Application of a novel Active Allothetic Place Avoidance task (AAPA) in testing a pharmacological model of psychosis in rats: comparison with the Morris Water Maze

Administration of a non-competitive NMDA antagonist dizocilpine (MK-801) was proposed to be an animal model of psychosis. NMDA-receptor blockade is accompanied by increased locomotion, behavioral deficits, and other changes resembling psychotic symptoms. However, the role of NMDA-receptors in organizing brain representations is not understood yet. We tested the effect of NMDA-receptor blockade by systemic administration of dizocilpine at two different doses (0.1 or 0.2 mg/kg) in a recently designed Active Allothetic Place Avoidance (AAPA), a task which requires rats to separate spatial stimuli from two continuously dissociated subsets. The effect of dizocilpine on learning in the AAPA task was compared with its effect on acquisition of the reference memory version of the Morris Water Maze task. Both doses impaired performance in the Morris Water Maze task, whereas only the higher dose impaired performance in the AAPA task. The Morris Water Maze appears to be more sensitive to dizocilpine-induced behavioral deficit than the AAPA task. These findings support the notion that these two tasks are differentially dependent on the NMDA-receptor function.     

Water T-maze,an improved method to assess spatial working memory in rats: Pharmacological validation

The present study was performed to validate a spatial working memory task using pharmacological manipulations. The water escape T-maze combines the advantages of the Morris water maze and the T-maze while minimizing the disadvantages. Scopolamine (1 mg/kg), a drug that affects cognitive function in spatial working memory tasks, significantly decreased the rats’ performance in the present delayed alternation task. Glutamate neurotransmission plays an important role in the maintenance of working memory; rats treated with dizocilpine (MK-801; 0.125–0.25 mg/kg), a N-methyl-d-aspartate (NMDA) receptor antagonist, were impaired in this task. In agreement with evidence showing a functional interaction between ionotropic and metabotropic glutamatergic receptors, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a mGlu₅ receptor antagonist, at a dose (1 mg/kg) which by itself had no significant effects, enhanced MK-801-induced impairments of spatial working memory. These evidences suggest that the water escape T-maze might be a valid method to assess spatial working memory, sensitive to pharmacological manipulations.     

The role of nitric oxide in the emotional learning of rats in the plus-maze

The present study evaluated the role of nitric oxide (NO) in the transfer latency (TL) paradigm in the elevated plus-maze. Male Wistar rats received i.p. injections of either 0.9% Saline, N(omega) Nitro-L-arginine-methyl-ester (L-NAME, an inhibitor of NO synthesis), d-NAME (inert isomer), scopolamine (SCO, antagonist of muscarinic receptors), or MK-801 (antagonist of NMDA receptors) and, after 30 min, were submitted to TL procedure. In an independent experiment, the ability of the same L-NAME treatments in changing the arterial pressure and blood glucose level (BGL) was evaluated in conscious rats. The treatment with SCO (1 mg kg(-1)), MK-801 (0.15 mg kg(-1)) and L-NAME (10 and 50 mg kg(-1)), but not with D-NAME, impaired the TL learning. The L-NAME-induced TL deficit was counteracted by L-ARG (100 and 200 mg kg(-1)), while the co-administration of sub-effective doses of L-NAME and MK-801 failed to impair the TL learning. The L-NAME (50 mg kg(-1)) treatment failed to alter the BGL. All treatments with L-NAME induced hypertension, but the rats treated with L-NAME (5 mg kg(-1)) were still able to learn the TL task. The data indicate that the TL deficit induced by L-NAME (10 and 50 mg kg(-1)) is not due to either hypertension or changes in the BGL. It is also possible to establish that NO production is important for emotional learning underlying the TL procedure in rats.     

