Spatial memory and stereotypic behaviour of animals in radial arm mazes

Controlled Cortical Impact Leads to Cognitive and Motor Function Deficits that Correspond to Cellular Pathology in a Piglet Traumatic Brain Injury Model

Traumatic brain injury (TBI) is a leading cause of death and disability in the United States, with children who sustain a TBI having a greater risk of developing long-lasting cognitive, behavioral, and motor function deficits. This has led to increased interest in utilizing large animal models to study pathophysiologic and functional changes after injury in hopes of identifying novel therapeutic targets. In the present study, a controlled cortical impact (CCI) piglet TBI model was utilized to evaluate cognitive, motor, and histopathologic outcomes. CCI injury (4 m/sec velocity, 9 mm depression, 400 msec dwell time) was induced at the parietal cortex. Compared with normal pigs (n = 5), TBI pigs (n = 5) exhibited appreciable cognitive deficiencies, including significantly impaired spatial memory in spatial T-maze testing and a significant decrease in exploratory behaviors followed by marked hyperactivity in open field testing. Additionally, gait analysis revealed significant increases in cycle time and stance percent, significant decreases in hind reach, and a shift in the total pressure index from the front to the hind limb on the affected side, suggesting TBI impairs gait and balance. Pigs were sacrificed 28 days post-TBI and histological analysis revealed that TBI lead to a significant decrease in neurons and a significant increase in microglia activation and astrogliosis/astrocytosis at the perilesional area, a significant loss in neurons at the dorsal hippocampus, and significantly increased neuroblast proliferation at the subventricular zone. These data demonstrate a strong relationship between TBI-induced cellular changes and functional outcomes in our piglet TBI model that lay the framework for future studies that assess the ability of therapeutic interventions to contribute to functional improvements.

The anaesthetic combination of ketamine/midazolam does not alter the acquisition of spatial and motor tasks in adult mice

The ketamine/midazolam association of a dissociative with a sedative agent is used for the induction and maintenance of anaesthesia in laboratory animals. Anaesthesia may interfere with research results through side-effects on the nervous system, such as memory impairment. It is known that ketamine and midazolam affect cognition; however, their effects have not been clarified when used in a context of balanced anaesthesia. Thus, this study evaluated the effects of ketamine/midazolam on the acquisition of motor and of a spatial memory task in adult mice. Twenty-eight C57BL/6 adult male mice were divided into three groups: untreated control, treated with ketamine/midazolam (75 mg/kg / 10 mg/kg) and treated with midazolam (10 mg/kg) groups. Respiratory rate, heart rate and systolic pressure were measured every 5 min in the animals treated with ketamine/midazolam, as this was the only group that exhibited loss of the righting reflex. One day after treatment, animals were tested in the open field, rotarod and radial arm maze. There were no differences between treatments regarding open-field activity, rotarod performance or number of working and reference memory errors in the radial arm maze task. In conclusion, the learning process of spatial and motor tasks was not disrupted by the anaesthetic combination of ketamine/midazolam. These results suggest its safe use in adult mice in projects where acquisition of a spatial and motor task is necessary.

Preweaning manganese exposure causes hyperactivity, disinhibition, and spatial learning and memory deficits associated with altered dopamine receptor and transporter levels

