Molecular Mechanisms Underlying Emotional Learning and Memory in the Lateral Amygdala

Acquisition and generalization of emotional and neural responses to faces associated with negative and positive feedback behaviours

Faces can acquire emotional meaning by learning to associate individuals with specific behaviors. Here, we investigated emotional evaluation and brain activations toward faces of persons who had given negative or positive evaluations to others. Furthermore, we investigated how emotional evaluations and brain activation generalize to perceptually similar faces. Valence ratings indicated learning and generalization effects for both positive and negative faces. Brain activation, measured with functional magnetic resonance imaging (fMRI), showed significantly increased activation in the fusiform gyrus (FG) to negatively associated faces but not positively associated ones. Remarkably, brain activation in FG to faces to which emotional meaning (negative and positive) was successfully generalized was decreased compared to neutral faces. This suggests that the emotional relevance of faces is not simply associated with increased brain activation in visual areas. While, at least for negative conditions, faces paired with negative feedback behavior are related to potentiated brain responses, the opposite is seen for perceptually very similar faces despite generalized emotional responses.

EphB2 activation in neural stem cells in the basolateral amygdala facilitates neurogenesis and enhances long-term memory

Many brain diseases lead to a reduction in the number of functional neurons and it would be of value to be able to increase the number of neurons in the affected brain areas. In this study, we examined whether we can promote neural stem cells to produce mature neurons and whether an increase in the mature neurons can affect cognitive performance. We detected that the EphB2 receptor is localized in immature basolateral amygdala (BLA) neurons. We therefore aimed to increase the level of EphB2 activity in neural stem cells (NSCs) in the BLA and examine the effects on the production of mature neurons and cognition. Toward that end, we utilized a photoactivatable EphB2 construct (optoEphB2) to increase EphB2 forward signaling in NSCs in the BLA. We revealed that the activation of optoEphB2 in NSCs in the BLA increased the level of immature and mature neurons in the BLA. We further found that activation of optoEphB2 in BLA NSCs enhanced auditory, but not contextual, long-term fear memory formation. Impairing EphB2 forward signaling did not affect the level of immature and mature neurons in the BLA. This study provides evidence that NSCs can be promoted to produce mature neurons by activating EphB2 to enhance specific brain functions.

An insight into crosstalk among multiple signalling pathways contributing to the pathophysiology of PTSD and depressive disorders

Post-traumatic stress disorder (PTSD) and depressive disorders represent two significant mental health challenges with substantial global prevalence. These are debilitating conditions characterized by persistent, often comorbid, symptoms that severely impact an individual's quality of life. Both PTSD and depressive disorders are often precipitated by exposure to traumatic events or chronic stress. The profound impact of PTSD and depressive disorders on individuals and society necessitates a comprehensive exploration of their shared and distinct pathophysiological features. Although the activation of the stress system is essential for maintaining homeostasis, the ability to recover from it after diminishing the threat stimulus is also equally important. However, little is known about the main reasons for individuals' differential susceptibility to external stressful stimuli. The solution to this question can be found by delving into the interplay of stress with the cognitive and emotional processing of traumatic incidents at the molecular level. Evidence suggests that dysregulation in these signalling cascades may contribute to the persistence and severity of PTSD and depressive symptoms. The treatment strategies available for this disorder are antidepressants, which have shown good efficiency in normalizing symptom severity; however, their efficacy is limited in most individuals. This calls for the exploration and development of innovative medications to address the treatment of PTSD. This review delves into the intricate crosstalk among multiple signalling pathways implicated in the development and manifestation of these mental health conditions. By unravelling the complexities of crosstalk among multiple signalling pathways, this review aims to contribute to the broader knowledge base, providing insights that could inform the development of targeted interventions for individuals grappling with the challenges of PTSD and depressive disorders.

Astrocytic phagocytosis in the medial prefrontal cortex jeopardises postoperative memory consolidation in mice

Memory impairment is one of the main characteristics of postoperative cognitive dysfunction. It remains elusive how postoperative pathological changes of the brain link to the memory impairment. The clinical setting of perioperation was mimicked via partial hepatectomy under sevoflurane anaesthesia together with preoperative restraint stress (Hep-Sev-stress) in mice. Memory changes were assessed with fear conditioning. The medial prefrontal cortex (mPFC)-dorsal hippocampus connectivity was evaluated with injecting neurotracer 28 days before surgery. Astrocytic activation was limited via injecting AAV-GFAP-hM4Di-eGFP into the mPFC. Astrocytic and microglial phagocytosis of synapses were visualised with co-labelling hippocampal neuronal axon terminals with PSD-95 and S100β or Iba1. Neuroinflammation and oxidative stress status were also detected. Hep-Sev-stress impaired the memory consolidation (mean [standard error], 49.91 [2.55]% vs. 35.40 [3.97]% in the contextual memory, p = 0.007; 40.72 [2.78]% vs. 27.77 [2.22]% in cued memory, p = 0.002) and the cued memory retrieval (39.00 [3.08]% vs. 24.11 [2.06]%, p = 0.001) in mice when compared with these in the naïve controls. Hep-Sev-stress damaged the connectivity from the dorsal hippocampus to mPFC but not from the mPFC to the dorsal hippocampus and increased the astrocytic but not microglial phagocytosis of hippocampal neuronal axon terminals in the mPFC. The intervention also induced neuroinflammation and oxidative stress in the dorsal hippocampus and the mPFC in a regional-dependent manner. Limiting astrocyte activation in the mPFC alleviated memory consolidation impairment induced by Hep-Sev-stress. Postoperative memory consolidation was impaired due to astrocytic phagocytosis-induced connectivity injury from the dorsal hippocampus to the medial prefrontal cortex.

Fear Learning: An Evolving Picture for Plasticity at Synaptic Afferents to the Amygdala

Unraveling the neuronal mechanisms of fear learning might allow neuroscientists to make links between a learned behavior and the underlying plasticity at specific synaptic connections. In fear learning, an innocuous sensory event such as a tone (called the conditioned stimulus, CS) acquires an emotional value when paired with an aversive outcome (unconditioned stimulus, US). Here, we review earlier studies that have shown that synaptic plasticity at thalamic and cortical afferents to the lateral amygdala (LA) is critical for the formation of auditory-cued fear memories. Despite the early progress, it has remained unclear whether there are separate synaptic inputs that carry US information to the LA to act as a teaching signal for plasticity at CS-coding synapses. Recent findings have begun to fill this gap by showing, first, that thalamic and cortical auditory afferents can also carry US information; second, that the release of neuromodulators contributes to US-driven teaching signals; and third, that synaptic plasticity additionally happens at connections up- and downstream of the LA. Together, a picture emerges in which coordinated synaptic plasticity in serial and parallel circuits enables the formation of a finely regulated fear memory.

Central stress pathways in the development of cardiovascular disease

PURPOSE

Mental stress is of essential consideration when assessing cardiovascular pathophysiology in all patient populations. Substantial evidence indicates associations among stress, cardiovascular disease and aberrant brain-body communication. However, our understanding of the flow of stress information in humans, is limited, despite the crucial insights this area may offer into future therapeutic targets for clinical intervention.

METHODS

Key terms including mental stress, cardiovascular disease and central control, were searched in PubMed, ScienceDirect and Scopus databases. Articles indicative of heart rate and blood pressure regulation, or central control of cardiovascular disease through direct neural innervation of the cardiac, splanchnic and vascular regions were included. Focus on human neuroimaging research and the flow of stress information is described, before brain-body connectivity, via pre-motor brainstem intermediates is discussed. Lastly, we review current understandings of pathophysiological stress and cardiovascular disease aetiology.

