Role of the basolateral amygdala in memory consolidation

Identification of a stress-responsive subregion of the basolateral amygdala in male rats

The basolateral amygdala (BLA) is reliably activated by psychological stress and hyperactive in conditions of pathological stress or trauma; however, subsets of BLA neurons are also readily activated by rewarding stimuli and can suppress fear and avoidance behaviours. The BLA is highly heterogeneous anatomically, exhibiting continuous molecular and connectivity gradients throughout the entire structure. A critical gap remains in understanding the anatomical specificity of amygdala subregions, circuits, and cell types explicitly activated by acute stress and how they are dynamically activated throughout stimulus exposure. Using a combination of topographical mapping for the activity-responsive protein FOS and fiber photometry to measure calcium transients in real-time, we sought to characterize the spatial and temporal patterns of BLA activation in response to a range of novel stressors (shock, swim, restraint, predator odour) and non-aversive, but novel stimuli (crackers, citral odour). We report four main findings: (1) the BLA exhibits clear spatial activation gradients in response to novel stimuli throughout the medial-lateral and dorsal-ventral axes, with aversive stimuli strongly biasing activation towards medial aspects of the BLA; (2) novel stimuli elicit distinct temporal activation patterns, with stressful stimuli exhibiting particularly enhanced or prolonged temporal activation patterns; (3) changes in BLA activity are associated with changes in behavioural state; and (4) norepinephrine enhances stress-induced activation of BLA neurons via the ß-noradrenergic receptor. Moving forward, it will be imperative to combine our understanding of activation gradients with molecular and circuit-specificity.

Beyond the hippocampus: Amygdala and memory functioning in older adults

BACKGROUND

Medial temporal lobe atrophy has been linked to decline in neuropsychological measures of explicit memory function. While the hippocampus has long been identified as a critical structure in learning and memory processes, less is known about contributions of the amygdala to these functions. We sought to investigate the relationship between amygdala volume and memory functioning in a clinical sample of older adults with and without cognitive impairment.

METHODS

A serial clinical sample of older adults that underwent neuropsychological assessment at an outpatient neurology clinic was selected for retrospective chart review. Patients were included in the study if they completed a comprehensive neuropsychological assessment within six months of a structural magnetic resonance imaging scan. Regional brain volumes were quantified using Neuroreader® software. Associations between bilateral hippocampal and amygdala volumes and memory scores, derived from immediate and delayed recall conditions of a verbal story learning task and a visual design reconstruction task, were examined using mixed-effects general linear models, controlling for total intracranial volume, scanner model, age, sex and education. Partial correlation coefficients, adjusted for these covariates, were calculated to estimate the strength of the association between volumes and memory scores.

RESULTS

A total of 68 (39 F, 29 M) participants were included in the analyses, with a mean (SD) adjusted age of 80.1 (6.0) and educational level of 15.9 (2.5) years. Controlling for age, sex, education, and total intracranial volume, greater amygdala volumes were associated with better verbal and visual memory performance, with effect sizes comparable to hippocampal volume. No significant lateralized effects were observed. Partial correlation coefficients ranged from 0.47 to 0.33 (p<.001).

CONCLUSION

These findings contribute to a growing body of knowledge identifying the amygdala as a target for further research in memory functioning. This highlights the importance of considering the broader functioning of the limbic system in which multiple subcortical structures contribute to memory processes and decline in older adults.

Knowledge mapping of the relationship between norepinephrine and memory: a bibliometric analysis

Introduction

Memory is a fundamental cognitive function for successful interactions with a complex environment. Norepinephrine (NE) is an essential component of catecholamine induced by emotional arousal, and numerous studies have demonstrated that NE is a key regulator in memory enhancement. We therefore conducted a bibliometric analysis to represent the knowledge pattern of the literature on the theme of NE-memory relationship.

Methods

The WOSCC database was selected to extract literature published during 2003-2022. The collected data of annual production, global cooperation, research structure and hotspots were analyzed and visualized.

Results

Our results showed that research on the links between NE and memory displayed a considerable development trend over the last two decades. The USA had a leading position in terms of scientific outputs and collaborations. Meanwhile, University of California Irvine contributed the most publications. Benno Roozendaal and James McGaugh were the most prolific authors in this field, and Neurobiology of Learning and Memory had the highest number of publications on this topic. The research emphasis has evolved from memory-related diseases and brain regions to neural mechanisms for different types of memory at neural circuit levels.

Conclusion

Our bibliometric analysis systematically analyzed the literature on the links between NE and memory from a bibliometric perspective. The demonstrated results of the knowledge mapping would provide valuable insights into the global research landscape.

Increased inhibitory activity in the basolateral amygdala and decreased anxiety during estrus: A potential role for ASIC1a channels

The amygdala is central to emotional behavior, and the excitability level of the basolateral nucleus of the amygdala (BLA) is associated with the level of anxiety. The excitability of neuronal networks is significantly controlled by GABAergic inhibition. Here, we investigated whether GABAergic inhibition in the BLA is altered during the rat estrous cycle. In rat amygdala slices, most principal BLA neurons display spontaneous IPSCs (sIPSCs) in the form of "bursts" of inhibitory currents, occurring rhythmically at a frequency of about 0.5 Hz. The percentage of BLA neurons displaying sIPSC bursts, along with the inhibitory charge transferred by sIPSCs and the frequency of sIPSC bursts, were significantly increased during the estrus phase; increased inhibition was accompanied by reduced anxiety in the open field, the light-dark box, and the acoustic startle response tests. sIPSC bursts were blocked by ibuprofen, an antagonist of acid-sensing-1a channels (ASIC1a), whose activity is known to increase by decreasing temperature. A transient reduction in the temperature of the slice medium, strengthened the sIPSCs bursts; this effect was blocked in the presence of ibuprofen. Further analysis of the sIPSC bursts during estrus showed significantly stronger rhythmic inhibitory activity in early estrus, when body temperature drops, compared with late estrus. To the extent that these results may relate to humans, it is suggested that "a calmer amygdala" due to increased inhibitory activity may underlie the positive affect in women around ovulation time. ASIC1a may contribute to increased inhibition, with their activity facilitated by the body-temperature drop preceding ovulation.

Dissociation and false memory: the moderating role of trauma and cognitive ability

The term dissociation is often used to refer to a diverse range of psychological symptoms, including perceptual impairments, emotional detachment, and memory fragmentation. In the present study, we examined whether there was a relation between participants' self-reports of dissociative experiences and their memory performance in the Deese-Roediger-McDermott (DRM) paradigm-a laboratory-based procedure that is frequently used to investigate false memory. University students (N = 298) completed the Dissociative Experiences Scale (DES) and the Traumatic Life Events Questionnaire (TLEQ). Participants were also administered a standardised intelligence test (Shipley-2), and they were tested in the DRM paradigm. Overall, experiencing trauma and dissociation, as well as lower levels of cognitive ability, were associated with higher false memory. These findings are discussed in the context of the activation monitoring theory of DRM false memory.

