Induction of NGFI-B mRNA following contextual fear conditioning and its blockade by diazepam

Molecular pathways underlying sympathetic autonomic overshooting leading to fear and traumatic memories: looking for alternative therapeutic options for post-traumatic stress disorder

The sympathoadrenal medullary system and the hypothalamic-pituitary-adrenal axis are both activated upon stressful events. The release of catecholamines, such as dopamine, norepinephrine (NE), and epinephrine (EPI), from sympathetic autonomic nerves participate in the adaptive responses to acute stress. Most theories suggest that activation of peripheral β-adrenoceptors (β-ARs) mediates catecholamines-induced memory enhancement. These include direct activation of β-ARs in the vagus nerve, as well as indirect responses to catecholamine-induced glucose changes in the brain. Excessive sympathetic activity is deeply associated with memories experienced during strong emotional stressful conditions, with catecholamines playing relevant roles in fear and traumatic memories consolidation. Recent findings suggest that EPI is implicated in fear and traumatic contextual memories associated with post-traumatic stress disorder (PTSD) by increasing hippocampal gene transcription (e.g., Nr4a) downstream to cAMP response-element protein activation (CREB). Herein, we reviewed the literature focusing on the molecular mechanisms underlying the pathophysiology of memories associated with fear and traumatic experiences to pave new avenues for the treatment of stress and anxiety conditions, such as PTSD.

Evaluation of behavioural selection processes in conflict scenarios using a newly developed mouse behavioural paradigm

Selecting an appropriate behaviour is critical for survival in conflict scenarios, wherein animals face both appetitive and aversive stimuli. Behavioural selection consists of multiple processes: (1) animals remain quiet in a safe place to avoid aversive stimuli (suspension), (2) once they decide to take risks to approach appetitive stimuli, they assess the risks (risk assessment), and (3) they act to reach the reward. However, most studies have not addressed these distinct behavioural processes separately. Here, we developed a new experimental paradigm called the three-compartment conflict task to quantitatively evaluate conflict processes. Our apparatus consisted of start, flat, and grid compartments. Mice needed to explore the grid compartment, where they might receive foot shocks while trying to obtain sucrose. Applying foot shocks increased sucrose acquisition latency in subsequent trials, reflecting elevated conflict levels throughout trials. The time spent in the start compartment and the number of retreats were determined to measure the conflict levels in suspension and risk assessment, respectively. Foot shocks increased these parameters, whereas diazepam decreased them. Our new paradigm is valuable for quantitatively evaluating distinct behavioural processes and contributes to developing effective treatments for psychiatric disorders associated with maladaptive behaviours in conflict scenarios.

Benzodiazepine-induced anterograde amnesia: detrimental side effect to novel study tool

Benzodiazepines (BZDs) are anxiolytic drugs that act on GABAa receptors and are used to treat anxiety disorders. However, these drugs come with the detrimental side effect of anterograde amnesia, or the inability to form new memories. In this review we discuss, behavioral paradigms, sex differences and hormonal influences affecting BZD-induced amnesia, molecular manipulations, including the knockout of GABAa receptor subunits, and regional studies utilizing lesion and microinjection techniques targeted to the hippocampus and amygdala. Additionally, the relationship between BZD use and cognitive decline related to Alzheimer's disease is addressed, as there is a lack of consensus on whether these drugs are involved in inducing or accelerating pathological cognitive deficits. This review aims to inspire new research directions, as there is a gap in knowledge in understanding the cellular and molecular mechanisms behind BZD-induced amnesia. Understanding these mechanisms will allow for the development of alternative treatments and potentially allow BZDs to be used as a novel tool to study Alzheimer's disease.

