Spatial contextual recognition memory updating is modulated by dopamine release in the dorsal hippocampus from the locus coeruleus.

Detecting novelty is critical to consolidate declarative memories, such as spatial contextual recognition memory. It has been shown that stored memories, when retrieved, are susceptible to modification, incorporating new information through an updating process. Catecholamine release in the hippocampal CA1 region consolidates an object location memory (OLM). This work hypothesized that spatial contextual memory updating could be changed by decreasing catecholamine release in the hippocampal CA1 terminals from the locus coeruleus (LC). In a mouse model expressing Cre-recombinase under the control of the tyrosine hydroxylase (TH) promoter, memory updating was impaired by photoinhibition of the CA1 catecholaminergic terminals from the LC (LC-CA1) but not from the ventral tegmental area (VTA-CA1). In vivo microdialysis confirmed that the extracellular concentration of both dopamine (DA) and noradrenaline (NA) decreased after photoinhibition of the LC-CA1 terminals (but not VTA-CA1) during the OLM update session. Furthermore, DA D1/D5 and beta-adrenergic receptor antagonists disrupted behavior, but only the former impaired memory updating. Finally, photoinhibition of LC-CA1 terminals suppressed long-term potentiation (LTP) induction in Schaffer's collaterals as a plausible mechanism for memory updating. These data will help understand the underpinning mechanisms of DA in spatial contextual memory updating.

Early-life and chronic exposure to high-fat diet alters noradrenergic and glutamatergic neurotransmission in the male rat amygdala and hippocampus under cognitive challenges.

Childhood obesity increases the risk of health and cognitive disorders in adulthood. Consuming high-fat diets (HFD) during critical neurodevelopmental periods, like childhood, impairs cognition and memory in humans and animals, affecting the function and connectivity of brain structures related to emotional memory. However, the underlying mechanisms of such phenomena need to be better understood. This study aimed to investigate the neurochemical profile of the amygdala and hippocampus, brain structures involved in emotional memory, during the acquisition of conditioned odor aversion in male rats that consumed a HFD from weaning to adulthood. The rats gained weight, experienced metabolic changes, and reduced insulin sensitivity and glucose tolerance. Rats showed enhanced odor aversion memory, contrary to the expected cognitive impairments. This memory enhancement was accompanied by increased noradrenergic and glutamatergic neurotransmission in the amygdala and hippocampus. Importantly, this upregulation was specific to stimuli exposure, as basal neurotransmitter levels remained unaltered by the HFD. Our results suggest that HFD modifies cognitive function by altering neurochemical signaling, in this case, upregulating neurotransmitter levels rendering a stronger memory trace, demonstrating that metabolic dysfunctions do not only trigger exclusively detrimental plasticity processes but also render enhanced plastic effects depending on the type of information.

Inhibition of hippocampal palmitoyl acyltransferase activity impairs spatial learning and memory consolidation.

Protein palmitoylation regulates trafficking, mobilization, localization, interaction, and distribution of proteins through the palmitoyl acyltransferases (PATs) enzymes. Protein palmitoylation controls rapid and dynamic changes of the synaptic architecture that modifies the efficiency and strength of synaptic connections, a fundamental mechanism to generate stable and long-lasting memory traces. Although protein palmitoylation in functional synaptic plasticity has been widely described, its role in learning and memory processes is poorly understood. In this work, we found that PATs inhibition into the hippocampus before and after the training of Morris water maze (MWM) and object location memory (OLM) impaired spatial learning. However, we demonstrated that PATs inhibition during the retrieval does not affect the expression of spatial memory in both MWM and OLM. Accordingly, long-term potentiation induction is impaired by inhibiting PATs into the hippocampus before high-frequency electrical stimulation but not after. These findings suggest that PATs activity is necessary to modify neural plasticity, a mechanism required for memory acquisition and consolidation. Like phosphorylation, active palmitoylation is required to regulate the function of already existing proteins that change synaptic strength in the hippocampus to acquire and later consolidate spatial memories.

Synergistic photoactivation of VTA-catecholaminergic and BLA-glutamatergic projections induces long-term potentiation in the insular cortex.