Interactive effect of MK-801 and pre-training on spatial learning in rats

In experiment 1, the effect of an NMDA receptor antagonist, MK-801, on the formation of the spatial representation was investigated. The administration of 0.1 mg/kg of MK-801 induced learning deficits in rats (n = 10) with the Morris watermaze task. However, when rats (n = 10) were pre-trained in the same task without drug treatment, and then trained in the same task in a different environment under the influence of the same amount of the drug, their performance was not impaired. The result suggests that rats treated with MK-801 can acquire a spatial representation of their environment, and that the impairment shown by the drug-treated rats without pre-training may be due to the impairment in the learning of the problem-solving strategy required for the watermaze place task. Experiment 2 examined this possibility. Rats (n = 10) were pre-trained with a visual cue discrimination task without drug treatment and then trained in the place task with MK-801 (0.1 mg/kg) treatment. They did not show impairment in the place task, indicating that rats treated with MK-801 can learn a new problem-solving strategy. Thus the learning deficits of MK-801-treated rats that have not been pre-trained do not seem to be due to impaired acquisition of the spatial representation or of the learning of strategy required to solve the watermaze place task.     

Assessment of sustained attention in ad libitum fed Wistar rats: effects of MK-801

RATIONALE: Rodent models designed to assess cognitive function, such as sustained attention tasks, use food and/or fluid restriction in order to motivate responding. However, evidence indicates that dietary restriction can have profound effects on brain function and on the neurobehavioral effects of drugs. OBJECTIVE: The primary objective of this study was to demonstrate the feasibility of using ad libitum fed rats to assess sustained attention in an operant 2-choice reaction time (2-CRT) task. Because N-methyl-D-aspartate (NMDA) receptor function is critical for sustaining attention in animal models, the effects of the NMDA antagonist MK-801 on 2-CRT performance were also assessed. METHODS: Male Wistar rats (n = 20) rats were trained to perform an operant 2-CRT task. A 10% sucrose solution was used as the reinforcer. After performance levels stabilized, the effects of MK-801 (0.01-0.12 mg/kg, IP) were assessed. RESULTS: Stable levels of performance on the final version of the 2-CRT task was established after 2-3 months of training. Consistent with prior reports, correct trials varied as a function of stimulus light duration (1000 ms: 67 +/- 3%, 500 ms: 59 +/- 3%, 100 ms: 51 +/- 3%, 50 ms: 43 +/- 2%). Administration of 0.06 mg/kg MK-801 significantly increased choice accuracy. Administration of 0.12 mg/kg MK-801 significantly slowed reaction times and resulted in pronounced motor incoordination. CONCLUSIONS: This study demonstrates that ad libitum fed rats can be trained to perform a 2-CRT task. However, the levels of choice accuracy are lower than typically observed under conditions of dietary restriction. The increase in choice accuracy following MK-801 is consistent with the effects of psychomotor stimulants and may suggest sustained attention was slightly enhanced by MK-801.     

NMDA receptors are involved in Ginkgo extract-induced facilitation on memory retention of passive avoidance learning in rats

Herbal therapies are commonly used to enhance memory and learning. Ginkgo biloba has shown to be one of the most popular herbs that is used to treat amnesia and retard age related memory deficits. Although, there have been several reports on the memory enhancing effects of Ginkgo, involvement of glutamatergic system that plays pivotal role in learning and memory has not been precisely assessed so far. The current study intended to investigate the effect of Ginkgo intake on amnesia while NMDA (N-methyl D-aspartic acid) receptors blocked by the administration of MK-801. The study used passive avoidance (PA) task to investigate the effect of chronic administration of Ginkgo extract (40 and 90 mg/kg; oral) on the memory span in male Wistar rats, suffering from MK-801-induced forgetfulness (0.06 and 0.1 mg/kg; i.p.). The results indicate that Ginkgo was able to remove MK-801-induced forgetfulness, indicating that Ginkgo can affect memory retention but not effect on passive avoidance acquisition, using pathways other than glutamatergic system as well. The results might indicate that Ginkgo extract can be effective in removing forgetfulness caused by inhibiting NMDA receptors from performing their activities.     