Gene expression in the dorsolateral and ventromedial prefrontal cortices implicates immune-related gene networks in PTSD

Studies evaluating neuroimaging, genetically predicted gene expression, and pre-clinical genetic models of PTSD, have identified PTSD-related abnormalities in the prefrontal cortex (PFC) of the brain, particularly in dorsolateral and ventromedial PFC (dlPFC and vmPFC). In this study, RNA sequencing was used to examine gene expression in the dlPFC and vmPFC using tissue from the VA National PTSD Brain Bank in donors with histories of PTSD with or without depression (dlPFC n = 38, vmPFC n = 35), depression cases without PTSD (n = 32), and psychopathology-free controls (dlPFC n = 24, vmPFC n = 20). Analyses compared PTSD cases to controls. Follow-up analyses contrasted depression cases to controls. Twenty-one genes were differentially expressed in PTSD after strict multiple testing correction. PTSD-associated genes with roles in learning and memory (FOS, NR4A1), immune regulation (CFH, KPNA1) and myelination (MBP, MOBP, ERMN) were identified. PTSD-associated genes partially overlapped depression-associated genes. Co-expression network analyses identified PTSD-associated networks enriched for immune-related genes across the two brain regions. However, the immune-related genes and association patterns were distinct. The immune gene IL1B was significantly associated with PTSD in candidate-gene analysis and was an upstream regulator of PTSD-associated genes in both regions. There was evidence of replication of dlPFC associations in an independent cohort from a recent study, and a strong correlation between the dlPFC PTSD effect sizes for significant genes in the two studies (r = 0.66, p < 2.2 × 10⁻¹⁶). In conclusion, this study identified several novel PTSD-associated genes and brain region specific PTSD-associated immune-related networks.

Conditioned stimulus presentations alter anxiety level in fear-conditioned mice

It is generally believed that fear is rapidly triggered by a distinct cue while anxiety onset is less precise and not associated with a distinct cue. Although it has been claimed that both processes can be measured with certain independence of each other, it is unclear how exactly they differ. In this study, we measured anxiety in mice that received discriminative fear conditioning using behavioral, heart rate and calcium (Ca²⁺) responses in the ventral hippocampal CA1 (vCA1) neurons. We found that the occurrence of fear significantly interfered with anxiety measurements under various conditions. Diazepam reduced basal anxiety level but had no effect during the presentation of conditioned stimulus (CS). Injection of an inhibitory peptide of PKMzeta (ZIP) into the basolateral amygdala almost entirely abolished CS-triggered fear expression and reduced anxiety to basal level. Heart rate measures suggested a small reduction in anxiety during CS-. Calcium responses in the lateral hypothalamus-projecting vCA1 neurons showed a steady decay during CS suggesting a reduced anxiety. Thus, under our experimental conditions, CS presentations likely reduce anxiety level in the fear-conditioned mice.

Effects of a Flavonoid-Rich Fraction on the Acquisition and Extinction of Fear Memory: Pharmacological and Molecular Approaches

The effects of flavonoids have been correlated with their ability to modulate the glutamatergic, serotoninergic, and GABAergic neurotransmission; the major targets of these substances are N-methyl-D-aspartic acid receptor (NMDARs), serotonin type1A receptor (5-HT_1ARs), and the gamma-aminobutyric acid type A receptors (GABA_ARs). Several studies showed that these receptors are involved in the acquisition and extinction of fear memory. This study assessed the effects of treatment prior to conditioning with a flavonoid-rich fraction from the stem bark of Erythrina falcata (FfB) on the acquisition and extinction of the conditioned suppression following pharmacological manipulations and on gene expression in the dorsal hippocampus (DH). Adult male Wistar rats were treated before conditioned fear with FfB, vehicle, an agonist or antagonist of the 5-HT_1AR, GABA_ARs or the GluN2B-NMDAR or one of these antagonists before FfB treatment. The effects of these treatments on fear memory retrieval, extinction training and extinction retrieval were evaluated at 48, 72, and 98 h after conditioning, respectively. We found that activation of GABA_ARs and inactivation of GluN2B-NMDARs play important roles in the acquisition of lick response suppression. FfB reversed the effect of blocking GluN2B-NMDARs on the conditioned fear and induced the spontaneous recovery. Blocking the 5-HT_1AR and the GluN2B-NMDAR before FfB treatment seemed to be associated with weakening of the spontaneous recovery. Expression of analysis of DH samples via qPCR showed that FfB treatment resulted in the overexpression of Htr1a, Grin2a, Gabra5, and Erk2 after the retention test and of Htr1a and Erk2 after the extinction retention test. Moreover, blocking the 5-HT1ARs and the GluN2B-NMDARs before FfB treatment resulted in reduced Htr1a and Grin2b expression after the retention test, but played a distinct role in Grin2a and Erk2 expression, according session evaluated. We show for the first time that the serotoninergic and glutamatergic receptors are important targets for the effect of FfB on the conditioned fear and spontaneous recovery, in which the ERK signaling pathway appears to be modulated. Further, these results provide important information regarding the role of the DH in conditioned suppression. Taken together, our data suggest that FfB represents a potential therapy for preventing or treating memory impairments.

