Vasopressin analogues and spatial working memory in the 24-arm radial maze

The effect of vasopressin analogues dAVP, dDAVP, and desgly NH₂ dDAVP on working memory was tested in the 24-arm radial maze in twelve 6-month-old and twelve 19-month-old rats. No age dependent effects were found. All three peptides tested (3 μg/kg) tended to improve the performance but only the desgly NH₂ dDAVP significantly decreased the number of errors. A second application of desgly NH₂ dDAVP was ineffective. The specificity of activation of memory mechanisms by desgly NH₂ dDAVP can be questioned.     

Behavioral tactics among rats in a radial maze

The experiments were carried out on rats of Wistar (W) and Krushinsky-Molodkina (KM) lines, differing in the level of task performance in conditions of multiple choice of food sources in a 12ray radial symmetrical maze. It is shown that in the radial maze, the rats of both lines use a number of behavioural tactics. To determine the influence of changes of environmental spatial characteristics while preserving the main experimental strategy--never revisit the places of reinforcement,--on the peculiarities of tactics manifestations maze modifications were elaborated. Besides the environmental procedure was changed. Under all conditions the rats of W line solved the task. According to the situation, they either preserved former tactics or developed some new ones. The rats of KM line could not solve the task in changed conditions. In most sessions, appearance or absence of given tactics was not adequate to new conditions. The presence of the necessary tactics not always facilitated the task solving. Thus, for the realization of adequate reactions, the presence of necessary tactics is not sufficient: their "tuning" is needed depending on situation. The possibility is supposed of genetic determination of rats ability to some tactics. However, it is emphasized, that tactics are not strongly fixed, as their realization depends on environmental conditions.     

Testosterone modulates performance on a spatial working memory task in male rats

Gonadal hormones have been shown to modulate memory retention in female rats. The current experiments examine the role of testicular hormones in modulating the performance of male rats on two spatial water maze tasks. In the first study, castrated and intact rats were trained on the visible platform and hidden platform versions of the Morris water maze task. Castration did not affect performance on either version of this reference memory task with castrated and intact rats demonstrating similar performance both during acquisition and on post-training probe trials. In the second experiment, castrated and intact rats were tested on a delayed-matching-to-place version of the water maze. Rats received a series of trial pairs in the maze with a hidden platform located in the same pool location on the exposure and retention trials of each pair; between pairs of trials, however, the platform was repositioned to a novel pool location. The interval between trials was either 10- or 60-min and memory retention, taken as the difference between the pathlengths on the exposure and retention trials, declined as the interval increased. Relative to intact males, castrated males demonstrated impaired working memory retention at 60-min but not at 10-min retention intervals. This interval-dependent impairment in working memory retention was reversed by physiologic levels of testosterone replacement. These findings indicate that castration does not significantly affect acquisition or probe trial performance on a classic reference memory task but does impair spatial working memory retention, an effect that is reversed by exogenous testosterone.     

Effects of the NMDA antagonist MK-801 on radial maze performance in histidine-deficient rats

We examined the effects of a histidine-deficient diet on brain histamine contents as well as on learning and memory using the eight-arm radial maze in rats. A significant decrease in histamine content in the hippocampus was observed after long-term feeding of rats with a histidine-deficient diet. At the same time, significant enhancement of the acquisition process in radial maze performance was also observed. Pyrilamine did not show a significant effect on radial maze performance in histidine-deficient rats. On the other hand, pyrilamine caused a significant spatial memory deficit in control rats. Scopolamine was effective in inhibiting spatial memory in both histidine-deficient and control rats. MK-801 caused spatial memory deficits more potently in histidine-deficient rats than in controls. Brain glycine contents showed a significant increase in the hippocampus in histidine-deficient rats. These results indicated that the spatial memory deficits induced by MK-801 in histidine-deficient rats are closely related to increased glycine levels and activation of NMDA receptors.     

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.     

Social isolation improves working memory at reversal but not primary radial-arm maze learning in rats

Social isolation starting from the 21st day of birth affected neither a short-term nor a long-term memory in male rats at primary acquisition learning in an 8-arm radial maze. A number of the short-term and long-term memory errors were substantially decreased during primary learning but the difference between groups was not significant. Isolates were faster to start a search in an individual trial and took less time to finish offa trial. During the reversal learning, when baited and non-baited arms were reversed, the isolates outperformed of socially reared rats on working but not reference memory task. In overall they made twice less working memory errors than socially reared animals. During the reversal learning the isolates were also faster than non-isolates in initiation and completion of a trial. Maternal separation of rat's pups on the postnatal days 1-21 for 4 hr per day did not affect either working or reference memory on both primary and reversal learning. The data obtained are discussed on basis of influence of stress in early postnatal life on hypothalamo-pituitary axis and its effects on behavior of adult animals.     

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.     

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.     

