Inhibitory Avoidance Learning Research Articles

The herbicide glyphosate inhibits hippocampal long-term potentiation and learning through activation of pro-inflammatory signaling

Glyphosate, a herbicide marketed as Roundup, is widely used but there are concerns this exposure could impair cognitive function. In the CA1 region of rat hippocampal slices, we investigated whether glyphosate alters synaptic transmission and long-term potentiation (LTP), a cellular model of learning and memory. Our hypothesis is that glyphosate alters neuronal function and impairs LTP induction via activation of pro-inflammatory processes. Roundup depressed excitatory synaptic potentials(EPSPs) in a dose-dependent manner with complete suppression at 2000 mg/L. At concentrations ≤ 20 mg/L Roundup did not affect basal transmission, but 4 mg/L Roundup administered for 30 min inhibited LTP induction. Acute administration of 10–100 μM glyphosate also inhibited LTP induction. Minocycline, an inhibitor of microglial activation, and TAK-242, an inhibitor of toll-like receptor 4 (TLR4), both overcame the inhibitory effects of 100 µM glyphosate. Similarly, lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS), a different TLR4 antagonist, overcame the inhibitory effects. In addition, ISRIB (integrated stress response inhibitor) and quercetin, an inhibitor of endoplasmic reticulum stress, overcame the inhibitory effects. We also observed that in vivo glyphosate injection (16.9 mg/kg i.p.) impaired one-trial inhibitory avoidance learning. This learning deficit was overcome by TAK-242. These observations indicate that glyphosate can impair cognitive function through pro-inflammatory signaling in microglia.

Acrylamide inhibits long-term potentiation and learning involving microglia and pro-inflammatory signaling

Acrylamide is a chemical used in various industries and a product following high-temperature cooking of vegetables containing asparagine. Environmental or dietary exposure to acrylamide could impair cognitive function because of its neurotoxicity. Using rat hippocampal slices, we tested whether acrylamide alters induction of long-term potentiation (LTP), a cellular model of learning and memory. We hypothesized that acrylamide impairs cognitive function via activation of pro-inflammatory cytokines because robust upregulation of NLRP3 inflammasome has been reported. Although acrylamide up to 3 mM did not alter basal synaptic transmission, incubation with 10 μM or acute administration of 100 μM acrylamide inhibited induction of LTP. Inhibitors of toll-like receptor 4 (TLR4), and minocycline, an inhibitor of microglial activation, overcame the effects of acrylamide on LTP induction. Furthermore, we observed that acrylamide failed to inhibit LTP after administration of MCC950, an inhibitor of NLRP3, or in the presence of Interleukin-1 receptor antagonist (IL-1Ra). We also found that in vivo acrylamide injection transiently impaired body weight gain and impaired one-trial inhibitory avoidance learning. This learning deficit was overcome by MCC950. These results indicate that cognitive impairment by acrylamide is mediated by mechanisms involving microglia and release of cytokines via NLRP3 activation.

The D2-like Dopamine Receptor Agonist Quinpirole Microinjected Into the Ventral Pallidum Dose-Dependently Inhibits the VTA and Induces Place Aversion.

BackgroundThe ventral pallidum (VP) is a dopaminoceptive forebrain structure regulating the ventral tegmental area (VTA) dopaminergic population activity. We have recently demonstrated that in the VP, the D2-like dopamine (DA) receptor agonist quinpirole dose dependently facilitates memory consolidation in inhibitory avoidance and spatial learning. According to our hypothesis, quinpirole microinjected into the VP can modulate the VTA DAergic activity and influence motivation and learning processes of rats.MethodsQuinpirole was microinjected at 3 different doses into the VP of male rats, and controls received vehicle. Single unit recordings were employed to assess VTA DAergic activity. To investigate the possible reinforcing or aversive effect of quinpirole in the VP, the conditioned place preference paradigm was used.ResultsOur results showed that intra-VP quinpirole microinjection regulates VTA DAergic neurons according to an inverted U-shaped dose-response curve. The largest dose of quinpirole decreased the population activity and strongly reduced burst activity of the DAergic neurons in the first hour after its application. In contrast, the 2 smaller doses increased DA population activity, but their effect started with a delay 1 hour after their microinjection. The CPP experiments revealed that the largest dose of quinpirole in the VP induced place aversion in the rats. Furthermore, the largest dose of quinpirole induced an acute locomotor activity reduction, while the medium dose led to a long-duration increase in locomotion.ConclusionsIn summary, quinpirole dose dependently regulates VTA DAergic activity as well as the motivation and motor behavior of the rats at the level of the VP.