Effects of the NMDA receptor antagonist MK-801 on short-interval timing in rats

Effects of MK-801, an N-methyl-D-aspartate antagonist, on short-interval timing were examined using the peak-interval (PI) and PI-gap procedures. Fisher 344 rats were given daily injections of 0.025 mg/kg, 0.05 mg/kg, and 0.2 mg/kg MK-801. The main results were (a) 0.2 mg/kg MK-801 produced an immediate overestimation of the criterion time; (b) MK-801 increased peak rate of responding; (c) 0.2 mg/kg MK-801 produced an increase in variability; (d) during the PI-gap procedure, a reset pattern was observed for all rats (MK-801 and saline). Results suggest that MK-801 has at least 2 effects. First, MK-801 interferes with short-interval timing by producing an overestimation of time and a nonscalar increase in variability. Second, MK-801 increases response rate, suggesting a decrease in response inhibition.     

Memory performance and scopolamine: Hypoactivity of the thalamus revealed by cytochrome oxidase histochemistry

Spatial memory learning is related to the functioning of a neuronal circuit composed of cortical, hippocampal and diencephalic brain regions. The Morris water maze (MWM) is frequently used to assess spatial memory in rats. In this study, the neuronal functional activity of some brain limbic system regions after a memory task in adult male Wistar rats injected with scopolamine (1.0 mg/kg, i.p.) was assessed using cytochrome oxidase (COx) histochemistry. The rats were trained following a working memory schedule in the MWM. A trained group injected with saline and an untreated control group were examined to compare changes in COx activity in the dorsal hippocampus, anterior thalamus, mammillary nuclei, prefrontal cortex and ventral tegmental area. The scopolamine-treated group showed an impairment of spatial learning. Also, a decrease in COx activity was found in this group as compared to the saline group in the anteroventral and anteromedial thalamic nuclei. Overall, these findings suggest that memory deficits induced by scopolamine may be due to impairment of the cholinergic function in the anterior thalamic nuclei.     

3,4 methylenedioxymethamphetamine (ecstasy) impairs eight-arm radial maze performance and arm entry pattern in rats

The recreational use of 3,4 methylenedioxymethamphetamine (ecstasy) in humans has been associated with memory impairment. The present study examined whether ecstasy impairs short- and long-term working memory and the pattern of arm entries in rats tested in the 8-arm radial maze with a 2-hr delay. After completing the training session, the rats were given a single dose of ecstasy (1, 2, or 3 mg/kg ip) 20 min before the test. The highest dose slightly affected short-term working memory. Under conditions of delay, there was a progressive deficit in long-term working memory, starting from 1 mg/kg. Under both test conditions, 2 and 3 mg/kg flattened the pattern of arm entry. None of the doses caused hyperlocomotion or stereotypy in the radial maze. These findings suggest that acute ecstasy mainly affects the long-term components of working memory and disrupts the pattern of arm entry in a way similar to serotonergic agents.     

Methadone disrupts performance on the working memory version of the Morris water task

The aim of the study was to examine if administration of the mu-opiate agonist methadone hydrochloride resulted in deficits in performance on the Morris water tank task, a widely used test of spatial cognition. To this end, after initial training on the task, Long-Evans rats were administered saline or methadone at either 1.25, 2.5 or 5 mg/kg ip 15 min prior to testing. The performance of the highest-dose methadone group was inferior to that of the controls on the working memory version of the Morris task. There were also differences between the groups on the reference memory version of the task, but this result cannot be considered reliable. These data show that methadone has its most profound effect on cognition in rats when efficient performance on the task requires attention to and retention of new information, in this case, the relationship between platform location and the extramaze cues.     