RESULTS

Structural and functional changes to corticolimbic circuitry encode stress information, integrated by the hypothalamus and amygdala. Pre-autonomic brain-body relays to brainstem and spinal cord nuclei establish dysautonomia and lead to alterations in baroreflex functioning, firing of the sympathetic fibres, cellular reuptake of norepinephrine and withdrawal of the parasympathetic reflex. The combined result is profoundly adrenergic and increases the likelihood of cardiac myopathy, arrhythmogenesis, coronary ischaemia, hypertension and the overall risk of future sudden stress-induced heart failure.

CONCLUSIONS

There is undeniable support that mental stress contributes to the development of cardiovascular disease. The emerging accumulation of large-scale multimodal neuroimaging data analytics to assess this relationship promises exciting novel therapeutic targets for future cardiovascular disease detection and prevention.

Does high fidelity neonatal resuscitation simulation increase salivary cortisol levels of health care providers?

BACKGROUND

The use of simulation-based medical education is strongly recommended to insure neonatal resuscitation skills for health caregivers. High fidelity simulation was executed to allow the evaluation of technical and non-technical skills. Salivary cortisol level was considered reliable biomarkers of adrenocortical activity and useful tool to learning assessment and stress response.

METHODS

Our primary aim was to test changes in salivary cortisol levels before and after the simulation for neonatal resuscitation between high and low fidelity setting. Secondary aim was to evaluate salivary cortisol level in the participants, leader and not leader. Fifty-two health care providers were divided in ratio 1:1 into low-fidelity (LF group) and high-fidelity scenario (HF group) of neonatal resuscitation. In each group the participants assumed the role of team leader or not team leader. Salivary samples were collected from all participants 5 minutes before and after each simulation scenario by using oral swab. Analysis of difference was analyzed by Kruskal Wallis Test.

RESULTS

Salivary cortisol levels were significantly higher in HF group (N.=26) than LF group (N.=26) before the performance (5.407 mmol/L vs. 3.090 mmol/L; P=0.018). In the HF group, salivary cortisol levels were significantly lower after simulation than before (P=0.007), moreover not team leader showed higher salivary cortisol levels before of the simulation than after (P=0.003). Team leaders showed higher salivary cortisol levels than not team leader after high-fidelity scenario (P=0.039).

CONCLUSIONS

High-fidelity simulation scenario had a great impact on stress level, furthermore leaders showed higher salivary cortisol levels than not team leaders.

The Neuroendocrine Impact of Acute Stress on Synaptic Plasticity

Stress induces changes in nervous system function on different signaling levels, from molecular signaling to synaptic transmission to neural circuits to behavior-and on different time scales, from rapid onset and transient to delayed and long-lasting. The principal effectors of stress plasticity are glucocorticoids, steroid hormones that act with a broad range of signaling competency due to the expression of multiple nuclear and membrane receptor subtypes in virtually every tissue of the organism. Glucocorticoid and mineralocorticoid receptors are localized to each of the cellular compartments of the receptor-expressing cells-the membrane, cytosol, and nucleus. In this review, we cover the neuroendocrine effects of stress, focusing mainly on the rapid actions of acute stress-induced glucocorticoids that effect changes in synaptic transmission and neuronal excitability by modulating synaptic and intrinsic neuronal properties via activation of presumed membrane glucocorticoid and mineralocorticoid receptors. We describe the synaptic plasticity that occurs in 4 stress-associated brain structures, the hypothalamus, hippocampus, amygdala, and prefrontal cortex, in response to single or short-term stress exposure. The rapid transformative impact of glucocorticoids makes this stress signal a particularly potent effector of acute neuronal plasticity.

The Basolateral Amygdala: The Core of a Network for Threat Conditioning, Extinction, and Second-Order Threat Conditioning

Threat conditioning, extinction, and second-order threat conditioning studied in animal models provide insight into the brain-based mechanisms of fear- and anxiety-related disorders and their treatment. Much attention has been paid to the role of the basolateral amygdala (BLA) in such processes, an overview of which is presented in this review. More recent evidence suggests that the BLA serves as the core of a greater network of structures in these forms of learning, including associative and sensory cortices. The BLA is importantly regulated by hippocampal and prefrontal inputs, as well as by the catecholaminergic neuromodulators, norepinephrine and dopamine, that may provide important prediction-error or learning signals for these forms of learning. The sensory cortices may be required for the long-term storage of threat memories. As such, future research may further investigate the potential of the sensory cortices for the long-term storage of extinction and second-order conditioning memories.

Rac1 GTPase activation impairs fear conditioning-induced structural changes in basolateral amygdala neurons and long-term fear memory formation

Long-term memory formation leads to enduring alterations in synaptic efficacy and neuronal responses that may be created by changes in neuronal morphology. We show that fear conditioning leads to a long-lasting increase in the volume of the primary and secondary dendritic branches, but not of distal branches, of neurons located at the basolateral amygdala (BLA). The length of the dendritic branches is not affected by fear conditioning. Fear conditioning leads to an enduring increase in the length and volume of dendritic spines, especially in the length of the spine neck and the volume of the spine head. Fear conditioning does not affect dendritic spine density. We further reveal that activation of Rac1 in BLA during fear conditioning impairs long-term auditory, but not contextual, fear conditioning memory. Activation of Rac1 during fear conditioning prevents the enduring increase in the dendritic primary branch volume and dendritic spines length and volume. Rac1 activation per se has no effect on neuronal morphology. These results show that fear conditioning induces changes known to reduce the inhibition of signal propagation along the dendrite and the increase in synaptic efficacy whereas preventing these changes, by Rac1 activation, impairs fear memory formation.

Neuroserpin gene therapy inhibits retinal ganglion cell apoptosis and promotes functional preservation in glaucoma

Our research has proven that the inhibitory activity of the serine protease inhibitor neuroserpin (NS) is impaired because of its oxidation deactivation in glaucoma. Using genetic NS knockout (NS-/-) and NS overexpression (NS+/+ Tg) animal models and antibody-based neutralization approaches, we demonstrate that NS loss is detrimental to retinal structure and function. NS ablation was associated with perturbations in autophagy and microglial and synaptic markers, leading to significantly enhanced IBA1, PSD95, beclin-1, and LC3-II/LC3-I ratio and reduced phosphorylated neurofilament heavy chain (pNFH) levels. On the other hand, NS upregulation promoted retinal ganglion cell (RGC) survival in wild-type and NS-/- glaucomatous mice and increased pNFH expression. NS+/+Tg mice demonstrated decreased PSD95, beclin-1, LC3-II/LC3-I ratio, and IBA1 following glaucoma induction, highlighting its protective role. We generated a novel reactive site NS variant (M363R-NS) resistant to oxidative deactivation. Intravitreal administration of M363R-NS was observed to rescue the RGC degenerative phenotype in NS-/- mice. These findings demonstrate that NS dysfunction plays a key role in the glaucoma inner retinal degenerative phenotype and that modulating NS imparts significant protection to the retina. NS upregulation protected RGC function and restored biochemical networks associated with autophagy and microglial and synaptic function in glaucoma.

