Morris Water Escape Task Research Articles

Emotional reactivity and cognitive performance in aversively motivated tasks: a comparison between four rat strains.

BackgroundCognitive function might be affected by the subjects' emotional reactivity. We assessed whether behavior in different tests of emotional reactivity is correlated with performance in aversively motivated learning tasks, using four strains of rats generally considered to have a different emotional reactivity.MethodsThe performance of male Brown Norway, Lewis, Fischer 344, and Wistar Kyoto rats in open field (OF), elevated plus-maze (EPM), and circular light-dark preference box (cLDB) tasks, which are believed to provide measures of emotional reactivity, was evaluated. Spatial working and reference memory were assessed in two aversively motivated learning and memory tasks: the standard and the "repeated acquisition" versions of the Morris water maze escape task, respectively. All rats were also tested in a passive avoidance task. At the end of the study, levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid, and 5-HT turnover in the hippocampus and frontal cortex were determined.ResultsStrain differences showed a complex pattern across behavioral tests and serotonergic measures. Fischer 344 rats had the poorest performance in both versions of the Morris water escape task, whereas Brown Norway rats performed these tasks very well but the passive avoidance task poorly. Neither correlation analysis nor principal component analysis provided convincing support for the notion that OF, EPM, and cLDB tasks measure the same underlying trait.ConclusionsOur findings do not support the hypothesis that the level of emotional reactivity modulates cognitive performance in aversively motivated tasks. Concepts such as "emotional reactivity" and "learning and memory" cannot adequately be tapped with only one behavioral test. Our results emphasize the need for multiple testing.

Analysis of spatial orientation strategies of male and female Wistar rats in a Morris water escape task

In the present study we investigated spatial navigation in male and female Wistar rats in the Morris water escape task. Rats were subjected to procedures which required the use of a place (PLACE), cue (CUE) and egocentric (EGO) response to learn the task efficiently. In a first experiment rats were successively tested in the PLACE, CUE and EGO condition and in a second experiment the order of tasks was reversed. The first experiment showed that female rats swam longer distances and took more time to find the platform in the PLACE task. Further, the female rats spent less time near the previous platform position than the male rats during probe trial. No sex difference was found in the CUE and EGO task. In the second experiment, the female rats took longer to find the platform than the male rats in the EGO task. In the CUE and PLACE task no differences between the sexes was found during acquisition. However, the male rats spent more time near the previous platform position than the female rats during the probe trial of the PLACE task. On basis of present data it is concluded that the use of a PLACE-based strategy is better in male Wistar rats. CUE learning is not sex-dependent. The ability to use EGO strategies appears not to be different between male and female Wistar rats, but appears dependent on pre-exposure to the task.

Two months makes a difference in spatial orientation learning in very old FBNF1 rats

Age-related changes in cognitive performance may be more pronounced in the period near or exceeding the median life span. Therefore, we compared the acquisition of a Morris water escape task by two groups of very old Fischer344 × Brown Norway hybrid rats. The mean age difference between the two groups of rats (a 33- to 34-month-old group versus a 35- to 36-month-old group) was about 2 months. Both groups of rats initially had the same level of performance, but then the younger group learned to escape onto the submerged platform faster, swimming a shorter distance, than the older group. By the fifth acquisition session, the younger rats needed only half the time and swam a shorter distance before they reached the platform than the older rats. These differences in learning were not due to different locomotor abilities as both groups had a similar swimming speed. These results suggest that age-related changes in cognitive performance are indeed more pronounced in the period around the median life span. We also discussed different set-ups to perform cross-sectional age-comparison studies. If there are not sufficient animals from one batch, it may be worthwhile to combine animals from different batches per age group, provided that breeding, rearing, housing, and testing conditions are highly standardized.