The nucleus reuniens, a thalamic relay for cortico-hippocampal interaction in recent and remote memory consolidation

The consolidation of declarative memories is believed to occur mostly during sleep and involves a dialogue between two brain regions, the hippocampus and the medial prefrontal cortex. The information encoded during experience by neuronal assemblies is replayed during sleep leading to the progressive strengthening and integration of the memory trace in the prefrontal cortex. The gradual transfer of information from the hippocampus to the medial prefrontal cortex for long-term storage requires the synchronization of cortico-hippocampal networks by different oscillations, like ripples, spindles, and slow oscillations. Recent studies suggest the involvement of a third partner, the nucleus reuniens, in memory consolidation. Its bidirectional connections with the hippocampus and medial prefrontal cortex place the reuniens in a key position to relay information between the two structures. Indeed, many topical works reveal the original role that the nucleus reuniens occupies in different recent and remote memories consolidation. This review aimed to examine these contributions, as well as its functional embedment in this complex memory network, and provide some insights on the possible mechanisms.

Dynamic behavior of the locus coeruleus during arousal-related memory processing in a multi-modal 7T fMRI paradigm

A body of animal and human evidence points to the norepinephrine (NE) locus coeruleus (LC) system in modulating memory for arousing experiences, but whether the LC would recast its role along memory stages remains unknown. Sedation precluded examination of LC dynamics during memory processing in animals. Here, we addressed the contribution of the LC during arousal-associated memory processing through a unique combination of dedicated ultra-high-field LC-imaging methods, a well-established emotional memory task, online physiological and saliva alpha-amylase measurements in young adults. Arousal-related LC activation followed amygdala engagement during encoding. During consolidation and recollection, activation transitioned to hippocampal involvement, reflecting learning and model updating. NE-LC activation is dynamic, plays an arousal-controlling role, and is not sufficient but requires interactions with the amygdala to form adaptive memories of emotional experiences. These findings have implications for understanding contributions of LC dysregulation to disruptions in emotional memory formation, observed in psychiatric and neurocognitive disorders.

The protective effect of alpha lipoic acid (ALA) on social interaction memory, but not passive avoidance in sleep-deprived rats

Sleep is involved in maintaining energy, regulating heat, and recovering tissues. Furthermore, proper cognitive functions need sufficient sleep. Many studies have revealed the impairment effect of sleep deprivation (SD) on cognitive functions including learning and memory. Alpha lipoic acid (ALA) is a potent free radical scavenger, biological antioxidant, and neuroprotective agent. Furthermore, ALA improves learning and memory performance, decreases oxidative stress, and enhances antioxidant biomarkers. In this study, we aimed to investigate the effect of ALA on social interaction and passive avoidance memories in sleep-deprived rats. Total sleep deprivation (TSD) apparatus was used to induce SD (for 24 h). Three-chamber paradigm test and shuttle box apparatus were used to evaluate social interaction and passive avoidance memory, respectively. Rats' locomotor apparatus was used to assess locomotion. ALA was administered intraperitoneally at doses of 17 and 35 mg/kg for 3 consecutive days. The results showed SD impaired both types of memories. ALA at the dose of 35 mg/kg restored social interaction memory in sleep-deprived rats; while, at the dose of 17 mg/kg attenuated impairment effect of SD. Moreover, ALA at the dose of 35 mg/kg impaired passive avoidance memory in sham-SD rats and at both doses did not rescue passive avoidance memory in sleep-deprived rats. In conclusion, ALA showed impairment effect on passive avoidance memory, while improved social interaction memory in sleep-deprived rats.

Amphetamine and the Smart Drug 3,4-Methylenedioxypyrovalerone (MDPV) Induce Generalization of Fear Memory in Rats

Human studies have consistently shown that drugs of abuse affect memory function. The psychostimulants amphetamine and the "bath salt" 3,4-methylenedioxypyrovalerone (MDPV) increase brain monoamine levels through a similar, yet not identical, mechanism of action. Findings indicate that amphetamine enhances the consolidation of memory for emotional experiences, but still MDPV effects on memory function are underinvestigated. Here, we tested the effects induced by these two drugs on generalization of fear memory and their relative neurobiological underpinnings. To this aim, we used a modified version of the classical inhibitory avoidance task, termed inhibitory avoidance discrimination task. According to such procedure, adult male Sprague-Dawley rats were first exposed to one inhibitory avoidance apparatus and, with a 1-min delay, to a second apparatus where they received an inescapable footshock. Forty-eight hours later, retention latencies were tested, in a randomized order, in the two training apparatuses as well as in a novel contextually modified apparatus to assess both strength and generalization of memory. Our results indicated that both amphetamine and MDPV induced generalization of fear memory, whereas only amphetamine enhanced memory strength. Co-administration of the β-adrenoceptor antagonist propranolol prevented the effects of both amphetamine and MDPV on the strength and generalization of memory. The dopaminergic receptor blocker cis-flupenthixol selectively reversed the amphetamine effect on memory generalization. These findings indicate that amphetamine and MDPV induce generalization of fear memory through different modulations of noradrenergic and dopaminergic neurotransmission.

Developmental changes in plasticity, synaptic, glia, and connectivity protein levels in rat basolateral amygdala

The basolateral complex of amygdala (BLA) processes emotionally arousing aversive and rewarding experiences. The BLA is critical for acquisition and storage of threat-based memories and the modulation of the consolidation of arousing explicit memories, that is, the memories that are encoded and stored by the medial temporal lobe. In addition, in conjunction with the medial prefrontal cortex (mPFC), the BLA plays an important role in fear memory extinction. The BLA develops relatively early in life, but little is known about the molecular changes that accompany its development. Here, we quantified relative basal expression levels of sets of plasticity, synaptic, glia, and connectivity proteins in the rat BLA at various developmental ages: postnatal day 17 (PN17, infants), PN24 (juveniles), and PN80 (young adults). We found that the levels of activation markers of brain plasticity, including phosphorylation of CREB at Ser133, CamKIIα at Thr286, pERK1/pERK2 at Thr202/Tyr204, and GluA1 at Ser831 and Ser845, were significantly higher in infant and juvenile compared with adult brain. In contrast, age increase was accompanied by a significant augmentation in the levels of proteins that mark synaptogenesis and synapse maturation, such as synaptophysin, PSD95, SynCAM, GAD65, GAD67, and GluN2A/GluN2B ratio. Finally, we observed significant age-associated changes in structural markers, including MAP2, MBP, and MAG, suggesting that the structural connectivity of the BLA increases over time. The biological differences in the BLA between developmental ages compared with adulthood suggest the need for caution in extrapolating conclusions based on BLA-related brain plasticity and behavioral studies conducted at different developmental stages.