The presentation of novel stimuli induces a reliable dopamine release in the insular cortex (IC) from the ventral tegmental area (VTA). The novel stimuli could be associated with motivational and emotional signals induced by cortical glutamate release from the basolateral amygdala (BLA). Dopamine and glutamate are essential for acquiring and maintaining behavioral tasks, including visual and taste recognition memories. In this study, we hypothesize that the simultaneous activation of dopaminergic and glutamatergic projections to the neocortex can underlie synaptic plasticity. High-frequency stimulation of the BLA-IC circuit has demonstrated a reliable long-term potentiation (LTP), a widely acknowledged synaptic plasticity that underlies memory consolidation. Therefore, the concurrent optogenetic stimulation of the insula's glutamatergic and dopaminergic terminal fibers would induce reliable LTP. Our results confirmed that combined photostimulation of the VTA and BLA projections to the IC induces a slow-onset LTP. We also found that optogenetically-induced LTP in the IC relies on both glutamatergic NMDA receptors and dopaminergic D1/D5 receptors, suggesting that the combined effects of these neurotransmitters can trigger synaptic plasticity in the neocortex. Overall, our findings provide compelling evidence supporting the essential role of both dopaminergic and glutamatergic projections in modulating synaptic plasticity within the IC. Furthermore, our results suggest that the synergistic actions of these projections have a pivotal influence on the formation of motivational memories.

Maintenance of conditioned place avoidance induced by gastric malaise requires NMDA activity within the ventral hippocampus.

It has been reported that during chemotherapy treatment, some patients can experience nausea before pharmacological administration, suggesting that contextual stimuli are associated with the nauseating effects. There are attempts to reproduce with animal models the conditions under which this phenomenon is observed to provide a useful paradigm for studying contextual aversion learning and the brain structures involved. This manuscript assessed the hippocampus involvement in acquiring and maintaining long-term conditioned place avoidance (CPA) induced by a gastric malaise-inducing agent, LiCl. Our results demonstrate that a reliable induction of CPA is possible after one acquisition trial. However, CPA establishment requires a 20-min confinement in the compartment associated with LiCl administration. Interestingly, both hippocampal regions seem to be necessary for CPA establishment; nonetheless, inactivation of the ventral hippocampus results in a reversion of avoidance and turns it into preference. Moreover, we demonstrate that activation of dorsal/ventral hippocampal NMDA receptors after CS-US association is required for long-term CPA memory maintenance.

Cortical neurochemical signaling of gustatory stimuli and their visceral consequences during the acquisition and consolidation of taste aversion memory.

The insular cortex (IC) has a crucial role in taste recognition memory, including conditioned taste aversion (CTA). CTA is a learning paradigm in which a novel taste stimulus (CS) is associated with gastric malaise (US), inducing aversion to the CS in future encounters. The role of the IC in CTA memory formation has been extensively studied. However, the functional significance of neurotransmitter release during the presentation of taste stimuli and gastric malaise-inducing agents remains unclear. Using microdialysis in free-moving animals, we evaluated simultaneous changes in glutamate, norepinephrine and dopamine release in response to the presentation of an innate appetitive or aversive gustatory novel stimulus, as well as after i.p. administration of isotonic or hypertonic gastric malaise-inducing solutions. Our results demonstrate that the presentation of novel stimuli, regardless of their innate valence, induces an elevation of norepinephrine and dopamine. Administration of a gastric malaise inducing agent (LiCl) promotes an elevation of glutamate regardless of its concentration. In comparison, norepinephrine release is related to the LiCl concentration and its equimolar NaCl control. Additionally, we evaluated their functional role on short and long-term taste aversion memory. Results indicate that the blockade of noradrenergic ß1,2 receptors in the IC spares CTA acquisition and memory consolidation. In contrast, blockade of dopamine D1/D5 receptors impaired CTA consolidation, whereas the NMDA receptor blockade impedes both acquisition and consolidation of CTA. These results suggest that dopaminergic and noradrenergic release are related to the salience of conditioned taste stimuli. However, only cortical D1/D5 dopaminergic activity, but not the noradrenergic ß1,2 activity, is involved in the acquisition and consolidation of taste memory formation. Additionally, glutamatergic activity signals visceral distress caused by LiCl administration and activates NMDA receptors necessary for the acquisition and consolidation of long-lasting taste aversion memory.

Telomere length and oxidative stress variations in a murine model of Alzheimer's disease progression.