Different rankings of inbred mouse strains on the Morris maze and a refined 4-arm water escape task

The submerged platform or Morris water escape task is widely used to study genetic variation in spatial learning and memory, but interpretation is sometimes difficult because of wall hugging, jumping off the platform, floating or non-spatial swim strategies. We modified the task by introducing four wide arms into the circular tank and adding features that reduced, eliminated, or compensated for several competing behaviors. Three versions of the 4-arm task were evaluated in detail, and the third version yielded good results for six of eight inbred strains. Furthermore, the 4-arm task could be scored adequately without computerized video tracking. Although performance on the 4-arm task was generally superior to the Morris maze, the extent of the improvement was strain dependent. Two strains with retinal degeneration (C3H/HeJ, FVB/NJ) performed poorly on both the Morris and 4-arm mazes, whereas C57BL/6J and DBA/2J did well on both mazes. A/J performed poorly on the Morris task but became very proficient on the 4-arm maze, despite its strong tendency to hug the walls of the tank. The BALB/cByJ strain, on the other hand, exhibited the best probe trial performance on the Morris maze but was very slow in acquiring the 4-arm task. We conclude that no single task can reveal the full richness of spatially guided behavior in a wide range of mouse genotypes.

Absence of long-term behavioral effects after sub-chronic administration of low doses of methamidophos in male and female rats

Putative long-term learning and memory effects of low-dose exposure to the cholinesterase inhibitor organophosphate methamidophos (Tamaron®) early in life were studied in two parallel studies in middle-aged rats. Methamidophos was administered via the drinking water to female and male Wistar rats using nominal concentrations of 0 (control), 0.5, 1.5 and 4.5 ppm active ingredient for 16 weeks. Animals were then maintained for a recovery period of about 14 months without treatment. They were tested in the standard and repeated acquisition version of the Morris water escape task in two series of tests starting 33 and 55 weeks after termination of the methamidophos treatment. Functional observations and motor activity measurements preceded each series of testing. Exposure to methamidophos was confirmed by measurement of brain cholinesterase (ChE-B) at the end of the 16 weeks of treatment in satellite animals. At 4.5 ppm a biologically relevant reduction in ChE-B activity was observed without clinical signs of intoxication (males: 66%, females: 64% of control activity). Mid- and low-dose exposure to methamidophos revealed ChE-B activity of 90% and 100% in males and 88% and 97% in females, respectively. General examinations of the animals during treatment revealed no clinical signs suggesting cholinergic stimulation. Functional observations and motor activity measurements exhibited no relevant differences between treatment groups and controls. Neither the performance in the standard Morris water escape task that predominantly measures spatial reference memory, nor in the repeated acquisition task in the Morris tank, which predominantly measures spatial working memory, was affected by treatment with methamidophos. A small number of statistically significant differences were noted in the mean performance level between treatment groups, or between treatment by sex groups in both versions of the Morris task. However, these findings appeared to be idiosyncratic for a particular experiment and were not supported by findings from the other. They were consequently not considered as reflecting a consistent effect of methamidophos on learning and memory. In conclusion, administration of low doses of methamidophos to female and male Wistar rats for 16 weeks during early adulthood did not impair spatial working and reference memory in the Morris water escape task 33 and 55 weeks after cessation of treatment.

Spatial discrimination deficits by excitotoxic lesions in the Morris water escape task

The effects of the cholinesterase inhibitors (ChEI) metrifonate and donepezil were assessed on spatial performance of rats with bilateral lesions of the entorhinal cortex (EC), which is thought to model early changes in the brains of patients suffering from Alzheimer’s disease. In the present study, we found that spatial discrimination deficits in rats, induced by bilateral ibotenic acid (IBO) lesions of the EC region can partially be antagonised by treatment with the cholinesterase inhibitors metrifonate (30 mg kg −1) and donepezil (0.3 and 3 mg kg −1). Performance was improved in the spatial discrimination task compared with that of the EC-lesioned control group. It is concluded that the rat with bilateral EC lesions is a suitable deficit model for the assessment of effects of putative Alzheimer therapeutics.