Transcription factor Nr4a1 couples sympathetic and inflammatory cues in CNS-recruited macrophages to limit neuroinflammation

The molecular mechanisms that link the sympathetic stress response and inflammation remain obscure. Here we found that the transcription factor Nr4a1 regulated the production of norepinephrine (NE) in macrophages and thereby limited experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Lack of Nr4a1 in myeloid cells led to enhanced NE production, accelerated infiltration of leukocytes into the central nervous system (CNS) and disease exacerbation in vivo. In contrast, myeloid-specific deletion of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, protected mice against EAE. Furthermore, we found that Nr4a1 repressed autocrine NE production in macrophages by recruiting the corepressor CoREST to the Th promoter. Our data reveal a new role for macrophages in neuroinflammation and identify Nr4a1 as a key regulator of catecholamine production by macrophages.

The Notch intracellular domain represses CRE-dependent transcription

Members of the cyclic-AMP response-element binding protein (CREB) transcription factor family regulate the expression of genes needed for long-term memory formation. Loss of Notch impairs long-term, but not short-term, memory in flies and mammals. We investigated if the Notch-1 (N1) exerts an effect on CREB-dependent gene transcription. We observed that N1 inhibits CREB mediated activation of cyclic-AMP response element (CRE) containing promoters in a γ-secretase-dependent manner. We went on to find that the γ-cleaved N1 intracellular domain (N1ICD) sequesters nuclear CREB1α, inhibits cAMP/PKA-mediated neurite outgrowth and represses the expression of specific CREB regulated genes associated with learning and memory in primary cortical neurons. Similar transcriptional effects were observed with the N2ICD, N3ICD and N4ICDs. Together, these observations indicate that the effects of Notch on learning and memory are, at least in part, via an effect on CREB-regulated gene expression.

The PDE4 inhibitor HT-0712 improves hippocampus-dependent memory in aged mice

Aging is associated with declines in memory and cognitive function. Here, we evaluate the effects of HT-0712 on memory formation and on cAMP response element-binding protein (CREB)-regulated genes in aged mice. HT-0712 enhanced long-term memory formation in normal young mice at brain concentrations similar to those found to increase CRE-mediated gene expression in hippocampal neurons. Aged mice showed significantly poorer contextual and trace conditioning compared with young-adult mice. In aged mice, a single injection of HT-0712 significantly boosted contextual and trace long-term memory. Additional effects of HT-0712 were seen in a spatial memory task. Our parallel biochemical experiments revealed that inductions of the CREB-regulated genes, cFos, Zif268, and Bdnf, after fear conditioning were diminished in aged mice. HT-0712 facilitated expression of these CREB-regulated genes in aged hippocampus, indicating that the drug engages a CREB-regulated mechanism in vivo. These findings corroborate and extend our previous results on the mechanism of action of HT-0712 and its efficacy to enhance memory formation. Our data also indicate that HT-0712 may be effective to treat age-associated memory impairment in humans.

Stress and glucocorticoid regulation of NR4A genes in mice

The NR4A nuclear receptors subgroup, comprising Nur77 (NR4A1), Nurr1 (NR4A2), and Nor1 (NR4A3), are orphan receptors induced by a variety of signals, including stress. These receptors are described as early response genes and in vitro studies have shown that they take part in regulation of the hypothalamic-pituitary-adrenal (HPA) axis, the major stress-responsive neuroendocrine system. This study analyzes further the interweaving of NR4A receptors with the HPA axis at rest and after a restraint stress in vivo in mice. We show that each NR4A member has a similar mRNA expression pattern and low levels of expression at rest except, in particular in hippocampus for Nurr1 and in adrenals for Nur77. After restraint stress, mRNA expression of each NR4A is markedly induced in adrenals and pituitary and significantly in hypothalamus. In higher cerebral regions, such as cortex, hippocampus, and amygdala, induction of NR4A mRNA elicited by stress was very moderate or undetected. The influence of glucocorticoids on NR4A mRNA expression was analyzed by comparing wild-type and Cbg k.o. mice used as a model of glucocorticoid hyposignaling. Nur77 mRNA and protein expression and a downstream Nur77 target gene were found to be affected in the hypothalamus and pituitary of the Cbg k.o. mice but not in hippocampus and cortex. These results further support a physiological role of NR4A orphan receptors in the glucocorticoid response to stress.

