Passive Avoidance Learning Test Research Articles

Erythropoietin improves neuronal proliferation in dentate gyrus of hippocampal formation in an animal model of Alzheimer's disease.

Background:Alzheimer's disease (AD) is a prevalent disorder with severe learning and memory defects. Because it has been demonstrated that erythropoietin (EPO) has positive effects on the central nervous system, the aim of this study was to evaluate the effect of EPO on neuronal proliferation in dentate gyrus of hippocampal formation in a well-defined model for AD.Materials and Methods:A rat model of sporadic dementia of Alzheimer's type was established by a bilateral intracerebroventricular injection of streptozotocin (ICV-STZ). Impairment of learning and memory was confirmed 2 weeks after ICV-STZ injection by passive avoidance learning test and then rats were divided into fourgroups:Control, control-EPO, Alzheimer and Alzheimer-EPO. EPO was injected intraperitoneally every other day with a dose of 5000 IU/kg and, finally, the rats were anesthetized and decapitated for immunohistochemical study and neurogenesis investigation (by Ki67 method) in dentate gyrus of hippocampal formation.Results:The results driven from the histological study showed that EPO significantly increases neuronal proliferation in dentate gyrus of hippocampus in the Alzheimer-EPO group compared with the control, control-EPO and Alzheimer groups; however, there were no differences between the other groups.Conclusion:Our results show that even though EPO in intact animals doesnot change neurogenesis in dentate gyrus, it can nonetheless significantly increase neurogenesis if there is an underlying disorder like neurodegenerative diseases.

The effect of red grape juice on Alzheimer′s disease in rats

Background:Alzheimer's disease is a neurodegenerative disease appearing as a result of free radicals and oxidative stress. Antioxidants agents boost memory and control Alzheimer's disease. Since red grape juice contains antioxidant agents, its effects on speed of learning and improvement of memory was studied in Alzheimer's rats.Materials and Methods:Alzheimer's model was induced by bilateral infusion of streptozocine into lateral ventricles of brain of male rats. Rats drank 10% red grape juice for 21 days. Passive avoidance learning test was used for measuring memory and learning in rats.Results:Our results showed that learning and memory in STZ-group decreased significantly compared to Sham group. However, intake of red grape juice increased speed of learning and improvement of memory in Alzheimer's rats.Conclusions:Our results suggest that there are active ingredients in red grape juice, which probably have therapeutic and preventive effects on cognitive impairments in Alzheimer's disease.

Neuroprotective effects of mesenchymal stem cell transplantation in animal model of cerebellar degeneration

Background: The cerebellum has been considered a key structure for the processes involved in sensorimotor integration ultimately leading to motor planning and execution of coordinated movement. Thus, motor deficits and behavioral changes can be associated with cerebellar degeneration.Methods: Here, the chemical neurotoxin pyridine-2,3-dicarboxylic acid (quinolinic acid, QA) used to create partially cerebellar degeneration in adult Wistar rats suitable for use in stem cell transplantation studies. Stereotaxicaly administration of QA (0·2 mmol) in the right cerebellar hemisphere (folia VI) caused noticeable motor disturbance in all treated animals. Forty-eights hours after causing lesion, rat bone marrow-derived mesenchymal stem cells (MSCs) were transplanted into damaged cerebellar hemisphere. We investigated the role of MSC transplantation in forms of motor and non-motor learning that involves the cerebellum and its neuroprotective effects in Purkinje cells loss.Results: CM-Dil labeling showed that the transplanted MSCs survived and migrated in the cerebellum 6 weeks after transplantation. The MSC-transplanted group showed markedly improved functional performance on the rotating rod test (P≤0·0001) and beam walking test (P≤0·0001) during 6 weeks compared with the controls. For non-motor learning, we used passive avoidance learning test in 3 weeks after transplantation. The results showed that MSC transplantation prevented the development of memory deficit caused by cerebellar degeneration (P≤0·001). Stereological analysis in 6 weeks after transplantation showed that QA significantly decreases Purkinje cells in vehicle-treated rats and MSC transplantation is neuroprotective and decreases Purkinje cell loss in MSC-treated rats (P≤0·0001).Conclusion: The results indicate that transplantation of MSCs can significantly reduce the behavioral and neuroanatomical abnormalities of these animals during 6 weeks after engraftment. According to results of this assay, cell therapy by means of bone marrow-derived adult stem cells promises for treatment of cerebellar diseases.