Neurophysiology of threat processing bias in combat-related post-traumatic stress disorder

Post‐traumatic stress disorder (PTSD) is a debilitating condition that may develop after experiencing a traumatic event. Combat exposure increases an individual's chance of developing PTSD, making veterans especially susceptible to the disorder. PTSD is characterized by dysregulated emotional networks, memory deficits, and a hyperattentive response to perceived threatening stimuli. Recently, there have been a number of imaging studies that show structural and functional abnormalities associated with PTSD; however, there have been few studies utilizing electroencephalography (EEG). The goal of this study was to characterize **EEG brain dynamics in individuals with PTSD, in order to better understand the neurophysiological underpinnings of some of the salient features of PTSD, such as threat‐processing bias. Veterans of Operation Enduring Freedom/Iraqi Freedom completed an implicit visual threat semantic memory recognition task with stimuli that varied on both category (animals, items, nature, and people) and feature (threatening and nonthreatening) membership, including trauma‐related stimuli. Combat veterans with PTSD had slower reaction times for the threatening stimuli relative to the combat veterans without PTSD (VETC). There were trauma‐specific effects in frontal regions, with theta band EEG power reductions for the threatening combat scenes in the PTSD patients compared to the VETC group. Additionally, a moderate negative correlation was observed between trauma‐specific frontal theta power and hyperarousal symptoms as measured by clinically administered PTSD scale. These findings complement and extend current models of cortico‐limbic dysfunction in PTSD. The moderate negative correlation between frontal theta power and hyperarousal endorsements suggests the utility of these measures as therapeutic markers of symptomatology in PTSD patients.

Inactivation of the interpositus nucleus blocks the acquisition of conditioned responses and timing changes in conditioning-specific reflex modification of the rabbit eyeblink response

Conditioning-specific reflex modification (CRM) of the rabbit eyeblink response is an associative phenomenon characterized by increases in the frequency, size, and peak latency of the reflexive unconditioned eyeblink response (UR) when the periorbital shock unconditioned stimulus (US) is presented alone following conditioning, particularly to lower intensity USs that produced minimal responding prior to conditioning. Previous work has shown that CRM shares many commonalities with the conditioned eyeblink response (CR) including a similar response topography, suggesting the two may share similar neural substrates. The following study examined the hypothesis that the interpositus nucleus (IP) of the cerebellum, an essential part of the neural circuitry of eyeblink conditioning, is also required for the acquisition of CRM. Tests for CRM occurred following delay conditioning under muscimol inactivation of the IP and also after additional conditioning without IP inactivation. Results showed that IP inactivation blocked acquisition of CRs and the timing aspect of CRM but did not prevent increases in UR amplitude and area. Following the cessation of inactivation, CRs and CRM latency changes developed similarly to controls with intact IP functioning, but with some indication that CRs may have been facilitated in muscimol rabbits. In conclusion, CRM timing and CRs both likely require the development of plasticity in the IP, but other associative UR changes may involve non-cerebellar structures interacting with the eyeblink conditioning circuitry, a strong candidate being the amygdala, which is also likely involved in the facilitation of conditioning. Other candidates worth consideration include the cerebellar cortex, prefrontal and motor cortices.

Basolateral Amygdala Inputs to the Medial Entorhinal Cortex Selectively Modulate the Consolidation of Spatial and Contextual Learning

Although evidence suggests that the basolateral amygdala (BLA) and dorsal hippocampus (DH) work together to influence the consolidation of spatial/contextual learning, the circuit mechanism by which the BLA selectively modulates spatial/contextual memory consolidation is not clear. The medial entorhinal cortex (mEC) is a critical region in the hippocampus-based system for processing spatial information. As an efferent target of the BLA, the mEC is a candidate by which the BLA influences the consolidation of such learning. To address several questions regarding this issue, male Sprague Dawley rats received optogenetic manipulations of different BLA afferents immediately after training in different learning tasks. Optogenetic stimulation of the BLA-mEC pathway using ChR2(E123A) after spatial and cued-response Barnes maze training enhanced and impaired retention, respectively, whereas optical inhibition of the pathway using eNpHR3.0 produced trends in the opposite direction. Similar stimulation of the BLA-posterior dorsal striatum pathway had no effect. BLA-mEC stimulation also selectively enhanced retention for the contextual, but not foot shock, component of a modified contextual fear-conditioning procedure. In both sets of experiments, only stimulation using bursts of 8 Hz light pulses significantly enhanced retention, suggesting the importance of driving activity in this frequency range. An 8 Hz stimulation of the BLA-mEC pathway increased local field potential power in the same frequency range in the mEC and in the DH. Together, the present findings suggest that the BLA modulates the consolidation of spatial/contextual memory via projections to the mEC and that activity within the 8 Hz range is critical for this modulation.SIGNIFICANCE STATEMENT The mechanism by which the basolateral amygdala (BLA) influences the consolidation of spatial/contextual memory is unknown. Using an optogenetic approach with multiple behavioral procedures, we found that immediate posttraining 8 Hz stimulation of BLA projections to the medial entorhinal cortex (mEC) enhanced retention for spatial/contextual memory, impaired retention for cued-response memory, and had no effect on foot shock learning for contextual fear conditioning. Electrophysiological recordings confirmed that 8 Hz stimulation of this pathway increased activity in the 8 Hz range in the mEC and in the dorsal hippocampus, a region critical for spatial memory consolidation. This suggests that coordinated BLA activity with downstream regions in the 8 Hz activity range immediately after training is important for consolidation of multiple memory forms.