Interactive effects of morphine and scopolamine,MK-801, propanolol on spatial working memory in rhesus monkeys

Opiate, cholinergic, glutamatergic and beta-adrenergic neurotransmitters play key roles in learning and memory in humans and animals. Dysfunction of the interactions between these neurotransmitters may induce human diseases. In the present study, the interactions of morphine and acetylcholine (ACh), NMDA, and beta-adrenergic receptor antagonist (scopolamine, MK-801, and propanolol) were evaluated in a single-blind design by co-administrations of morphine and these drugs in a delayed response in rhesus monkeys. The results indicated that: (1) Co-administration of morphine and scopolamine deteriorated spatial working memory. (2) Co-treatment of morphine and MK-801 restored impairment caused by morphine and MK-801 in a dose-depending pattern. (3) Morphine plus propranolol impaired spatial working memory. High dose of morphine (0.01 mg/kg) reversed impaired spatial working memory induced by single propranolol and morphine treatment. These data suggested that the interactions of morphine and AChergic, NMDAergic and beta-adrenergic compounds were involved in spatial working memory in rhesus monkeys.     

N-acetyl cysteine supplementation prevents impairment of spatial working memory functions in rats following exposure to hypobaric hypoxia

Exposure to high altitude (HA), especially extreme altitude, is associated with impairment of cognitive functions including memory and increased oxidative stress. However, the underlying mechanisms involved are not well understood. It is hypothesized that HA induced oxidative stress may be one of the factors underlying hypoxia induced memory impairment. The aim of the present study was to investigate the effect of hypobaric hypoxia (HH) on spatial working and reference memory functions, oxidative stress markers in rats and effect of supplementation of N-acetyl cysteine (NAC). The rats were divided into four groups. Group I served as normoxic (n=6), Group II served as hypoxic (n=6), Group III as hypoxia group treated with NAC (n=6) and Group IV served as normoxic group treated with NAC (n=6). Group II & III were exposed to HH for 3 days equivalent to 6100 m and received oral NAC supplementation (750 mg/kg) daily. Rats from all the groups were trained in Morris Water Maze (MWM) task for 8 consecutive days. Spatial working and reference memory were tested immediately after the termination of HH and then the rats were sacrificed for estimation of oxidative stress markers in hippocampus. Rats displayed significant deficits in spatial working memory, and increased oxidative stress along with decrease in antioxidant status on hypoxic exposure. Supplementation with NAC in hypoxia-exposed group improved spatial memory performance, and decreased oxidative stress. These findings indicate that hypoxic exposure is associated with increased oxidative stress, which may have caused memory deficit in rats exposed to simulated HA.     

Manipulation of D2 receptors with quinpirole and sulpiride affects locomotor activity before spatial behavior of rats in an active place avoidance task

Dopamine-mediated neurotransmission is widely studied with respect to motivation, motor activity and cognitive processes. The aim of the present study was to evaluate the role of D2 receptors in the behavior of rats in the active allothetic place avoidance (AAPA) task. D2 receptor agonist quinpirole and antagonist sulpiride were administered intraperitoneally 20min prior to behavioral testing. Administration of quinpirole led to dose-dependent increase of locomotion; the spatial efficiency was spared across the dose range studied (0.05-1.0mg/kg). In contrast, sulpiride decreased locomotor activity at a dose not influencing spatial efficiency (60mg/kg); the highest dose of sulpiride (100mg/kg) caused a deficit in both locomotor and spatial behaviors. The results suggest a relatively lesser importance of D2 receptors for spatial efficiency in the AAPA task, with a predominant influence of D2 receptor ligands on motor activity.     

MK-801对新生鼠脑外伤性神经变性的超微结构的影响

目的:研究非竞争性N-甲基-D-天门冬氨酸受体拮抗剂MK-801对新生鼠创伤性颅脑损伤(TBI)后同侧顶叶皮质和海马神经元超微结构的影响.方法:新生7 d SD大鼠,被随机分成正常对照组和实验组(实验组给予MK-801 1 mg/kg,并且细分为创伤前30 min给药、创伤即刻给药和创伤后30 min给药3个亚组).造模24 h取材,透射电镜下观察神经细胞超微结构的变化.结果:创伤后30 min给药的神经细胞出现胞质和核染色质的浓缩深染,胞质内充满大小不等的空泡;创伤即刻组的神经细胞胞质内线粒体有肿胀,但胞核的变化不明显.结论:适时和适量运用MK-180能延迟神经细胞核染色质和粒线体的变性损伤,使之停留在损伤早期,为临床联合其他药物治疗赢得时间.     