Curcumin Exerts Neuroprotective Effects Against Homocysteine Intracerebroventricular Injection-Induced Cognitive Impairment and Oxidative Stress in Rat Brain

Aging is the major risk factor for neurodegenerative diseases and oxidative stress and is involved in their pathophysiology. Oxidative stress can induce neuronal damage and modulate intracellular signaling, ultimately leading to neuronal death by apoptosis or necrosis. In this study we investigated the neuroprotective properties of the natural polyphenolic antioxidant compound, curcumin, against homocysteine (Hcy) neurotoxicity. Curcumin (5, 15, or 45 mg/kg) was injected intraperitoneally once daily for a period of 10 days beginning 5 days prior to Hcy (0.2 micromol/microl) intracerebroventricular injection in rats. Biochemical and behavioral studies, including passive avoidance learning and locomotor activity tests, were evaluated 24 hours after the last injection of curcumin or vehicle. Results indicated that Hcy induces lipid peroxidation and increases malondialdehyde (MDA) and superoxide anion (SOA) levels in whole rat brain. In addition, Hcy impaired memory retention in the passive avoidance learning test. However, curcumin treatment significantly decreased MDA and SOA levels and improved learning and memory in rats. These results suggest that Hcy may induce lipid peroxidation in rat brain and that polyphenol treatment (curcumin) improves learning and memory deficits by protecting the nervous system against oxidative stress.

Neuroprotective effects of the polyphenolic antioxidant agent, Curcumin, against homocysteine-induced cognitive impairment and oxidative stress in the rat

Aging is the major risk factor for neurodegenerative diseases and oxidative stress is involved in the pathophysiology of these diseases. In this study, the possible antioxidant and neuroprotective properties of the polyphenolic antioxidant compound, Curcumin against homocysteine (Hcy) neurotoxicity was investigated. Curcumin (5 and 50 mg/kg) was injected intraperitonealy once daily for a period of 10 days beginning 5 days prior to Hcy (0.2 μmol/μl) intrahippocampal injection in rats. Biochemical and behavioral studies, including passive avoidance learning and locomotor activity tests were studied 24 h after the last Curcumin or its vehicle injection. We detected Malondialdehyde (MDA) and Super oxide anion (SOA) in rats' hippocampi. Results indicated that Hcy could induce lipid peroxidation and increase MDA and SOA levels in rats' hippocampi. Additionally, Hcy impaired memory retention in passive avoidance learning test. However, Curcumin treatment decreased MDA and SOA levels significantly as well as improved learning and memory in rats. Histopathological analysis also indicated that Hcy could decrease hippocampus cell count and Curcumin inhibited this toxic effect. These results suggest that Hcy may induce lipid peroxidation in rats' hippocampi and polyphenol treatment (Curcumin) improved learning and memory deficits by protecting the nervous system against Hcy toxicity.

Effects of intra-hippocampal D-AP5 injections on one trial passive avoidance learning in adult laying hens (Gallus gallus domesticus).

Domestic chickens are an established model organism for studies on learning and memory. Commonly, the chicks are used as subjects in several different learning tests, including one trial learning tests. However, for adult laying hens no such one trial learning tests have been established. In particular, there is no test established which focuses on the role of the hippocampus, a brain region, which is often critically involved in learning and memory consolidation. In this study we investigated the inhibitory effects of intra-hippocampal D-AP5 injections on a specific one trial passive avoidance learning test in adult laying hens (Gallus gallus domesticus). We used a step down avoidance learning paradigm (SDA) which is frequently used in rodents. Intra-hippocampal injections of D-AP5 impaired the learning abilities of adult laying hens compared to sham-injected control subjects. Thus, the experiments revealed that the hippocampus is critically involved in learning the inhibitory SDA task. Our results further indicate that the step down avoidance paradigm is suitable to examine learning and memory processes in adult laying hens.