Oscillatory Synchronous Inhibition in the Basolateral Amygdala and its Primary Dependence on NR2A-containing NMDA Receptors

Synchronous, rhythmic firing of GABAergic interneurons is a fundamental mechanism underlying the generation of brain oscillations, and evidence suggests that NMDA receptors (NMDARs) play a key role in oscillatory activity by regulating the activity of interneurons. Consistent with this, derangement of brain rhythms in certain neuropsychiatric disorders, notably schizophrenia and autism, is associated with NMDAR hypofunction and loss of inhibitory interneurons. In the basolateral amygdala (BLA)-dysfunction of which is involved in a host of neuropsychiatric diseases-, principal neurons display spontaneous, rhythmic "bursts" of inhibitory activity, which could potentially be involved in the orchestration of oscillations in the BLA network; here, we investigated the role of NMDARs in these inhibitory oscillations. Rhythmic bursts of spontaneous IPSCs (0.5 Hz average burst frequency) recorded from rat BLA principal cells were blocked or significantly suppressed by D-AP5, and could be driven by NMDAR activation alone. BLA interneurons generated spontaneous bursts of suprathreshold EPSCs at a similar frequency, which were also blocked or reduced by D-AP5. PEAQX (GluN2A-NMDAR antagonist; 0.4 μM) or Ro-25-6981 (GluN2B-NMDAR antagonist; 5 μM) suppressed the IPSC and EPSC bursts; suppression by PEAQX was significantly greater than that by Ro-25-6981. Immunohistochemical labeling revealed the presence of both GluN2A- and GluN2B-NMDARs on GABAergic BLA interneurons, while, functionally, GluN2A-NMDARs have the dominant role, as suggested by a greater reduction of NMDA-evoked currents by PEAQX versus Ro-25-6981. Entrainment of BLA principal neurons in an oscillatory generation of inhibitory activity depends primarily on activation of GluN2A-NMDARs, and interneuronal GluN2A-NMDARs may play a significant role.

Administration of a Histone Deacetylase Inhibitor into the Basolateral Amygdala Enhances Memory Consolidation, Delays Extinction, and Increases Hippocampal BDNF Levels

Gene expression related to the formation and modification of memories is regulated epigenetically by chromatin remodeling through histone acetylation. Memory formation and extinction can be enhanced by treatment with inhibitors of histone deacetylases (HDACs). The basolateral amygdala (BLA) is a brain area critically involved in regulating memory for inhibitory avoidance (IA). However, previous studies have not examined the effects of HDAC inhibition in the amygdala on memory for IA. Here we show that infusion of an HDAC inhibitor (HDACi), trichostatin A (TSA), into the BLA, enhanced consolidation of IA memory in rats when given at 1.5, 3, or 6 h posttraining, but not when the drug was infused immediately after training. In addition, intra-BLA administration of TSA immediately after retrieval delayed extinction learning. Moreover, we show that intra-BLA TSA in rats given IA training increased the levels of brain-derived neurotrophic factor in the dorsal hippocampus, but not in the BLA itself. These findings reveal novel aspects of the regulation of fear memory by epigenetic mechanisms in the amygdala.

Emotional Modulation of Learning and Memory: Pharmacological Implications

Memory consolidation involves the process by which newly acquired information becomes stored in a long-lasting fashion. Evidence acquired over the past several decades, especially from studies using post-training drug administration, indicates that emotional arousal during the consolidation period influences and enhances the strength of the memory and that multiple different chemical signaling systems participate in this process. The mechanisms underlying the emotional influences on memory involve the release of stress hormones and activation of the basolateral amygdala, which work together to modulate memory consolidation. Moreover, work suggests that this amygdala-based memory modulation occurs with numerous types of learning and involves interactions with many different brain regions to alter consolidation. Additionally, studies suggest that emotional arousal and amygdala activity in particular influence synaptic plasticity and associated proteins in downstream brain regions. This review considers the historical understanding for memory modulation and cellular consolidation processes and examines several research areas currently using this foundational knowledge to develop therapeutic treatments.

Translational Approaches Targeting Reconsolidation

Maladaptive learned responses and memories contribute to psychiatric disorders that constitute a significant socio-economic burden. Primary treatment methods teach patients to inhibit maladaptive responses, but do not get rid of the memory itself, which explains why many patients experience a return of symptoms even after initially successful treatment. This highlights the need to discover more persistent and robust techniques to diminish maladaptive learned behaviours. One potentially promising approach is to alter the original memory, as opposed to inhibiting it, by targeting memory reconsolidation. Recent research shows that reactivating an old memory results in a period of memory flexibility and requires restorage, or reconsolidation, for the memory to persist. This reconsolidation period allows a window for modification of a specific old memory. Renewal of memory flexibility following reactivation holds great clinical potential as it enables targeting reconsolidation and changing of specific learned responses and memories that contribute to maladaptive mental states and behaviours. Here, we will review translational research on non-human animals, healthy human subjects, and clinical populations aimed at altering memories by targeting reconsolidation using biological treatments (electrical stimulation, noradrenergic antagonists) or behavioural interference (reactivation-extinction paradigm). Both approaches have been used successfully to modify aversive and appetitive memories, yet effectiveness in treating clinical populations has been limited. We will discuss that memory flexibility depends on the type of memory tested and the brain regions that underlie specific types of memory. Further, when and how we can most effectively reactivate a memory and induce flexibility is largely unclear. Finally, the development of drugs that can target reconsolidation and are safe for use in humans would optimize cross-species translations. Increasing the understanding of the mechanism and limitations of memory flexibility upon reactivation should help optimize efficacy of treatments for psychiatric patients.

Prolonged corticosterone exposure induces dendritic spine remodeling and attrition in the rat medial prefrontal cortex

The stress-responsive hypothalamo-pituitary-adrenal (HPA) axis plays a central role in promoting adaptations acutely, whereas adverse effects on physiology and behavior following chronic challenges may result from overactivity of this system. Elevations in glucocorticoids, the end-products of HPA activation, play roles in adaptive and maladaptive processes by targeting cognate receptors throughout neurons in limbic cortical networks to alter synaptic functioning. Because previous work has shown that chronic stress leads to functionally relevant regressive alterations in dendritic spine shape and number in pyramidal neurons in the medial prefrontal cortex (mPFC), this study examines the capacity of sustained increases in circulating corticosterone (B) alone to alter dendritic spine morphology and density in this region. Subcutaneous B pellets were implanted in rats to provide continuous exposure to levels approximating the circadian mean or peak of the steroid for 1, 2, or 3 weeks. Pyramidal neurons in the prelimbic area of the mPFC were selected for intracellular fluorescent dye filling, followed by high-resolution three-dimensional imaging and analysis of dendritic arborization and spine morphometry. Two or more weeks of B exposure decreased dendritic spine volume in the mPFC, whereas higher dose exposure of the steroid resulted in apical dendritic retraction and spine loss in the same cell population, with thin spine subtypes showing the greatest degree of attrition. Finally, these structural alterations were noted to persist following a 3-week washout period and corresponding restoration of circadian HPA rhythmicity. These studies suggest that prolonged disruptions in adrenocortical functioning may be sufficient to induce enduring regressive structural and functional alterations in the mPFC. J. Comp. Neurol. 524:3729-3746, 2016. © 2016 Wiley Periodicals, Inc.