Two waves of transcription are required for long-term memory in the honeybee

Storage of information into long-term memory (LTM) usually requires at least two waves of transcription in many species. However, there is no clear evidence of this phenomenon in insects, which are influential models for memory studies. We measured retention in honeybees after injecting a transcription inhibitor at different times before and after conditioning. We identified two separate time windows during which the transcription blockade impairs memory quantitatively and qualitatively, suggesting the occurrence of an early transcription wave (triggered during conditioning) and a later one (starting several hours after learning). Hence insects, like other species, would require two transcription waves for LTM formation.

Differential roles for Nr4a1 and Nr4a2 in object location vs. object recognition long-term memory

Nr4a1 and Nr4a2 are transcription factors and immediate early genes belonging to the nuclear receptor Nr4a family. In this study, we examine their role in long-term memory formation for object location and object recognition. Using siRNA to block expression of either Nr4a1 or Nr4a2, we found that Nr4a2 is necessary for both long-term memory for object location and object recognition. In contrast, Nr4a1 appears to be necessary only for object location. Indeed, their roles in these different types of long-term memory may be dependent on their expression in the brain, as NR4A2 was found to be expressed in hippocampal neurons (associated with object location memory) as well as in the insular and perirhinal cortex (associated with object recognition memory), whereas NR4A1 showed minimal neuronal expression in these cortical areas. These results begin to elucidate how NR4A1 and NR4A2 differentially contribute to object location versus object recognition memory.

Common brain activations for painful and non-painful aversive stimuli

BACKGROUND

Identification of potentially harmful stimuli is necessary for the well-being and self-preservation of all organisms. However, the neural substrates involved in the processing of aversive stimuli are not well understood. For instance, painful and non-painful aversive stimuli are largely thought to activate different neural networks. However, it is presently unclear whether there is a common aversion-related network of brain regions responsible for the basic processing of aversive stimuli. To help clarify this issue, this report used a cross-species translational approach in humans (i.e. meta-analysis) and rodents (i.e. systematic review of functional neuroanatomy).

RESULTS

Animal and human data combined to show a core aversion-related network, consisting of similar cortical (i.e. MCC, PCC, AI, DMPFC, RTG, SMA, VLOFC; see results section or abbreviation section for full names) and subcortical (i.e. Amyg, BNST, DS, Hab, Hipp/Parahipp, Hyp, NAc, NTS, PAG, PBN, raphe, septal nuclei, Thal, LC, midbrain) regions. In addition, a number of regions appeared to be more involved in pain-related (e.g. sensory cortex) or non-pain-related (e.g. amygdala) aversive processing.

CONCLUSIONS

This investigation suggests that aversive processing, at the most basic level, relies on similar neural substrates, and that differential responses may be due, in part, to the recruitment of additional structures as well as the spatio-temporal dynamic activity of the network. This network perspective may provide a clearer understanding of why components of this circuit appear dysfunctional in some psychiatric and pain-related disorders.

Neuroanatomical substrates involved in cannabinoid modulation of defensive responses

Administration of Cannabis sativa derivatives causes anxiolytic or anxiogenic effects in humans and laboratory animals, depending on the specific compound and dosage used. In agreement with these findings, several studies in the last decade have indicated that the endocannabinoid system modulates neuronal activity in areas involved in defensive responses. The mechanisms of these effects, however, are still not clear. The present review summarizes recent data suggesting that they involve modulation of glutamate and GABA-mediated neurotransmission in brain sites such as the medial prefrontal cortex, amygdaloid complex, bed nucleus of the stria terminalis, hippocampus and dorsal periaqueductal gray. Moreover, we also discuss results indicating that, in these regions, the endocannabinoid system could be particularly engaged by highly stressful situations.

