Training of rats of the Wistar and Krushinskii-Molodkinaia lines in a radial maze

The experiments were conducted on rats of Wistar (W) and Krushinsky--Molodkina (KM) (with audiogenic epilepsy) lines in 12-rays radial-symmetrical labyrinth. The trained rats of W line made less erroneous (repeated) visits to the labyrinth corridors than the rats of KM line. The corridors repeatedly visited by the rats of W line were more frequently situated near the unvisited corridors. No definite sequence of corridors' visiting by the rats of both lines was observed; still there was a tendency to choose corridors the most remoted from each other. This tendency intensified in the process of training. This is considered as one of tactics of rats' behaviour, providing for adequate reactions in definite surrounding conditions.     

Spatial-motor asymmetry in rat behavior

The experiments were carried out on rats in three different mazes: U-shape, complicated linear and 12-beam radial. Series of tests differed by succession of rats learning in the mazes and the character of reinforcement. Most of the rats manifested a spatial-motor asymmetry (SMA) in all used situations. Under all conditions SMA increased in the process of learning parallel to a decrease of the errors number or the time of the task performing. In the group of rats sequently learning in different mazes, the direction of moving changed with changes in spatial characteristics of the medium. Preliminary training of rats in conditions creating SMA, promoted its acceleration in new conditions. The conclusion is made that the rats have no physiological mechanism which rigidly fixes a single (in all conditions) direction of runs. SMA is considered as a behavioural tactics which is corrected in the process of training and which provides for an adequate behaviour.     

Behavioral impairments in Morris water maze in rats selectively bred for audiogenic seizure susceptibility (Krushinsky-Molodkina strain)

Krushinsky-Molodkina rats (KM strain) with genetically determined seizure susceptibility (clonic and tonic seizures in response to the sound of an electric bell, Krushinsky, 1960) were tested in two versions of Morris water maze and compared with normal albino rats (Sprague-Dawley and Wistar). The tests revealed a learning deficit in KM rats. They showed slow acquisition in both the spatial version of the test and the version with the platform, less efficient strategy of searching for target platform, and high scores of floating and thigmotaxis. However, males of KM rats (not females) did not differ significantly from Wistar strain in the probe trial in the spatial variant of the Morris test. No preference for searching for the platform at the place of its previous localization was observed in KM females. Together with our previous findings of the low scores in Revecz-Krushinsky test and data of other authors (Batuev et al., 1983) concerning a working memory deficit in the radial maze, the results suggest the of complex cognitive deficit combined with possible increased stress reactivity in KM rats.     

Sex differences in the long-term effect of preweanling isolation stress on memory retention

Social experiences during development can powerfully modulate later neuroendocrine and behavioral system. In the present study, male and female rat pups experienced daily bouts of social isolation for 6 h per day or control conditions during the third postnatal week. Performance on a 12-arm radial maze with 8 arms consistently baited with food reward was examined in adulthood. During the social isolation, both male and female pups exhibited a significant increase in plasma corticosterone levels. When tested on the radial arm maze as adults, the performance of female rats that had experienced social isolation during development was not affected; however, male rats in the isolation condition initially exhibited impairments in working memory but not reference memory. Despite achieving comparable asymptotic levels of performance on the maze, male rats that experienced social isolation during the third week demonstrated disruption in working memory retention when radial arm maze trials were interrupted after the fourth arm choice. Thus, while male rats that experience social isolation during the third week of life eventually perform comparably to controls on the standard radial arm maze task, their ability to retain information over a delay remains impaired. These findings highlight an important sex difference in the long-term effects of stress during this period of late preweanling development.     

Thyroliberin-induced motor asymmetry as an indicator of the individual behavioral strategy of rats in a radial labyrinth

The individual peculiarities of functional changes in motor asymmetry determined by behavioral test in T-maze have been shown in experiments with rats (nonpedigree and line LATI). The application of thyroliberin (10 mkg/kg) causes and increases the left-side lateralization which introduces alteration in the individual strategy of the successive round of 12 rays of radial maze with food during solution of spatial orientation task.     

Study of the role of different types of glutamate receptors in spatial memory in rats]

A comparative study was performed to assess effects of different antagonists of glutamate receptors on spatial discrimination of rats in 8-arm radial and water mazes. Noncompetitive NMDA receptor blocker MK-801 in the dose 0.10 mg/kg and higher impaired the accuracy of performance in radial maze, whereas in the doses 0.05--0.30 mg/kg in water maze. Quisqualate IAMPA- and 2-amino-4-phosphonobutyrate (2-APB) I antagonists glutamate diethyl ester (250--500 mg/kg) and 2-APB (50--100 mg/kg), respectively, only increased time to complete radial maze performance and failed to alter choice accuracy. Both antagonists at the same doses did not affect performance of water maze task. The involvement of each type of glutamate receptors in different stages of spatial discrimination process in rats was discussed.     