A Proinflammatory Stimulus Disrupts Hippocampal Plasticity and Learning via Microglial Activation and 25-Hydroxycholesterol.

Inflammatory cells, including macrophages and microglia, synthesize and release the oxysterol 25-hydroxycholesterol (25HC), which has antiviral and immunomodulatory properties. Here, we examined the effects of lipopolysaccharide (LPS), an activator of innate immunity, on 25HC production in microglia, and the effects of LPS and 25HC on CA1 hippocampal synaptic plasticity and learning. In primary microglia, LPS markedly increases the expression of cholesterol 25-hydroxylase (Ch25h), the key enzyme involved in 25HC synthesis, and increases the levels of secreted 25HC. Wild-type microglia produced higher levels of 25HC than Ch25h knock-out (KO) microglia with or without LPS. LPS treatment also disrupts long-term potentiation (LTP) in hippocampal slices via induction of a form of NMDA receptor-dependent metaplasticity. The inhibitory effects of LPS on LTP were mimicked by exogenous 25HC, and were not observed in slices from Ch25h KO mice. In vivo, LPS treatment also disrupts LTP and inhibits one-trial learning in wild-type mice, but not Ch25h KO mice. These results demonstrate that the oxysterol 25HC is a key modulator of synaptic plasticity and memory under proinflammatory stimuli.SIGNIFICANCE STATEMENT Neuroinflammation is thought to contribute to cognitive impairment in multiple neuropsychiatric illnesses. In this study, we found that a proinflammatory stimulus, LPS, disrupts hippocampal LTP via a metaplastic mechanism. The effects of LPS on LTP are mimicked by the oxysterol 25-hydroxycholesterol (25HC), an immune mediator synthesized in brain microglia. Effects of LPS on both synaptic plasticity and one-trial inhibitory avoidance learning are eliminated in mice deficient in Ch25h (cholesterol 25-hydroxylase), the primary enzyme responsible for endogenous 25HC synthesis. Thus, these results indicate that 25HC is a key mediator of the effects of an inflammatory stimulus on hippocampal function and open new potential avenues to overcome the effects of neuroinflammation on brain function.

Dynamics of Dendritic Spines in Dorsal Striatum after Retrieval of Moderate and Strong Inhibitory Avoidance Learning

In marked contrast to the ample literature showing that the dorsal striatum is engaged in memory consolidation, little is known about its involvement in memory retrieval. Recent findings demonstrated significant increments in dendritic spine density and mushroom spine counts in dorsal striatum after memory consolidation of moderate inhibitory avoidance (IA) training; further increments were found after strong training. Here, we provide evidence that in this region spine counts were also increased as a consequence of retrieval of moderate IA training, and even higher mushroom spine counts after retrieval of strong training; by contrast, there were fewer thin spines after retrieval. Similar changes in mushroom and thin spine populations were found in the ventral striatum (nucleus accumbens), but they were related to the aversive stimulation and not to memory retrieval. These results suggest that memory retrieval is a dynamic process which produces neuronal structural plasticity that might be necessary for maintaining or strengthening assemblies that encode stored information.

Ketamine treatment upon memory retrieval reduces fear memory in marmoset monkeys

Emotionally arousing experiences are retained very well as seen in posttraumatic stress disorder (PTSD). Various lines of evidence indicate that reactivation of these memories renders them labile which offers a potential time-window for intervention. We tested in non-human primates whether ketamine, administered during fear memory reactivation, affected passive (inhibitory) avoidance learning. For the consolidation of contextual emotional memory, the unescapable foot-shock paradigm in a passive avoidance task with two compartments (dark vs illuminated) was used. After entering the dark compartment, marmoset monkeys received four random foot-shocks (1 mA, 4 s) within 15-min. This stressful exposure increased the saliva cortisol and heart rate and impaired REM-sleep (p<0.05). One week later the monkeys were re-exposed to the stressful situation for the reconsolidation of the fearful experience. During the re-exposure the monkeys were treated with ketamine (0.5 mg/kg) or saline. In week 3, the monkeys were placed in the experimental setting to test their memory for the fearful experience. In contrast to the vehicle-treated monkeys, who avoided the dark compartment, the ketamine-treated monkeys entered the dark compartment that was previously associated with the fearful experience (p<0.05). Post-mortem analysis of the hippocampus showed that ketamine-treated animals exhibited less doublecortin positive neurons and BrdU-labeled cells in the dentate gyrus. This study reveals that a single low dose of ketamine, administered upon fear retrieval in monkeys, reduce contextual fear memory and attenuate neurogenesis in the hippocampus. These are important findings for considering ketamine as a potential candidate to target traumatic memories in PTSD.

