Inhibitory Avoidance Task Research Articles

The Involvement of NLRP3 on the Effects of Minocycline in an AD-Like Pathology Induced by β-Amyloid Oligomers Administered to Mice.

Alzheimer's disease (AD) is a neurodegenerative disease which is characterized by progressive memory loss, the accumulation of β-amyloid peptide (Aβ) (mainly Aβ1-42), and more recently, by neuroinflammation, which has been highlighted as playing a central role in the development and progress of AD. This study utilized 100-day-old Balb/c mice for the induction of an AD-like dementia model. The animals were administered with Aβ1-42 oligomers (400pmol/site) or artificial cerebrospinal fluid (ACSF) into the left cerebral ventricle. Twenty-four hours after intracerebroventricular administration, the animals were treated with minocycline (50mg/kg, via oral gavage) for 17days. The animals' locomotion was evaluated using the open-field test. The spatial memory was tested using the Y-maze, and the aversive memory was evaluated using the inhibitory avoidance task. Treatment with minocycline was shown to improve both spatial and aversive memories in mice that were submitted to the dementia model. In addition, minocycline reduced the levels of Aβ and microglial activation in the animals that received the administration of Aβ1-42 oligomers. Moreover, the results suggest that the decrease in microglial activation occurred because of a reduction in the levels of toll-like receptors 2 (TLR2) content, and its adapter protein MyD88, as well as a reduction in the levels of the protein NLRP3, which is indispensable in the assembly of inflammasome. These observations were evaluated via immunohistochemistry and confirmed using the Western blot analysis. Treatment with minocycline had no effect in preventing apoptotic morphologic alterations of the neurons. Thus, the anti-inflammatory effect of minocycline involves TLR2 receptors and NLRP3, besides being beneficial by ameliorating memory impairments. Graphical Abstract.

Blood-brain barrier breakdown, memory impairment and neurotoxicity caused in mice submitted to orally treatment with thymol

Several evidences have related the biochemical and pharmacological properties of thymol, but the possible neurotoxic effects of this compound remain unknown and not evaluated. Thus, the purpose of this study was to evaluate whether intake of thymol in different doses (10, 20 and 40 mg/kg) induce neurotoxicity and behavioral alterations using mice as experimental model, as well as the involvement of blood-brain barrier (BBB) and brain neurotransmitters in these alterations. Thymol (20 and 40 mg/kg) significantly decrease latency time to inhibitory avoidance task when compared to control group, indicating a memory loss after 30 days of oral treatment. Also, thymol (20 and 40 mg/kg) induced a significant increase on BBB permeability to Evan’s blue dye when compared to control group, which is an indicative of BBB breakdown. Moreover, a significant increase of brain acetylcholinesterase (AChE) was observed in mice treated with 40 mg/kg of thymol, while the activity of sodium-potassium pump (Na+, K+-ATPase) was inhibited in mice treated with 20 and 40 mg/kg thymol when compared to control group. Finally, mice that received 20 and 40 mg/kg thymol showed a significant increase on cerebral reactive oxygen species (ROS) levels and cerebral xanthine oxidase (XO) activity compared to control group. Based on these evidences, the rupture of BBB can be considered an important pathway linked in thymol-induced memory loss. Also, the augmentation of brain ROS levels elicited by increase on XO activity may be a via involved in the damage to BBB, and an oxidative pathway that impairs the activity of brain neurotransmitters, as AChE and Na+, K+-ATPase. In summary, the dose of 10 mg/kg thymol can be safe and without neurotoxic effects in a period of 30 days of intake.