Alzheimer's disease (AD) is the most common cause of dementia, and ageing is its major risk factor. Changes in telomere length have been associated with ageing and some degenerative diseases. Our aim was to explore some of the molecular changes caused by the progression of AD in a transgenic murine model (3xTg-AD; B6; 129-Psen1 Tg (APPSwe, tauP301L) 1Lfa). Telomere length was assessed by qPCR in both brain tissue and peripheral blood cells and compared between three age groups: 5, 9 and 13 months. In addition, a possible effect of oxidative stress on telomere length and AD progression was explored. Shorter telomeres were found in blood cells of older transgenic mice compared to younger and wild-type mice but no changes in telomere length in the hippocampus. An increase in oxidative stress with age was found for all strains, but no correlation was found between oxidative stress and shorter telomere length for transgenic mice. Telomere length and oxidative stress are affected by AD progression in the 3xTg-AD murine model. Changes in blood cells are more noticeable than changes in brain tissue, suggesting that systemic changes can be detected early in the disease in this murine model.

Age-Dependent Decline in Synaptic Mitochondrial Function Is Exacerbated in Vulnerable Brain Regions of Female 3xTg-AD Mice.

Synaptic aging has been associated with neuronal circuit dysfunction and cognitive decline. Reduced mitochondrial function may be an early event that compromises synaptic integrity and neurotransmission in vulnerable brain regions during physiological and pathological aging. Thus, we aimed to measure mitochondrial function in synapses from three brain regions at two different ages in the 3xTg-AD mouse model and in wild mice. We found that aging is the main factor associated with the decline in synaptic mitochondrial function, particularly in synapses isolated from the cerebellum. Accumulation of toxic compounds, such as tau and Aß, that occurred in the 3xTg-AD mouse model seemed to participate in the worsening of this decline in the hippocampus. The changes in synaptic bioenergetics were also associated with increased activation of the mitochondrial fission protein Drp1. These results suggest the presence of altered mechanisms of synaptic mitochondrial dynamics and their quality control during aging and in the 3xTg-AD mouse model; they also point to bioenergetic restoration as a useful therapeutic strategy to preserve synaptic function during aging and at the early stages of Alzheimer's disease (AD).

Memory trace reactivation and behavioral response during retrieval are differentially modulated by amygdalar glutamate receptors activity: interaction between amygdala and insular cortex.

The insular cortex (IC) is required for conditioned taste aversion (CTA) retrieval. However, it remains unknown which cortical neurotransmitters levels are modified upon CTA retrieval. Using in vivo microdialysis, we observed that there were clear elevations in extracellular glutamate, norepinephrine, and dopamine in and around the center of the gustatory zone of the IC during CTA retrieval. Additionally, it has been reported that the amygdala-IC interaction is highly involved in CTA memory establishment. Therefore, we evaluated the effects of infusions of an AMPA receptor antagonist (CNQX) and a NMDA receptor antagonist (APV) into the amygdala on CTA retrieval and IC neurotransmitter levels. Infusion of APV into the amygdala impaired glutamate augmentation within the IC, whereas dopamine and norepinephrine levels augmentation persisted and a reliable CTA expression was observed. Conversely, CNQX infusion into the amygdala impaired the aversion response, as well as norepinephrine and dopamine augmentations in the IC. Interestingly, CNQX infusion did not affect glutamate elevation in the IC. To evaluate the functional meaning of neurotransmitters elevations within the IC on CTA response, we infused specific antagonists for the AMPA, NMDA, D1, and ß-adrenergic receptor before retrieval. Results showed that activation of AMPA, D1, and ß-adrenergic receptors is necessary for CTA expression, whereas NMDA receptors are not involved in the aversion response.

Hippocampal release of dopamine and norepinephrine encodes novel contextual information.

