Increased excitatory amino acid transporter 2 levels in basolateral amygdala astrocytes mediate chronic stress–induced anxiety-like behavior

The conventional perception of astrocytes as mere supportive cells within the brain has recently been called into question by empirical evidence, which has revealed their active involvement in regulating brain function and encoding behaviors associated with emotions.Specifically, astrocytes in the basolateral amygdala have been found to play a role in the modulation of anxiety-like behaviors triggered by chronic stress. Nevertheless, the precise molecular mechanisms by which basolateral amygdala astrocytes regulate chronic stress–induced anxiety-like behaviors remain to be fully elucidated. In this study, we found that in a mouse model of anxiety triggered by unpredictable chronic mild stress, the expression of excitatory amino acid transporter 2 was upregulated in the basolateral amygdala. Interestingly, our findings indicate that the targeted knockdown of excitatory amino acid transporter 2 specifically within the basolateral amygdala astrocytes was able to rescue the anxiety-like behavior in mice subjected to stress. Furthermore, we found that the overexpression of excitatory amino acid transporter 2 in the basolateral amygdala, whether achieved through intracranial administration of excitatory amino acid transporter 2agonists or through injection of excitatory amino acid transporter 2-overexpressing viruses with GfaABC1D promoters, evoked anxiety-like behavior in mice. Our single-nucleus RNA sequencing analysis further confirmed that chronic stress induced an upregulation of excitatory amino acid transporter 2 specifically in astrocytes in the basolateral amygdala. Moreover, through in vivo calcium signal recordings, we found that the frequency of calcium activity in the basolateral amygdala of mice subjected to chronic stress was higher compared with normal mice.After knocking down the expression of excitatory amino acid transporter 2 in the basolateral amygdala, the frequency of calcium activity was not significantly increased, and anxiety-like behavior was obviously mitigated. Additionally, administration of an excitatory amino acid transporter 2 inhibitor in the basolateral amygdala yielded a notable reduction in anxiety level among mice subjected to stress. These results suggest that basolateral amygdala astrocytic excitatory amino acid transporter 2 plays a role in in the regulation of unpredictable chronic mild stress-induced anxiety-like behavior by impacting the activity of local glutamatergic neurons, and targeting excitatory amino acid transporter 2 in the basolateral amygdala holds therapeutic promise for addressing anxiety disorders.

Dip2a regulates stress susceptibility in the basolateral amygdala

Dysregulation of neurotransmitter metabolism in the central nervous system contributes to mood disorders such as depression, anxiety, and post–traumatic stress disorder. Monoamines and amino acids are important types of neurotransmitters. Our previous results have shown that disco-interacting protein 2 homolog A(Dip2a) knockout mice exhibit brain development disorders and abnormal amino acid metabolism in serum. This suggests that DIP2A is involved in the metabolism of amino acid–associated neurotransmitters. Therefore, we performed targeted neurotransmitter metabolomics analysis and found that Dip2a deficiency caused abnormal metabolism of tryptophan and thyroxine in the basolateral amygdala and medial prefrontal cortex. In addition, acute restraint stress induced a decrease in 5-hydroxytryptamine in the basolateral amygdala. Additionally, Dip2a was abundantly expressed in excitatory neurons of the basolateral amygdala, and deletion of Dip2a in these neurons resulted in hopelessness-like behavior in the tail suspension test. Altogether, these findings demonstrate that DIP2A in the basolateral amygdala may be involved in the regulation of stress susceptibility. This provides critical evidence implicating a role of DIP2A in affective disorders.

Differential Effect of Unilateral Amygdalar GABAA Receptor Agonist Injection on Low- and High-Anxiety Rats

The influence of γ-aminobutyric type-A (GABAA) receptors agonist (muscimol hydrobromide, 0.1 μg/0.5 μl) injections into the right or left basolateral amygdala (BLA) on the behavior of high-anxiety (HA) and low-anxiety (LA) rats subjected to the elevated plus-maze (EPM) test was investigated. Anxiolytic-like effects (increase of open-arm entries and open-arm time) was revealed only after administration of muscimol into the left (but not right) amygdala of HA animals. No effect was observed upon administration of muscimol to LA rats. These findings suggest an important role in anxiety regulation of the amygdalar GABA levels, and the assumed GABA hemispheric lateralization.

Investigating the inhibition of NMDA glutamate receptors in the basolateral nucleus of the amygdala on the pain and inflammation induced by formalin in male Wistar rats

BACKGROUND： The role of the amygdala in controlling emotional pain has been emphasized in several studies. In this study, the role of the NMDA glutamate receptors in the basolateral nucleus of the amygdala （BLA） in regulating inflammation and emotional pain, induced by formalin, was studied in male rats. METHODS： Male Wistar rats, weighing 250±0 g, were injected with 20 μL of 2% formalin into the paw of the right hind limb. Memantine, at doses of 1 and 5 μg/rat, was injected bilaterally into the BLA five minutes prior to injecting formalin. Following the injection, the pain and inflammation of the paws were measured using Dubbison-Dennis and mercury immersion methods, respectively. The behavior of the animals, including licking time and foot volume, was assessed. RESULTS： The results showed that the inactivation of the NMDA receptors in the BLA in the acute phase of pain reduced the licking time （the emotional aspect of pain）. However, at a high dose （5μg/rat）, memantine exacerbates the pain induced by formalin in the chronic phase. Additionally, the inhibition of the NMDA receptors in the BLA by memantine enhanced the formalin-induced increase in foot volume （inflammation） in a dose-dependent manner. CONCLUSION： The study showed that the NMDA glutamate receptors in the BLA are crucial for the emotional pain and inflammation in both chronic and acute phases of formalin-induced pain. However, their roles are more pronounced in the chronic phase than in the acute phase of pain.