Folic acid supplementation during pregnancy prevents cognitive impairments and BDNF imbalance in the hippocampus of the offspring after neonatal hypoxia-ischemia

Folic acid (FA) supplementation (400 μg/day) has been recommended during pregnancy to prevent neural tube defects. However, in some countries, flours are required to be fortified with FA, possibly increasing the levels of this vitamin in pregnant women. Our previous studies have evidenced a dual effect of the FA treatment in a rat model of neonatal hypoxia-ischemia (HI). Aiming to better correlate with humans, this paper evaluated the effects of two different levels of FA supplementation during pregnancy on memory parameters and neuronal survival and plasticity in the hippocampus of rats submitted to the neonatal HI. During pregnancy, female Wistar rats received one of these diets: standard (SD), supplemented with 2 mg/kg of FA or with 20 mg/kg of FA. At the 7th PND, rats suffered the HI procedure. At the 60th PND rats were evaluated in the open field, Morris water maze, novel-object recognition and inhibitory avoidance tasks. Furthermore, neuronal density, synaptophysin densitometry and BDNF concentration were assessed in the hippocampus. Both doses of FA prevented the HI-induced memory impairments. The supplementation reversed the BDNF late increase in the hippocampus of the HI rats, but did not inhibit the neuronal death. In conclusion, FA supplementation during pregnancy prevented memory deficits and BDNF imbalance after neonatal HI. These findings are particularly relevant because neuroprotection was achieved even in the high level of FA supplementation during pregnancy, indicating that this intervention would be considered secure for the offspring development.

Tetrahydrobiopterin improves hippocampal nitric oxide-linked long-term memory

Tetrahydrobiopterin (BH4) is synthesized by the combined action of three metabolic pathways, namely de novo synthesis, recycling, and salvage pathways. The best-known function of BH4 is its mandatory action as a natural cofactor of the aromatic amino acid hydroxylases and nitric oxide synthases. Thus, BH4 is essential for the synthesis of nitric oxide, a retrograde neurotransmitter involved in learning and memory. We investigated the effect of BH4 (4–4000 pmol) intracerebroventricular administration on aversive memory, and on BH4 metabolism in the hippocampus of rodents. Memory-related behaviors were assessed in Swiss and C57BL/6 J mice, and in Wistar rats. It was consistently observed across all rodent species that BH4 facilitates aversive memory acquisition and consolidation by increasing the latency to step-down in the inhibitory avoidance task. This effect was associated with a reduced threshold to generate hippocampal long-term potentiation process. In addition, two inhibitors of memory formation (N(ω)-nitro-L-arginine methyl ester - L-Name – and dizocilpine - MK-801 -) blocked the enhanced effect of BH4 on memory, while the amnesic effect was not rescue by the co-administration of BH4 or a cGMP analog (8-Br-cGMP). The data strongly suggest that BH4 enhances aversive memory by activating the glutamatergic neurotransmission and the retrograde activity of NO. It was also demonstrated that BH2 can be converted into BH4 by activating the BH4 salvage pathway under physiological conditions in the hippocampus. This is the first evidence showing that BH4 enhances aversive memory and that the BH4 salvage pathway is active in the hippocampus.

Bombesin-induced enhancement of memory consolidation in male and female rat pups: Role of glutamatergic and dopaminergic systems

Previous studies have shown that the neuropeptide bombesin (BBS) enhances consolidation of specifically for inhibitory avoidance memory in adult rats. However, its effect on memory consolidation during premature period is not clear as well. Thus, this study evaluated the effect of BBS and its interaction with glutamatergic and dopaminergic systems on memory consolidation in rat pups. Male and female rat pups (30 days old) were trained in an inhibitory avoidance (IA) task (0.5 mA, 3 s footshock). Memory retention was tested 24 h later during which the latency to re-enter to the shock compartment was recorded. First, the effects of different doses (0.001, 0.0025, 0.005, 0.01 and 0.02 mg/kg) of BBS injected immediately following training were tested. Then, the effect of the most effective dose of BBS obtained in the previous experiment was examined in the presence of the glutamate NMDA receptor antagonist MK-801 (0.05 mg/kg), the dopamine D1 receptor antagonist SCH-23390 (0.05 mg/kg) and the dopamine D2 receptor antagonist sulpiride (20 mg/kg). Findings indicate that BBS significantly enhances memory consolidation at all tested doses in male pups and at a dose of 0.01 mg/kg in female pups. MK-801, SCH-23390 and sulpiride administration before BBS injection in individual groups significantly blocked BBS-induced memory enhancement. Our findings indicate that similar to adult rats, BBS enhances memory consolidation in developing rat. This enhancing effect is mediated, at least in part, via an interaction with glutamatergic and dopaminergic systems.