The detection and processing of novel information encountered in our environment is crucial for proper adaptive behavior and learning. Hippocampus is a prime structure for novelty detection that receives high-level inputs including context information. It is of our interest to understand the mechanisms by which the hippocampus processes contextual information. For this, we performed in vivo microdyalisis in order to monitor extracellular changes in neurotransmitter levels during Object Location Memory (OLM), a behavioral protocol developed to evaluate contextual information processing in recognition memory. Neurotransmitter release was evaluated in the dorsal hippocampus and insular cortex during OLM in 3-month-old B6129SF2/J mice. We found a simultaneous release of dopamine and norepinephrine in hippocampus during OLM, while neurochemical activity remained unaltered in the cortex. Additionally, we administered 6-hydroxy-dopamine (6-OHDA), a neurotoxic compound selective to dopaminergic and noradrenergic neurons, in the dorsal hippocampus in a different group of mice. Depletion of catecholaminergic terminals in the hippocampus by 6-OHDA impaired OLM but did not affect novel object recognition. Our results support the relevance of hippocampal catecholaminergic neurotransmission in recognition memory. The significance of catecholaminergic function may be extended to the clinical field as it has been reported that innervation of hippocampus by the noradrenergic and dopaminergic system is reduced and atrophied in aging and Alzheimer's disease brain. © 2017 Wiley Periodicals, Inc.

Determinants to trigger memory reconsolidation: The role of retrieval and updating information.

Long-term memories can undergo destabilization/restabilization processes, collectively called reconsolidation. However, the parameters that trigger memory reconsolidation are poorly understood and are a matter of intense investigation. Particularly, memory retrieval is widely held as requisite to initiate reconsolidation. This assumption makes sense since only relevant cues will induce reconsolidation of a specific memory. However, recent studies show that pharmacological inhibition of retrieval does not avoid memory from undergoing reconsolidation, indicating that memory reconsolidation occurs through a process that can be dissociated from retrieval. We propose that retrieval is not a unitary process but has two dissociable components; one leading to the expression of memory and the other to reconsolidation, referred herein as executer and integrator respectively. The executer would lead to the behavioral expression of the memory. This component would be the one disrupted on the studies that show reconsolidation independence from retrieval. The integrator would deal with reconsolidation. This component of retrieval would lead to long-term memory destabilization when specific conditions are met. We think that an important number of reports are consistent with the hypothesis that reconsolidation is only initiated when updating information is acquired. We suggest that the integrator would initiate reconsolidation to integrate updating information into long-term memory.

New Insights on Retrieval-Induced and Ongoing Memory Consolidation: Lessons from Arc.

The mainstream view on the neurobiological mechanisms underlying memory formation states that memory traces reside on the network of cells activated during initial acquisition that becomes active again upon retrieval (reactivation). These activation and reactivation processes have been called "conjunctive trace." This process implies that singular molecular events must occur during acquisition, strengthening the connection between the implicated cells whose synchronous activity must underlie subsequent reactivations. The strongest experimental support for the conjunctive trace model comes from the study of immediate early genes such as c-fos, zif268, and activity-regulated cytoskeletal-associated protein. The expressions of these genes are reliably induced by behaviorally relevant neuronal activity and their products often play a central role in long-term memory formation. In this review, we propose that the peculiar characteristics of Arc protein, such as its optimal expression after ongoing experience or familiar behavior, together with its versatile and central functions in synaptic plasticity could explain how familiarization and recognition memories are stored and preserved in the mammalian brain.

Retrieval is not necessary to trigger reconsolidation of object recognition memory in the perirhinal cortex.

Memory retrieval has been considered as requisite to initiate memory reconsolidation; however, some studies indicate that blocking retrieval does not prevent memory from undergoing reconsolidation. Since N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors in the perirhinal cortex have been involved in object recognition memory formation, the present study evaluated whether retrieval and reconsolidation are independent processes by manipulating these glutamate receptors. The results showed that AMPA receptor antagonist infusions in the perirhinal cortex blocked retrieval, but did not affect memory reconsolidation, although NMDA receptor antagonist infusions disrupted reconsolidation even if retrieval was blocked. Importantly, neither of these antagonists disrupted short-term memory. These data suggest that memory underwent reconsolidation even in the absence of retrieval.

The forgotten insular cortex: its role on recognition memory formation.

For a long time, the insular cortex (IC) has been related with taste physiology and taste memory processes in animal studies. Recently, the role of the IC has been highlighted by findings involving the IC in non-taste memory formation in both human and animal studies. Recognition memory is based on the ability to assess the familiarity of a previously encountered stimulus, and it is considered a form of declarative memory. In this work, I am proposing that the IC and its related circuitry are highly involved in the conversion of novel to familiar stimulus for both object and taste recognition memory. In addition, I will review some of the molecular mechanisms involved in the modification of novelty to familiarity memory processes, including the role of epigenetic mechanisms on the consolidation of recognition memory within the IC. In the second part of the paper, I will review some of the possible mechanisms to transform a novel taste into a familiar aversive taste by a functional interaction between the IC and the amygdala. In summary, the IC is an important area that will open a new avenue for the study of the mechanisms involved in the neurobiology of learning and memory in the near future.