Identifying a network of brain regions involved in aversion-related processing: a cross-species translational investigation

The ability to detect and respond appropriately to aversive stimuli is essential for all organisms, from fruit flies to humans. This suggests the existence of a core neural network which mediates aversion-related processing. Human imaging studies on aversion have highlighted the involvement of various cortical regions, such as the prefrontal cortex, while animal studies have focused largely on subcortical regions like the periaqueductal gray and hypothalamus. However, whether and how these regions form a core neural network of aversion remains unclear. To help determine this, a translational cross-species investigation in humans (i.e., meta-analysis) and other animals (i.e., systematic review of functional neuroanatomy) was performed. Our results highlighted the recruitment of the anterior cingulate cortex, the anterior insula, and the amygdala as well as other subcortical (e.g., thalamus, midbrain) and cortical (e.g., orbitofrontal) regions in both animals and humans. Importantly, involvement of these regions remained independent of sensory modality. This study provides evidence for a core neural network mediating aversion in both animals and humans. This not only contributes to our understanding of the trans-species neural correlates of aversion but may also carry important implications for psychiatric disorders where abnormal aversive behavior can often be observed.

Distinctive features of Egr transcription factor regulation and DNA binding activity in CA1 of the hippocampus in synaptic plasticity and consolidation and reconsolidation of fear memory

Activity-dependent regulation of Egr1/Zif268, a transcription factor (TF) of the Egr family, is essential for stabilization of dentate gyrus synaptic plasticity and consolidation and reconsolidation of several forms of memory. The gene can be rapidly induced in selective brain circuits after certain types of learning or after recall. Here, we focused on area CA1 and examined regulation of Egr1, Egr2, and Egr3 mRNA and protein, and their DNA binding activity to the Egr response element (ERE) at different times after LTP in vivo and after learning and recall of a fear memory. We found LTP in CA1 leads to rapid induction of the three Egrs, however only Egr1 protein was overexpressed without a co-ordinated change in binding activity, indicating a fundamental difference between CA1 and dentate gyrus LTP. Our investigations in fear memory reveal that both learning and retrieval lead to an increase in binding of constitutively expressed Egr1 and Egr3 to the ERE, but not Egr2. Memory recall was also associated with increased Egr1 protein translation. The nature and temporal dynamics of these changes and tests for interactions between TFs suggest that in addition to ERE-mediated transcription, Egr1 in CA1 may interact with the TF c-Fos to regulate genes via other DNA response elements.

The role of NR4A transcription factors in memory formation

In various physiological contexts, Nr4a genes are transcribed in response to external stimuli as part of an immediate early response that initiates a cascade of gene expression ultimately leading to distinct physiological outcomes in each of these contexts. The signaling pathway that initiates Nr4a gene expression in most of these contexts consists of elevated intracellular cAMP activating PKA, which in turn leads to phosphorylation of CREB and new gene synthesis. This cAMP-PKA-CREB pathway is a central molecular pathway in the formation of a long-term memory. Indeed, learning induces Nr4a family gene expression, and long-term memory formation requires at least two waves of transcription after learning, suggesting that NR4A nuclear receptors may contribute to the second of these waves of gene expression. In this article, we review insights gained in other physiological contexts regarding Nr4a function and regulation, and highlight how these lessons can be applied to the study of memory formation.

A novel, rapidly acquired and persistent spatial memory task that induces immediate early gene expression

Background

The Morris water maze task is a hippocampus-dependent learning and memory test that typically takes between 3 days to 2 weeks of training. This task is used to assess spatial learning and induces the expression of genes known to be crucial to learning and memory in the hippocampus. A major caveat in the protocol is the prolonged duration of training, and difficulty of assessing the time during training in which animals have learned the task. We introduce here a condensed version of the task that like traditional water maze tasks, creates lasting hippocampus-dependent spatial cognitive maps and elicits gene expression following learning.

Methods

This paradigm was designed for rats to quickly acquire a hippocampus-dependent spatial cognitive map and retain this memory for at least 24 hours. To accomplish this, we interspersed visible and hidden training trials, delivering them in a massed fashion so training takes a maximum of 15 minutes. Learning was assessed based on latencies to the platform during each training trial, as well as time spent in the goal quadrant during probe testing 30 minutes and 24 hours after training. Normal rats were compared to two impaired cohorts (rats with fimbria-fornix lesions and rats administered NMDA receptor antagonist (CPP)). To quantitate hippocampal expression of known learning genes, real-time polymerase chain reaction (RT-PCR) was performed on hippocampal cDNA.