Pharmacological inhibition of 2-arachidonoilglycerol hydrolysis enhances memory consolidation in rats through CB2 receptor activation and mTOR signaling modulation

The endocannabinoid system is a key modulator of memory consolidation for aversive experiences. We recently found that the fatty acid amide hydrolase (FAAH) inhibitor URB597, which increases anandamide levels by inhibiting its hydrolysis, facilitates memory consolidation through a concurrent activation of both cannabinoid receptor type 1 (CB1) and 2 (CB2). Here, we investigated the role played on memory consolidation by the other major endocannabinoid, 2-arachidonoylglycerol (2-AG). To this aim, we tested the effects of pharmacological inhibition of monoacylglycerol lipase (MAGL) through systemic administration of the MAGL inhibitor JZL184 to rats immediately after training of the inhibitory avoidance task. Pharmacological enhancement of 2-AG tone facilitated memory consolidation through activation of CB2 receptor signaling. Moreover, we found that increased 2-AG signaling prevented the activation of the mammalian target of rapamycin (mTOR) signaling pathway in the hippocampus through a CB2-dependent mechanism. Our results identify a fundamental role for 2-AG and CB2 receptors in the modulation of memory consolidation for aversive experiences.

The effect of CA1 dopaminergic system on amnesia induced by harmane in mice.

In the present study, the effects of bilateral injections of dopaminergic drugs into the hippocampal CA1 regions (intra-CA1) on harmane-induced amnesia were examined in mice. We used a single-trial step-down inhibitory avoidance task for the assessment of memory acquisition in adult male mice. Our data indicated that pre-training intra-peritoneal (i.p.) administration of harmane (12mg/kg) impaired memory acquisition. Moreover, intra-CA1 administration of dopamine D1 receptor agonist, SKF38393 (0.25µg/mouse), dopamine D1 receptor antagonist, SCH23390 (0.25µg/mouse), dopamine D2 receptor agonist, quinpirole (0.125 and 0.25µg/mouse) and dopamine D2 receptor antagonist, sulpiride (0.2 and 0.4µg/mouse) decreased the learning of a single-trial inhibitory avoidance task. Furthermore, pre-training intra-CA1 injection of sub-threshold doses of SKF38393 (0.0625µg/mouse) or sulpiride (0.1µg/mouse) increased pre-training harmane (4 and 8mg/kg, i.p.)-induced amnesia. On the other hand, pre-training intra-CA1 injection of a sub-threshold dose of SCH23390 (0.0625µg/mouse) reversed amnesia induced by an effective dose of harmane (12mg/kg; i.p.). In addition, Pre-training intra-CA1 injection of quinpirole (0.0625µg/mouse) had no effect on memory impairment induced by harmane. These findings indicate the involvement of CA1 dopaminergic system on harmane-induced impairment of memory acquisition.