Low-density lipoprotein receptor-knockout mice display impaired spatial memory associated with a decreased synaptic density in the hippocampus

The low-density lipoprotein receptor (LDLR) is the first described receptor for apolipoprotein E (apoE). We hypothesize that the absence of the LDLR, similar to the absence of apoE, results in impaired learning and memory processes. Six-month-old homozygous Ldlr−/− and wild-type littermates (Ldlr+/+), maintained on a standard lab chow diet, were used. Unlike humans, Ldlr−/− mice, under these conditions, do not develop atherosclerosis. The results of the Morris water escape task revealed an impaired spatial memory in the Ldlr−/− mice in comparison with Ldlr+/+ mice. Also in a T-maze task, the working memory performance of the Ldlr−/− mice was impaired. Furthermore, Ldlr−/− mice, in comparison with Ldlr+/+ mice, display a decreased number of synaptophysin-immunoreactive presynaptic boutons in the hippocampus CA1. In conclusion, the results show in mice deficiency for the LDLR results in impaired hippocampal-dependent memory functions. A decrease in the number of presynaptic boutons may underlay these behavioral alterations. Therefore, the LDLR may be an important receptor for apoE in the central nervous system.

A detailed analysis of rats’ spatial memory in a probe trial of a Morris task

In the present study, we evaluated the search behavior of rats during a probe trial of a Morris water escape task. More specifically, the spatial memory during different stages of a 2 min probe trial in different zones was examined. After rats were trained for 4 days with four trials per day, their spatial memory was tested in a first probe trial. The rats showed a preference for the target quadrant during each of four 30-s intervals. The time in the annulus decreased across the four 30-s intervals. The preference for the previous target quadrant was also observed in a second probe trial, when the rats had received additional training for 4 days with four trials per day. However, the time spent in the annulus was highest during the first 30-s of the probe trial, and was lower and similar during the next three 30-s intervals. Therefore, probe trials of 60 s seem to underestimate the spatial ability of rats. It appears that using a quadrant for assessing the performance may overestimate the spatial ability of a rat. Our findings suggest that the evaluation of the spatial memory of rats in a probe trial in the Morris water escape task requires a more detailed analysis.

Chronic cognitive effects of bilateral subdural haematomas in the rat

Humans suffering from subdural haematomas often show long-term cognitive dysfunctions. For identifying putative, recovery-enhancing therapeutics, animal models need to be developed in which recovery of function can be measured. For investigating whether and which type of recovery, i.e. spontaneous or training-induced recovery, or continuous partial retardation, is present in the rat model for bilateral subdural haematomas, spatial navigation abilities were assessed in the Morris water escape task in independent groups of rats at 1, 2, 4, 8, or 18 weeks after surgery. Complete spontaneous recovery seemed to occur at 8 weeks after injury. However, at 18 weeks after injury, the subdural haematoma caused a renewed deterioration of water maze performance, which was of a lesser degree than the impairments observed immediately after injury. This second phase performance deterioration was accompanied by an increase in generalised astrocyte reactivity. The rat subdural haematoma model provides an interesting tool for investigating spontaneous recovery processes of spatial navigation (8 weeks after injury), but also for progressive brain dysfunctions, considering the second phase of behavioural impairments seen at 18 weeks after injury.

Assessment of age-associated cognitive deficits in rats: a tricky business

Every living organism is affected by changes as a consequence of aging. Perhaps the most appropriate concept to describe age-related changes is that of ‘functional age’. Laboratory rodents are especially suited as models of cognitive aging in humans, because they have a relatively short life-span and because many tests have been developed to investigate their cognitive performance. Examples from studies using the Morris water escape task were chosen to describe and discuss factors which must be considered before drawing conclusions about age-related cognitive deficits. In particular, the roles of rearing and housing conditions, of sensorimotor impairments, and of motivational differences between young and old rats are discussed. Conclusions are drawn about how aging studies should be conceived and performed.

