrease in meal sizes. In combination with anterograde neural tracing and slice patch-clamp recordings, we found optogenetic stimulation of PVT OTR terminals excited neurons in the posterior basolateral amygdala (pBLA) and nucleus accumbens core (NAcC) as well as local PVT neurons through monosynaptic glutamatergic transmissions. Photostimulation of OTR-expressing PVT-NAcC projections promoted food-seeking, whereas selective activation of PVT-pBLA projections produced little effect on feeding. In contrast to selective activation of OTR terminals, photostimulation of a broader population of glutamatergic PVT terminals exerted direct excitation followed by indirect lateral inhibition on neurons in both NAcC and anterior basolateral amygdala. Together, these results suggest that OTR-expressing PVT neurons are a distinct population of PVT glutamate neurons that regulate feeding motivation through projections to NAcC.SIGNIFICANCE STATEMENT The paraventricular thalamus plays an important role in the regulation of feeding motivation. However, because of the diversity of paraventricular thalamic neurons, the specific neuron types promoting food motivation remain elusive. In this study, we provide evidence that oxytocin receptor-expressing neurons are a specific group of glutamate neurons that primarily project to the nucleus accumbens core and posterior amygdala. We found that activation of these neurons promotes the motivation for food reward and increases meal frequency through projections to the nucleus accumbens core but not the posterior amygdala. As a result, we postulate that oxytocin receptor-expressing neurons in the paraventricular thalamus and their projections to the nucleus accumbens core mainly regulate feeding motivation but not food consumption.

Claustrum mediates bidirectional and reversible control of stress-induced anxiety responses.

The processing of stress responses involves brain-wide communication among cortical and subcortical regions; however, the underlying mechanisms remain elusive. Here, we show that the claustrum (CLA) is crucial for the control of stress-induced anxiety-related behaviors. A combined approach using brain activation mapping and machine learning showed that the CLA activation serves as a reliable marker of exposure to acute stressors. In TRAP2 mice, which allow activity-dependent genetic labeling, chemogenetic activation of the CLA neuronal ensemble tagged by acute social defeat stress (DS) elicited anxiety-related behaviors, whereas silencing of the CLA ensemble attenuated DS-induced anxiety-related behaviors. Moreover, the CLA received strong input from DS-activated basolateral amygdala neurons, and its circuit-selective optogenetic photostimulation temporarily elicited anxiety-related behaviors. Last, silencing of the CLA ensemble during stress exposure increased resistance to chronic DS. The CLA thus bidirectionally controls stress-induced emotional responses, and its inactivation can serve as a preventative strategy to increase stress resilience.

Brain Injury Effects on Neuronal Activation and Synaptic Transmission in the Basolateral Amygdala of Adult Male and Female Wistar Rats.

Traumatic brain injury (TBI) is defined as brain damage produced by an external mechanical force that leads to behavioral, cognitive, and psychiatric sequelae. The basolateral amygdala (BLA) is involved in emotional regulation, and its function and morphology are altered following TBI. Little is known about potential sex-specific effects of TBI on BLA neuronal function, but it is critical for the field to identify potential sex differences in TBI effects on brain and behavior. Here, we hypothesized that TBI would produce sex-specific acute (1 h) effects on BLA neuronal activation, excitability, and synaptic transmission in adult male and female rats. Forty-nine Wistar rats (n = 23 males and 26 females) were randomized to TBI (using lateral fluid percussion) or Sham groups in two separate studies. Study 1 used in situ hybridization (i.e., RNAscope) to measure BLA expression of c-fos (a marker of cell activation), vGlut, and vGat (markers of glutamatergic and GABAergic neurons, respectively) messenger RNA (mRNA). Study 2 used slice electrophysiology to measure intrinsic excitability and excitatory/inhibitory synaptic transmission in putative pyramidal neurons in the BLA. Physiological measures of injury severity were collected from all animals. Our results show that females exhibit increased apnea duration and reduced respiratory rate post-TBI relative to males. In male and female rats, TBI increased c-fos expression in BLA glutamatergic cells but not in BLA GABAergic cells, and TBI increased firing rate in BLA pyramidal neurons. Further, TBI increased spontaneous excitatory and inhibitory postsynaptic current (sEPSC and sIPSC) amplitude in BLA neurons of females relative to all other groups. TBI increased sEPSC frequency in BLA neurons of females relative to males but did not alter sIPSC frequency. In summary, lateral fluid percussion produced different physiological responses in male and female rats, as well as sex-specific alterations in BLA neuronal activation, excitability, and synaptic transmission 1 h after injury.