Radial arm maze performance of rats following repeated low level microwave radiation exposure

We examined the possibility of changes in "working" memory of rats following whole body exposure to microwave (MW) radiation. During each of 10 days, we exposed rats within circularly polarized waveguides for 45 min to 2450 MHz fields at whole body SARs of 0.6 W/kg (2 micros pulses, 500 pps), followed by testing in a 12 arm, radial arm maze (RAM). Rats received a preexposure injection of one of three psychoactive compounds or saline, to determine whether a compound would interact with MW exposure to affect performance in the maze. Error rate, i.e., reentry into arms already visited, and time to criterion data for 10 consecutive days of testing were analyzed by a three way analysis of variance (ANOVA) using main effects of "exposure" and "drug" and a repeated factor of "test day." Our alpha limit for significance was P <.05. Analyzes of error rates revealed no significant exposure effect, no significant drug effect and no significant interaction between the two main factors. There was a significant difference in test days, as expected, with repeated test-trial days, which indicates that learning was accomplished. There was no significant interaction of test day and the other two factors. The results of our analyzes of time to criterion data included no significant exposure effect, a significant drug effect, a significant test day effect, and a significant interaction between drug and test day factors. Post hoc analyzes of the drug factor revealed that rats treated with either physostigmine or nalrexone hydrochloride, took significantly longer to complete the maze task than rats pretreated with saline or with naloxone methodide. We conclude that there is no evidence from the current study that exposure to of MW radiation under parameters examined caused decrements in the ability of rats to learn the spatial memory task.     

The effect of alcoholization on the behavioral reactions of rats in an 8-arm radial maze

The influence of 20% alcohol consumption on training of low-active rats in 8-arm radial maze was studied. One group of animals was trained before and the other group after the alcoholization. All the animals acquired the conditioned reaction in the radial maze. However, the behavioral difference between the groups consisted in spatially-motor asymmetry. The rats trained before the alcohol consumption had less stereotyped behavior and more distinctly preferred to enter the maze arms at the angle of 45 degrees than the animals trained after the alcohol consumption. After the alcohol consumption, rats more frequently refused from behavioral task performance in comparison with the animals trained after the alcoholization. The influence of alcohol consumption of learning and memory in low-active rats is discussed.     

Asymmetry of movement direction as a tactic in the feeding behavior of rats

The sign and degree of spatial-motor asymmetry in rats were studied in conditions both of spontaneous or signalled choice in an U-maze and spontaneous multiple choice in a radial labyrinth. It was shown that during investigation of a new environment, motor asymmetry in rats was feebly expressed in all conditions of experiments, irrespective of the labyrinth scheme and experimental procedures. In the process of training, adequate behaviour was formed and in some conditions a distinctly expressed spatial asymmetry appeared, while in other cases it was absent. Apparently, while investigating an "unknown" situation (where rats can move rightwards and leftwards), the strategy of "displacement" is characteristic of them. Later the rate of asymmetry manifestation depends on concrete spatial and temporal characteristics of already "familiar" surroundings.     

Behavior and spatial learning in birds in radial maze

Studies of spatial learning and memory of birds in radial maze are reviewed. The radial maze variants (standard, giant and open-field analog) are described; procedural problems of bird testing are discussed. Radial maze task performance of birds is compared with that of laboratory rats as a well-studied standard. Specific features of spatial learning in various taxonomic avian groups (pigeon, tits, corvids, chickens and others) are considered. The results of spatial memory studies in closely-related species with different ecology (food storing behavior, degree of caching specialization) and experiments with migrant birds and homing pigeons are discussed.     

Rats have trouble associating all three parts of the time-place-event memory code

The ability of animals to associate an event with predictable time and place information confers a major biological advantage. The current research uses a variety of procedures and paradigms (e.g. place preference, radial arm maze, Morris water maze, T-maze, go no-go) to show that rats, unlike pigeons [e.g. Anim Learn Behav 22 (1994) 143] do not readily make an event-time-place association. They do make associations between event-time and event-place information, however. These findings are in disagreement with Gallistel's (The Organization of Learning, MIT Press, Cambridge, MA ) theory that claims that animals automatically store a memory code that has these three pieces of information. The present research is in line with the work of others who also find that rats do not readily make daily time-place associations [Behav Processes 23 (1997) 232; Behav Processes 52 (2000) 11; Behav Processes 49 (2000) 21; Anim Learn Behav 28 (2000) 298]. An interesting finding that did emerge from the present research was that at least some rats can use a circadian timer to solve a time-of-day discrimination if the task is a go no-go discrimination.     