Acute high-intensity noise induces rapid Arc protein expression but fails to rapidly change GAD expression in amygdala and hippocampus of rats: Effects of treatment with D-cycloserine

Tinnitus is a devastating auditory disorder impacting a growing number of people each year. The aims of the current experiment were to assess neuronal mechanisms involved in the initial plasticity after traumatic noise exposure that could contribute to the emergence of tinnitus and to test a potential pharmacological treatment to alter this early neural plasticity. Specifically, this study addressed rapid effects of acute noise trauma on amygdalo-hippocampal circuitry, characterizing biomarkers of both excitation and inhibition in these limbic regions, and compared them to expression of these same markers in primary auditory cortex shortly after acute noise trauma. To assess excitatory plasticity, activity-regulated cytoskeleton-associated (Arc) protein expression was evaluated in male rats 45 min after bilateral exposure to acute high-intensity noise (16 kHz, 115 dB SPL, for 1 h), sufficient to cause acute cochlear trauma, a common cause of tinnitus in humans and previously shown sufficient to induce tinnitus in rat models of this auditory neuropathology. Western blot analyses confirmed that up-regulation of amygdalo-hippocampal Arc expression occurred rapidly post-noise trauma, corroborating several lines of evidence from our own and other laboratories indicating that limbic brain structures, i.e. outside of the classical auditory pathways, exhibit plasticity early in the initiation of tinnitus. Western blot analyses revealed no noise-induced changes in amygdalo-hippocampal expression of glutamate decarboxylase (GAD), the biosynthetic enzyme required for GABAergic inhibition. No changes in either Arc or GAD protein expression were observed in primary auditory cortex in this immediate post-noise exposure period, confirming other reports that auditory cortical plasticity may not occur until later in the development of tinnitus. As a further control, our experiments compared Arc protein expression between groups exposed to the quiet background of a sound-proof chamber to those exposed not only to the traumatic noise described above, but also to an intermediate, non-traumatic noise level (70 dB SPL) for the same duration in each of these three brain regions. We found that non-traumatic noise did not up-regulate Arc protein expression in these brain regions. To see if changes in Arc expression due to acute traumatic noise exposure were stress-related, we compared circulating serum corticosterone in controls and rats exposed to traumatic noise at the time when changes in Arc were observed, and found no significant differences in this stress hormone in our experimental conditions. Finally, the ability of D-cycloserine (DCS; an NMDA-receptor NR1 partial agonist) to reduce or prevent the noise trauma-related plastic changes in the biomarker, Arc, was tested. D-cycloserine prevented traumatic noise-induced up-regulation of Arc protein expression in amygdala but not in hippocampus, suggesting that DCS alone is not fully effective in eliminating regionally-specific early plastic changes after traumatic noise exposure.

The amygdala and prioritization of declarative memories

The present review highlights results from recent studies that delivered brief electrical stimulation to the basolateral complex of the amygdala in rats to reveal its capacity to prioritize declarative memories on a moment-to-moment basis even after the moment has passed. The results indicate that this memory enhancement depends on the hippocampus and elicits intrahippocampal gamma synchrony that possibly corresponds with sharpened hippocampal spike-timing dependent plasticity. These recent findings are discussed in relation to past studies of emotional memory in rodents and humans.

Retrieving fear memories, as time goes by…

Research in fear conditioning has provided a comprehensive picture of the neuronal circuit underlying the formation of fear memories. In contrast, our understanding of the retrieval of fear memories is much more limited. This disparity may stem from the fact that fear memories are not rigid, but reorganize over time. To bring some clarity and raise awareness about the time-dependent dynamics of retrieval circuits, we review current evidence on the neuronal circuitry participating in fear memory retrieval at both early and late time points following auditory fear conditioning. We focus on the temporal recruitment of the paraventricular nucleus of the thalamus (PVT) for the retrieval and maintenance of fear memories. Finally, we speculate as to why retrieval circuits change with time, and consider the functional strategy of recruiting structures not previously considered as part of the retrieval circuit.

Additive sex-specific influence of common non-synonymous DISC1 variants on amygdala, basal ganglia, and white cortical surface area in healthy young adults

The disrupted-in-schizophrenia-1 (DISC1) gene is known for its role in the development of mental disorders. It is also involved in neurodevelopment, cognition, and memory. To investigate the association between DISC1 variants and brain morphology, we analyzed the influence of the three common non-synonymous polymorphisms in DISC1 on specific brain structures in healthy young adults. The volumes of brain regions were determined in 145 subjects by magnetic resonance imaging and automated analysis using FreeSurfer. Genotyping was performed by high resolution melting of amplified products. In an additive genetic model, rs6675281 (Leu607Phe), rs3738401 (Arg264Gln), and rs821616 (Ser704Cys) significantly explained the volume variance of the amygdala (p = 0.007) and the pallidum (p = 0.004). A higher cumulative portion of minor alleles was associated with larger volumes of the amygdala (p = 0.005), the pallidum (p = 0.001), the caudate (p = 0.024), and the putamen (p = 0.007). Sex-stratified analysis revealed a strong genetic effect of rs6675281 on putamen and pallidum in females but not in males and an opposite influence of rs3738401 on the white cortical surface in females compared to males. The strongest single association was found for rs821616 and the amygdala volume in male subjects (p < 0.001). No effect was detected for the nucleus accumbens. We report-to our knowledge-for the first time a significant and sex-specific influence of common DISC1 variants on volumes of the basal ganglia, the amygdala and on the cortical surface area. Our results demonstrate that the additive model of all three polymorphisms outperforms their single analysis.

Fear Memory

Fear memory is the best-studied form of memory. It was thoroughly investigated in the past 60 years mostly using two classical conditioning procedures (contextual fear conditioning and fear conditioning to a tone) and one instrumental procedure (one-trial inhibitory avoidance). Fear memory is formed in the hippocampus (contextual conditioning and inhibitory avoidance), in the basolateral amygdala (inhibitory avoidance), and in the lateral amygdala (conditioning to a tone). The circuitry involves, in addition, the pre- and infralimbic ventromedial prefrontal cortex, the central amygdala subnuclei, and the dentate gyrus. Fear learning models, notably inhibitory avoidance, have also been very useful for the analysis of the biochemical mechanisms of memory consolidation as a whole. These studies have capitalized on in vitro observations on long-term potentiation and other kinds of plasticity. The effect of a very large number of drugs on fear learning has been intensively studied, often as a prelude to the investigation of effects on anxiety. The extinction of fear learning involves to an extent a reversal of the flow of information in the mentioned structures and is used in the therapy of posttraumatic stress disorder and fear memories in general.