Calcineurin Links Ca2+Dysregulation with Brain Aging

Brain aging is associated with altered Ca(2+) regulation. However, many Ca(2+) signal transduction mechanisms have not been explored in the aged brain. Here, we report that cytosolic expression and activity of the Ca(2+)-dependent protein phosphatase calcineurin (CaN) increases in the hippocampus during aging. CaN changes were paralleled by increased activation, but not expression, of CaN-regulated protein phosphatase 1 and a reduction in the phosphorylation state of CaN substrates involved in cell survival (i.e., Bcl-2-associated death protein and cAMP response element-binding protein). The age-related increase in CaN activity was not attributable to the inability of CaN to translocate to the membrane and was reduced by blocking L-type Ca(2+) channels. Finally, increased CaN activity correlated with memory function as measured with the Morris water escape task. The results suggest that altered regulation of CaN is one of the processes that could link Ca(2+) dyshomeostasis to age-related changes in neural function and cognition.

Perinatal asphyxia results in changes in presynaptic bouton number in striatum and cerebral cortex — a stereological and behavioral analysis

Deficits in cognitive function have been related to quantitative changes in synaptic population, particularly in the cerebral cortex. Here, we used an established model of perinatal asphyxia that induces morphological changes, i.e. neuron loss in the cerebral cortex and striatum, as well as behavioural deficits. We hypothesized that perinatal asphyxia may lead to a neurodegenerative process resulting in cognitive impairment and altered presynaptic bouton numbers in adult rats. We studied cognitive performance at 18 months and presynaptic bouton numbers at 22 months following perinatal asphyxia. Data of the spatial Morris water escape task did not reveal clear memory or learning deficits in aged asphyctic rats compared to aged control rats. However, a memory impairment in aged rats versus young rats was observed, which was more pronounced in asphyctic rats. We found an increase in presynaptic bouton density in the parietal cortex, whereas no changes were found in striatum and frontal cortex in asphyctic rats. An increase of striatal volume was observed in asphyctic rats, leading to an increase in presynaptic bouton numbers in this area. These findings stress the issue that volume measurements have to be taken into account when determining presynaptic bouton density. Furthermore, perinatal asphyxia led to region-specific changes in presynaptic bouton numbers and it worsened the age-related cognitive impairment. These results suggest that perinatal asphyxia induced neuronal loss, which is compensated for by an increase in presynaptic bouton numbers.

Effects of subdural haematoma on sensorimotor functioning and spatial learning in rats

Twenty per cent of all strokes are haemorrhagic in character and are associated with severe disturbances in sensorimotor behaviour and cognition. Although spontaneous recovery of pre-stroke functioning occurs in some cases, the process is demanding, slow, and often incomplete. A first step in the preclinical testing of new putative, neuroprotective and recovery-supporting therapeutics is to validate animal models of brain injury. In a series of four experiments we evaluated the behavioural impairments and the time course of recovery of functional deficits in rats with an experimentally induced subdural haematoma. We found that unilateral subdural haematoma resulted in dysfunction in both simple reflexive (experiment 1) and skilled sensorimotor behaviour (experiment 2). Reflexive behaviour did not recover, or recovered only marginally, and neither did the deficits in skilled forepaw use. Bilateral subdural haematoma impaired the learning and memory performance of adult (experiment 3) and old rats (experiment 4) in the Morris water escape task. Considering the diversity of the deficits found in our experiments, we conclude that different models are needed to cover the broad range of deficits seen in stroke patients.

Effects of the size of the Morris water tank on spatial discrimination learning in the CFW1 mouse

The spatial orientation of mice and rats in tasks such as the Morris water escape task is guided by extramaze cues. Using data from the control groups of mice used in two drug-finding experiments, we addressed the question whether the size of the Morris water tank affects spatial learning in mice. In these experiments, CFW1 mice had been tested in either a small or a large water tank. Reanalysis of the data revealed that pool size did not affect learning or bias for the previous training quadrant. The Morris water escape task appears to act as a severe stressor in particular mouse strains, and a high stress level may interfere with the learning ability or performance of mice, which may have serious consequences for the interpretation of data. This is of special relevance when assessing the Morris maze performance of strains of mice with a different sensitivity to stress. We conclude that mice can best be tested in a small pool, because the time and distance swum to find and escape onto the platform is decreased and the probability of success (that is, of encountering the platform) is increased. This will reduce stress and hence increase the comparability of data between different strains of mice.