Cognitive rescue in aging through prior training in rats

Cognitive decline in spatial memory is seen in aging. Understanding affected processes in aging is vital for developing methods to improve wellbeing. Daily memory persistence can be influenced by events around the time of learning or by prior experiences in early life. Fading memories in young can last longer if a novel event is introduced around encoding, a process called behavioral tagging. Based on this principle, we asked what processes are affected in aging and if prior training can rescue them. Two groups of aged rats received training in an appetitive delayed matching-to-place task. One of the groups additionally received prior training of the same task in young and in mid-life, constituting a longitudinal study. The results showed long-term memory decline in late aging without prior training. This would reflect affected encoding and consolidation. On the other hand, short-term memory was preserved and novelty at memory reactivation and reconsolidation enabled memory maintenance in aging. Prior training improved cognition through facilitating task performance, strengthening short-term memory and intermediate memory, and enabling encoding-boosted long-term memory. Implication of these findings in understanding brain mechanisms in cognitive aging and in beneficial effects of prior training is discussed.

Amygdala activity and amygdala-hippocampus connectivity: Metabolic diseases, dementia, and neuropsychiatric issues

With rapid aging of the population worldwide, the number of people with dementia is dramatically increasing. Some studies have emphasized that metabolic syndrome, which includes obesity and diabetes, leads to increased risks of dementia and cognitive decline. Factors such as insulin resistance, hyperglycemia, high blood pressure, dyslipidemia, and central obesity in metabolic syndrome are associated with synaptic failure, neuroinflammation, and imbalanced neurotransmitter levels, leading to the progression of dementia. Due to the positive correlation between diabetes and dementia, some studies have called it "type 3 diabetes". Recently, the number of patients with cognitive decline due to metabolic imbalances has considerably increased. In addition, recent studies have reported that neuropsychiatric issues such as anxiety, depressive behavior, and impaired attention are common factors in patients with metabolic disease and those with dementia. In the central nervous system (CNS), the amygdala is a central region that regulates emotional memory, mood disorders, anxiety, attention, and cognitive function. The connectivity of the amygdala with other brain regions, such as the hippocampus, and the activity of the amygdala contribute to diverse neuropathological and neuropsychiatric issues. Thus, this review summarizes the significant consequences of the critical roles of amygdala connectivity in both metabolic syndromes and dementia. Further studies on amygdala function in metabolic imbalance-related dementia are needed to treat neuropsychiatric problems in patients with this type of dementia.

GADD34 suppresses eIF2α phosphorylation and improves cognitive function in Alzheimer's disease-model mice

Alzheimer's disease (AD) causes neurodegeneration, leading to cognitive impairment and memory loss. Our previous studies have demonstrated that the induction of growth arrest and DNA damage-inducible gene 34 (GADD34) by quercetin can affect eukaryotic translation initiation factor 2α (eIF2α) phosphorylation-activated transcription factor 4 (ATF4) signaling. However, the relationship between GADD34 expression and cognitive function has not been clarified. In this study, we determined the direct effect of GADD34 on memory. To achieve this, truncated GADD34 (GADD34.5) was injected into the mouse brain to suppress eIF2α phosphorylation and evaluate memory. The injection of GADD34.5 into the hippocampus in AD-model mice did not improve novel object recognition but improved novel object location. The injection of GADD34.5 into the amygdala also resulted in the maintenance of contextual fear memory based on the fear condition test. These results suggest that GADD34 is effective in improving memory for spatial cognition and contextual fear conditioning in AD by inhibiting eIF2α phosphorylation. In summary, GADD34 suppresses eIF2α phosphorylation in the brain and prevents memory loss. As quercetin feeding increases GADD34 expression, it might be used in preventative applications for AD.

Danger Changes the Way the Brain Consolidates Neutral Information; and Does So by Interacting with Processes Involved in the Encoding of That Information

This study examined the effect of danger on consolidation of neutral information in two regions of the rat (male and female) medial temporal lobe: the perirhinal cortex (PRh) and basolateral amygdala complex (BLA). The neutral information was the association that forms between an auditory stimulus and a visual stimulus (labeled S2 and S1) across their pairings in sensory preconditioning. We show that, when the sensory preconditioning session is followed by a shocked context exposure, the danger shifts consolidation of the S2-S1 association from the PRh to the BLA; and does so by interacting with processes involved in encoding of the S2-S1 pairings. Specifically, we show that the initial S2-S1 pairing in sensory preconditioning is encoded in the BLA and not the PRh; whereas the later S2-S1 pairings are encoded in the PRh and not the BLA. When the sensory preconditioning session is followed by a context alone exposure, the BLA-dependent trace of the early S2-S1 pairings decays and the PRh-dependent trace of the later S2-S1 pairings is consolidated in memory. However, when the sensory preconditioning session is followed by a shocked context exposure, the PRh-dependent trace of the later S2-S1 pairings is suppressed and the BLA-dependent trace of the initial S2-S1 pairing is consolidated in memory. These findings are discussed with respect to mutually inhibitory interactions between the PRh and BLA, and the way that these regions support memory in other protocols, including recognition memory in people.SIGNIFICANCE STATEMENT The perirhinal cortex (PRh) and basolateral amygdala complex (BLA) process the pairings of neutral auditory and visual stimuli in sensory preconditioning. The involvement of each region in this processing is determined by the novelty/familiarity of the stimuli as well as events that occur immediately after the preconditioning session. Novel stimuli are represented in the BLA; however, as these stimuli are repeatedly presented without consequence, they come to be represented in the PRh. Whether the BLA- or PRh-dependent representation is consolidated in memory depends on what happens next. When nothing of significance occurs, the PRh-dependent representation is consolidated and the BLA-dependent representation decays; but when danger is encountered, the PRh-dependent representation is inhibited and the BLA-dependent representation is selected for consolidation.

Fear Conditioning Leads to Enduring Alterations in RNA Transcripts in Hippocampal Neuropil that are Dependent on EphB2 Forward Signaling

Alterations in mRNA transcription have been associated with changes in brain functions. We wanted to examine if fear conditioning causes long-term changes in transcriptome profiles in the basolateral amygdala (BLA) and hippocampus using RNA-Seq and laser microdissection microscopy. We further aimed to uncover whether these changes are involved in memory formation by monitoring their levels in EphB2^lacZ/lacZ mice, which lack EphB2 forward signaling and can form short-term fear conditioning memory but not long-term fear conditioning memory. We found transcriptome signatures unique to each brain region that are comprise of specific cellular pathways. We also revealed that fear conditioning leads to alterations in mRNAs levels 24 h after training in hippocampal neuropil, but not in hippocampal cell layers or BLA. The two main groups of altered mRNAs encode proteins involved in neuronal transmission, neuronal morphogenesis and neuronal development and the vast majority are known to be enriched in neurons. None of these mRNAs levels were altered by fear conditioning in EphB2^lacZ/lacZ mice, which were also impaired in long-term fear memory. We show here that fear conditioning leads to an enduring alteration in mRNAs levels in hippocampal neuropil that is dependent on processes mediated by EphB2 that are needed for long-term memory formation.

Metabotropic glutamate receptors and cognition: From underlying plasticity and neuroprotection to cognitive disorders and therapeutic targets

Metabotropic glutamate (mGlu) receptors are G protein-coupled receptors that play pivotal roles in mediating the activity of neurons and other cell types within the brain, communication between cell types, synaptic plasticity, and gene expression. As such, these receptors play an important role in a number of cognitive processes. In this chapter, we discuss the role of mGlu receptors in various forms of cognition and their underlying physiology, with an emphasis on cognitive dysfunction. Specifically, we highlight evidence that links mGlu physiology to cognitive dysfunction across brain disorders including Parkinson's disease, Alzheimer's disease, Fragile X syndrome, post-traumatic stress disorder, and schizophrenia. We also provide recent evidence demonstrating that mGlu receptors may elicit neuroprotective effects in particular disease states. Lastly, we discuss how mGlu receptors can be targeted utilizing positive and negative allosteric modulators as well as subtype specific agonists and antagonist to restore cognitive function across these disorders.