Structural and functional neural adaptations in obstructive sleep apnea: An activation likelihood estimation meta-analysis

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The right basolateral amygdala, the hippocampus and the right insular cortex are important nodes in obstructive sleep apnea (OSA).

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Functional characterization of these regions suggested associated dysfunction of emotional, sensory, and limbic processes in OSA.

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Connectivity analysis demonstrated that these regions are part of a joint network comprising the anterior insula, posterior-medial frontal cortex and thalamus.

Obstructive sleep apnea (OSA) is a common multisystem chronic disorder. Functional and structural neuroimaging has been widely applied in patients with OSA, but these studies have often yielded diverse results. The present quantitative meta-analysis aims to identify consistent patterns of abnormal activation and grey matter loss in OSA across studies. We used PubMed to retrieve task/resting-state functional magnetic resonance imaging and voxel-based morphometry studies. Stereotactic data were extracted from fifteen studies, and subsequently tested for convergence using activation likelihood estimation. We found convergent evidence for structural atrophy and functional disturbances in the right basolateral amygdala/hippocampus and the right central insula. Functional characterization of these regions using the BrainMap database suggested associated dysfunction of emotional, sensory, and limbic processes. Assessment of task-based co-activation patterns furthermore indicated that the two regions obtained from the meta-analysis are part of a joint network comprising the anterior insula, posterior-medial frontal cortex and thalamus. Taken together, our findings highlight the role of right amygdala, hippocampus and insula in the abnormal emotional and sensory processing in OSA.

Anxiolytic and nootropic activity of Vetiveria zizanioides roots in mice

Background:

Vetiveria zizanioides (VZ) (family: Poaceae), an aromatic plant commonly known as “Vetiver” has been used for various ailments. Concerning the various ailments being listed as the traditional uses of VZ, no mention about anxiety and memory was found.

Objective:

The present study examined the anxiolytic and memory enhancing activity of ethanolic extract of V. zizanioides (EEVZ) dried roots in mice.

Materials and Methods:

Activity of EEVZ was assessed using models of anxiety (elevated plus-maze [EPM], light/dark test, hole board test, marble-burying test) and learning and memory (EPM, passive shock avoidance paradigm).

Results:

EEVZ at doses of 100, 200, and 300 mg/kg b.w. illustrated significant anxiolytic activity indicated by increase in time spent and number of entries in open arm, time spent in lightened area, number of head poking and number marble buried when compared to that of diazepam (1 mg/kg b.w.), a reference standard. The same treatment showed a significant decrease in transfer latency to reach open arm, shock-free zone, and number of mistakes when compared to that of scopolamine (0.3 mg/kg b.w.). EEVZ in all the doses (100, 200, and 300 mg/kg b.w.) significantly decreased mortality in sodium nitrite (250 mg/kg b.w.) induced hypoxia and also significantly increases contraction induced by acetylcholine on rat ileum preparation.

Conclusion:

The result emanated in the present investigation revealed EEVZ possesses significant anxiolytic and nootropic activity by possibly interplaying with neurotransmitters implicated in anxiety and learning and memory.

Electroacupuncture pretreatment exhibits anti-depressive effects by regulating hippocampal proteomics in rats with chronic restraint stress

The clinical effect of electroacupuncture on depression is widely recognized. However, the signal transduction pathways and target proteins involved remain unclear. In the present study, rat models of chronic restraint stress were used to explore the mechanism by which electroacupuncture alleviates depression. Rats were randomly divided into control, model, and electroacupuncture groups. Chronic restraint stress was induced in the model and electroacupuncture groups by restraining rats for 28 days. In the electroacupuncture group, electroacupuncture pretreatment at Baihui (GV20) and Yintang (GV29) acupoints was performed daily (1 mA, 2 Hz, discontinuous wave, 20 minutes) prior to restraint for 28 days. Open field tests and body weight measurements were carried out to evaluate the depressive symptoms at specific time points. On day 28, the crossing number, rearing number, and body weights of the model group were significantly lower than those in the control group. Behavior test results indicated that rat models of depressive-like symptoms were successfully established by chronic restraint stress combined with solitary raising. On day 28, an isobaric tag for a relative and absolute quantitation-based quantitative proteomic approach was performed to identify differentially expressed proteins in hippocampal samples obtained from the model and electroacupuncture groups. The potential function of these differential proteins was predicted through the use of the Cluster of Orthologous Groups of proteins (COG) database. Twenty-seven differential proteins (uncharacteristic proteins expected) were selected from the model and electroacupuncture groups. In addition to unknown protein functions, COG are mainly concentrated in general prediction function, mechanism of signal transduction, amino acid transport and metabolism groups. This suggests that electroacupuncture improved depressive-like symptoms by regulating differential proteins, and most of these related proteins exist in nerve cells.

The effect of insulin and insulin-like growth factors on hippocampus- and amygdala-dependent long-term memory formation

Recent work has reported that the insulin-like growth factor 2 (IGF2) promotes memory enhancement. Furthermore, impaired insulin or IGF1 functions have been suggested to play a role in the pathogenesis of neurodegeneration and cognitive impairments, hence implicating the insulin/IGF system as an important target for cognitive enhancement and/or the development of novel treatments against cognitive disorders. Here, we tested the effect of intracerebral injections of IGF1, IGF2, or insulin on memory consolidation and persistence in rats. We found that a bilateral injection of insulin into the dorsal hippocampus transiently enhances hippocampal-dependent memory and an injection of IGF1 has no effect. None of the three peptides injected into the amygdala affected memories critically engaging this region. Together with previous data on IGF2, these results indicate that IGF2 produces the most potent and persistent effect as a memory enhancer on hippocampal-dependent memories. We suggest that the memory-enhancing effects of insulin and IGF2 are likely mediated by distinct mechanisms.

Differential effects of modafinil on memory in naïve and memory-impaired rats

Modafinil is a wake-promoting drug and has been approved for the treatment of excessive daytime sleepiness in narcolepsy and obstructive sleep apnea. Modafinil was shown to improve learning and memory in rodents, and to reverse memory deficits induced by sleep deprivation or stress. However, depending on the memory paradigm used, modafinil might also impair memory. We aimed to investigate the effects of modafinil on memory consolidation and retrieval for object recognition and inhibitory avoidance in naïve adult rats. We also investigated whether acute or chronic administration of modafinil would reverse memory deficits induced by iron overload, a model of memory impairment related to neurodegenerative disorders. Adult naïve rats received modafinil (0.0, 0.75, 7.5 or 75 mg/kg) either immediately after training or 1 h prior to testing in object recognition or inhibitory avoidance. Iron-treated rats received modafinil immediately after training in object recognition. In order to investigate the effects of chronic modafinil, iron-treated rats received daily injections of modafinil for 17 days, and 24 h later they were trained in object recognition or inhibitory avoidance. Acute modafinil does not affect memory consolidation or retrieval in naive rats. A single injection of modafinil at the highest dose was able to recover recognition memory in iron-treated rats. Chronic modafinil completely recovered iron-induced recognition memory and emotional memory deficits. Additional preclinical and clinical studies are necessary in order to support the applicability of modafinil in recovering memory impairment associated with neurodegenerative disorders.