P.6.b.002 Genetic polymorphism of alcohol metabolizing enzymes, CYP2E1, in Korean male and female alcoholics

Cannabinoid and endocannabinoid systems have been implicated in several physiological functions including modulation of cognition. In this study we evaluated the effects and interaction between fatty-acid amide hydrolase (FAAH) inhibitor URB597 and CB1 receptor agonist WIN55, 212-2 on memory using object recognition and passive avoidance learning (PAL) tests. Learning and memory impairment was induced by WIN 55, 212-2 administration (1 mg/kg, i.p.) 30 min before the acquisition trial. URB597 (0.1, 0.3 and 1 mg/kg, i.p.) or SR141716A (1 mg/kg, i.p.) was injected to rats 10 min before WIN 55, 212-2 or URB597 respectively. URB597 (0.3 and 1 mg/kg) but not 0.1 mg/kg induced higher discrimination index (DI) in object recognition test and enhanced memory acquisition in PAL test. The cognitive enhancing effect of URB597 was blocked by a CB1 receptor antagonist, SR141716A which at this dose alone had no effect on cognition. WIN55, 212-2 caused cognition deficits in both tests. URB597 (0.3 and 1 mg/kg) treatment could alleviate the negative influence of WIN 55, 212-2 on cognition and memory. These results indicate URB597 potential to protect against memory deficits induced by cannabinoid. Therefore, in combination with URB597 beneficial effects, this study suggests that URB597 has recognition and acquisition memory enhancing effects. It may also constitute a novel approach for the treatment of cannabinoid induced memory deficits and lead to a better understanding of the brain mechanisms underlying cognition.

Long-term antioxidant supplementation attenuates oxidative stress markers and cognitive deficits in senescent-accelerated OXYS rats

Oxidative damage of biomolecules increases with age and is postulated to be a major causal factor of various neurodegenerative disorders. Consequently, the concept of neuroprotection by antioxidants has been developed. Recently we have shown that the behaviour of young senescent-accelerated OXYS rats is similar to the behaviour of old Wistar animals. To determine the role of oxidative stress in this phenomenon we investigated age-related changes in protein carbonyls (PrC), lipid peroxides (LP), reduced glutathione (GSH), α-tocopherol (TP) and SOD activity in the brain of OXYS and Wistar rats. We also studied the effect of long-term supplementation with bilberry extract (2 g/kg of diet) and Vitamin E (140 mg/kg of diet) on oxidative stress markers and on learning in passive avoidance test. In both rat strains LP, PrC and TP increased with age and at 24 months PrC was significantly higher ( p < 0.0001) in OXYS rats. At 3 months GSH was higher and SOD activity was lower in OXYS rats than in Wistar rats. SOD activity decreased with age in OXYS whereas increased in Wistar rats. Cognitive impairments in OXYS rats were manifested earlier than significant differences in the level of brain oxidative stress markers between two strains. By contrast, differences in antioxidant systems of Wistar and OXYS rats were registered at 3 months. Antioxidants attenuated cognitive deficits in OXYS rats, providing evidence for therapeutic role of antioxidants. Nevertheless, the exact mechanisms of neuroprotective effects of antioxidants in vivo and the real impact of oxidative stress on the development of cognitive impairments in OXYS rats still needs to be further investigated.