Distinct Transcriptomic Profiles in the Dorsal Hippocampus and Prelimbic Cortex Are Transiently Regulated following Episodic Learning

A fundamental, evolutionarily conserved biological mechanism required for long-term memory formation is rapid induction of gene transcription upon learning in relevant brain areas. For episodic types of memories, two regions undergoing this transcription are the dorsal hippocampus (dHC) and prelimbic (PL) cortex. Whether and to what extent these regions regulate similar or distinct transcriptomic profiles upon learning remain to be understood. Here, we used RNA sequencing in the dHC and PL cortex of male rats to profile their transcriptomes in untrained conditions (baseline) and at 1 h and 6 d after inhibitory avoidance learning. We found that, of 33,713 transcripts, >14,000 were significantly expressed at baseline in both regions and ∼3000 were selectively enriched in each region. Gene Ontology biological pathway analyses indicated that commonly expressed pathways included synapse organization, regulation of membrane potential, and vesicle localization. The enriched pathways in the dHC were gliogenesis, axon development, and lipid modification, while in the PL cortex included vesicle localization and synaptic vesicle cycle. At 1 h after learning, 135 transcripts changed significantly in the dHC and 478 in the PL cortex; of these, only 34 were shared. Biological pathways most significantly regulated by learning in the dHC were protein dephosphorylation, glycogen and glucan metabolism, while in the PL cortex were axon development and axonogenesis. The transcriptome profiles returned to baseline by 6 d after training. Thus, a significant portion of dHC and PL cortex transcriptomic profiles is divergent, and their regulation upon learning is largely distinct and transient.SIGNIFICANCE STATEMENT Long-term episodic memory formation requires gene transcription in several brain regions, including the hippocampus and PFC. The comprehensive profiles of the dynamic mRNA changes that occur in these regions following learning are not well understood. Here, we performed RNA sequencing in the dorsal hippocampus and prelimbic cortex, a PFC subregion, at baseline, 1 h, and 6 d after episodic learning in rats. We found that, at baseline, dorsal hippocampus and prelimbic cortex differentially express a significant portion of mRNAs. Moreover, learning produces a transient regulation of region-specific profiles of mRNA, indicating that unique biological programs in different brain regions underlie memory formation.

Oxysterols Modulate the Acute Effects of Ethanol on Hippocampal N-Methyl-d-Aspartate Receptors, Long-Term Potentiation, and Learning.

Ethanol is a noncompetitive inhibitor of N-methyl-d-aspartate receptors (NMDARs) and acutely disrupts hippocampal synaptic plasticity and learning. In the present study, we examined the effects of oxysterol positive allosteric modulators (PAMs) of NMDARs on ethanol-mediated inhibition of NMDARs, block of long-term potentiation (LTP) and long-term depression (LTD) in rat hippocampal slices, and defects in one-trial learning in vivo. We found that 24S-hydroxycholesterol and a synthetic oxysterol analog, SGE-301, overcame effects of ethanol on NMDAR-mediated synaptic responses in the CA1 region but did not alter acute effects of ethanol on LTD; the synthetic oxysterol, however, overcame acute inhibition of LTP. In addition, both oxysterols overcame persistent effects of ethanol on LTP in vitro, and the synthetic analog reversed defects in one-trial inhibitory avoidance learning in vivo. These results indicate that effects of ethanol on both LTP and LTD arise by complex mechanisms beyond NMDAR antagonism and that oxysterol NMDAR PAMS may represent a novel approach for preventing and reversing acute ethanol-mediated changes in cognition.SIGNIFICANCE STATEMENTEthanol acutely inhibits hippocampal NMDARs, LTP, and learning. This study found that certain oxysterols that are NMDAR-positive allosteric modulators can overcome the acute effects of ethanol on NMDARs, LTP, and learning. Oxysterols differ in their effects from agents that inhibit integrated cellular stress responses.