Results

We show that massed training using alternating visible and hidden training trials generates robust short-term working and long-term reference memories in rats. Like the traditional Morris water maze paradigm, this task requires proper hippocampal function, as rats with fimbria-fornix lesions and rats administered CPP fail to learn the spatial component of the task. Furthermore, training in this paradigm elicits hippocampal expression of genes upregulated following learning in a variety of spatial tasks: homer1a, cfos and zif268.

Conclusions

We introduce here a condensed version of the Morris water maze, which is like a traditional water maze paradigm, in that it is hippocampus-dependent, and elicits hippocampal expression of learning genes. However, this task is administered in 15 minutes and induces spatial memory for at least 24 hours.

Behavioral effects of neuropeptides in rodent models of depression and anxiety

In recent years, studies have advocated neuropeptide systems as modulators for the behavioral states found in mood disorders such as depression and anxiety disorders. Neuropeptides have been tested in traditional animal models and screening procedures that have been validated by known antidepressants and anxiolytics. However, it has become clear that although these tests are very useful, neuropeptides have distinct behavioral effects and dose-dependent characteristics, and therefore, use of these tests with neuropeptides must be done with an understanding of their unique characteristics. This review will focus on the behavioral actions of neuropeptides and their synthetic analogs, particularly in studies utilizing various preclinical tests of depression and anxiety. Specifically, the following neuropeptide systems will be reviewed: corticotropin-releasing factor (CRF), urocortin (Ucn), teneurin C-terminal associated peptide (TCAP), neuropeptide Y (NPY), arginine vasopressin (AVP), oxytocin, the Tyr-MIF-1 family, cholecystokinin (CCK), galanin, and substance P. These neuropeptide systems each have a unique role in the regulation of stress-like behavior, and therefore provide intriguing therapeutic targets for mood disorder treatment.

Endocannabinoid system and fear conditioning

The endocannabinoid system has been proposed to modulate neuronal functions involved in distinct types of defensive reactions, possibly counteracting the harmful consequences of stressful stimuli. However, the precise brain sites for this action remain to be further explored. This chapter summarizes the data about the role of the endocannabinoid system in the processing of conditioned fear as well as the potential neural subtract for its actions.

The activity-regulated cytoskeletal-associated protein (Arc/Arg3.1) is required for memory consolidation of pavlovian fear conditioning in the lateral amygdala

The activity-regulated cytoskeletal-associated protein (Arc/Arg3.1) is an immediate early gene that has been widely implicated in hippocampal-dependent learning and memory and is believed to play an integral role in synapse-specific plasticity. Here, we examined the role of Arc/Arg3.1 in amygdala-dependent Pavlovian fear conditioning. We first examined the regulation of Arc/Arg3.1 mRNA and protein after fear conditioning and LTP-inducing stimulation of thalamic inputs to the lateral amygdala (LA). Quantitative real-time PCR, in situ hybridization, Western blotting and immunohistochemistry revealed a significant upregulation of Arc/Arg3.1 mRNA and protein in the LA relative to controls. In behavioral experiments, intra-LA infusion of an Arc/Arg3.1 antisense oligodeoxynucleotide (ODN) was observed to be anatomically restricted to the LA, taken up by LA cells, and to promote significant knockdown of Arc/Arg3.1 protein. Rats given intra-LA infusions of multiple doses of the Arc/Arg3.1 ODN showed an impairment of LTM (tested approximately 24 later), but no deficit in STM (tested 3 h later) relative to controls infused with scrambled ODN. Finally, to determine whether upregulation of Arc/Arg3.1 occurs downstream of ERK/MAPK activation, we examined Arc/Arg3.1 expression in rats given intra-LA infusion of the MEK inhibitor U0126. Relative to vehicle controls, infusion of U0126 impaired training-induced increases in Arc/Arg3.1 expression. These findings suggest that Arc/Arg3.1 expression in the amygdala is required for fear memory consolidation, and further suggest that Arc/Arg3.1 regulation in the LA is downstream of the ERK/MAPK signaling pathway.