Hippocampal microRNA-mRNA regulatory network is affected by physical exercise

BackgroundIt is widely known that physical activity positively affects the overall health and brain function. Recently, microRNAs (miRNAs) have emerged as potential regulators of numerous biological processes within the brain. These molecules modulate gene expression post-transcriptionally by inducing mRNA degradation and inhibiting the translation of target mRNAs. MethodsTo verify whether the procognitive effects of physical exercise are accompanied by changes in the activity of miRNA-mRNA network in the brain, differential expression analysis was performed in the hippocampus of control (CTL) and exercised (Ex) rats subjected to 4 weeks of treadmill exercise. Cognition was evaluated by a multiple trial inhibitory avoidance (MTIA) task and Illumina next-generation sequencing (NGS) was used for miRNA and mRNA profiling. ResultsExercise improved memory retention but not acquisition in the MTIA task. It was observed that 4 miRNAs and 54 mRNAs were significantly altered in the hippocampus of Ex2 (euthanized 2 h after the last exercise bout) group when compared to CTL group. Bioinformatic analysis showed an inverse correlation between 3 miRNAs and 6 target mRNAs. The miRNAs miR-129-1-3p and miR-144-5p were inversely correlated to the Igfbp5 and Itm2a, respectively, and the miR-708-5p presented an inverse correlation with Cdkn1a, Per2, Rt1-a2. ConclusionThe exercise-induced memory improvements are accompanied by changes in hippocampal miRNA-mRNA regulatory network. General significancePhysical exercise can affect brain function through modulation of epigenetics mechanisms involving miRNA regulation.

Low arsenic concentrations impair memory in rat offpring exposed during pregnancy and lactation: Role of α7 nicotinic receptor, glutamate and oxidative stress

Inorganic arsenic (iAs) is an important natural pollutant. Millions of individuals worldwide drink water with high levels of iAs. Arsenic exposure has been associated to cognitive deficits. However, the underlying mechanisms remain unknown. In the present work we investigated in female adult offspring the effect of the exposure to low arsenite sodium levels through drinking water during pregnancy and lactation on short- and long-term memory. We also considered a possible underlying neurotoxic mechanism. Pregnant rats were exposed during pregnancy and lactation to environmentally relevant iAs concentrations (0.05 and 0.10 mg/L). In 90-day-old female offspring, short-term memory (STM) and long-term memory (LTM) were evaluated using a step-down inhibitory avoidance task. In addition, we evaluated the α7 nicotinic receptor (α7-nAChR) expression, the transaminases and the oxidative stress levels in hippocampus. The results showed that the exposure to 0.10 mg/L iAs in this critical period produced a significant impairment in the LTM retention. This behavioral alteration might be associated with several events that occur in the hippocampus: decrease in α7-nAChR expression, an increase of glutamate levels that may produce excitotoxicity, and a decrease in the antioxidant enzyme catalase (CAT) activity.

A1 adenosine receptors in the striatum play a role in the memory impairment caused by sleep deprivation through downregulation of the PKA pathway.

Sleep deprivation is known to affect memory formation, but how it interacts with different memory systems is not completely understood. Adenosine, a homeostatic regulator of sleep that has an increased extracellular concentration during sleep deprivation, is one of the neuromodulators that may be involved in this interaction. The A1 adenosine receptor is involved in both sleep regulation and memory formation. Among other pathways, the A1 receptor decreases cAMP levels in the cytosol and thus also regulates protein kinase A (PKA) and exchange protein activated by cAMP (EPAC) activity. To verify the role of the A1 receptor in the memory impairment caused by sleep deprivation, we tested the effect of 96 h of sleep deprivation (SD) and the administration of DPCPX, an A1 receptor antagonist on male Wistar rats prior to the training sessions for two memory tasks that relies on the hippocampal function: the multiple trial inhibitory avoidance (MTIA) task, which also requires the striatum, and the contextual fear conditioning (CFC) task, which does not. We also evaluated the effect of SD, DPCPX and the MTIA training session on the protein expression levels of the A1 receptor, PKA phosphorylation and EPAC activity in both the hippocampus and the striatum. Sleep deprivation impaired the performance in the test sessions of both tasks; DPCPX was able to prevent the impairment in the MTIA test but not in the CFC test. SD increased A1 receptor protein expression levels in the striatum but not in the hippocampus and also decreased PKA phosphorylation in both structures; DPCPX prevented this decrease in the striatum, but not in the hippocampus. Finally, SD had no effect on EPAC activity in either of the structures. These results indicate that the A1 adenosine receptors play a role in the memory impairment caused by sleep deprivation in tasks that involve the striatum through modulation of the cAMP/PKA pathway.