Kainate-induced functional deficits are not blocked by MK-801

Male, Fischer-344 rats were pretreated with MK-801 (0.1, 1.0 or 10.0 mg/kg, i.p.) prior to bilateral injection of kainate (0.33 micrograms/site) into the dorsal and ventral hippocampus. Kainate impaired the acquisition of a water maze acquisition task 4 weeks after surgery, an effect not attenuated by pretreatment with MK-801. However, higher doses (1.0 and 10.0 mg/kg) of MK-801 reduced the amount of kainate-induced granule cell and to some extent CA1 pyramidal cell damage in the hippocampus. Kainate-induced CA3/CA4 damage was not affected by MK-801 pretreatment. MK-801 (10 mg/kg) also reduced the amount of thalamic damage produced by kainate. These data support the conclusion that intrahippocampal kainate-induced destruction of CA3/CA4 pyramidal cells is mediated by non-N-methyl-D-aspartate (non-NMDA) receptors and that kainate-induced loss of these cells is associated with the neurobehavioral effects of intrahippocampally administered kainate.     

离子型谷氨酸受体拮抗剂MK-801浓度与全脑缺血再灌注大鼠海马内源性神经干细胞的增殖**

背景：脑缺血再灌注后,过度释放的兴奋性氨基酸可通过N-甲基-D-天冬氨酸(NMDA)受体激活内源性神经干细胞,促使其增殖、分化,修复神经细胞,但同时也导致细胞内钙离子超载,引起神经细胞的损伤。 目的：观察NMDA受体拮抗剂MK-801浓度对脑缺血再灌注大鼠海马内源性神经干细胞增殖的影响。 方法：SD大鼠随机分为正常对照组、手术对照组及MK-801 0.2,0.4,0.6,0.8,1.0,1.2 mg/kg组。除正常对照组外,大鼠首先进行侧脑室插管,3 d后进行4条血管阻断方法制备大鼠全脑缺血再灌注模型。在模型制作前30 min按照不同浓度侧脑室注射MK-801。正常对照组和手术对照组侧脑室注射同剂量的生理盐水。免疫组织化学、RT-PCR技术检测各组脑海马nestin阳性细胞及其mRNA表达。 结果与结论：MK-801浓度在0.8 mg/kg以下时,用药组大鼠脑海马nestin mRNA及蛋白的表达与手术对照组差异无显著性意义(P > 0.05),呈现高表达;当MK-801浓度达到0.8 mg/kg时,与手术对照组相比,用药组大鼠脑海马nestin基因及蛋白的表达明显下降(P < 0.05),并随浓度的增高呈递减趋势。提示MK-801在浓度为0.6 mg/kg时,即可抑制钙超载保护神经元,又有良好的刺激神经干细胞增殖作用。 关键词：离子型谷氨酸受体拮抗剂;脑缺血;再灌注;神经干细胞;MK-801 doi:10.3969/j.issn.1673-8225.2012.06.012     

N-methyl-D-aspartate receptor antagonist MK-801 and spatial memory representation: working memory is impaired in an unfamiliar environment but not in a familiar environment.

Female Sprague-Dawley rats were injected with the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 or saline 30 min before daily testing in spatial working memory (WM) and reference memory (RM) procedures in an 8-arm radial maze. MK-801 impaired RM and WM acquisition but not performance when rats were trained to criterion before drug administration. Neither a 2-hr nor a 4-hr delay between the first and last 2 correct WM choices impaired long-term WM. MK-801 impaired WM performance in trained rats only when rats were tested in a new environment. Thus, 2 mechanisms may be required for relational memory: an NMDA-dependent mechanism for acquiring long-term spatial representations and an NMDA-insensitive mechanism for operating on these stored representations.     