Benzimidazole derivatives. Part 5: Design and synthesis of new benzimidazole–arylpiperazine derivatives acting as mixed 5-HT 1A/5-HT 3 ligands

A series of new mixed benzimidazole–arylpiperazine derivatives were designed by incorporating in general structure III the pharmacophoric elements of 5-HT 1A and 5-HT 3 receptors. Compounds 1– 11 were synthesized and evaluated for binding affinity at both serotoninergic receptors, all of them exhibiting high 5-HT 3R affinity ( K i = 10–62 nM), and derivatives with an o-alkoxy group in the arylpiperazine ring showing nanomolar affinity for the 5-HT 1AR ( K i = 18–150 nM). Additionally, all the synthesized compounds were selective over α 1-adrenergic and dopamine D 2 receptors ( K i>1000–10,000 nM). Compound 3 was selected for further pharmacological characterization due to its interesting binding profile as mixed 5-HT 1A/5-HT 3 ligand with high affinity for both receptors (5-HT 1A: K i = 18.0 nM, 5-HT 3: K i = 27.2 nM). In vitro and in vivo findings suggest that this compound acts as a partial agonist at 5-HT 1ARs and as a 5-HT 3R antagonist. This novel mixed 5-HT 1A/5-HT 3 ligand was also effective in preventing the cognitive deficits induced by muscarinic receptor blockade in a passive avoidance learning test, suggesting a potential interest in the treatment of cognitive dysfunction.

Design and Synthesis of New Benzimidazole‐Arylpiperazine Derivatives Acting as Mixed 5‐HT1A/5‐HT3 Ligands.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Spatial memory impairment in OLETF rats without cholecystokinin – a receptor

Cholecystokinin (CCK) is one of the most abundant neurotransmitter peptides in the brain. As Otsuka Long-Evans Tokushima Fatty (OLETF) rats lack CCK-A receptor because of a genetic abnormality, we examined whether learning and memory were impaired in these animals using both Morris water maze (MWM) and step-through type passive avoidance (PA) learning test. In the MWM test, memory impairment was observed in OLETF rats. The number of errors was also significantly higher, and that of the correct choices was significantly lower in OLETF rats compared to the controls [Long-Evans Tokushima Otsuka (LETO)] rats. In PA, OLETF rats did not show facilitating response 24 h after training. From these observations, we concluded that a spatial memory was impaired in the OLETF rats.

Design and synthesis of new benzimidazole-arylpiperazine derivatives acting as mixed 5-HT1A/5-HT3 ligands.

A series of new benzimidazole-arylpiperazine derivatives III were designed, synthesized and evaluated for binding affinity at serotoninergic 5-HT(1A) and 5-HT(3) receptors. Compound IIIc was identified as a novel mixed 5-HT(1A)/5-HT(3) ligand with high affinity for both serotonin receptors and excellent selectivity over alpha(1)-adrenergic and dopamine D(2) receptors. This compound was characterized as a partial agonist at 5-HT(1A)Rs and a 5-HT(3)R antagonist, and was effective in preventing the cognitive deficits induced by muscarinic receptor blockade in a passive avoidance learning test.

Effects of passive-avoidance training on sleep-wake state-specific activity in the basolateral and central nuclei of the amygdala.

This study examined the effects of intense emotional learning on the sleep-wake state-specific electroencephalographic (EEG) activities of the basolateral (BLA) and central (CeA) nuclei of the amygdala. Rats were trained on a passive-avoidance learning (PAL) protocol that was followed by 6 hr of undisturbed polygraphic recording and a PAL test. After PAL training, the total amount of REM sleep decreased: high-frequency EEG power decreased in the CeA during REM sleep and increased in the BLA during all sleep-wake stages. These results suggest that there is no homeostatic demand for REM sleep after intense emotional learning. However, the PAL-specific changes in the local EEG suggest that some form of memory processing may occur within the amygdala during REM sleep.

Involvement of microtubule integrity in memory impairment caused by colchicine

In order to fully evaluate the effects of colchicine treatment on learning ability in rats, colchicine was administered, and both Morris water maze (MWM) and step-through type passive avoidance (PA) learning tests were conducted. In both learning tests, infusion of colchicine into the rat dentate gyrus, at two distinct bilateral rostrocaudal locations, potently impaired memory function in a dose-dependent manner (0.01–2.0 μg/site), whereas systemic injection of colchicine (50–300 μg/kg) did not. In the MWM test, memory impairment was observed even at doses where there was no evidence of any histological changes in the dentate granule cells. This suggests that functional deterioration, that is, learning impairment was induced by the dysfunction of microtubules and/or axons, was caused by colchicine. Moreover, ameliorated learning behavior was observed with chronic treatment of β-estradiol 3-benzoate, which has been suggested to have an important role as an adjuvant treatment for younger Alzheimer's disease (AD), immediately after colchicine infusion (0.3 μg). These results indicate that the animal model accompanying the colchicine-induced functional defect showing early tau pathology, but not neuronal cell degeneration, may well mimic comparatively early stage of AD.