Inhibitors of cellular stress overcome acute effects of ethanol on hippocampal plasticity and learning

Ethanol intoxication can produce marked changes in cognitive function including states in which the ability to learn and remember new information is completely disrupted. These defects likely reflect changes in the synaptic plasticity thought to underlie memory formation. We have studied mechanisms contributing to the adverse effects of ethanol on hippocampal long-term potentiation (LTP) and provided evidence that ethanol-mediated LTP inhibition involves a form of metaplasticity resulting from local metabolism of ethanol to acetaldehyde and untimely activation of N-methyl-d-aspartate receptors (NMDARs), both of which are neuronal stressors. In the present studies, we sought to understand the role of cellular stress in LTP defects, and demonstrate that ethanol's effects on LTP in the CA1 hippocampal region are overcome by agents that inhibit cellular stress responses, including ISRIB, a specific inhibitor of integrated stress responses, and GW3965, an agonist that acts at liver X receptors (LXRs) and dampens cellular stress. The agents that alter LTP inhibition also prevent the adverse effects of acute ethanol on one trial inhibitory avoidance learning. Unexpectedly, we found that the LXR agonist but not ISRIB overcomes effects of ethanol on synaptic responses mediated by N-methyl-d-aspartate receptors (NMDARs). These results have implications for understanding the adverse effects of ethanol and possibly for identifying novel paths to treatments that can prevent or overcome ethanol-induced cognitive dysfunction.

Role of Hippocampal 5-HT6 Receptors in Glucocorticoid-Induced Enhancement of Memory Consolidation in Rats.

Introduction:of the study: Post-training administration of glucocorticoids enhance memory consolidation of inhibitory avoidance learning. Given the involvement of 5-HT6 receptors in memory processing and the interaction of glucocorticoids with the brain serotonergic system in modulating memory processing, we investigated whether the effect of glucocorticoids on the consolidation of emotionally arousing training depends on hippocampal 5-HT6 receptors.Methods:Rats were trained in an inhibitory avoidance task and immediately received the systemic injections of corticosterone (CORT) as well as the intra-hippocampal injections of 5-HT receptors agonist or antagonist. The memory retention test was done 48 hours after training and immediately after the behavioral test, the animals were sacrificed and the hippocampi (left and right) rapidly dissected out for molecular studies.Results:Post-training injections of different doses of CORT (1.25, 2.5, 5, and 10 mg/kg) enhanced memory retention in a dose-dependent manner. The CORT-induced enhancement of memory consolidation was blocked by bilateral intra-hippocampal injections of 5-HT6 receptor antagonist SB271046 (5 or 10 ng/per side), but not agonist EMD386088 (5 or 10 ng/per side). Furthermore, systemic CORT reduced 5-HT6 receptor mRNA and protein expression in the hippocampus. Both doses of 5-HT6 receptor agonist and antagonist significantly enhanced and reduced the expression of the 5-HT6 receptor, respectively, and both ligands at the higher dose (10 ng) enhanced memory consolidation. Moreover, CORT injection attenuated and enhanced, respectively, the effects of agonist and antagonist on 5-HT6 receptor expression.Conclusion:These behavioral and molecular findings indicated an interaction between glucocorticoids and hippocampal 5-HT6 receptors in the consolidation of emotionally arousing experiences.

Inhibition of transcription and translation in dorsal hippocampus does not interfere with consolidation of memory of intense training.

Findings of several experiments indicate that many treatments that typically interfere with memory consolidation are ineffective in preventing or attenuating memory induced by intense training. As extensive evidence suggests that the consolidation of newly acquired memories requires gene expression and de novo protein synthesis the present study investigated whether intense training prevents consolidation impairment induced by blockers of mRNA and protein synthesis. Rats were given a single inhibitory training trial using a moderate (1.0 mA) or a relatively intense (2.0 mA) foot-shock. Bilateral hippocampal infusions of the mRNA synthesis blocker DRB (10, 40 or 80 ng/0.5 µL/hemisphere) or the protein synthesis inhibitor anisomycin (ANI), an inhibitor de novo protein synthesis (15.62, 31.25, or 62.50 µg/0.5 µL/hemisphere) were administered 15 min prior to training. Retention was measured at 30 min or 48 h following training. DRB and ANI impaired memory of moderate training in a dose-dependent manner without affecting short-term memory. In contrast, memory consolidation was not impaired in the groups trained with 2.0 mA. The findings showed that: (1) inhibitors of transcription and translation in the hippocampus impair the consolidation of memory of inhibitory avoidance learning induced by moderate levels of aversive stimulation and (2) blocking of mRNA and protein synthesis does not prevent the consolidation of memory induced by relatively high levels of aversive stimulation. These findings do not support the hypothesis that gene expression and de novo protein synthesis are necessary steps for long-term memory formation as memory was not impaired if intense foot-shock was used in training.