Modified water maze for studying spatial memory of rats

A method for evaluation of impairments of spatial memory in rats is put forward. Sensitivity of the advanced method based on the principles of Morris' water maze was compared with that of the classic prototype. Efficiency of the advanced method was assessed by dose- and time-dependent effects of agroclavine on the spatial memory of rats. Agroclavine (10 micrograms/kg) was shown to produce spatial memory impairment in rats. The obtained results also indicate that the modernized maze is more sensitive in revealing impairments of the spatial memory in rats than the classic water maze.     

Neonatal exposure to intermittent hypoxia enhances mice performance in water maze and 8-arm radial maze tasks

Hypoxia has generally been reported to impair learning and memory. Here we established a hypoxia-enhanced model. Intermittent hypoxia (IH) was simulated at 2 km (16.0% O2) or 5 km (10.8% O2) in a hypobaric chamber for 4 h/day from birth to 1, 2, 3, or 4 week(s), respectively. Spatial learning and memory ability was tested in the Morris water maze (MWM) task at ages of postnatal day 36 (P36)-P40 and P85-89, respectively, and in the 8-arm maze task at P60-68. The long-term potentiation (LTP), synaptic density, and phosphorylated cAMP-responsive element-binding protein (p-CREB) level in the hippocampus were measured in mice at P36 under the IH for 4 weeks (IH-4w). The results showed that IH for 3 weeks (IH-3w) and IH-4w at 2 km significantly reduced the escape latencies of mice at P36-40 in the MWM task with significantly enhanced retention, and this spatial enhancement was further confirmed by the 8-arm maze test in mice at P60-68. The improvement in MWM induced by IH-4w at 2 km was still maintained in mice at P85-89. IH-4w at 2 or 5 km significantly increased amplitude of LTP, the number of synapse, and the p-CREB level in the hippocampus of P36 mice. These results indicated that IH (4 h/day) exposure to neonatal mice at 2 km for 3 or 4 weeks enhanced mice spatial learning and memory, which was related to the increased p-CREB, LTP, and synapses of hippocampus in this model.     

Haploinsufficiency of the arginine-vasopressin gene is associated with poor spatial working memory performance in rats

Behavioral pharmacological studies have implicated a role for the neurophysin arginine-vasopressin in learning and memory. Vasopressin, and its analogues, can produce either improvements or impairments in mnemonic functions, effects that depend upon the agent administered, the memory process measured and the task employed. As recent data have implicated vasopressin in regulating the cognitive functions of the prefrontal cortex, we sought to determine whether changes in vasopressinergic tone would affect a form of memory that is dependent upon this brain region. To that end, we used a genetic approach to examine how haploinsufficiency of the vasopressin gene affects working memory performance. Specifically, we tested a naturally occurring null-mutant rat on an operant delayed-non-match-to-position task. Male and female heterozygous and wild-type rats were trained to perform this working memory task, and the effects of varying the delay across which they had to maintain task information were systematically varied. Although vasopressin-deficient rats omitted fewer trials and completed trials more quickly, they exhibited delay-dependent deficits of choice accuracy. The genotype effects were not modified by sex. Collectively, these data indicate that even partial vasopressin deficiency can trigger deficits of spatial working memory performance and add to the growing body of results supporting a regulatory control of neocortical-dependent cognitive functions by this neurohormone.     

Effects of amyloid beta peptide (25-35) on the behavior of rats in a radial maze

Impairment of cognitive functions, particularly long-term (episodic) and working memory, is one of the earliest prognostic symptoms of Alzheimer's disease, both cognitive impairment and neurodegeneration being mediated by amyloid-beta neurotoxicity. Effects of intracerebroventricular administration of amyloid-beta peptide (25-35) [A beta(25-35)] to rats on the retention of previously learned task in an 8-armed radial maze was studied. A beta(25-35) was injected bilaterally, at doses of 15 or 30 nmol/rat, 7 days after the preliminary learning. The performance in the maze was tested 60 days after the surgery. A beta(25-35) impaired the short-term memory, with no significant effect on the long-term memory. No dose dependence could be demonstrated.     

Contextual control of rats' foraging behaviour in a radial maze

This study demonstrated that with experience rats were able to discriminate the background contextual cues in order to foraging correctly in an eight-arm radial maze if the background contexts signaled to the rats which of two bait patterns was in effect in that context. Four of the eight arms were context-dependent: two arms were baited in the "night" context, while the other two were baited in the "daytime" context. The remaining four arms were context-independent: three of them were never baited, while the remaining one was baited in both contexts. The rats gradually began to avoid the arms that were uniquely baited in the other context, suggesting a contextual or conditional control of arm selection. Interestingly, these rats also showed better performance in avoiding the never-baited arms, compared with control rats. Namely, disambiguating the incentive values of the four arms by contextual cues collaterally facilitated the context-independent arm performance. Another interesting finding of the present study is that the rats did not visit the always-baited arm earlier than the arms uniquely baited in that context.     

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.     