Infusion of methylphenidate into the basolateral nucleus of amygdala or anterior cingulate cortex enhances fear memory consolidation in rats

The psychostimulant methylphenidate (MPD; also called Ritalin) is a blocker of dopamine and norepi-nephrine transporter. It has been clinically used for treatment of Attention Deficit and Hyperactivity Disorder (ADHD). There have been inconsistent reports regarding the effects of systemically adminis-tered MPD on learning and memory, either in animals or humans. In the present study, we investigated the effect of direct infusion of MPD into the basolateral nucleus of amygdala (BLA) or the anterior cin-gulate cortex (ACC) on conditioned fear memory. Rats were trained on a one-trial step-through inhibi-tory avoidance task. MPD was infused bilaterally into the BLA or the ACC, either at ‘0’ or 6 h post-training. Saline was administered as control. Memory retention was tested 48 h post-training. In-tra-BLA or intra-ACC infusion of MPD ‘0’ h but not 6 h post-training significantly improved 48-h memory retention: the MPD-treated rats had significant longer step-through latency than controls. The present results indicate that action of MPD in the BLA or the ACC produces a beneficial effect on the consoli-dation of inhibitory avoidance memory.

Whole-Brain Map of Long-Range Monosynaptic Inputs to Different Cell Types in the Amygdala of the Mouse

The amygdala,which is involved in various behaviors and emotions,is reported to connect with the whole brain.However,the long-range inputs of distinct cell types have not yet been defined.Here,we used a retrograde trans-synaptic rabies virus to generate a whole-brain map of inputs to the main cell types in the mouse amygdala.We identified 37 individual regions that projected to neurons expressing vesicular glutamate transporter 2,78 regions to parvalbumin-expressing neurons,104 regions to neurons expressing protein kinase C-δ,and 89 regions to somatostatin-expressing neurons.The amygdala received massive projections from the isocortex and striatum.Several nuclei,such as the caudate-putamen and the CA1 field of the hippocampus,exhibited input preferences to different cell types in the amygdala.Notably,we identified several novel input areas,including the substantia innominata and zona incerta.These findings provide anatomical evidence to help understand the precise connections and diverse functions of the amygdala.

Changes of glucocorticoid receptor mRNA expression in basolateral amygdale-kindled rats

Background Glucocorticoid receptor （GR） is believed to be a major factor in brain maturation and in modulation of a series of brain activity. Hippocampal neurons are abundant in glucocorticoid receptor, and there is significant change in GR expression under certain pathological state. Epilepsy is a special pathological state of the central nervous system. This study aimed to explore the role of GR in epilepsy by observing the change and functions of GR in hippocampus with a basolateral amygdale-electrical kindled rat epilepsy model. Methods Firstly, we established the basolateral amygdale-electrical kindled rat epilepsy model. Then GR mRNA expression in the hippocampus was assayed by semi-quantitative reverse transcription-PCR in this experiment. In addition, the processes of epileptic seizures were observed and electroencephalograms were recorded. One-way analysis of variance （ANOVA） was employed for comparing means of multiple groups, followed Fisher＇s least significant difference （LSD） for paired comparison. Results The rats were successfully kindled after an average of （13.50＋3.99） times electrical stimulation, in which it was showed that GR mRNA expression reduced obviously as compared with the control group and the sham groups （P 〈0.001）. The down-regulation of GR mRNA expression was abated or reversed by some anti-epilepsy drugs （P 〈0.001 compared with the epilepsy group）, accompanied by attenuation of seizures and improvement of electroencephalograms. Conclusions Down-regulation of hippocampal GR mRNA expression may be related to the kindling. Anti-epilepsy drugs exposure can retard this change.

Memory Trace for Fear Extinction:Fragile yet Reinforceable

Fear extinction is a biological process in which learned fear behavior diminishes without anticipated reinforcement,allowing the organism to re-adapt to ever-changing situations.Based on the behavioral hypothesis that extinction is new learning and forms an extinction memory,this new memory is more readily forgettable than the original fear memory.The brain’s cellular and synaptic traces underpinning this inherently fragile yet reinforceable extinction memory remain unclear.Intriguing questions are about the whereabouts of the engram neurons that emerged during extinction learning and how they constitute a dynamically evolving functional construct that works in concert to store and express the extinction memory.In this review,we discuss recent advances in the engram circuits and their neural connectivity plasticity for fear extinction,aiming to establish a conceptual framework for understanding the dynamic competition between fear and extinction memories in adaptive control of conditioned fear responses.