White Environment Can Be Used as an Aversive Stimulus in Zebrafish Inhibitory Avoidance Learning.

The two-factor theory predicts that the acquisition of avoidance responses is dependent on fear reduction; as such, drugs that reduce or increase fear or anxiety states should alter inhibitory avoidance (IA) acquisition. The present experiment used white spaces as aversive unconditioned stimuli in IA in zebrafish. Adult zebrafishes were tested in three experiments: validation of white compartment as aversive in IA; open field test; and effect of antidepressant (fluoxetine, imipramine) and anxiolytic (diazepam, clonazepam). The data show the effectiveness of the white compartment as an aversive stimulus in IA. Antidepressant fluoxetine did not alter and imipramine impairs avoidance acquisition in higher doses. Imipramine also produced a sedative effect in lower doses. Anxiolytic and stimulant drugs facilitated learning at doses which did not impair locomotion, suggesting that pharmacological manipulation of other factors in addition to fear/anxiety can impact aversive learning in zebrafish.

Effects of anisomycin infusions into the dorsal striatum on memory consolidation of intense training and neurotransmitter activity

The most influential hypothesis about the neurobiological basis of memory consolidation posits that this process is dependent upon de novo protein synthesis. Strong support for this proposition has been provided by a multitude of experiments showing that protein synthesis inhibitors (PSIs) interfere with consolidation. However, this hypothesis has been challenged by the results of studies showing that PSIs also produce a host of side effects that, by themselves, could account for their amnestic effects. It has been demonstrated that amnestic treatments become innocuous when administered to animals that have been subjected to intense training in a variety of learning tasks. We now report that while infusion of anisomycin (ANI), a PSI, into the dorsal striatum (DS) impairs memory consolidation of inhibitory avoidance learning in response to moderate aversive stimuli, such impairment by ANI is overcome by application of an intense stimulus. We also confirmed that ANI induces inhibition of protein synthesis in the DS, as evidenced by a reduction of the activity-regulated cytoskeletal associated protein (Arc). We found, for the first time, that ANI also induces an increased concentration of serotonin in the DS, which, by itself, may account for the interference with memory consolidation. These findings suggest that de novo protein synthesis in the dorsal striatum is not necessary for the consolidation of intense emotionally arousing experiences. The possibility of a non-genomic-dependent mechanism of memory consolidation is discussed.

Preproenkephalin-expressing ventral pallidal neurons control inhibitory avoidance learning

The ventral pallidum (VP) is a critical component of the basal ganglia neurocircuitry regulating learning and decision making; however, its precise role in controlling associative learning of environmental stimuli conditioned to appetitive or aversive outcomes is still unclear. Here, we investigated the expression of preproenkephalin, a polypeptide hormone previously shown to be expressed in nucleus accumbens neurons controlling aversive learning, within GABAergic and glutamatergic VP neurons. Next, we explored the behavioral consequences of chemicogenetic inhibition or excitation of preproenkephalin-expressing VP neurons on associative learning of reward- or aversion-paired stimuli in autoshaping and inhibitory avoidance tasks, respectively. We reveal for the first time that preproenkephalin is expressed predominantly in GABAergic rather than glutamatergic VP neurons, and that excitation of these preproenkephalin-expressing VP neurons was sufficient to impair inhibitory avoidance learning. These findings indicate the necessity for inhibition of preproenkephalin-expressing VP neurons for avoidance learning, and suggest these neurons as a potential therapeutic target for psychiatric disorders associated with maladaptive aversive learning.

Prefrontal-amygdala plasticity enabled by observational fear.