Ghrelin infusion into the basolateral amygdala suppresses CTA memory formation in rats via the PI3K/Akt/mTOR and PLC/PKC signaling pathways.

Ghrelin is a circulating orexigenic hormone that promotes feeding behavior and regulates metabolism in humans and rodents. We previously reported that local infusion of ghrelin into the basolateral amygdala (BLA) blocked memory acquisition for conditioned taste aversion (CTA) by activating growth hormone secretagogue receptor 1a. In this study, we further explored the underlying mechanism and signaling pathways mediating ghrelin modulation of CTA memory in rats. Pharmacological agents targeting distinct signaling pathways were infused into the BLA during conditioning. We showed that preadministration of the PI3K inhibitor LY294002 abolished the repressive effect of ghrelin on CTA memory. Moreover, LY294002 pretreatment prevented ghrelin from inhibiting Arc and zif268 mRNA expression in the BLA triggered by CTA memory retrieval. Preadministration of rapamycin eliminated the repressive effect of ghrelin, while Gsk3 inhibitors failed to mimic ghrelin's effect. In addition, PLC and PKC inhibitors microinfused in the BLA blocked ghrelin's repression of CTA acquisition. These results demonstrate that ghrelin signaling in the BLA shapes CTA memory via the PI3K/Akt/mTOR and PLC/PKC pathways. We conducted in vivo multichannel recordings from mouse BLA neurons and found that microinjection of ghrelin (20 µM) suppressed intrinsic excitability. By means of whole-cell recordings from rat brain slices, we showed that bath application of ghrelin (200 nM) had no effect on basal synaptic transmission or synaptic plasticity of BLA pyramidal neurons. Together, this study reveals the mechanism underlying ghrelin-induced interference with CTA memory acquisition in rats, i.e., suppression of intrinsic excitability of BLA principal neurons via the PI3K/Akt/mTOR and PLC/PKC pathways.

Sex-specific divergent maturational trajectories in the postnatal rat basolateral amygdala

SummaryIn rodents and humans, the basolateral amygdala (BLA), essential for emotional behaviors, is profoundly reorganized during adolescence. We compared in both sexes the morphology, neuronal, and synaptic properties of BLA neurons in rats at puberty and adulthood. BLA neurons were more excitable in males than in females at adulthood. At pubescence, male action potentials were smaller and shorter than females’ while fast afterhyperpolarizations were larger in males. During postnatal maturation, spine length increased and decreased in females and males, respectively, while there was a reduction in spine head size in females. Excitatory synaptic properties, estimated from stimuli-response relationships, spontaneous post-synaptic currents, and AMPA/NMDA ratio also displayed sex-specific maturational differences. Finally, the developmental courses of long-term potentiation and depression were sexually dimorphic. These data reveal divergent maturational trajectories in the BLA of male and female rats and suggest sex-specific substrates to the BLA linked behaviors at adolescence and adulthood.