Recombinant human erythropoietin induces neuroprotection, activates MAPK/CREB pathway, and rescues fear memory after traumatic brain injury with delayed hypoxemia in mice

Therapeutic interventions targeting secondary insults, such as delayed hypoxemia, provide a unique opportunity for treatment in severe traumatic brain injury (TBI). Erythropoietin (EPO) is a hypoxia-responsive cytokine with important roles in neurodevelopment, neuroprotection and neuromodulation. We hypothesized that recombinant human erythropoietin (rhEPO) administration would mitigate injury in a combined injury model of TBI and delayed hypoxemia. Utilizing a clinically relevant murine model of TBI and delayed hypoxemia, we characterized how ongoing rhEPO administration influenced neurogenesis, neuroprotection, synaptic density and, behavioral outcomes early after TBI, and the impact on long-lasting outcomes 6 months after injury. We employed novel object recognition (NOR) and fear conditioning to assess long-term memory. At 1-month post-injury, we observed a significant increase in cued-fear memory response in the rhEPO-injured mice compared with vehicle-injured mice. This was associated with neuroprotection and neurogenesis in the hippocampus and mitogen-activated protein kinase (MAPK)/cAMP response element-binding protein (CREB) signaling activation and increased of excitatory synaptic density in the amygdala. Early rhEPO treatment after injury reduced neurodegeneration and increased excitatory synaptic density in the hippocampus and amygdala at 6 months post-injury. However at 6 months post-injury (4 months after discontinuation of rhEPO), we did not observe changes in behavioral assessments nor MAPK/CREB pathway activation. In summary, these data demonstrate that ongoing rhEPO treatment initiated at a clinically feasible time point improves neurological, cognitive, and histological outcomes after TBI in the setting of secondary hypoxemic insults.

Nck1 activity in lateral amygdala regulates long-term fear memory formation

Fear conditioning leads to long-term fear memory formation and is a model for studying fear-related psychopathological conditions such as phobias and post-traumatic stress disorder. Long-term fear memory formation is believed to involve alterations of synaptic efficacy mediated by changes in synaptic transmission and morphology in lateral amygdala (LA). Nck1 is a key neuronal adaptor protein involved in the regulation of the actin cytoskeleton and the neuronal processes believed to be involved in memory formation. However, the role of Nck1 in memory formation is not known. Here we explored the role of Nck1 in fear memory formation in lateral amygdala (LA). Reduction of Nck1 in excitatory neurons in LA enhanced long-term, but not short-term, auditory fear conditioning memory. Activation of Nck1, by using a photoactivatable Nck1 (PA-Nck1), during auditory fear conditioning in excitatory neurons in LA impaired long-term, but not short-term, fear memory. Activation of Nck1 immediately or a day after fear conditioning did not affect fear memory. The hippocampal-mediated contextual fear memory was not affected by the reduction or activation of Nck1 in LA. We show that Nck1 is localized to the presynapses in LA. Nck1 activation in LA excitatory neurons decreased the frequency of AMPA receptors-mediated miniature excitatory synaptic currents (mEPSCs). Nck1 activation did not affect GABA receptor-mediated inhibitory synaptic currents (mIPSCs). These results show that Nck1 activity in excitatory neurons in LA regulates glutamate release and sets the threshold for fear memory formation. Moreover, our research shows that Nck1 may serve as a target for pharmacological treatment of fear and anxiety disorders.

Extracellular signal-regulated kinase in the basolateral amygdala is required for reconsolidation of heroin-associated memory

Reconsolidation of heroin-associated memory is an independent memory process that occurs following retrieval, which is essential for the sustained capacity of an associative drug stimulus to precipitate heroin-seeking. Extracellular signal-regulated kinase (ERK) in the basolateral amygdala (BLA) mediates the reconsolidation of drug memory. In the present study, we utilized a rat model of drug craving and relapse to verify the hypothesis that the reconsolidation of heroin-associated memory requires ERK in an instrumental heroin-seeking behavior, focusing on the BLA brain region, which is crucial for synaptic plasticity and memory processes. We found that bilateral intra-BLA infusions of U0126 (1 μg/0.5 μl), an ERK inhibitor, immediately after retrieving heroin-associated memory significantly reduced cue-induced and drug-induced reinstatement and spontaneous recovery of heroin-seeking compared to the vehicle. Furthermore, this inhibitory effect was related to the characteristic of reconsolidation. Conversely, no effect was observed on the heroin-seeking behavior when the intra-BLA infusion of U0126 was administered 6 h after the heroin-associated memory retrieval or without memory retrieval. Together, these data suggest that disrupting the reconsolidation of heroin-associated memory via an ERK inhibitor may serve as a promising option for treating relapse in opiate addicts.

CD73-Mediated Formation of Extracellular Adenosine Is Responsible for Adenosine A2A Receptor-Mediated Control of Fear Memory and Amygdala Plasticity

Adenosine A2A receptors (A2AR) control fear memory and the underlying processes of synaptic plasticity in the amygdala. In other brain regions, A2AR activation is ensured by ATP-derived extracellular adenosine formed by ecto-5'-nucleotidase or CD73. We now tested whether CD73 is also responsible to provide for the activation of A2AR in controlling fear memory and amygdala long-term potentiation (LTP). The bilateral intracerebroventricular injection of the CD73 inhibitor αβ-methylene ADP (AOPCP, 1 nmol/ventricle/day) phenocopied the effect of the A2AR blockade by decreasing the expression of fear memory, an effect disappearing in CD73-knockout (KO) mice and in forebrain neuronal A2AR-KO mice. In the presence of PPADS (20 μM) to eliminate any modification of ATP/ADP-mediated P2 receptor effects, both AOPCP (100 μM) and the A2AR antagonist, SCH58261 (50 nM), decreased LTP magnitude in synapses of projection from the external capsula into the lateral amygdala, an effect eliminated in slices from both forebrain neuronal A2AR-KO mice and CD73-KO mice. These data indicate a key role of CD73 in the process of A2AR-mediated control of fear memory and underlying synaptic plasticity processes in the amygdala, paving the way to envisage CD73 as a new therapeutic target to interfere with abnormal fear-like emotional processing.

Vasopressin acts as a synapse organizer in limbic regions by boosting PSD95 and GluA1 expression

Hypothalamic arginine vasopressin (AVP)-containing magnocellular neurosecretory neurons (AVPMNN) emit collaterals to synaptically innervate limbic regions influencing learning, motivational behaviour, and fear responses. Here, we characterize the dynamics of expression changes of two key determinants for synaptic strength, the postsynaptic density (PSD) proteins AMPAR subunit GluA1 and PSD scaffolding protein 95 (PSD95), in response to in vivo manipulations of AVPMNN neuronal activation state, or exposure to exogenous AVP ex vivo. Both long-term water deprivation in vivo, which powerfully upregulates AVPMNN metabolic activity, and exogenous AVP application ex vivo, in brain slices, significantly increased GluA1 and PSD95 expression as measured by western blotting, in brain regions reportedly receiving direct ascending innervations from AVPMNN (i.e., ventral hippocampus, amygdala and lateral habenula). By contrast, the visual cortex, a region not observed to receive AVPMNN projections, showed no such changes. Ex vivo application of V1a and V1b antagonists to ventral hippocampal slices ablated the AVP stimulated increase in postsynaptic protein expression measured by western blotting. Using a modified expansion microscopy technique, we were able to quantitatively assess the significant augmentation of PSD95 and GLUA1 densities in subcellular compartments in locus coeruleus tyrosine hydroxylase immunopositive fibres, adjacent to AVP axon terminals. Our data strongly suggest that the AVPMNN ascending system plays a role in the regulation of the excitability of targeted neuronal circuits through upregulation of key postsynaptic density proteins corresponding to excitatory synapses.