Observing fear in others (OF) is a form of social stress. In mice, it enhances inhibitory avoidance learning and causes the formation of silent synapses in the prefrontal-amygdala pathway. Here, we report that OF made that pathway prone to facilitation both ex vivo and in vivo. Ex vivo, OF enabled induction of long-term potentiation (LTP), expressed mostly postsynaptically and occluded by inhibitory avoidance training. In vivo, OF enabled facilitation of the dmPFC-BLA pathway by inhibitory avoidance training. The facilitation persisted during the first 4 h after the training when the prefrontal cortex and amygdala are involved in memory consolidation. Thus, the OF-generated silent synapses likely enable plasticity that may enhance the consolidation of inhibitory avoidance memories.

Effects Following Intracerebroventricular Injection of Immunosuppressant Cyclosporine A On Inhibitory Avoidance Learning and Memory in Mice

Background: Protein phosphatase-2B or calcineurin (CN) is the main phosphatase and a critical regulator of cellular pathways for learning, memory, and plasticity. Cyclosporine A(CyA), a phosphatase and peptidyl-prolyl cis/trans isomerase inhibitor, is a common immune suppressant extensively used in tissue transplantation. To further clarify the role of CN in different stages of learning and memory, the aim of the present study was to evaluate the role of CyA in an inhibitory avoidance (IA) model in mice.Materials and Methods: Using intracerebroventricular (ICV) injection of different doses of CyA (0.5, 5, and 50 nM) at different periods (pre-/post-training and pre-test), the effect of the drug was evaluated in a step-down IA paradigm. The latency of step-down (sec) was considered a criterion for memory performance. Results: The pre-training injections of CyA (0.5, 5 nM), however not of 50 nM, impaired IA learning acquisition. The post-training injection of high-dose CyA (50 nM) impaired memory consolidation. The pre-test ICV CyA injection did not impair memory retrieval; the ICV injection of CyA caused no change in locomotion. Conclusion: These findings suggest that CyA selectively interferes with acquisition, retention, but not retrieval, of information processing in mice. Given the crucial role of CN in common signaling pathway of memory performance and cognition, it could be a probable therapeutic target in the treatment of a wide variety of neurological conditions involving memory. [GMJ.2018;7:e1044]

Effects Following Intracerebroventricular Injection of Immunosuppressant Cyclosporine A On Inhibitory Avoidance Learning and Memory in Mice

Background: Protein phosphatase-2B or calcineurin (CN) is the main phosphatase and a critical regulator of cellular pathways for learning, memory, and plasticity. Cyclosporine A(CyA), a phosphatase and peptidyl-prolyl cis/trans isomerase inhibitor, is a common immune suppressant extensively used in tissue transplantation. To further clarify the role of CN in different stages of learning and memory, the aim of the present study was to evaluate the role of CyA in an inhibitory avoidance (IA) model in mice.&#x0D; Materials and Methods: Using intracerebroventricular (ICV) injection of different doses of CyA (0.5, 5, and 50 nM) at different periods (pre-/post-training and pre-test), the effect of the drug was evaluated in a step-down IA paradigm. The latency of step-down (sec) was considered a criterion for memory performance.&#x0D; Results: The pre-training injections of CyA (0.5, 5 nM), however not of 50 nM, impaired IA learning acquisition. The post-training injection of high-dose CyA (50 nM) impaired memory consolidation. The pre-test ICV CyA injection did not impair memory retrieval; the ICV injection of CyA caused no change in locomotion.&#x0D; Conclusion: These findings suggest that CyA selectively interferes with acquisition, retention, but not retrieval, of information processing in mice. Given the crucial role of CN in common signaling pathway of memory performance and cognition, it could be a probable therapeutic target in the treatment of a wide variety of neurological conditions involving memory. [GMJ.2018;7:e1044]

Effects Following Intracerebroventricular Injection of Immunosuppressant Cyclosporine A On Inhibitory Avoidance Learning and Memory in Mice.

Background: Protein phosphatase-2B or calcineurin (CN) is the main phosphatase and a critical regulator of cellular pathways for learning, memory, and plasticity. Cyclosporine A(CyA), a phosphatase and peptidyl-prolyl cis/trans isomerase inhibitor, is a common immune suppressant extensively used in tissue transplantation. To further clarify the role of CN in different stages of learning and memory, the aim of the present study was to evaluate the role of CyA in an inhibitory avoidance (IA) model in mice. Materials and Methods: Using intracerebroventricular (ICV) injection of different doses of CyA (0.5, 5, and 50 nM) at different periods (pre-/post-training and pre-test), the effect of the drug was evaluated in a step-down IA paradigm. The latency of step-down (sec) was considered a criterion for memory performance. Results: The pre-training injections of CyA (0.5, 5 nM), however not of 50 nM, impaired IA learning acquisition. The post-training injection of high-dose CyA (50 nM) impaired memory consolidation. The pre-test ICV CyA injection did not impair memory retrieval; the ICV injection of CyA caused no change in locomotion. Conclusion: These findings suggest that CyA selectively interferes with acquisition, retention, but not retrieval, of information processing in mice. Given the crucial role of CN in common signaling pathway of memory performance and cognition, it could be a probable therapeutic target in the treatment of a wide variety of neurological conditions involving memory.