Protective effects of banana pectin against aluminum-induced cognitive impairment and aluminum accumulation in mice

To investigate the effect of pectin on absorption and bio-toxicity of aluminum, pectin extract (100 mg kg−1 d−1) from banana pulp was orally administrated to aluminum exposed mice (35 mg kg−1 d−1) for 6 weeks. Our result showed that body weight gain of the mice treated with aluminum plus banana pectin was 32.5% higher than that of mice exposed to aluminum alone after 6 weeks of the administration. In both the step-down inhibitory avoidance task and Morris water maze test, memory retention of aluminum-exposed mice was significantly improved by the pectin administration. Treatment with banana pectin effectively prevented absorption of aluminum from the gastrointestinal tract, total aluminum excretion of mice treated with banana pectin plus aluminum was 9.3% higher than that of mice exposed to aluminum alone on the 12th day. Aluminum level in serum, cerebrum, or cerebellum of mice treated with aluminum plus banana pectin was 30.8%, 17.5%, or 17.9% lower than that of mice exposed to aluminum alone on the 42nd day, respectively. In conclusion, banana pectin extract can effectively reduce aluminum toxicity in mice.

Agmatine inhibits nicotine withdrawal induced cognitive deficits in inhibitory avoidance task in rats: Contribution of α2-adrenoceptors

Nicotine abstinence following chronic exposure is associated with impairments in memory and variety of cognitive functions. Daily nicotine (2 mg/kg, sc, four times daily) administration for 14 days and its abrupt withdrawal significantly impaired avoidance learning in inhibitory avoidance task as indicated by a significant decrease in the step through latency. Animals injected with agmatine (10–40 μg/rat, icv) from day 7 to 14 before the first daily dose of nicotine (2 mg/kg, sc) showed increased step through latencies during retrieval test. Similarly Intracerebroventricular injection of l-arginine (25–100 μg/rat), a biosynthetic precursor of agmatine and arcaine (50 μg −100 μg/rat), an agmatinase inhibitor, also increased the step through latency during retrieval test in nicotine withdrawn animals. In separate experiments, α2-adrenoceptor agonist, clonidine (0.5–1 μg/rat, icv) not only demonstrated significant increase in the step through latency as in nicotine withdrawn rats but also potentiated the pharmacological effect of agmatine. In contrast, pre-treatment of α2-adrenoceptor antagonist, yohimbine (0.5 μg/rat, icv) antagonized the memory enhancing effect of agmatine (20 μg/rat, icv) in nicotine withdrawn rats. In addition, brain agmatine analysis carried out at 72 h time point of nicotine withdrawal showed marked decrease in basal brain agmatine content as compared to control. Overall, the data indicate that agmatine attenuates nicotine withdrawal induced memory impairment through modulation of α2adrenergic receptors. Thus, agmatine might have therapeutic implications in the treatment of cognitive deficits following nicotine withdrawal.

Taraxerol as a possible therapeutic agent on memory impairments and Alzheimer’s disease: Effects against scopolamine and streptozotocin-induced cognitive dysfunctions

Alzheimer’s disease (AD) is a neurodegenerative disorder associated with cognitive impairment and cholinergic neuronal death, characteristic of the effect of time on biochemical neuronal function. The use of medicinal plants as an alternative form of prevention, or even as a possible treatment of AD, is therefore interesting areas of research, since the standard drugs have many side effects. Taraxerol (TRX) is a triterpene that has been isolated from several plant species, and its various pharmacological properties have already been identified, such the acetylcholinesterase (AChE) inhibition activity in vitro. There is a lack of information in literature that confirms the effect of TRX in an animal AD-like model. Seeking to fill this gap in the literature, in the present work we assessed the effect of TRX on AChE activity in the animals’ encephalon and hippocampus. We also investigated the effect of TRX (1.77 µM/side, 0.5 μL) isolated from leaves of Eugenia umbelliflora Berg. on aversive memory impairments induced by scopolamine (2 µg/side, 0.5 µL) infused into rat hippocampus, and the effect of TRX (0.89 and 1.77 µM/side, 0.5 μL) on aversive memory impairments induced by streptozotocin (STZ) (2.5 mg/mL, 2.0 µL) infused i.c.v. into mice, using the step-down inhibitory avoidance task. We found that TRX significantly inhibited AChE activity in the animal’s hippocampus. Furthermore, TRX significantly improved scopolamine and STZ-induced memory impairment. Taking together, these results confirms its AChE activity inhibition in animals and indicate that TRX has anti-amnesic activity that may hold significant therapeutic value in alleviating certain memory impairments observed in AD.