Behavioral effects of apamin, a selective inhibitor of the SK Ca-channel, in mice and rats

Apamin, a highly selective and potent peptide that blocks the SK Ca-channels has been suggested to be a cognition enhancer. We tested apamin in the Morris water escape task, in shock motivated avoidance tasks, and in operant tasks in the Skinnerbox. We also used non-cognitive tests, such as the rat forced swimming test and cocaine-induced locomotor activity in the open field, and a test to assess the side effect profile. Mice and rats from different strains, and rats of different ages were used. The rat studies provided only weak support for the notion that apamin acts as a cognition enhancer. More convincing evidence was obtained from the mouse studies. Overt side effects of apamin were found at the dose of 0.3 mg kg −1. This dose was close to, or even overlapped, the doses which improved cognition in mice. We conclude that apamin is a poor tool to assess the role of SK Ca-channels in learning and memory processes.

The effects of subdural haematoma on spatial learning in the rat

Although memory deficits are one of the most persistent consequences of human subdural haematoma, cognitive functioning has hardly been investigated in the rat subdural haematoma model. In the present study, the effects on spatial learning of right- and left-sided unilateral subdural haematoma and of bilateral subdural haematoma induced above the sensorimotor cortical areas were evaluated. Spatial learning was assessed by standard acquisition in the Morris water escape task (five sessions). Additional issues addressed were sensorimotor functioning (footprint analysis), recovery of cognitive functioning (tested by an overtraining and a reversal training) and replicability of induced cognitive deficits. Following unilateral subdural haematoma surgery, hardly any impairments in the Morris water escape task were observed: rats with a unilateral right-sided subdural haematoma showed very mild, transient deficits, whereas rats with left-sided subdural haematoma were indistinguishable from controls. Bilateral subdural haematoma surgery led to a clear, although transient, performance deficit. We conclude that animals with bilateral subdural haematoma may provide a promising cognitive deficit model for investigating recovery of function.

Spatial learning deficits in rats after injection of vincristine into the dorsal hippocampus

In the present study, performance in the Morris water escape task after bilateral lesioning of the dorsal hippocampus induced by the microtubule poison vincristine is discussed as a cognitive deficit model in rats. As we are especially interested in spontaneous or pharmacologically induced recovery processes after experimentally induced cognitive dysfunctions, the model should fulfil a number of criteria. Firstly, a clear dose–effect relationship between the dose of vincristine and the amount of spatial learning impairments should be present. Secondly, lesions must remain within the target area. Thirdly, there should be an observable behavioural recovery or compensation of the induced deficit. Two experiments evaluated the influence of the application volume (experiment 1) and the concentration of vincristine (experiment 2) on lesion location and size, and on spatial learning. The results of both experiments demonstrated that the effect of vincristine on the performance in the Morris water escape task seems to be characterized by an “all-or-none” relationship. Concentrations above a “threshold” value induced severe damage in the hippocampus and adjacent brain structures, whereas concentrations below the “threshold” value had marginal or no effects. The non-selective and highly toxic properties of vincristine make this neurotoxin an unsuitable tool for the establishment of a learning and memory deficit model.

Cognitive performance and biochemical markers in septum, hippocampus and striatum of rats after an i.c.v. injection of streptozotocin: a correlation analysis