Effects of cannabidiol and diazepam on behavioral and cardiovascular responses induced by contextual conditioned fear in rats

Cannabidiol (CBD) is a non-psychotomimetic compound from Cannabis sativa that induces anxiolytic-like effects similar to diazepam in animal models of innate aversive behavior. However, the effects of CBD contextual conditioned fear have not been studied. Therefore, the aim of this work was to compare the behavioral and cardiovascular effects of CBD and diazepam, a prototype anxiolytic, in animals submitted to a contextual conditioned fear paradigm. Male Wistar rats were submitted to a 10min conditioning session (six footshocks, 2.5 mA, 3s, delivered at pseudo-random intervals). The behavioral and cardiovascular responses to the context were measured 24h later in a 10 min test session. Diazepam (2.5 mg/kg), FG-7142 (8 mg/kg), a benzodiazepine inverse agonist, or CBD (10 mg/kg) were administered i.p. before the test session. Conditioned rats submitted to the aversive context exhibited more freezing behavior and a larger increase in blood pressure and heart rate as compared to non-conditioned animals. These effects were attenuated by CBD and diazepam in the conditioned animals. These drugs did not have any effect in non-conditioned rats. FG-7142 treatment failed to change the behavioral and cardiovascular responses to the aversive context. In conclusion, the results suggest that CBD has anxiolytic-like properties similar to those of diazepam in a rat model of conditioned fear to context.

An endogenous inhibitor of calcium/calmodulin-dependent kinase II is up-regulated during consolidation of fear memory

CaMKIINalpha and CaMKIINbeta are endogenous inhibitors of the abundant synaptic protein, calcium/calmodulin-dependent protein kinase II (CaMKII). CaMKII exerts a prominent function in memory formation and the endogenous inhibitors might be important regulators of CaMKII activity during this process. Here we investigated whether or not CaMKIINalpha and CaMKIINbeta gene expressions are regulated in the mouse hippocampus and amygdala after background contextual fear conditioning. Quantitative real-time PCR revealed that the hippocampal expression of CaMKIINalpha mRNA was up-regulated 30 and 60 min after conditioning. In contrast, CaMKIINbeta mRNA expression did not change. The up-regulation of CaMKIINalpha expression was specific for the fear memory because the context alone and a shock control did not induce any variation of transcription level. Quantification of in situ hybridization signals showed that CaMKIINalpha expression increased in hippocampal area CA1, in the dentate gyrus (DG) and in the lateral amygdala (LA) 30 min after training. Our findings show an up-regulation in the expression of the endogenous inhibitor gene CaMKIINalpha during consolidation of fear memory. The early onset and the amplitude of the up-regulation are similar to those of immediate-early genes. Taken together, our results suggest that the CaMKIINalpha inhibitor has a physiological role in controlling CaMKII activity from an early stage of memory consolidation.

Animal studies of amygdala function in fear and uncertainty: relevance to human research

This article reviews research in both animals and humans on the considerable progress made in elucidating a brain circuitry of fear, particularly the importance of the amygdala in fear conditioning. While there is considerable agreement about the participation of the amygdala in fear in both animals and humans, there are several issues about the function of the amygdala raised by the human research that have not been addressed by or may be answered by animal research. Three of these are addressed in this article: (1) is the amygdala involved in or necessary for both fear learning and unconditioned fear? (2) Does the amygdala code for intensity of fear? (3) Is the amygdala preferentially involved in fear, or is it also activated when there are no overt fear or aversive stimuli, but where the situation can be described as uncertain? We present evidence indicating that the rodent amygdala is involved in some types of fear (conditioned fear), but not all types (unconditioned fear), and may therefore have significance for a differential neurobiology of certain anxiety disorders in humans. Further, similar to the human amygdala, the rodent amygdala responds to varying intensities of aversive stimulation. Finally, it is suggested that, similar to humans, the rodent amygdala is involved in the evaluation of uncertainty. We conclude that progress on elucidating the role of the amygdala in fear is facilitated by corroboration of findings from both animal and human research.