Metabotropic Glutamate Receptor 5 in Amygdala Target Neurons Regulates Susceptibility to Chronic Social Stress

BackgroundMetabotropic glutamate receptor 5 (mGluR5) has been implicated in stress-related psychiatric disorders, particularly major depressive disorder. Although growing evidence supports the proresilient role of mGluR5 in corticolimbic circuitry in the depressive-like behaviors following chronic stress exposure, the underlying neural mechanisms, including circuits and molecules, remain unknown. MethodsWe measured the c-Fos expression and probability of neurotransmitter release in and from basolateral amygdala (BLA) neurons projecting to the medial prefrontal cortex (mPFC) and to the ventral hippocampus (vHPC) after chronic social defeat stress. The role of BLA projections in depressive-like behaviors was assessed using optogenetic manipulations, and the underlying molecular mechanisms of mGluR5 and downstream signaling were investigated by Western blotting, viral-mediated gene transfer, and pharmacological manipulations. ResultsChronic social defeat stress disrupted neural activity and glutamatergic transmission in both BLA projections. Optogenetic activation of BLA projections reversed the detrimental effects of chronic social defeat stress on depressive-like behaviors and mGluR5 expression in the mPFC and vHPC. Conversely, inhibition of BLA projections of mice undergoing subthreshold social defeat stress induced a susceptible phenotype and mGluR5 reduction. These two BLA circuits appeared to act in an independent way. We demonstrate that mGluR5 overexpression in the mPFC or vHPC was proresilient while the mGluR5 knockdown was prosusceptible and that the proresilient effects of mGluR5 are mediated through distinctive downstream signaling pathways in the mPFC and vHPC. ConclusionsThese findings identify mGluR5 in the mPFC and vHPC that receive BLA inputs as a critical mediator of stress resilience, highlighting circuit-specific signaling for depressive-like behaviors.

Convergent Coding of Recent and Remote Fear Memory in the Basolateral Amygdala

BackgroundIn both rodents and humans, the basolateral amygdala (BLA) is essential for encoding and retrieving conditioned fear memories. Although the BLA is a putative storage site for these memories, recent evidence suggests that they become independent of the BLA with the passage of time. MethodsWe systematically examined the role for the BLA in the retrieval of recent (1 day) and remote (2 weeks) fear memory using optogenetic, electrophysiological, and calcium imaging methods in male and female Long-Evans rats. Critically, we used a behavioral design that permits within-subjects comparison of recent and remote memory at the same time point; freezing behavior served as the index of learned fear. ResultsWe found that BLA c-Fos expression was similar after the retrieval of recent or remote fear memories. Extracellular single-unit recordings in awake, behaving animals revealed that single BLA neurons exhibit robust increases in spike firing to both recent and remote conditioned stimuli. Fiber photometry recordings revealed that these patterns of activity emerge from principal neurons. Consistent with these results, optogenetic inhibition of BLA principal neurons impaired conditioned freezing to both recent and remote conditioned stimuli. There were no sex differences in any of the measures or manipulations. ConclusionsThese data reveal that BLA neurons encode both recent and remote fear memories, suggesting substantial overlap in the allocation of temporally distinct events. This may underlie the broad generalization of fear memories across both space and time. Ultimately, these results provide evidence that the BLA is a long-term storage site for emotional memories.

Phase-specific synchronization of basolateral amygdalar neurons with neocortical slow oscillations

The basolateral amygdala (BLA) shows firing activity synchronized with neocortex slow oscillations, a form of <1-Hz oscillations that occur dominantly during slow-wave sleep or under anesthesia and is believed to contribute to the formation of emotional memories. Despite its importance for elucidating the neural circuits involved in the formation of emotional memories, the mechanism of the synchronization has remained unclear, mainly because it is difficult to record neuronal membrane potentials in deep brain regions, such as the BLA. We recorded membrane potentials of BLA neurons using a new method that enables whole-cell recording from deep brain regions in vivo. We found that BLA neurons transiently depolarized at late active phases in the slow oscillations. To determine the neural source of the depolarization of BLA neuros, we focused on the medial prefrontal cortex, whose axons projecting to the BLA is known to contribute to the formation of fear memories, as a candidate region that depolarizes BLA neurons during slow oscillations. BLA-projecting neurons were retrogradely labeled with channelrhodopsin-2 using retrograde adeno associated virus, and their firing activity was recorded using an opto-tagging method. These results provide insight into the neural mechanism that synchronizes the slow oscillations between the BLA and the neocortex and lead to the elucidation of the mechanism underlying the formation of emotional memories.