Behavioral tactics of rats receiving unequally distributed reinforcement in a radial maze

Rats behaviour was studied in 12-arms radial maze with food reinforcement of different volumes presented only in 6 passages. Dynamics of changes is shown in the process of learning both in the preference of the passages with greater volume of reinforcement and in the number of errors, characterizing the working and referent memories. In the trained rats, their behaviour is determined by at least two behavioural tactics: visiting more remote passages and choice in the beginning of the test of more reinforced passages.     

fMRI Hippocampal Activity During a VirtualRadial Arm Maze

Numerous studies have shown that the hippocampus is critical for spatial memory. Within nonhuman research, a task often used to assess spatial memory is the radial arm maze. Because of the spatial nature of this task, this maze is often used to assess the function of the hippocampus. Our goal was to extrapolate this task to humans and examine whether healthy undergraduates utilize their hippocampus while performing a virtual reality version of the radial arm maze task. Thirteen undergraduates performed a virtual radial arm maze during functional magnetic resonance imaging. The brain maps of activity reveal bilateral hippocampal BOLD signal changes during the performance of this task. However, paradoxically, this BOLD signal change decreases during the spatial memory component of the task. Additionally, we note frontal cortex activity reflective of working memory circuits. These data reveal that, as predicted by the rodent literature, the hippocampus is involved in performing the virtual radial arm maze in humans. Hence, this virtual reality version may be used to assess the integrity of hippocampus so as to predict risk or severity in a variety of psychiatric disorders.     

Estrogen Enhances Performance of Female Rats during Acquisition of a Radial Arm Maze

Estrogen can influence the expression of behaviors not associated directly with reproduction, including learning and memory. However, the effects of estrogen on learning and memory in mammals are complex, dependent on a variety of factors. The radial arm maze is a traditional experimental task that takes advantage of the natural foraging strategy of rats and provides an appropriate measure for studying the effects of estrogen on working memory in this species. In the experiments reported here, ovariectomized rats were implanted subcutaneously with 5-mm Silastic capsules containing 25% estradiol diluted with cholesterol. Control females received 5-mm Silastic capsules containing 100% cholesterol. Results of three separate experiments demonstrated that estradiol administered by Silastic implants for 30 days prior to eight-arm radial maze training, during the 24 days of maze training, or both significantly improved working memory performance compared to females treated with cholesterol alone, as indicated by improved arm choice accuracy over trials. The positive effect of estradiol exposure prior to training suggests that estrogen may induce neuronal changes that persist beyond the period of exposure with functional consequences for behavior.     

Small-scale spatial cognition in pigeons

Roberts and Van Veldhuizen's [Roberts, W.A., Van Veldhuizen, N., 1985. Spatial memory in pigeons on the radial maze. J. Exp. Psychol.: Anim. Behav. Proc. 11, 241-260] study on pigeons in the radial maze sparked research on landmark use by pigeons in lab-based tasks as well as variants of the radial-maze task. Pigeons perform well on open-field versions of the radial maze, with feeders scattered on the laboratory floor. Pigeons can also be trained to search precisely for buried food. The search can be based on multiple landmarks, but is sometimes controlled by just one or two landmarks, with the preferred landmarks varying across individuals. Findings are similar in landmark-based searching on a computer monitor and on a lab floor, despite many differences between the two kinds of tasks. A number of general learning principles are found in landmark-based searching, such as cue competition, generalization and peak shift, and selective attention. Pigeons also learn the geometry of the environment in which they are searching. Neurophysiological studies have implicated the hippocampal formation (HF) in avian spatial cognition, with the right hippocampus hypothesized to play a more important role in the spatial recognition of goal locations. Most recently, single-cell recording from the pigeon's hippocampal formation has revealed cells with different properties from the classic 'place' cells of rats, as well as differences in the two sides of the hippocampus.     

The volume of reinforcement and the structure of rat behavior in a radial labyrinth

In rats choice reaction was elaborated in 12 passages radial labyrinth with different volumes of food only in six of twelve passages. Then the conditions were modified: the first group of rats in the beginning of the experiment was placed to another labyrinth sector, and in the second group the food volume was changed in passages. In new situations in animals of both groups the reaction efficiency temporarily decreased, simultaneously the correction of behaviour structure took place. The character of behavioural tactics (tendencies to visit passages with larger food volume at the beginning of the experiment, spatial-motor asymmetry etc.) is described in dynamics of adaptation to new conditions. Factors determining the rats behaviour structure are discussed.     