Enhanced extinction of aversive memories in mice lacking SPARC-related protein containing immunoglobulin domains 1 (SPIG1/FSTL4).

Brain-derived neurotrophic factor (BDNF) plays an important role in synaptic plasticity related to learning and memory. We previously reported that SPARC-related protein containing immunoglobulin domains 1 (SPIG1, also known as Follistatin-like protein 4, FSTL4) binds to pro-BDNF and negatively regulates BDNF maturation; however, its neurological functions, particularly in learning and memory, have not yet been elucidated. We herein examined the electrophysiological and behavioral phenotypes of Spig1-knockout (Spig1-KO) mice. Adult Spig1-KO mice exhibited greater excitability and facilitated long-term potentiation (LTP) in the CA1 region of hippocampal slices than age- and sex-matched wild-type (WT) mice. Facilitated LTP was reduced to the level of WT by the bath application of an anti-BDNF antibody to hippocampal slices. A step-through inhibitory avoidance learning paradigm revealed that the extinction of aversive memories was significantly enhanced in adult Spig1-KO mice, while they showed the normal acquisition of aversive memories; besides, spatial reference memory formation was also normal in the standard Morris water maze task. An intracerebroventricular (icv) injection of anti-BDNF in the process of extinction learning transiently induced the recurrence of aversive memories in Spig1-KO mice, but exerted no effects in WT mice. These results indicate a critical role for SPIG1 in BDNF-mediated synaptic plasticity in extinction of inhibitory avoidance memory.

Cross state-dependency of learning between arachidonylcyclopropylamide (ACPA) and muscimol in the mouse dorsal hippocampus

The aim of the present study was to examine cross state-dependent learning between ACPA (a selective cannabinoid CB1 receptor agonist) and muscimol (a selective GABAA receptor agonist) in the step-down inhibitory avoidance learning task. The dorsal hippocampal CA1 regions of adult male NMRI mice were bilaterally cannulated, and all drugs were microinjected into the intended sites of injection.Post-training and/or pre-test administration of ACPA (1 and 2ng/mouse) dose-dependently induced amnesia. Pre-test microinjection of the same doses of ACPA reversed the post-training ACPA-induced amnesia. This event has been named ACPA state-dependent learning (SDL).Post-training and/or pre-test microinjection of muscimol (0.05 and 0.1μg/mouse) dose-dependently induced amnesia. Pre-test administration of the same doses of muscimol reversed the post-training muscimol-induced amnesia, suggesting muscimol SDL.The amnesia induced by post-training administration of ACPA was reversed by pre-test administration of muscimol (0.05 and 0.1μg/mouse). Furthermore, the pre-test microinjection of muscimol (0.025 and 0.05μg/mouse) with an ineffective dose of ACPA (0.5ng/mouse) significantly restored memory retrieval and induced ACPA SDL.In another series of experiments, the amnesia induced by post-training administration of muscimol was reversed by pre-test administration of ACPA (1 and 2ng/mouse). Moreover, pre-test microinjection of ACPA (0.5 and 1ng/mouse) with an ineffective dose of muscimol (0.025μg/mouse) significantly restored memory retrieval and induced muscimol SDL.It is important to note that pre-test intra-CA1 injection of a selective GABAA receptor antagonist, bicuculline (0.125 and 0.25μg/mouse), 5min before the administration of muscimol (0.1μg/mouse) or ACPA (2ng/mouse) dose-dependently inhibited muscimol- and ACPA-induced SDL, respectively. Pre-test intra-CA1 administration of bicuculline (0.0625, 0.125 and 0.25μg/mouse) by itself did not affect memory retention.In conclusion, the data strongly revealed a cross SDL among ACPA and muscimol in the dorsal hippocampal CA1 regions.