Aging-related episodic memory decline: are emotions the key?

Episodic memory refers to the recollection of personal experiences that contain information on what has happened and also where and when these events took place. Episodic memory function is extremely sensitive to cerebral aging and neurodegerative diseases. We examined episodic memory performance with a novel test in young (N = 17, age: 21–45), middle-aged (N = 16, age: 48–62) and aged but otherwise healthy participants (N = 8, age: 71–83) along with measurements of trait and state anxiety. As expected we found significantly impaired episodic memory performance in the aged group as compared to the young group. The aged group also showed impaired working memory performance as well as significantly decreased levels of trait anxiety. No significant correlation between the total episodic memory and trait or state anxiety scores was found. The present results show an age-dependent episodic memory decline along with lower trait anxiety in the aged group. Yet, it still remains to be determined whether this difference in anxiety is related to the impaired episodic memory performance in the aged group.

Epinephrine and glucose modulate training-related CREB phosphorylation in old rats: relationships to age-related memory impairments

Epinephrine enhances memory in young adult rats, in part, by increasing blood glucose levels needed to modulate memory. In old rats, epinephrine is deficient at raising blood glucose levels and thus is only moderately effective at enhancing memory. In contrast, systemic glucose injections improve memory in old rats, with resulting memory performance equal to that of young rats. The diminished response of glucose to training in old rats may blunt downstream neurochemical and molecular mechanisms needed to upregulate memory processes. In the first experiment, young adult and old rats were trained on an inhibitory avoidance task with immediate post-training injections of aCSF or glucose into the dorsal hippocampus. Old rats had significant memory impairments compared to young rats 7 days after training. Intrahippocampal injections of glucose reversed age-related deficits, improving memory scores in old rats to values seen in young rats. A second experiment examined age-related changes in activation of the transcription factor CREB, which is widely implicated in memory formation and may act downstream of hormonal and metabolic signals. Activation was assessed in response to training with systemic injections of epinephrine and glucose at doses known to enhance memory. Young adult and old rats were trained on inhibitory avoidance with immediate post-training systemic injections of saline, epinephrine, or glucose. After training, old rats had significant impairments in CREB phosphorylation in area CA1 and the dentate gyrus region of the hippocampus, and in the basolateral and lateral amygdala. Epinephrine and glucose attenuated age-related deficits in CREB phosphorylation, but were more effective in the amygdala and hippocampus, respectively. Together, these results support the view that age-related changes in blood glucose responses to epinephrine contribute to memory impairments, which may be related to alterations in regional patterns of CREB phosphorylation.

Order of exposure to pleasant and unpleasant odors affects autonomic nervous system response

When mammals are exposed to an odor, that odor is expected to elicit a physiological response in the autonomic nervous system. An unpleasant aversive odor causes non-invasive stress, while a pleasant odor promotes healing and relaxation in mammals. We hypothesized that pleasant odors might reduce a stress response previously induced by an aversive predator odor. Rats were thus exposed to pleasant and unpleasant odors in different orders to determine whether the order of odor exposure had an effect on the physiological response in the autonomic nervous system. The first trial examined autonomic nerve activity via sympathetic and parasympathetic nerve response while the second trial examined body temperature response. Initial exposure to a pleasant odor elicited a positive response and secondary exposure to an unpleasant odor elicited a negative response, as expected. However, we found that while initial exposure to an unpleasant odor elicited a negative stress response, subsequent secondary exposure to a pleasant odor not only did not alleviate that negative response, but actually amplified it. These findings were consistent for both the autonomic nerve activity response trial and the body temperature response trial. The trial results suggest that exposure to specific odors does not necessarily result in the expected physiological response and that the specific order of exposure plays an important role. Our study should provide new insights into our understanding of the physiological response in the autonomic nervous system related to odor memory and discrimination and point to areas that require further research.

Anxiolytic-like effect of losartan injected into amygdala of the acutely stressed rats

It has been recognized that the stress-related peptides are involved in anxiety states. Angiotensin II receptor blockade by systemic administration of the AT(1) receptor antagonists has been proposed as a new treatment possibility for anxiety disorders. For better understanding of the related mechanisms, in this study we evaluated effects of bilateral intraamygdaloid injections of 2 (LOS 2) and 4 (LOS 4) μg of losartan (LOS), a selective AT(1) receptor antagonist, on the behavior of the not stressed and acutely stressed rats in an elevated "plus" maze. Under non-stress conditions, LOS 4 increased time spent in the open arms (p < 0.01), number of extreme open arm arrivals (p < 0.05), time per entry (p < 0.01), and the number of total arm entries (p < 0.05) showing thus considerable anxiolytic activity. The open arm extreme arrivals were increased by LOS 4 in both not stressed (p < 0.05) and stressed (p < 0.05) rats. When no stressed and stressed LOS 4 animals were compared, time per entry and the number of closed arm entries (p < 0.05, both) were decreased in the latter group. Moreover, the LOS 4 stressed rats had significantly increased open/closed arm quotient (p < 0.05) as compared to the both control and LOS 4 non-stress group (p < 0.05, both). These findings suggest that the AT(1) receptor blockade in amygdala is important for the anxiolytic action of LOS (and probably other AT(1) receptor blockers) under both non-stress and stress conditions.

Cycloheximide impairs and enhances memory depending on dose and footshock intensity

This experiment examined the effects on memory of interactions of cycloheximide dose and training foot shock intensity. Mice received injections of cycloheximide (120 mg/kg, s.c.) or saline 30 min prior to inhibitory avoidance training with shock intensities of 100, 150, 250 or 300 μA (1 s duration). Memory was tested 48 h later. The saline control mice showed increasing memory latencies as a function of shock intensity. The ability of cycloheximide to impair memory increased as the training shock intensity increased. In a second experiment, mice were trained with a 200 μA (1 s duration) shock and received injections of saline or cycloheximide at one of several doses (30, 60 or 120 mg/kg). Under these training conditions, cycloheximide enhanced memory in an inverted-U dose-response manner. These findings are consistent with prior findings suggesting that protein synthesis inhibitors act on memory by altering modulators of memory formation as a secondary consequence of the inhibition of protein synthesis rather than by interfering with training-initiated synthesis of proteins required for memory formation.