Low-level exposure to pulsed 900 MHz microwave radiation does not cause deficits in the performance of a spatial learning task in mice

There is some concern that short-term memory loss or other cognitive effects may be associated with the use of mobile cellular telephones. In this experiment, the effect of repeated, acute exposure to a low intensity 900 MHz radiofrequency (RF) field pulsed at 217 Hz was explored using an appetitively-motivated spatial learning and working memory task. Adult male C57BL/6J mice were exposed under far field conditions in a GTEM cell for 45 min each day for 10 days at an average whole-body specific energy absorption rate (SAR) of 0.05 W/kg. Their performance in an 8-arm radial maze was compared to that of sham-exposed control animals. All behavioral assessments were performed without handlers having knowledge of the exposure status of the animals. Animals were tested in the maze immediately following exposure or after a delay of 15 or 30 min. No significant field-dependent effects on performance were observed in choice accuracy or in total times to complete the task across the experiment. These results suggest that exposure to RF radiation simulating a digital wireless telephone (GSM) signal under the conditions of this experiment does not affect the acquisition of the learned response. Further studies are planned to explore the effects of other SARs on learned behavior. Bioelectromagnetics 21:151-158, 2000. Published 2000 Wiley-Liss, Inc.     

The role of catecholamines in retention performance of a partially baited radial eight-arm maze for rats

To assess the possible involvement of catecholaminergic neurotransmitters in maintenance of spatial cognition, the present work investigated the effects of dopaminergic and noradrenergic receptor antagonists on memory performance of rats in a partially baited radial eight-arm maze. Food-deprived rats were first trained to enter the arms baited with chocolate, and each subject was then randomly assigned to receive further training in either a place version or a cue version of the task. A specific pattern with four arms being baited was used throughout experimentation as the procedure for the place task; whereas four randomly chosen arms, each cued with a piece of sandpaper on the arm entrance, were baited from trial to trial as the procedure of the cue task. For drug evaluation, well-trained subjects were challenged with systemic injections of SCH23390, spiperone, haloperidol, prazosin, yohimbine, and propranolol. Regarding the place task, SCH23390, haloperidol, and propranolol, but not the other three drugs, significantly impaired behavioral performance by increasing the number of arm entries as well as the time to complete the task. The accuracy of performance as measured by the number of entries on the cue task was not significantly affected by any of these drugs tested. However, the times to complete the cue task were significantly increased with all drugs except yohimbine. These data show that blocking different catecholaminergic receptor subtypes produced distinct deficit patterns on the retention performance in a partially baited radial eight-arm maze. Evidently, both D1 and D2 dopamine receptors as well as beta noradrenergic receptors are important in expression of spatial memory.     

A morphofunctional analysis of the participation of the cerebral cortex in the habituation of Krushinski?-Molodkina strain rats to an epileptogenic stimulus

Systematic action of epileptogenic stimulus (sound) leads to gradual lowering of the level of convulsive readiness (LCR) in rats of KM (Krushinski'i-Molodkina) line to the formation of the habituation, to blocking of convulsive seizures. It is shown that at single action of sound, functional switching-off of the cerebral cortex causes LCR lowering but does not prevent the development of the epileptiform seizure. Alongside with it, in conditions of repeated sound action, functional decortication considerably retards LCR lowering. After cessation of the cortical depression, during which the rats were given systematic sound exposition, sharp LCR lowering takes place. If the habituation has been already formed, then the subsequent switching-off of the cortex does not lead to LCR growth. Ultrastructural characteristics of asymmetric axo-dendritic and axo-spine synapses in the auditory cerebral cortex of KM line rats in the moment of convulsive seizure testifies to their active functioning, while against the background of short-term habituation to epileptogenic stimulus signs of lowering of the efficiency of synaptic transmission are revealed in these synapses. The obtained results allow to suggest that in the rats of KM line the neocortex takes part in antiepileptic defensive reactions, in LCR regulation in connection with formation of the habituation to systematic action of epileptogenic stimulus.     

Tool Use Specific Adult Neurogenesis and Synaptogenesis in Rodent (Octodon degus) Hippocampus

We previously demonstrated that degus (Octodon degus), which are a species of small caviomorph rodents, could be trained to use a T-shaped rake as a hand tool to expand accessible spaces. To elucidate the neurobiological underpinnings of this higher brain function, we compared this tool use learning task with a simple spatial (radial maze) memory task and investigated the changes that were induced in the hippocampal neural circuits known to subserve spatial perception and learning. With the exposure to an enriched environment in home cage, adult neurogenesis in the dentate gyrus of the hippocampus was augmented by tool use learning, but not radial maze learning, when compared to control conditions. Furthermore, the proportion of new synapses formed in the CA3 region of the hippocampus, the target area for projections of mossy fiber axons emanating from newborn neurons, was specifically increased by tool use learning. Thus, active tool use behavior by rodents, learned through multiple training sessions, requires the hippocampus to generate more novel neurons and synapses than spatial information processing in radial maze learning.