In the present study we evaluated the effects of an intracerebroventricular injection of streptozotocin on cognitive behavior and biochemical markers in the brain of middle-aged Wistar rats. Intracerebroventricular injected streptozotocin has previously been reported to decrease the central metabolism of glucose. We found that streptozotocin-treated rats showed an impaired cognitive performance in the delayed non-matching to position task and the Morris water escape task. Glial fibrillary acidic protein, an indicator of reactive astroglial changes, was measured in three different (soluble, Triton X-100 soluble and crude cytoskeletal) protein fractions and its content in the fractions of the septum, hippocampus and striatum of streptozotocin-treated rats was increased. Furthermore, the glial fibrillary acidic protein response of each protein fraction to streptozotocin treatment appeared to be differently regulated. In streptozotocin-treated rats the choline acetyltransferase activity was decreased in the hippocampus only, which was correlated with the hippocampal glial fibrillary acidic protein contents of all three hippocampal protein fractions, thus suggesting that the cholinergic deficit is a consequence of direct damage to the hippocampus. The cognitive deficits in both tasks were related to the increased glial fibrillary acidic protein contents, especially of the soluble and cytoskeletal fraction, and the decreased choline acetyltransferase activity in the hippocampus. Taken together, these findings indicate that it is important to take into account which protein fraction has been used for measuring the glial fibrillary acidic protein response to a stressor. Furthermore, intracerebroventricular injected streptozotocin may provide a relevant model for studying neurodegenerative changes due to a metabolic insufficiency and testing neuroprotective effects of substances.

Local inhibition of hippocampal nitric oxide synthase does not impair place learning in the Morris water escape task in rats.

Recent studies have provided evidence that nitric oxide (NO) has a role in certain forms of memory formation. Spatial learning is one of the cognitive abilities that has been found to be impaired after systemic administration of an NO-synthase inhibitor. As the hippocampus has a pivotal role in spatial orientation, the present study examined the role of hippocampal NO in spatial learning and reversal learning in a Morris task in adult rats. It was found that N omega-nitro-L-arginine infusions into the dorsal hippocampus affected the manner in which the rats were searching the submerged platform during training, but did not affect the efficiency to find the spatial location of the escape platform. Hippocampal NO-synthase inhibition did not affect the learning of a new platform position in the same water tank (i.e. reversal learning). Moreover, no treatment effects were observed in the probe trials (i.e. after acquisition and after reversal learning), indicating that the rats treated with N omega-nitro-L-arginine had learned the spatial location of the platform. These findings were obtained under conditions where the NO synthesis in the dorsal hippocampus was completely inhibited. On the basis of the present data it was concluded that hippocampal NO is not critically involved in place learning in rats.

Acute effects of acetyl-l-carnitine on sodium cyanide-induced behavioral and biochemical deficits

In the present study we investigated the effects of acute treatment with acetyl- l-carnitine (50 mg⧹kg, i.v. 90 min before the sodium cyanide injection) on a sodium cyanide-induced behavioral deficit in the Morris water escape task. In a first experiment the spatial discrimination performance of the rats was found to be dose-dependently impaired after an i.c.v. injection of sodium cyanide (2.5 and 5.0 μg). Acute treatment with acetyl- l-carnitine was found to increase the behavioral deficit after sodium cyanide. these findings were replicated in a second experiment. Based on these results it can be argued that an acute administration of acetyl- l-carnitine appears to potentiate a sodium cyanide-induced behavioral deficit. An additional in vitro experiment with rat brain synaptosomes showed clear effects of administered sodium cyanide on the energy-dependent incorporation of inositol into phosphoinositides and on the ATP concentration. In vitro acetyl- l-carnitine administration had no effect on the sodium cyanide-induced energy depletion. The negative behavioral findings are in contrast with our previously found protective effect of chronic treatment with acetyl- l-carnitine (via drinking water) on the sodium cyanide-induced behavioral deficit. Since chronic acetyl- l-carnitine treatment has no effect on the phosphoinositide metabolism it was suggested that acetyl- l-carnitine may act via the formation of an ATP-independent reservoir of activated acyl groups. Thus, fatty acids as acylated derivatives can be used for reacylation processes during an acute period of energy depletion. However, we have no clear explanation for the discrepancy in behavioral results between the chronic vs acute treatment of acetyl- l-carnitine at present. Further research is needed to characterize the mechanism of action of acetyl- l-carnitine in relation to sodium cyanide.