Role of 5-HT6 receptors in memory formation.

Mice lacking the 5-HT(6) receptor presented neither gross anatomical or behavioral abnormalities nor obvious changes in microscopic brain morphology, and their performance in rotarod, open field and novel object testing paradigms revealed no differences compared with wild-type animals. Nevertheless, an association between the 5-HT(6) receptor polymorphism C267T and Alzheimer's disease has been reported. Interestingly, the 5-HT(6) antisense oligonucleotide decreased 5-HT(6) gene expression and enhanced spatial learning acquisition in the water maze. Similarly, injection of the 5-HT(6) receptor antagonist Ro-04-6790 improved learning consolidation in an autoshaping task, while mCPP, scopolamine and dizocilpine decreased performance. The effect induced by scopolamine or dizocilpine, but not that induced by mCPP, was completely or partially reversed by Ro-04-6790. Ro-04-6790 did not modify the 8-OH-DPAT facilitatory effects on learning consolidation. Since Ro-04-6790 facilitatory effect was unaffected by 5-HT(1A), 5-HT(2A/2B/2C), 5-HT(3), 5-HT(4) or 5-HT(7) receptor blockade, the facilitatory effect induced by Ro-04-6790 involved specifically 5-HT6 receptors. Similarly, the 5-HT(6) receptor antagonist SB-271046 improved retention in the water maze and produced a significant performance improvement in aged rats in an operant-delayed alternation task. A series of Ro-04-6790 analogues that penetrate the brain and specifically bind to 5-HT(6) receptors reversed scopolamine-induced retention deficit in a passive avoidance learning test. Collectively, these data provide further support to the notion that 5-HT systems, via 5-HT(6) receptors, also play a significant role in memory formation under normal and dysfunctional memory conditions.

Effects of indeloxazine hydrochloride, a cerebral activator, on brain function in rodents

The effects of indeloxazine hydrochloride on brain function were examined using forced swimming and passive avoidance learning tests in rodents. The pharmacologic actions of indeloxazine were compared with those of piracetam, aniracetam, and amitriptyline. When tested at oral (po) doses of 10 to 50 mg/kg, indeloxazine (50 mg/kg po, P < 0.01) and amitriptyline (50 mg/kg po, P < 0.05) shortened the period of immobility in forced swimming in mice. Impairment of passive avoidance learning in scopolamine-treated rats was ameliorated after administration of indeloxazine (20 mg/kg po, P < 0.05) but worsened after amitriptyline (4 mg/kg intraperitoneal, P < 0.01). When tested from 30 to 300 mg/kg po, the pharmacologic actions of piracetam and aniracetam were weak and nonsignificant in both tests. These results suggest that indeloxazine may possess antidepressant activity similar to that of amitriptyline but is distinct from amitriptyline in terms of its lack of anticholinergic properties and potential for ameliorating impaired brain functions such as those involving learning behavior. Furthermore, indeloxazine appears to exert a wider range of activity on brain funtions than either piracetam or aniracetam.