The day I told Karim Nader, "Don't do the study"

Karim Nader changed the course of memory research by reviving interest in the mostly forgotten topic of post-retrieval manipulations of memory. In this paper I summarize the events leading up to his ground-breaking study in my lab on so-called memory reconsolidation, and the effects of that study on the field.

Hyperexcitability: From Normal Fear to Pathological Anxiety and Trauma

Hyperexcitability in fear circuits is suggested to be important for development of pathological anxiety and trauma from adaptive mechanisms of fear. Hyperexcitability is proposed to be due to acquired sensitization in fear circuits that progressively becomes more severe over time causing changing symptoms in early and late pathology. We use the metaphor and mechanisms of kindling to examine gains and losses in function of one excitatory and one inhibitory neuropeptide, corticotrophin releasing factor and somatostatin, respectively, to explore this sensitization hypothesis. We suggest amygdala kindling induced hyperexcitability, hyper-inhibition and loss of inhibition provide clues to mechanisms for hyperexcitability and progressive changes in function initiated by stress and trauma.

Action-Shapers and Their Neuro-Immunological Foundations

Not all our intentions translate into actions, as our capacity to act may be influenced by a variety of mental and biochemical factors. In this article, we present a comprehensive account of how neuro-immunological processes affect our intentional abilities and our capacity to act. We do so by extending the theory of thought-shapers (TTS) through the notion of action-shapers and combining this theory with the essential embodiment thesis (EE). This thesis about the mind-body relation says that human minds are necessarily and completely embodied. Action-shapers dynamically constitute the action-space of individuals, affecting their capacity to take action or to select one course of action over another. We highlight the effects and interactions of neuro-immunological effective processes in the body to demonstrate how they shape the action-space. In this article, we consider neuro-immunological effective processes that influence the gut-brain axis, chronic stress, high levels of sugar intake, the amygdala and the effects of prolonged stress. We investigate the effects of these processes on the perception and on the capacity to form intentions and act on them. We conclude the paper by providing a concise account of action-shapers, in which we attempt to summarize the line of argumentation and provide suggestions for further research.

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.

As soon as there was life, there was danger: the deep history of survival behaviours and the shallower history of consciousness

It is often said that fear is a universal innate emotion that we humans have inherited from our mammalian ancestors by virtue of having inherited conserved features of their nervous systems. Contrary to this common sense-based scientific point of view, I have argued that what we have inherited from our mammalian ancestors, and they from their distal vertebrate ancestors, and they from their chordate ancestors, and so forth, is not a fear circuit. It is, instead, a defensive survival circuit that detects threats, and in response, initiates defensive survival behaviours and supporting physiological adjustments. Seen in this light, the defensive survival circuits of humans and other mammals can be conceptualized as manifestations of an ancient survival function-the ability to detect danger and respond to it-that may in fact predate animals and their nervous systems, and perhaps may go back to the beginning of life. Fear, on the other hand, from my perspective, is a product of cortical cognitive circuits. This conception is not just of academic interest. It also has practical implications, offering clues as to why efforts to treat problems related to fear and anxiety are not more effective, and what might make them better. This article is part of the theme issue 'Systems neuroscience through the lens of evolutionary theory'.

Contextual Fear Memory Maintenance Changes Expression of pMAPK, BDNF and IBA-1 in the Pre-limbic Cortex in a Layer-Specific Manner

Post-traumatic stress disorder (PTSD) is a debilitating and chronic fear-based disorder. Pavlovian fear conditioning protocols have long been utilised to manipulate and study these fear-based disorders. Contextual fear conditioning (CFC) is a particular Pavlovian conditioning procedure that pairs fear with a particular context. Studies on the neural mechanisms underlying the development of contextual fear memories have identified the medial prefrontal cortex (mPFC), or more specifically, the pre-limbic cortex (PL) of the mPFC as essential for the expression of contextual fear. Despite this, little research has explored the role of the PL in contextual fear memory maintenance or examined the role of neuronal mitogen-activated protein kinase (pMAPK; ERK 1/2), brain-derived neurotrophic factor (BDNF), and IBA-1 in microglia in the PL as a function of Pavlovian fear conditioning. The current study was designed to evaluate how the maintenance of two different long-term contextual fear memories leads to changes in the number of immune-positive cells for two well-known markers of neural activity (phosphorylation of MAPK and BDNF) and microglia (IBA-1). Therefore, the current experiment is designed to assess the number of immune-positive pMAPK and BDNF cells, microglial number, and morphology in the PL following CFC. Specifically, 2 weeks following conditioning, pMAPK, BDNF, and microglia number and morphology were evaluated using well-validated antibodies and immunohistochemistry (n = 12 rats per group). A standard CFC protocol applied to rats led to increases in pMAPK, BDNF expression and microglia number as compared to control conditions. Rats in the unpaired fear conditioning (UFC) procedure, despite having equivalent levels of fear to context, did not have any change in pMAPK, BDNF expression and microglia number in the PL compared to the control conditions. These data suggest that alterations in the expression of pMAPK, BDNF, and microglia in the PL can occur for up to 2 weeks following CFC. Together the data suggest that MAPK, BDNF, and microglia within the PL of the mPFC may play a role in contextual fear memory maintenance.

Mechanisms of higher-order learning in the amygdala

Adaptive behaviour is under the potent control of environmental cues. Such cues can acquire value by virtue of their associations with outcomes of motivational significance, be they appetitive or aversive. There are at least two ways through which an environmental cue can acquire value, through first-order and higher-order conditioning. In first-order conditioning, a neutral cue is directly paired with an outcome of motivational significance. In higher-order conditioning, a cue is indirectly associated with motivational events via a directly conditioned first-order stimulus. The present article reviews some of the associations that support learning in first- and higher-order conditioning, as well as the role of the BLA and the molecular mechanisms involved in these two types of learning.

Physiological and Behavioral Mechanisms of Thermoregulation in Mammals

This review analyzes the main anatomical structures and neural pathways that allow the generation of autonomous and behavioral mechanisms that regulate body heat in mammals. The study of the hypothalamic neuromodulation of thermoregulation offers broad areas of opportunity with practical applications that are currently being strengthened by the availability of efficacious tools like infrared thermography (IRT). These areas could include the following: understanding the effect of climate change on behavior and productivity; analyzing the effects of exercise on animals involved in sporting activities; identifying the microvascular changes that occur in response to fear, pleasure, pain, and other situations that induce stress in animals; and examining thermoregulating behaviors. This research could contribute substantially to understanding the drastic modification of environments that have severe consequences for animals, such as loss of appetite, low productivity, neonatal hypothermia, and thermal shock, among others. Current knowledge of these physiological processes and complex anatomical structures, like the nervous systems and their close relation to mechanisms of thermoregulation, is still limited. The results of studies in fields like evolutionary neuroscience of thermoregulation show that we cannot yet objectively explain even processes that on the surface seem simple, including behavioral changes and the pathways and connections that trigger mechanisms like vasodilatation and panting. In addition, there is a need to clarify the connection between emotions and thermoregulation that increases the chances of survival of some organisms. An increasingly precise understanding of thermoregulation will allow us to design and apply practical methods in fields like animal science and clinical medicine without compromising levels of animal welfare. The results obtained should not only increase the chances of survival but also improve quality of life and animal production.