Toward a limbic cortical inhibitory network: implications for hypothalamic-pituitary-adrenal responses following chronic stress

A network of interconnected cell groups in the limbic forebrain regulates hypothalamic-pituitary-adrenal (HPA) axis activation during emotionally stressful experiences, and disruption of these systems is broadly implicated in the onset of psychiatric illnesses. A significant challenge has been to unravel the circuitry and mechanisms providing for regulation of HPA output, as these limbic forebrain regions do not provide any direct innervation of HPA effector cell groups in the paraventricular hypothalamus (PVH). Recent evidence will be highlighted that endorses a discrete region within the bed nuclei of the stria terminalis serving as a neural hub for integrating and relaying HPA-inhibitory influences to the PVH during emotional stress, whereas the prevailing view has involved a more complex organization of mulitple cell groups arranged in parallel between the forebrain and PVH. A hypothesis will be advanced that accounts for the capacity of this network to constrain the magnitude and/or duration of HPA axis output in response to emotionally stressful experiences, and for how chronic stress-induced synaptic reorganization in key cell groups may lead to an attrition of these influences, resulting in HPA axis hyperactivity.

Prazosin for the treatment of nightmares related to posttraumatic stress disorder: a review of the literature

BACKGROUND

Posttraumatic stress disorder (PTSD) is a psychiatric disorder with symptoms that include insomnia due to hyperarousal and recurring nightmares. These symptoms are believed to be due to a conditioned response that is regulated by norepinephrine. Prazosin, an α(1) antagonist, can decrease levels of norepinephrine in the central nervous system, thereby reducing nightmares related to PTSD.

DATA SOURCES

A literature search was conducted for all studies evaluating the effectiveness of prazosin as therapy for nightmare symptoms of PTSD. MEDLINE was utilized to identify all English-language studies published between 1966 and March 2011. Keywords searched included prazosin, PTSD, and nightmares.

RESULTS

Eleven studies were identified, including 4 open-label trials, 4 retrospective chart reviews, and 3 placebo-controlled trials. Prazosin demonstrated favorable clinical efficacy and was found to be safe for relieving PTSD-associated nightmares.

CONCLUSIONS

Current data indicate that prazosin is an effective agent for the treatment of nightmares associated with PTSD. However, the data are limited by small study sizes, lack of diversified investigators, and lack of regional diversity.

Learning-dependent plasticity of hippocampal CA1 pyramidal neuron postburst afterhyperpolarizations and increased excitability after inhibitory avoidance learning depend upon basolateral amygdala inputs

Hippocampal pyramidal neurons in vitro exhibit transient learning-dependent reductions in the amplitude and duration of calcium-dependent postburst afterhyperpolarizations (AHPs), accompanied by other increases in excitability (i.e., increased firing rate, or reduced spike-frequency accommodation) after trace eyeblink conditioning or spatial learning, with a time-course appropriate to support consolidation of the learned tasks. Both these tasks require multiple days of training for acquisition. The hippocampus also plays a role in acquisition of single trial inhibitory avoidance learning. The current study assessed AHP plasticity in this single-trial learning task using in vitro tissue slices prepared at varying intervals posttrial using intracellular current-clamp recordings. Reduced AHPs and reduced accommodation were seen in ventral CA1 pyramidal neurons within 1 h posttraining, plasticity which persisted 24 h but was extinguished >72 h posttrial. There was also a reduction in ventral CA1 AHPs and accommodation 1 h following simple exposure to the IA apparatus (a novel context) but this change was extinguished by 24 h postexposure. Reductions in AHPs and accommodation were also seen in dorsal CA1 pyramidal neurons, but were delayed until 24 h posttrial and extinguished at >72 h posttrial. Finally, transient inactivation of the basolateral complex of the amygdala (with the local anesthetics lidocaine or bupivacaine) either immediately before or immediately posttrial blocked both learning and learning-dependent changes in excitability in the hippocampus assessed 24 h posttrial. CA3 pyramidal neurons showed no reductions in AHP peak amplitude or accommodation following IA training or context exposure.

Candidate hippocampal biomarkers of susceptibility and resilience to stress in a rat model of depression

Susceptibility to stress plays a crucial role in the development of psychiatric disorders such as unipolar depression and post-traumatic stress disorder. In the present study the chronic mild stress rat model of depression was used to reveal stress-susceptible and stress-resilient rats. Large-scale proteomics was used to map hippocampal protein alterations in different stress states. Membrane proteins were successfully captured by two-phase separation and peptide based proteomics. Using iTRAQ labeling coupled with mass spectrometry, more than 2000 proteins were quantified and 73 proteins were found to be differentially expressed. Stress susceptibility was associated with increased expression of a sodium-channel protein (SCN9A) currently investigated as a potential antidepressant target. Differential protein profiling also indicated stress susceptibility to be associated with deficits in synaptic vesicle release involving SNCA, SYN-1, and AP-3. Our results indicate that increased oxidative phosphorylation (COX5A, NDUFB7, NDUFS8, COX5B, and UQCRB) within the hippocampal CA regions is part of a stress-protection mechanism.

Lidocaine attenuates anisomycin-induced amnesia and release of norepinephrine in the amygdala

When administered near the time of training, protein synthesis inhibitors such as anisomycin impair later memory. A common interpretation of these findings is that memory consolidation requires new protein synthesis initiated by training. However, recent findings support an alternative interpretation that abnormally large increases in neurotransmitter release after injections of anisomycin may be responsible for producing amnesia. In the present study, a local anesthetic was administered prior to anisomycin injections in an attempt to mitigate neurotransmitter actions and thereby attenuate the resulting amnesia. Rats received lidocaine and anisomycin injections into the amygdala 130 and 120 min, respectively, prior to inhibitory avoidance training. Memory tests 48 h later revealed that lidocaine attenuated anisomycin-induced amnesia. In other rats, in vivo microdialysis was performed at the site of amygdala infusion of lidocaine and anisomycin. As seen previously, anisomycin injections produced large increases in release of norepinephrine in the amygdala. Lidocaine attenuated the anisomycin-induced increase in release of norepinephrine but did not reverse anisomycin inhibition of protein synthesis, as assessed by c-Fos immunohistochemistry. These findings are consistent with past evidence suggesting that anisomycin causes amnesia by initiating abnormal release of neurotransmitters in response to the inhibition of protein synthesis.