Diverse risk-avoidance behaviors in DISC1 mice are associated with different neuronal firing patterns in BLA neurons

It is very important to maintain normal levels of risk avoidance in daily life. We found that DISC1-NTM mice, which are a model for mental disorders, had a phenotype marked by a risk-avoidance impairment as measured in an open-field test (OFT). We used optogenetic methods to modulate glutamatergic neurons in the basolateral amygdala (BLA) in an attempt to rescue this risk-avoidance impairment. We found that photostimulation of BLA neurons at 20 Hz modified DISC1-NTM mouse behavior from low risk avoidance to high risk avoidance. We observed following photostimulation that, compared to controls, the number of entries to the center of the open field was lower and less time was spent in the central area. We also found that the time spent immobile was higher during photostimulation compared with WT mice. We also used a lower photostimulation frequency of 5 Hz, which activated BLA glutamatergic neurons and rescued the risk-avoidance impairment in DISC1-NTM mice. Our findings confirm that the BLA participates in diverse risk-avoidance behavior. Our results are also a reminder that differences in neuronal firing patterns within the same pathway may lead to different physiological functions.

Genetically identified amygdala-striatal circuits for valence-specific behaviors.

The basolateral amygdala (BLA) plays essential roles in behaviors motivated by stimuli with either positive or negative valence, but how it processes motivationally opposing information and participates in establishing valence-specific behaviors remains unclear. Here, by targeting Fezf2-expressing neurons in the BLA, we identify and characterize two functionally distinct classes in behaving mice, the negative-valence neurons and positive-valence neurons, which innately represent aversive and rewarding stimuli, respectively, and through learning acquire predictive responses that are essential for punishment avoidance or reward seeking. Notably, these two classes of neurons receive inputs from separate sets of sensory and limbic areas, and convey punishment and reward information through projections to the nucleus accumbens and olfactory tubercle, respectively, to drive negative and positive reinforcement. Thus, valence-specific BLA neurons are wired with distinctive input/output structures, forming a circuit framework that supports BLA’s roles in encoding, learning and executing valence-specific motivated behaviors.

Early life stress induces anxiety-like behavior during adulthood through dysregulation of neuronal plasticity in the basolateral amygdala

AimsEarly life stress (ELS) increases the risk of psychiatric diseases such as anxiety disorders and depression in later life. Hyperactivation of the basolateral amygdala (BLA) neurons plays a pivotal role in the pathogenesis of stress-related diseases. However, the functional roles of BLA neurons in ELS-induced anxiety disorders are not completely understood. Main methodsMice were subjected to maternal separation (MS) during postnatal days 3 to 21 to mimic ELS. Anxiety-like behavior was tested by open field test (OFT), elevated plus maze (EPM), and novelty suppressed feeding (NSF). Then, c-fos expression, a proxy for neuronal activity, was evaluated by immunofluorescence. Finally, synaptic transmission and intrinsic excitability were measured by whole-cell patch-clamp recordings. Key findingsMS significantly increased anxiety-like behavior in adulthood, as indicated by less time spent in the center area of the OFT, less time spent in and fewer entries to the open arms of the EPM, and increased latency to feed in NSF. Mechanistically, MS increased the expression of c-fos in BLA. MS enhanced the excitatory, but not inhibitory, synaptic transmission onto BLA projection neurons (PNs), which was caused by enhanced presynaptic glutamate release. Moreover, MS also markedly increased the intrinsic neuronal excitability of BLA PNs, probably due to the reduced medium afterhyperpolarization (mAHP) in BLA PNs. SignificanceOur results suggest that the changes of neuronal activity and synaptic transmission in the BLA PNs may play a crucial role in ELS-induced anxiety-like behavior, and these findings provide new insights into the pathological mechanisms of stress-related anxiety disorders.