Forebrain GluN2A overexpression impairs fear extinction and NMDAR-dependent long-term depression in the lateral amygdala

N-methyl-d-aspartic acid receptor (NMDAR)-dependent synaptic plasticity at the thalamus-lateral amygdala (T-LA) synapses is related to acquisition and extinction of auditory fear memory. However, the roles of the NMDAR GluN2A subunit in acquisition and extinction of auditory fear memory as well as synaptic plasticity at T-LA synapses remain unclear. Here, using electrophysiologic, molecular biological techniques and behavioral methods, we found that the forebrain specific GluN2A overexpression transgenic (TG) mice exhibited normal acquisition but impaired extinction of auditory fear memory. In addition, in vitro electrophysiological data showed normal basal synaptic transmission and NMDAR-dependent long-term potentiation (LTP) at T-LA synapses, but deficit in NMDAR-dependent long-term depression (LTD) at T-LA synapses in GluN2A TG mice. Consistent with the reduced NMDAR-dependent LTD, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization was also weakened during NMDAR-dependent LTD in GluN2A TG mice. Taken together, our findings for the first time indicate that GluN2A overexpression impairs extinction of auditory fear memory and NMDAR-dependent LTD at T-LA synapses, which further confirms the close relationship between NMDAR-dependent LTD and fear extinction.

Rac1 Signaling in Amygdala Astrocytes Regulates Fear Memory Acquisition and Retrieval

The importance of astrocytes in behavior control is increasingly appreciated, but little is known about the effects of their dynamic activity in regulating learning and memory. In the present study, we constructed AAVs of photoactivatable and photoinactivatable Ras-related C3 botulinum toxin substrate 1 (Rac1) under the mGFAP promoter, which enabled the manipulation of Rac1 activity in astrocytes by optical stimulation in free-moving mice. We found that both up-regulation and down-regulation of astrocytic Rac1 activity in the basolateral amygdala (BLA) attenuated memory acquisition in a fear conditioning mouse model. Meanwhile, neuronal activation in the BLA induced by memory acquisition was inhibited under both the up- and down-regulation of astrocytic Rac1 activity during training. In terms of the impact on fear memory retrieval, we found both up- and down-regulation of BLA astrocytic Rac1 activity impaired memory retrieval of fear conditioning and memory retrieval-induced neuronal activation. Notably, the effect of astrocytic Rac1 on memory retrieval was reversible. Our results demonstrate that the normal activity of astrocytic Rac1 is necessary for the activation of neurons and memory formation. Both activation and inactivation of astrocytic Rac1 activity in the BLA reduced the excitability of neurons, and thereby impaired fear memory acquisition and retrieval.

The role of p21-activated kinase in maintaining the fear learning-induced modulation of excitation/inhibition ratio in lateral amygdala

We study the relations between different learning paradigms and enduring changes in excitatory synaptic transmission. Here we show that auditory fear conditioning (AFC), but not olfactory fear conditioning (OFC) training, led to enduring enhancement in AMPA-mediated miniature EPSCs (mEPSCs). Moreover, olfactory unpaired training led to a stable significant reduction in excitatory synaptic transmission. However, olfactory discrimination learning (OD) did not modulate postsynaptic AMPA-mediated mEPSCs in LA. The p21-activated kinase (PAK) activity, previously shown to have a key role in maintaining persistent long-lasting enhancement in synaptic inhibition after OFC, has an opposing effect on excitatory synaptic transmission. PAK maintained the level of excitatory synaptic transmission in the amygdala in all experimental groups, except in neurons in the OFC trained rats. PAK also maintained excitatory synaptic transmission in all neurons of auditory fear conditioning and naïve training groups except in neurons of the auditory safety learning. Safety learning was previously shown in our study to enhance synaptic inhibition. We thus suggest that PAK maintains inhibitory synaptic transmission in a learning-dependent manner and on the other hand affects excitatory synaptic transmission only in groups where learning has not affected inhibitory transmission. Thus, PAK controls learning-induced changes in the excitation/inhibition balance.

Astrocytes and Behavior

Animal behavior was classically considered to be determined exclusively by neuronal activity, whereas surrounding glial cells such as astrocytes played only supportive roles. However, astrocytes are as numerous as neurons in the mammalian brain, and current findings indicate a chemically based dialog between astrocytes and neurons. Activation of astrocytes by synaptically released neurotransmitters converges on regulating intracellular Ca²⁺ in astrocytes, which then can regulate the efficacy of near and distant tripartite synapses at diverse timescales through gliotransmitter release. Here, we discuss recent evidence on how diverse behaviors are impacted by this dialog. These recent findings support a paradigm shift in neuroscience, in which animal behavior does not result exclusively from neuronal activity but from the coordinated activity of both astrocytes and neurons. Decoding how astrocytes and neurons interact with each other in various brain circuits will be fundamental to fully understanding how behaviors originate and become dysregulated in disease.

Resilience to fear: The role of individual factors in amygdala response to stressors

Resilience to stress is an adaptive process that varies individually. Resilience refers to the adaptation, or the ability to maintain or regain mental health, despite being subject to adverse situation. Resilience is a dynamic concept that reflects a combination of internal individual factors, including age and gender interacting with external factors such as social, cultural and environmental factors. In the last decade, we have witnessed an increase in the prevalence of anxiety disorders, including post-traumatic stress disorder. Given that stress in unavoidable, it is of great interest to understand the neurophysiological mechanisms of resilience, the individual factors that may contribute to susceptibility and promote efficacious approaches to improve resilience. Here, we address this complex question, attempting at defining clear and operational definitions that may allow us to improve our analysis of behavior incorporating individuality. We examine how individual perception of the stressor can alter the outcome of an adverse situation using as an example, the fear-conditioning paradigm and discuss how individual differences in the reward system can contribute to resilience. Given the central role of the endocannabinoid system in regulating fear responses and anxiety, we discuss the evidence that polymorphisms in several molecules of this signaling system contribute to different anxiety phenotypes. The endocannabinoid system is highly interconnected with the serotoninergic and dopaminergic modulatory systems, contributing to individual differences in stress perception and coping mechanisms. We review how the individual variability in these modulatory systems can be used towards a multivariable assessment of stress risk. Incorporating individuality in our research will allow us to define biomarkers of anxiety disorders as well as assess prognosis, towards a personalized clinical approach to mental health.

Cell-type specific knockout of peptidylglycine α-amidating monooxygenase reveals specific behavioral roles in excitatory forebrain neurons and cardiomyocytes

Neuropeptides and peptide hormones play a crucial role in integrating the many factors that affect physiologic and cognitive processes. The potency of many of these peptides requires an amidated amino acid at the C-terminus; a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), catalyzes this modification. Anxiety-like behavior is known to be altered in mice with a single functional Pam allele (Pam^+/- ) and in mice unable to express Pam in excitatory forebrain neurons (Pam^Emx1-cKO/cKO ) or in cardiomyocytes (Pam^Myh6-cKO/cKO ). Examination of PAM-positive and glutamic acid decarboxylase 67 (GAD)-positive cells in the amygdala of Pam^Emx1-cKO/cKO mice demonstrated the absence of PAM in pyramidal neurons and its continued presence in GAD-positive interneurons, suggestive of altered excitatory/inhibitory balance. Additional behavioral tests were used to search for functional alterations in these cell-type specific knockout mice. Pam^Emx1-cKO/cKO mice exhibited a less focused search pattern for the Barnes Maze escape hole than control or Pam^Myh6-cKO/cKO mice. While wildtype mice favor interacting with novel objects as opposed to familiar objects, both Pam^Emx1-cKO/cKO and Pam^Myh6-cKO/cKO mice exhibited significantly less interest in the novel object. Since PAM levels in the central nervous system of Pam^Myh6-cKO/cKO mice are unaltered, the behavioral effect observed in these mice may reflect their inability to produce atrial granules and the resulting reduction in serum levels of atrial natriuretic peptide. In the sociability test, male mice of all three genotypes spent more time with same-sex stranger mice; while control females showed no preference for stranger mice, female Pam^Emx1-cKO/cKO mice showed preference for same-sex stranger mice in all trials.