Role of glutamate receptors of central and basolateral amygdala nuclei on retrieval and reconsolidation of taste aversive memory.

There are a number of experiments showing an important involvement of amygdala N-methyl-d-aspartate (NMDA) glutamate receptors on consolidation of conditioned taste aversion (CTA) memory. Interestingly, recent evidence has shown that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors are particularly involved in CTA retrieval. Memory reconsolidation has been proposed as a destabilization and re-stabilization process induced by memory reactivation. We have recently suggested that reconsolidation could be enabled in the absence of retrieval. Hence, we decided to analyze the participation of AMPA and NMDA receptors of the central (CeA) and basolateral amygdala (BLA) in CTA memory retrieval and reconsolidation. To do so, we tested whether administrations of an AMPA receptor blocker (NBQX) or an NMDA receptor blocker (APV) 15 min before a second acquisition trial could have effects on taste aversion. We found that administration of NBQX in the BLA blocked retrieval, whereas APV blocked reconsolidation in the BLA, and consolidation in the CeA. When we administered both NBQX and APV into the BLA before the second acquisition trial, results showed impairment of both retrieval and reconsolidation. These results further support the idea that reconsolidation is independent of retrieval, since retrieval blockade in the BLA did not impair memory reconsolidation. These results suggest that glutamate receptors have different participation on retrieval and reconsolidation of CTA and further support the hypothesis that these two processes could be independent.

Differential role of insular cortex muscarinic and NMDA receptors in one-trial appetitive taste learning.

Our current understanding of the neurobiology of taste learning and memory has been greatly facilitated by the use of a reliable behavioural model, conditioned taste aversion (CTA). This model has revealed that the insular cortex (IC), specifically muscarinic and N-methyl-d-aspartate (NMDA) receptor activation in the IC, is critical for the formation of aversive taste memories. In contrast, current models of appetitive taste learning are less adequate, relying on the use of neophobic tastes (attenuation of neophobia) or on the integration of appetitive and aversive taste memories (latent inhibition of CTA). While these models have implicated IC muscarinic receptors, the involvement of NMDA receptors in the IC remains unclear. Here, we examined the role of both muscarinic and NMDA receptors in appetitive taste learning using a simple paradigm that is independent of neophobic and aversive components. First, we demonstrated that a single exposure to a novel taste, saccharin 0.1%, is sufficient to promote an appetitive taste memory as revealed by an increase in saccharin consumption during the second presentation. This increase was blocked by bilateral infusion in the IC of the muscarinic receptor antagonist, scopolamine. In contrast, infusion of the NMDA receptor antagonist, AP5, did not block appetitive taste learning but did abolish CTA. Therefore, common and distinct molecular substrates within the IC mediate appetitive versus aversive learning about the same taste.

The anterior insula and its projection to amygdala nuclei modulate the abstinence-exacerbated expression of conditioned place preference.

RATIONALE: Relapse into substance use is often triggered by exposure to drug-related environmental cues. The magnitude of drug seeking depends on the duration of abstinence, a phenomenon known as the incubation of drug craving. Clinical and preclinical research shows that the insular cortex is involved in substance use disorders and cue-induced drug seeking. However, the role of the insula on memory retrieval and motivational integration for cue-elicited drug seeking remains to be determined. OBJECTIVES: We investigated the role of the anterior insular cortex (aIC) and its glutamatergic projection to amygdala nuclei (aIC-AMY) on the expression of conditioned place preference (CPP) during early and late abstinence. METHODS: Male adult C57BL/6J mice underwent amphetamine-induced CPP, and their preference was tested following 1 or 14 days of abstinence. aIC and aIC-AMY functional role in CPP expression was assessed at both abstinence periods by employing optogenetic silencing and behavioral pharmacology. RESULTS: Compared to a single day, an exacerbated preference for the amphetamine-paired context was observed after 14 days of abstinence. Photoinhibition of either aIC or aIC-AMY projection reduced CPP expression following late but not early abstinence. Similarly, the antagonism of aIC NMDA receptors reduced CPP expression after 14 days of abstinence but not 1 day. CONCLUSIONS: These results suggest that aIC and its glutamatergic output to amygdala nuclei constitute critical neurobiological substrates mediating enhanced motivational cue reactivity during the incubation of amphetamine craving rather than contextual memory recall. Moreover, cortical NMDA receptor signaling may become sensitized during abstinence, ultimately modulating disproportioned drug seeking.