Tetrachlorodibenzo-p-dioxin exposure alters radial arm maze performance and hippocampal morphology in female AhR mice

Perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has been reported to alter spatial learning in rats tested on a radial arm maze (RAM). TCDD is believed to exert most of its effects through binding to the aryl hydrocarbon receptor (AhR). To determine whether the AhR mediates TCDD-induced alterations in spatial learning, we tested male and female AhR-knockout (AhR-/-), heterozygous (AhR+/-) and wild-type (AhR+/+) mice on the RAM. AhR+/- male and female mice were time mated, and treated dams were dosed with 5 microg TCDD/kg body weight on day 13 of gestation. When offspring reached adulthood, male and female AhR+/+, AhR+/- and AhR-/- mice from TCDD-exposed and unexposed litters were tested on the eight-arm RAM. After testing, we examined hippocampal morphology as visualized by the Timm's silver sulfide stain. TCDD-exposed female AhR+/- mice made more errors than their respective controls on the RAM and exhibited a decrease in the size of the intra- and infrapyramidal mossy fiber (IIP-MF) field of the hippocampus. None of the other TCDD-exposed groups differed from their respective control groups with regard to maze performance or hippocampal morphology. The reduction of IIP-MF field indicates a possible morphological basis for the learning deficit that was observed in the female AhR+/- mice. It is hypothesized that the effect of TCDD exposure is AhR dependent and that TCDD may alter GABAergic activity in the hippocampus of female mice during development.     

Participation of the nucleus accumbens in acquisition of spatial choice behavior in rats performing in a radial plus maze

The role of medial shell of the nucleus accumbens in acquisition of spatial behavior was studied in rats performing choice task in radial maze with asymmetrical water reinforcement. It has been found that the nucleus accumbens lesioned rats failed in finding larger rewards but preserve their reward-seeking behavior guided by visual discriminative stimuli. The results obtained are in good agreement with suggestion that the nucleus accumbens is a site of convergence of spatial information (from hippocampus) with reward information (from amygdala and VTA), providing bridge for effective limbic-motor interface underlying motivated goal-directed behavior in animals.     

Effects of nucleotides on learning and memory in a Morris water maze test in normal and basal forebrain-lesioned rats

The effects of nucleotides on learning and memory were studied in normal and basal forebrain-lesioned rats using a Morris water maze test. Chronic oral administration of a nucleotide mixture (500 mg/kg), containing an equal weight of the disodium salts of adenosine 5'-monophosphate, guanosine 5'-monophosphate, inosine 5'-monophosphate, cytidine 5'-monophosphate, and uridine 5'-monophosphate facilitated learning acquisition in normal rats. In basal forebrain-lesioned rats, administration of the nucleotide mixture showed a tendency to improve learning acquisition and memory retrieval. In the biochemical studies, no significant changes were observed in brain choline and acetylcholine levels by treatment with the nucleotide mixture at the doses tested in both normal and basal forebrain-lesioned rats. The nucleotides did not affect the monoaminergic systems in normal rats, but did cause some changes in these systems in basal forebrain-lesioned rats. The present studies indicate that nucleotides ameliorate learning and memory processes in normal rats, but not in basal forebrain-lesioned rats, and they also modulate the activity of the central monoaminergic systems under certain conditions.     

Effect of circadian phase on performance of rats in the Morris water maze task

The authors examined spatial working memory in the Morris water maze during the activity and rest periods of Wistar rats. Wheel-running activity was measured continuously as a marker of circadian phase. To minimize possible masking effects on performance, animals were placed in constant dim light the day before testing and tested in similar light conditions. Three experiments were run, each of them using animals varying in their previous experience in the water maze. Half of the animals of each experiment were tested 2 to 3 h after activity onset (active group), and the other half were tested 14 to 15 h after activity onset (inactive group). In the three experiments, a significant phase effect was observed in the animals' performance in the water maze; animals tested in the active phase showed steeper acquisition curves. These phase effects on performance are due to the animals' search pattern and not to a better acquisition and maintenance of spatial information; rats tested in the inactive phase found the platform faster on the first trial of the test, when the information on the location of the platform had not been presented to the animals. This effect vanished as the amount of training in the pool increased. Finally, swimming speed also showed a temporal effect, suggesting the existence of a phase effect for motivation to escape from the water; rats tested during their inactive phase tended to swim faster. All together, the data suggest a modulating effect of the biological clock on performance in the water maze, particularly when the animals are less experienced.     

Sleep deprivation effect upon spatial memory consolidation in rats after one-day learning in a Morris water maze

The effect of sleep deprivation by 'carousel' method on spatial memory consolidation in a Morris water maze was studied in Wistar male rats after one-day learning (in accordance to a protocol by Frick et al., 2000). It was found that after fast 3-hr learning the memory trace retains during 24-hr. Twenty four hour sleep deprivation followed learning impaired consolidation of spatial memory. So the rat model of a one-day learning is suitable for the studying of neurophysiological mechanisms of sleep deprivation effects on spatial memory consolidation.