Neurotrophin signalling in amygdala-dependent cued fear learning

The amygdala is a central hub for fear learning assessed by Pavlovian fear conditioning. Indeed, the prevailing hypothesis that learning and memory are mediated by changes in synaptic strength was shown most convincingly at thalamic and cortical afferents to the lateral amygdala. The neurotrophin brain-derived neurotrophic factor (BDNF) is known to regulate synaptic plasticity and memory formation in many areas of the mammalian brain including the amygdala, where BDNF signalling via tropomyosin-related kinase B (TrkB) receptors is prominently involved in fear learning. This review updates the current understanding of BDNF/TrkB signalling in the amygdala related to fear learning and extinction. In addition, actions of proBDNF/p75NTR and NGF/TrkA as well as NT-3/TrkC signalling in the amygdala are introduced.

An emotional-response model of bipolar disorders integrating recent findings on amygdala circuits

Because of our classification system limitations for defining psychiatric disorders and understanding their physiopathology, a new research area based on dimensions has emerged. It consists of exploring domains derived from fundamental behavioral components linked to neurobiological systems. Emotional processing is among the most affected dimensions in bipolar disorders (BD), but is excluded from the definition criteria. The purpose of this review is to synthesize the emotional responses disruption during the different phases of BD, using intensity and valence as the two key characteristics of emotions. We integrate those emotional disruptions into an original, emotion-based model contrasting with the current diagnostic frame built on mood. Emotional processing is underpinned by cortico-limbic circuits involving the amygdala. Recent publications showed the crucial role of the amygdala in emotional processes triggered by stimuli of negative, but also positive valence. We show how these neuroscience data can provide physiological basis for emotional disturbances observed in BD. We conclude with translational perspectives to improve the current knowledge about neural substrates underlying altered emotional responses characterizing BD.

MAP/ERK Signaling in Developing Cognitive and Emotional Function and Its Effect on Pathological and Neurodegenerative Processes

The signaling pathway of the microtubule-associated protein kinase or extracellular regulated kinase (MAPK/ERK) is a common mechanism of extracellular information transduction from extracellular stimuli to the intracellular space. The transduction of information leads to changes in the ongoing metabolic pathways and the modification of gene expression patterns. In the central nervous system, ERK is expressed ubiquitously, both temporally and spatially. As for the temporal ubiquity, this signaling system participates in three key moments: (i) Embryonic development; (ii) the early postnatal period; and iii) adulthood. During embryonic development, the system is partly responsible for the patterning of segmentation in the encephalic vesicle through the FGF8-ERK pathway. In addition, during this period, ERK directs neurogenesis migration and the final fate of neural progenitors. During the early postnatal period, ERK participates in the maturation process of dendritic trees and synaptogenesis. During adulthood, ERK participates in social and emotional behavior and memory processes, including long-term potentiation. Alterations in mechanisms related to ERK are associated with different pathological outcomes. Genetic alterations in any component of the ERK pathway result in pathologies associated with neural crest derivatives and mental dysfunctions associated with autism spectrum disorders. The MAP-ERK pathway is a key element of the neuroinflammatory pathway triggered by glial cells during the development of neurodegenerative diseases, such as Parkinson's and Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis, as well as prionic diseases. The process triggered by MAPK/ERK activation depends on the stage of development (mature or senescence), the type of cellular element in which the pathway is activated, and the anatomic neural structure. However, extensive gaps exist with regards to the targets of the phosphorylated ERK in many of these processes.

Morphological changes in subregions of hippocampus and amygdala in major depressive disorder patients

Despite many neuroimaging studies in the past years, the neuroanatomical substrates of major depressive disorder (MDD) subcortical structures are still not well understood. Since hippocampus and amygdala are the two vital subcortical structures that most susceptible to MDD, finding the evidence of morphological changes in their subregions may bring some new insights for MDD research. Combining structural magnetic resonance imaging (MRI) with novel morphometry analysis methods, we recruited 25 MDD patients and 28 healthy controls (HC), and investigated their volume and morphological differences in hippocampus and amygdala. Relative to volumetric method, our methods detected more significant global morphological atrophies (p<0.05). More precisely, subiculum and cornu ammonis (CA) 1 subregions of bilateral hippocampus, lateral (LA) and basolateral ventromedial (BLVM) of left amygdala and LA, BLVM, central (CE), amygdalostriatal transition area (ASTR), anterior cortical (ACO) and anterior amygdaloid area (AAA) of right amygdala were demonstrated prone to atrophy. Correlation analyses between each subject's surface eigenvalues and Hamilton Depression Scale (HAMD) were then performed. Correlation results showed that atrophy areas in hippocampus and amygdala have slight tendencies of expanding into other subregions with the development of MDD. Finally, we performed group morphometric analysis and drew the atrophy and expansion areas between MDD-Medicated group (only 19 medicated subjects in MDD group were included) and HC group, found some preliminary evidence about subregional morphological resilience of hippocampus and amygdala. These findings revealed new pathophysiologic patterns in the subregions of hippocampus and amygdala, which can help with subsequent smaller-scale MDD research.

From Isolated Emotional Memories to Their Competition During Conflict

Aversive or rewarding experiences are remembered better than those of lesser survival significance. These emotional memories, whether negative or positive, leave traces in the brain which can later be retrieved and strongly influence how we perceive, how we form associations with environmental stimuli and, ultimately, guide our decision-making. In this review aticle, we outline what constitutes an emotional memory by focusing on threat- and reward-related memories and describe how they are formed in the brain during learning and reformed during retrieval. Finally, we discuss how the field is moving from understanding emotional memory brain circuits separately, towards studying how these two opposing brain systems interact to guide choices during conflict. Here, we outline two novel tasks in rodents that model opposing binary choices (approach or avoid) guided by competing emotional memories. The prefrontal cortex (PFC) is a major integration hub of emotional information which is also known to be critical for decision-making. Consequently, brain circuits that involve this brain region may be key for understanding how the retrieval of emotional memories flexibly orchestrates adaptive choice behavior. Because several mental disorders (e.g., drug addiction and depression) are characterized by deficits in decision-making in the face of conflicting emotional memories (maladaptively giving more weight to one memory over the other), the development of choice-based animal models for emotional regulation could give rise to new approaches for the treatment of these disorders in humans.

Corticotropin-Releasing Factor Receptor-1 Neurons in the Lateral Amygdala Display Selective Sensitivity to Acute and Chronic Ethanol Exposure

The lateral amygdala (LA) serves as the point of entry for sensory information within the amygdala complex, a structure that plays a critical role in emotional processes and has been implicated in alcohol use disorders. Within the amygdala, the corticotropin-releasing factor (CRF) system has been shown to mediate some of the effects of both stress and ethanol, but the effects of ethanol on specific CRF1 receptor circuits in the amygdala have not been fully established. We used male CRF1:GFP reporter mice to characterize CRF1-expressing (CRF1+) and nonexpressing (CRF1-) LA neurons and investigate the effects of acute and chronic ethanol exposure on these populations. The CRF1+ population was found to be composed predominantly of glutamatergic projection neurons with a minority subpopulation of interneurons. CRF1+ neurons exhibited a tonic conductance that was insensitive to acute ethanol. CRF1- neurons did not display a basal tonic conductance, but the application of acute ethanol induced a δ GABAA receptor subunit-dependent tonic conductance and enhanced phasic GABA release onto these cells. Chronic ethanol increased CRF1+ neuronal excitability but did not significantly alter phasic or tonic GABA signaling in either CRF1+ or CRF1- cells. Chronic ethanol and withdrawal also did not alter basal extracellular GABA or glutamate transmitter levels in the LA/BLA and did not alter the sensitivity of GABA or glutamate to acute ethanol-induced increases in transmitter release. Together, these results provide the first characterization of the CRF1+ population of LA neurons and suggest mechanisms for differential acute ethanol sensitivity within this region.