Paradoxical Boosting of Weak and Strong Spatial Memories by Hippocampal Dopamine Uncaging.

The ability to remember changes in the surroundings is fundamental for daily life. It has been proposed that novel events producing dopamine release in the hippocampal CA1 region could modulate spatial memory formation. However, the role of hippocampal dopamine increase on weak or strong spatial memories remains unclear. We show that male mice exploring two objects located in a familiar environment for 5 min created a short-term memory (weak) that cannot be retrieved 1 d later, whereas 10 min exploration created a long-term memory (strong) that can be retrieved 1 d later. Remarkably, hippocampal dopamine elevation during the encoding of weak object location memories (OLMs) allowed their retrieval 1 d later but dopamine elevation during the encoding of strong OLMs promoted the preference for a familiar object location over a novel object location after 24 h. Moreover, dopamine uncaging after the encoding of OLMs did not have effect on weak memories whereas on strong memories diminished the exploration of the novel object location. Additionally, hippocampal dopamine elevation during the retrieval of OLMs did not allow the recovery of weak memories and did not affect the retrieval of strong memory traces. Finally, dopamine elevation increased hippocampal theta oscillations, indicating that dopamine promotes the recurrent activation of specific groups of neurons. Our experiments demonstrate that hippocampal dopaminergic modulation during the encoding of OLMs depends on memory strength indicating that hyperdopaminergic levels that enhance weak experiences could compromise the normal storage of strong memories.

Dopamine D1 receptor activity modulates object recognition memory consolidation in the perirhinal cortex but not in the hippocampus.

It has been proposed that distributed neuronal networks in the medial temporal lobe process different characteristics of a recognition event; the hippocampus has been associated with contextual recollection while the perirhinal cortex has been linked with familiarity. Here we show that D1 dopamine receptor activity in these two structures participates differentially in object recognition memory consolidation. The D1 receptor antagonist SCH23390 was infused bilaterally 15 min before a 5 min sample phase in either rats' perirhinal cortex or dorsal hippocampus, and they were tested 90 min for short-term memory or 24 h later for long-term memory. SCH23390 impaired long-term memory when infused in the perirhinal cortex but not when infused in the hippocampus. Conversely, when the D1 receptor agonist SKF38393 was infused 10 min before a 3 min sample phase in the perirhinal cortex, long-term memory was enhanced, however, this was not observed when the D1 agonist was infused in the hippocampus. Short-term memory was spared when SCH23390 or SKF38393 were infused in the perirhinal cortex or the dorsal hippocampus suggesting that acquisition was unaffected. These results suggest that dopaminergic transmission in these medial temporal lobe structures have a differential involvement in object recognition memory consolidation.

Post-acquisition release of glutamate and norepinephrine in the amygdala is involved in taste-aversion memory consolidation.

Amygdala activity mediates the acquisition and consolidation of emotional experiences; we have recently shown that post-acquisition reactivation of this structure is necessary for the long-term storage of conditioned taste aversion (CTA). However, the specific neurotransmitters involved in such reactivation are not known. The aim of the present study was to investigate extracellular changes of glutamate, norepinephrine, and dopamine within the rat amygdala using in vivo microdialysis during the acquisition and 1-h post-acquisition of CTA paradigm. Microdialysis monitoring showed a significant norepinephrine increase related to novel taste exposure and a glutamate increase after gastric malaise induction by i.p. LiCl administration. Interestingly, we found a spontaneous concomitant increase of glutamate and norepinephrine, but not dopamine, 45 min after conditioning, suggesting the presence of aversive learning-dependent post-acquisition signals in the amygdala. These signals seem to be involved in CTA consolidation process, since post-trial blockade of N-methyl-D-aspartate or ß-adrenergic receptors impaired long- but not short-term memory. These data suggest that CTA long-term storage involves post-acquisition release of glutamate and norepinephrine in the amygdala.