Environmental enrichment decreases avoidance responses in the elevated T-maze and delta FosB immunoreactivity in anxiety-related brain regions

Environmental enrichment (EE) is an animal management technique, which seems to improve adaptation to the experimental conditions of housing in laboratory animals. Previous studies have pointed to different beneficial effects of the procedure in the treatment of several disorders, including psychiatric conditions such as depression. The anxiolytic effects induced by EE, on the other hand, are not as clear. In fact, it has been proposed that EE acts as a mild stressor agent. To better understand the relationship of EE with anxiety-related responses, the present study exposed rats to one week of EE and subsequently tested these animals in the inhibitory avoidance and escape tasks of the elevated T-maze (ETM). In clinical terms, these responses have been respectively related to generalized anxiety and panic disorder. All animals were tested in an open field, immediately after the ETM, for locomotor activity assessment. Additionally, analysis of delta FosB protein immunoreactivity (FosB-ir) was used to map areas activated by EE exposure and plasma corticosterone measurements were performed. The results obtained demonstrate that exposure to EE for one week impaired avoidance responses, an anxiolytic-like effect, without altering escape reactions. Also, in animals submitted to the avoidance task EE exposure decreased FosB-ir in the cingulate cortex, dorsolateral and intermediate lateral septum, hippocampus (cornus of Ammon), anterior and dorsomedial hypothalamus, medial and basolateral amygdala and ventral region of the dorsal raphe nucleus. Although no behavioral differences were observed in animals submitted to the escape task, EE exposure also decreased FosB-ir in the cingulate cortex, hippocampus (dentate gyrus), lateral amygdala, paraventricular, anterior and ventromedial hypothalamus, dorsomedial periaqueductal gray and ventral and dorsal region of the dorsal raphe. No changes in corticosterone levels, however, were observed. These results contribute to a better understanding of the effects of EE on anxiety.

Changes in the element concentration of the dorsal hippocampus CA1 region during memory consolidation and reconsolidation

The concentration and distribution of Mg, P, Cl, K, Cu and Zn in the dorsal hippocampus CA1 region of rat brains were studied during memory consolidation and reconsolidation processes stimulated with inhibitory avoidance (IA) tests. Experimental rats were divided into four groups: i) group not submitted to inhibitory avoidance task (IA-N); ii) group submitted to inhibitory avoidance training session (IA-Y); iii) group submitted to inhibitory avoidance reactivation session but did not step down from the platform (IAR-N); and iv) group submitted to avoidance reactivation session and stepped down from the platform (IAR-Y). Elemental concentration and distribution in the CA1 hippocampus region were obtained through the Particle-Induced X-ray Emission (PIXE) technique. The results indicate that the concentration of Mg, P, Cl, K and Cu increased during memory consolidation. During the memory reconsolidation process, the concentrations of Mg, P, Cl and K increased, while Cu and Zn had no significant changes with respect to their basal condition. These results show that the major part of these elements may be engaged in memory consolidation could be also participating in memory reconsolidation. For all elements, the general trend related to their concentration did not change during reconsolidation regardless the presence of a novelty event, i.e. stepping down from the platform.

Assessing Mongolian gerbil emotional behavior: effects of two shock intensities and response-independent shocks during an extended inhibitory-avoidance task.