Efficacy of Long-Term Feeding of α-Glycerophosphocholine for Aging-Related Phenomena in Old Mice

α-Glycerophosphocholine (GPC) is a natural source of choline. It reportedly prevents aging-related decline in cognitive function, but the underlying mechanism remains unclear. Although it is understood that aging influences taste sensitivity and energy regulation, whether GPC exerts antiaging effects on such phenomena requires further elucidation. Here, we used old C57BL/6J mice that were fed a GPC-containing diet, to investigate the molecular mechanisms underlying the prevention of a decline in cognitive function associated with aging and examine the beneficial effects of GPC intake on aging-related phenomena, such as taste sensitivity and energy regulation. We confirmed that GPC intake reduces the aging-related decline in the expression levels of genes related to long-term potentiation. Although we did not observe an improvement in aging-related decline in taste sensitivity, there was a notable improvement in the expression levels of β-oxidation-associated genes in old mice. Our results suggest that the prevention of aging-related decline in cognitive function by GPC intake may be associated with the improvement of gene expression levels of long-term potentiation. Furthermore, GPC intake may positively influence lipid metabolism.

Learning-induced enduring changes in inhibitory synaptic transmission in lateral amygdala are mediated by p21-activated kinase

In this study we explored whether learning leads to enduring changes in inhibitory synaptic transmission in lateral amygdala (LA). We revealed that olfactory discrimination (OD) learning in rats led to a long-lasting increase in postsynaptic GABAA channel-mediated miniature inhibitory postsynaptic currents (mIPSCs) in LA. Olfactory fear conditioning, but not auditory fear conditioning, also led to enduring enhancement in GABAA-mediated mIPSCs. Auditory fear conditioning, but not olfactory fear conditioning or OD learning, induced an enduring reduction in the frequency but not the current of mIPSC events. We found that p21-activated kinase (PAK) activity is needed to maintain OD and olfactory fear conditioning learning-induced enduring enhancement of mIPSCs. Further analysis revealed that OD led to an increase in GABAA channel conductance whereas olfactory fear conditioning increased the number of GABAA channels. These alterations in GABAA channels conductance and level are controlled by PAK activity. Our study shows that the learning-induced increase in postsynaptic inhibitory transmission in LA is specific to the sensory modality. However, the mechanism that mediates the increase in inhibitory transmission, namely the increase in the conductance or in the level of GABAA channel, is learning specific.

NEW & NOTEWORTHY Here we studied whether learning leads to long-lasting alterations in inhibitory synaptic transmission in lateral amygdala (LA). We revealed that learning led to enduring changes in inhibitory synaptic transmission in LA that are affected by the sensory modality (auditory or olfaction) used during learning. However, the mechanism that mediated the changes in inhibitory transmission (alterations in GABAA channel level or conductance) depended on the type of learning. These long-lasting alterations are maintained by p21-activated kinase.

Role of Emotional Appraisal in Episodic Memory in a Sample of Argentinean Preschoolers

Emotional processing and episodic memory are closely related throughout childhood development. With respect to emotional episodic memory, available evidence shows that the consolidation of information is accompanied by an arousal that generates longer duration and persistence of the memory representations. In the case of early stages of development (i.e., first 5 years), it is less clear how these associations emerge and are modulated by individual and environmental factors. In this study, 116 4- to 5-years old Argentinean children from different socio-environmental contexts (i.e., favorable or unfavorable living conditions at home), performed a task of visual emotional memory in which they observed a set of 15 images with variable emotional valences (negative, neutral, and positive). The child’s task was to appraise each image using one of the following three possible valences: (a) drawings of faces with smiles (positive valence), (b) drawings of faces with tears and round mouth with edges down (negative valence), or (c) drawings of faces with horizontal mouth (neutral valence). Five years-old children exhibited greater accuracy appraisal. Individual differences in emotional accuracy appraisal allowed us to observe different performances in free recall of negative visual images. Accuracy appraisal did not vary between children with respect to gender, living conditions at home, or language ability. Seven to ten days after the emotional appraisal children were asked to tell the experimenter all the images they remembered (variables of interest: free recall of negative, positive, or neutral images). Results showed individual (age) differences. Specifically, 5-years-old children evoked more images than 4-years-old children. These findings contribute to the understanding of emotional memory in early developmental stages and raise the need to include emotional appraisal in the assessment of episodic memory.

Evidence that a defined population of neurons in lateral amygdala is directly involved in auditory fear learning and memory

Memory is thought to be encoded within networks of neurons within the brain, but the identity of the neurons involved and circuits they form have not been described for any memory. Previously, we used fos-tau-lacZ (FTL) transgenic mice to identify discrete populations of neurons in different regions of the brain which were specifically activated following fear conditioning. This suggested that these populations of neurons form nodes in a network that encodes fear memory. In particular, one population of learning activated neurons was found within a discrete region of the lateral amygdala (LA), a key nucleus required for fear conditioning. In order to provide evidence that this population is directly involved in fear conditioning, we have analysed the expression of a key molecular requirement for fear conditioning in LA, phosphorylated Extracellular Signal Regulated Kinase 1 and 2 (pERK1/2). The only neurons in LA that specifically expressed pERK1/2 following auditory fear conditioning were in the ventrolateral nucleus of the LA (LAvl), in the same discrete region where we found learning specific FTL⁺ neurons. Double labelling experiments in FTL mice showed that a substantial proportion of the learning activated neurons expressed both pERK1/2 and FTL. These experiments provide clear evidence that the learning specific neurons we identified within LAvl are directly involved in auditory fear conditioning. In addition, learning specific expression of pERK1/2 was found in a dense network of dendrites contained within the border region of the LAvl. This network of dendrites may represent an activated dendritic field involved in fear conditioning in LA.

Activation of EphB2 Forward Signaling Enhances Memory Consolidation

EphB2 is involved in enhancing synaptic transmission and gene expression. To explore the roles of EphB2 in memory formation and enhancement, we used a photoactivatable EphB2 (optoEphB2) to activate EphB2 forward signaling in pyramidal neurons in lateral amygdala (LA). Photoactivation of optoEphB2 during fear conditioning, but not minutes afterward, enhanced long-term, but not short-term, auditory fear conditioning. Photoactivation of optoEphB2 during fear conditioning led to activation of the cAMP/Ca²⁺ responsive element binding (CREB) protein. Application of light to a kinase-dead optoEphB2 in LA did not lead to enhancement of long-term fear conditioning memory or to activation of CREB. Long-term, but not short-term, auditory fear conditioning memory was impaired in mice lacking EphB2 forward signaling (EphB2^lacZ/lacZ). Activation of optoEphB2 in LA of EphB2^lacZ/lacZ mice enhanced long-term fear conditioning memory. The present findings show that the level of EphB2 forward signaling activity during learning determines the strength of long-term memory consolidation.