Neuroprotective effect of lamotrigine and MK-801 on rat brain lesions induced by 3-nitropropionic acid: evaluation by magnetic resonance imaging and in vivo proton magnetic resonance spectroscopy

Magnetic resonance imaging and in vivo proton magnetic resonance spectroscopy were used to evaluate the therapeutic effect of lamotrigine and MK-801 on rat brain lesions induced by 3-nitropropionic acid. Systemic administration of 3-nitropropionic acid (15 mg/kg per day) to two-month-old Sprague-Dawley rats (n = 10 for each group) for five consecutive days induced selective striatal and hippocampal lesions and specific behavioral change. Pretreatment with lamotrigine (10 mg/kg or 20 mg/kg per day) or MK-801 (2 mg/kg per day) attenuated the lesions and behavioral change. There were no significant differences in T2 values of the striatum and hippocampus among rats pretreated with MK-801, lamotrigine (20 mg/kg) and sham controls. Significant elevations of succinate/creatine and lactate/creatine ratios and decreases of N-acetylaspartate/creatine and choline/creatine ratios were observed after 3-nitropropionic acid injections (P < 0.001). The changes were nearly prevented after pretreatment with lamotrigine (20 mg/kg). However, the N-acetylaspartate/creatine in rats pretreated with lamotrigine (10 mg/kg) (P < 0.01) and MK-801 (P < 0.05) still showed significant reduction as compared with sham controls. Thus we conclude that both lamotrigine and MK-801 are effective in attenuation of brain lesions induced by 3-nitropropionic acid. A higher dose of lamotrigine provides a better neuroprotective effect than MK-801. With a better therapeutic effect and fewer side effects, lamotrigine is more promising for potential clinical application.     

Role of alpha1- and alpha2-adrenoceptors in the regulation of locomotion and spatial behavior in the active place avoidance task: a dose-response study

Studies on the neurotransmitter substrate of locomotion and place navigation occupy a central position in behavioral neuroscience. Active allothetic place avoidance (AAPA) is a task, in which animals are trained to avoid a room frame defined stable sector on a continuously rotating arena. The aim of the present study was to test the effect of the blockage of alpha1- and alpha2-adrenoceptors, using specific antagonists prazosin and idazoxan, on the locomotor activity and spatial behavior in the AAPA task. Both prazosin and idazoxan at the highest doses (4 and 6 mg/kg, respectively) were found to decrease the locomotor activity in the AAPA and they also impaired navigational performance. The results suggest that antagonizing alpha-adrenoceptors with systemically administered drugs affects locomotor activity together with avoidance behavior and does not cause a purely cognitive deficit in the AAPA task.     

The acute effects of MK-801 on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide in conscious and alpha-chloralose anaesthetized rats.

The dynamic effects of the non-competitive N-methyl-D-aspartate receptor antagonist, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine] , on cerebral blood flow and tissue partial pressures of oxygen and carbon dioxide were investigated in the striatal and occipital regions of conscious and anaesthetized rats by mass spectrometry. MK-801 (0.5 and 5 mg/kg, i.p.) induced a large increase in the blood flow of both cerebral regions of conscious rats, without significant changes in local tissue partial pressures of oxygen and carbon dioxide. The increase in cerebral blood flow was maximal within 30 min after injection. Its amplitude was independent of the dose of MK-801, but cerebral blood flow remained elevated for up to 4 h after 5 mg/kg MK-801, while it progressively decreased towards its basal level in rats given 0.5 mg/kg MK-801. The amplitude and time-course of the vascular changes were similar in the two cerebral regions studied. The difference in the changes in tissue partial pressure of oxygen induced by MK-801 and by a 6% CO2 inhalation suggests that the MK-801-induced rise in cerebral blood flow in conscious rats is, at least partly, due to an increase in oxidative metabolism. In contrast, MK-801 induced either no changes or decreases in cerebral blood flow in alpha-chloralose-anaesthetized rats. The present results should be taken into account not only to determine the mechanisms by which N-methyl-D-aspartate receptor antagonists may exert their neuroprotective effects but also to further elucidate the sites of action of MK-801 in the central nervous system.