Lack of the development of morphine tolerance in experimental amnesia: role of arginine vasopressin

The development of tolerance to morphine analgesia in amnesic model mice and the role of arginine vasopressin (AVP) in the underlying mechanism was examined. Hypoxia, brain ischemia, scopolamine and electroconvulsive shock (ECS) manipulation caused amnesia in the step-through type passive avoidance learning test performed at 24 h after the training trial. The amnesic state lasted for at least 3 days and recovered to naive control level on the 20th day after each manipulation. In all amnesic groups, radioimmunoassayable AVP content in hypothalamus was decreased, in particular, the reduction was significant in hypoxia and ischemia induced amnesic animals, then recovered to the control level by 20 days after each treatment. Daily morphine, 10 mg/kg, s.c. easily resulted in the development of tolerance to the analgesic effect in control animals. however, such treatment failed to develop tolerance in amnesic model animals, leaving the analgesic effect unchanged to the control levels. Daily pretreatment with i.c.v. AVP, dose-dependently reinstated the development of tolerance in amnesic model mice. When morphine injection was started from 20 days after the amnesia inducing treatment, tolerance developed as in a similar pattern as in control animals. Thus, amnesic model mice are deficient in brain AVP levels, and consequently, a certain level of AVP in the hypothalamus is required for maintaining the normal function such as the development of tolerance to morphine and the recovery from amnesia.

Facilitation of Memory Retrieval by Pre-Test Morphine and Its State Dependency in the Step-Through Type Passive Avoidance Learning Test in Mice

Amnesia produced by scopolamine and cycloheximide were reversed by morphine given 30 min before the test trial (pre-test), and pre-test morphine also facilitated the memory retrieval in the animals administered naloxone during the train ng trial. Similarly, pre-test scopolamine partially reversed the scopolamine-induced amnesia, but not significantly; and pre-test cycloheximide failed to reverse the cycloheximide-induced amnesia. These results suggest that the facilitation of memory retrieval by pre-test morphine might be the direct action of morphine rather than a state dependent effect.

Comparative studies of somatostatin-14 and some of its fragments on passive avoidance behavior, open field activity and on barrel rotation phenomenon in rats

Behavioral effects of somatostatin-14, and some of its fragments [somatostatin(3–8), somatostatin(9–14), somatostatin(7–10)] after intracerebroventricular (ICV) administration have been investigated in male rats. In a passive avoidance learning test, somatostatin-14 (0.6 nM) given immediately after the learning session increased the avoidance latency at 24 hr after the injection, when compared to a somatostatin(3–8) (0.6 nM)-treated group. However, compared to a saline-treated group, the peptides did not significantly influence the avoidance latency. Somatostatin-14 administered in higher dose (6.0 nM) decreased the avoidance latency compared to the saline-treated group, while its fragments did not influence it. In an open field behavioral test, immediately after the 24-hr passive avoidance test, 6 nM of somatostatin-14 decreased the rearing activity, while the fragments did not influence this behavior. Somatostatin-14 produced barrel rotation in a dose-related manner, but after the injection of a high dose of the peptide (12 nM) all of the animals died in cardiorespiratory failure (apnea, pulmonary oedema). The fragments did not produce barrel rotation.

Preparation of cerebral ischemia-induced amnesic model in mice and ameliorative effect of several compounds on the model

A simple and reliable method for the preparation of an ischemia-induced amnesic model was developed in mice and the model animals were employed for screening of the anti-amnesic effect of drugs. Under light thiopental anesthesia the bilateral carotid arteries were exfoliated from the surrounding tissues. Each artery was threaded through a small polyethylene tube, and the incision was sutured, leaving the tip of the tube and both ends of the thread out of the skin. To prevent the tube from falling off, both ends of the thread was ligated at the tip of the tube. Cerebral ischemia was attained by pulling the artery into the tube, and the occlusion was rapidly released by cutting the ligation in the thread and taking off the tube. Twenty-four hours after the surgery, the animals were used for the one trial passive avoidance learning test. In ddY strain mice, the amnesic state was obtained by 5 to 30 min cerebral ischemia, which was applied immediately after the acquisition trial. Mice of the ICR strain were more sensitive to the ischemic treatment and 2 min occlusion of the carotid arteries resulted in a high degree of amnesia. A potent prolyl endopeptidase inhibitor, Z-thiopro-thiazolidine, and 2 novel pyrrolidone derivatives, p-chlorobenzyl-2-pyrrolidone-5-carboxylate and N-(2-pyridylmethyl)-2-pyrrolidone-5-carboxamide, improved the acquisition of the passive avoidance response in the ischemia-induced amnesic models.