Memory reconsolidation engages only a subset of immediate-early genes induced during consolidation

The relationship between memory consolidation and reconsolidation at the molecular level is poorly understood. Here, we identify three immediate-early genes that are differentially regulated in the mouse hippocampus after contextual fear conditioning and reactivation of the context-shock memory: serum- and glucocorticoid-induced kinase 1 (SGK1), SGK3, and nerve growth factor-inducible gene B (NGFI-B). The upregulation of SGK1 expression was not specific for the context-shock association and therefore not suitable for a comparison of contextual memory consolidation and reconsolidation. SGK3 expression was upregulated during both consolidation and reconsolidation. Analysis of SGK3 expression showed that expression changes elicited by a context-shock association during consolidation can subsequently be recapitulated during reconsolidation and that the transcriptional changes induced by retrieval depend on the remoteness of the memory. On the other hand, we found that NGFI-B is regulated during consolidation but not reconsolidation. This consolidation-specific regulation occurs in hippocampal area CA1. Our discovery of a consolidation-specific transcription indicates that reconsolidation is only a partial recapitulation of consolidation at the transcriptional level. Such partial rather than total recapitulation may have evolved as a more economic and reliable mechanism for organisms to modify memory.

Cholecystokinin-2 (CCK2) receptor-mediated anxiety-like behaviors in rats

Cholecystokinin (CCK) is a neurotransmitter in the brain closely related to anxiety. Of the two CCK receptor subtypes, CCK(2) receptors are most implicated in the control of anxiety-related behavior. CCK(2) receptor activation causes anxiogenic effects while the blockade of this receptor has anxiolytic effects. This review focuses on the molecular mechanisms of CCK(2) receptors underlying anxiety-related behaviors of PVG hooded and Spraque-Dawley (SD) rats in two anxiety models (elevated plus-maze [EPM] and cat exposure test). PVG hooded rats showed prolonged freezing behavior in the cat exposure test while SD rats showed very low levels of freezing. A CCK(2) receptor antagonist (LY225910) attenuated freezing behavior in PVG hooded rats while a CCK(2) receptor agonist (CCK-4) increased freezing behavior in SD rats. In contrast, the two strains behaved similarly on the EPM. CCK-4 caused a pronounced anxiogenic effect in PVG hooded rats but only a slight effect in SD rats. CCK(2) antagonists also showed more pronounced anxiolytic effects in PVG hooded rats than in SD rats. CCK(2) receptor expression was greater in PVG hooded than in SD rats in the cortex and hippocampus. Genetic studies also demonstrated four differences in the DNA sequence of the CCK(2) receptor gene between the two rat strains.

The neurobiology of conditioned and unconditioned fear: a neurobehavioral system analysis of the amygdala

A neurobehavioral system approach to conditioned and unconditioned fear is presented. By employing reproducible fear behaviors in Pavlovian conditioning and unconditioned fear paradigms, it has been possible to delineate some differences in neural circuitry and cellular biology for conditioned and unconditioned fear. It is suggested that the basolateral complex of the amygdala and the central nucleus of the amygdala are part of the neural circuitry for fear conditioning but not for unconditioned fear to a predator odor. Furthermore, changes in expression of the transcription factor early growth response gene 1 in the lateral nucleus of the amygdala are shown to be important for contextual fear conditioning but not for unconditioned fear to a predator odor. In addition, data suggest that although conditioning to a synthetic predator odor, trimethylthiazoline, has been difficult to demonstrate, conditioning can occur by modifying by the environment. Finally, the relevance of the animal studies to human anxiety disorders is discussed.

Plasticity-associated molecular and structural events in the injured brain

Injury to the brain appears to create a fertile ground for functional and structural plasticity that is, at least partly, responsible for functional recovery. Increases in dendritic arborization, spine density, and synaptogenesis in both peri-injury and intact cortical areas are the potential morphological strategies that enable the brain to reorganize its neuronal circuits. These injury-initiated alterations are time-dependent and frequently proceed in interaction with behavior-related signals. A complex concert of a variety of genes/proteins is required to tightly control these changes. Two broad categories of molecules appear to be involved. First, regulatory molecules or effector molecules with regulatory function, such as immediate early genes/transcription factors, kinase network proteins, growth factors, and neurotransmitter receptors, and second, structural proteins, such as adhesion molecules and compounds of synapses, growth cones, and cytoskeleton. A better understanding of the processes contributing to postinjury plasticity may be an advantage for developing new and more effective therapeutic approaches. This knowledge might also shed light on other forms of brain plasticity, such as those involved in learning processes or ontogeny.