Despite step-down inhibitory avoidance procedures that have been widely implemented in rats and mice to study learning and emotion phenomena, performance of other species in these tasks has received less attention. The case of the Mongolian gerbil is of relevance considering the discrepancies in the parameters of the step-down protocols implemented, especially the wide range of foot-shock intensities (i.e., 0.4–4.0 mA), and the lack of information on long-term performance, extinction effects, and behavioral patterning during these tasks. Experiment 1 aimed to (a) characterize gerbils’ acquisition, extinction, and steady-state performance during a multisession (i.e., extended) step-down protocol adapted for implementation in a commercially-available behavioral package (Video Fear Conditioning System—MED Associates Fairfax, VT, USA), and (b) compare gerbils’ performance in this task with two shock intensities – 0.5 vs. 1.0 mA—considered in the low-to-mid range. Results indicated that the 1.0 mA protocol produced more reliable and clear evidence of avoidance learning, extinction, and reacquisition in terms of increments in freezing and on-platform time as well as suppression of platform descent. Experiment 2 aimed to (a) assess whether an alternate protocol consisting of a random delivery of foot shocks could replicate the effects of Experiment 1 and (b) characterize gerbils’ exploratory behavior during the step-down task (jumping, digging, rearing, and probing). Random shocks did not reproduce the effects observed with the first protocol. The data also indicated that a change from random to response-dependent shocks affects (a) the length of each visit to the platform, but not the frequency of platform descends or freezing time, and (b) the patterns of exploratory behavior, namely, suppression of digging and rearing, as well as increments in probing and jumping. Overall, the study demonstrated the feasibility of the extended step-down protocol for studying steady performance, extinction, and reacquisition of avoidance behavior in gerbils, which could be easily implemented in a commercially available system. The observation that 1.0 mA shocks produced a clear and consistent avoidance behavior suggests that implementation of higher intensities is unnecessary for reproducing aversive-conditioning effects in this species. The observed patterning of freezing, platform descents, and exploratory responses produced by the change from random to periodic shocks may relate to the active defensive system of the gerbil. Of special interest is the probing behavior, which could be interpreted as risk assessment and has not been reported in other rodent species exposed to step-down and similar tasks.

Slice Patch Clamp Technique for Analyzing Learning-Induced Plasticity

The slice patch clamp technique is a powerful tool for investigating learning-induced neural plasticity in specific brain regions. To analyze motor-learning induced plasticity, we trained rats using an accelerated rotor rod task. Rats performed the task 10 times at 30-s intervals for 1 or 2 days. Performance was significantly improved on the training days compared to the first trial. We then prepared acute brain slices of the primary motor cortex (M1) in untrained and trained rats. Current-clamp analysis showed dynamic changes in resting membrane potential, spike threshold, afterhyperpolarization, and membrane resistance in layer II/III pyramidal neurons. Current injection induced many more spikes in 2-day trained rats than in untrained controls. To analyze contextual-learning induced plasticity, we trained rats using an inhibitory avoidance (IA) task. After experiencing foot-shock in the dark side of a box, the rats learned to avoid it, staying in the lighted side. We prepared acute hippocampal slices from untrained, IA-trained, unpaired, and walk-through rats. Voltage-clamp analysis was used to sequentially record miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) from the same CA1 neuron. We found different mean mEPSC and mIPSC amplitudes in each CA1 neuron, suggesting that each neuron had different postsynaptic strengths at its excitatory and inhibitory synapses. Moreover, compared with untrained controls, IA-trained rats had higher mEPSC and mIPSC amplitudes, with broad diversity. These results suggested that contextual learning creates postsynaptic diversity in both excitatory and inhibitory synapses at each CA1 neuron. AMPA or GABAA receptors seemed to mediate the postsynaptic currents, since bath treatment with CNQX or bicuculline blocked the mEPSC or mIPSC events, respectively. This technique can be used to study different types of learning in other regions, such as the sensory cortex and amygdala.

Slice Patch Clamp Technique for Analyzing Learning-Induced Plasticity

The slice patch clamp technique is a powerful tool for investigating learning-induced neural plasticity in specific brain regions. To analyze motor-learning induced plasticity, we trained rats using an accelerated rotor rod task. Rats performed the task 10 times at 30-s intervals for 1 or 2 days. Performance was significantly improved on the training days compared to the first trial. We then prepared acute brain slices of the primary motor cortex (M1) in untrained and trained rats. Current-clamp analysis showed dynamic changes in resting membrane potential, spike threshold, afterhyperpolarization, and membrane resistance in layer II/III pyramidal neurons. Current injection induced many more spikes in 2-day trained rats than in untrained controls.To analyze contextual-learning induced plasticity, we trained rats using an inhibitory avoidance (IA) task. After experiencing foot-shock in the dark side of a box, the rats learned to avoid it, staying in the lighted side. We prepared acute hippocampal slices from untrained, IA-trained, unpaired, and walk-through rats. Voltage-clamp analysis was used to sequentially record miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) from the same CA1 neuron. We found different mean mEPSC and mIPSC amplitudes in each CA1 neuron, suggesting that each neuron had different postsynaptic strengths at its excitatory and inhibitory synapses. Moreover, compared with untrained controls, IA-trained rats had higher mEPSC and mIPSC amplitudes, with broad diversity. These results suggested that contextual learning creates postsynaptic diversity in both excitatory and inhibitory synapses at each CA1 neuron.AMPA or GABAA receptors seemed to mediate the postsynaptic currents, since bath treatment with CNQX or bicuculline blocked the mEPSC or mIPSC events, respectively. This technique can be used to study different types of learning in other regions, such as the sensory cortex and amygdala.

Methionine Administration in Pregnant Rats Causes Memory Deficit in the Offspring and Alters Ultrastructure in Brain Tissue.

In the present work, we evaluated the effect of gestational hypermethioninemia on locomotor activity, anxiety, memory, and exploratory behavior of rat offspring through the following behavior tests: open field, object recognition, and inhibitory avoidance. Histological analysis was also done in the brain tissue of pups. Wistar female rats received methionine (2.68μmol/g body weight) by subcutaneous injections during pregnancy. Control rats received saline. Histological analyses were made in brain tissue from 21 and 30days of age pups. Another group was left to recover until the 30th day of life to perform behavior tests. Results from open field task showed that pups exposed to methionine during intrauterine development spent more time in the center of the arena. In the object recognition memory task, we observed that methionine administration during pregnancy reduced total exploration time of rat offspring during training session. The test session showed that methionine reduced the recognition index. Regarding to inhibitory avoidance task, the decrease in the step-down latency at 1 and 24h after training demonstrated that maternal hypermethioninemia impaired short-term and long-term memories of rat offspring. Electron microscopy revealed alterations in the ultrastructure of neurons at 21 and 30days of age. Our findings suggest that the cell morphological changes caused by maternal hypermethioninemia may be, at least partially, associated to the memory deficit of rat offspring.

Post-training reversible disconnection of the ventral hippocampal-basolateral amygdaloid circuits impairs consolidation of inhibitory avoidance memory in rats.

The ventral hippocampus (VH) and the basolateral amygdala (BLA) are both crucial in inhibitory avoidance (IA) memory. However, the exact role of the VH–BLA circuit in IA memory consolidation is unclear. This study investigated the effect of post-training reversible disconnection of the VH–BLA circuit in IA memory consolidation. Male Wistar rats with implanted guide cannulae were trained with a one-trial IA task, then received immediate intracerebral injections of muscimol or saline, and were tested 24 h later. Muscimol injection into the bilateral BLA, or the unilateral VH and contralateral BLA, but not the unilateral VH and ipsilateral BLA, significantly decreased the retention latencies (versus saline treatment). The results suggest that the VH–BLA circuit could be an important circuit to modulate consolidation of IA memory in rats.