Epidemiological studies in children have reported associations between elevated dietary manganese (Mn) exposure and neurobehavioral and neurocognitive deficits. To better understand the relationship between early Mn exposure and neurobehavioral deficits, we treated neonate rats with oral Mn doses of 0, 25, or 50 mg Mn/kg/day over postnatal day (PND) 1-21, and evaluated behavioral performance using open arena (PND 23), elevated plus maze (PND 23), and 8-arm radial maze (PND 33-46) paradigms. Brain dopamine D1 and D2-like receptors, and dopamine transporter (DAT) densities were determined on PND 24, and blood and brain Mn levels were measured to coincide with behavioral testing (PND 24, PND 36). Preweaning Mn exposure caused hyperactivity and behavioral disinhibition in the open arena, but no altered behavior in the elevated plus maze. Manganese-exposed males committed significantly more reference and marginally more working errors in the radial arm maze compared to controls. Fewer Mn exposed males achieved the radial maze learning criterion, and they required more session days to reach it compared to controls. Manganese-exposed animals also exhibited a greater frequency of stereotypic response strategy in searching for the baited arms in the maze. These behavioral and learning deficits were associated with altered expression of the dopamine D1 and D2 receptors and the DAT in prefrontal cortex, nucleus accumbens, and dorsal striatum. These data corroborate epidemiological studies in children, and suggest that exposure to Mn during neurodevelopment significantly alters dopaminergic synaptic environments in brain nuclei that mediate control of executive function behaviors, such as reactivity and cognitive flexibility.

Maternal stress produces learning deficits associated with impairment of NMDA receptor-mediated synaptic plasticity

Stress in adulthood can have a profound effect on physiology and behavior, but the extent to which prolonged maternal stress affects the brain function of offspring when they are adult remains primarily unknown. In the present work, chronic immobilization stress to pregnant mice affected fetal growth and development. When pups born from stressed mice were reared to adulthood in an environment identical to that of nonstressed controls, several physiological parameters were essentially unaltered. However, spatial learning and memory was significantly impaired in the maternally stressed offspring in adulthood. Furthermore, electrophysiological examination revealed a significant reduction in NMDA receptor-mediated long-term potentiation in the CA1 area of hippocampal slices. Subsequent biochemical analysis demonstrated a substantial decrease in NR1 and NR2B subunits of the NMDA receptor in synapses of the hippocampus, and the interaction between these two subunits appeared to be reduced. These results suggest that prolonged maternal stress leads to long-lasting malfunction of the hippocampus, which extends to and is manifested in adulthood.

Hippocampal CA1 kindling but not long-term potentiation disrupts spatial memory performance

Long-term synaptic enhancement in the hippocampus has been suggested to cause deficits in spatial performance. Synaptic enhancement has been reported after hippocampal kindling that induced repeated electrographic seizures or afterdischarges (ADs) and after long-term potentiation (LTP) defined as synaptic enhancement without ADs. We studied whether repeated stimulations that gave LTP or ADs resulted in spatial performance deficits on the radial arm maze (RAM) and investigated the minimal number of ADs required for such deficits. Three experimental groups were run as follows: (1) 5 hippocampal ADs in 1 d (5-AD group), (2) 10 hippocampal ADs in 2 d (10-AD group), and (3) 12 -frequency primed-burst stimulations (PBSs) in 2 d in order to induce LTP without ADs (LTP group). Each experimental group was run together with a control group during the same time period. Rats were first trained in a spatial task on a radial arm maze with four of the eight arms baited, then given control or experimental treatment, and maze performance was tested in the first week (1-4 d) and fourth week (22-25 d) after treatment. Basal dendritic population excitatory postsynaptic potentials (pEPSPs) and medial perforant path (MPP)-evoked dentate gyrus population spike and polysynaptic CA1 excitation were recorded before and after experimental and control treatment. Spatial memory errors, in particular reference memory errors, were significantly higher in the 10-AD kindled group than any other group on the first and fourth week after treatment. Spatial memory errors were not significantly different in the 5-AD and LTP groups as compared with any control groups at any time. Basal dendritic pEPSP in CA1 was enhanced for about 1 wk after 12 PBSs, 10 ADs, or 5 ADs, while the dentate gyrus population spike and CA1 polysynaptic excitation evoked by MPP was increased for up to 4 wk after 10 ADs, but not 12 PBSs. Thus, distributed alteration of multiple synaptic transmission in the entorhinal-hippocampal circuit, but not LTP at the basal dendritic synapses in CA1, may disrupt spatial performance after 10 hippocampal ADs.

Deficits in spatial orientation of children with intrauterine growth retardation

The spatial orientation of intrauterine growth retarded (IUGR) children versus age-matched controls was examined using two spatial tests. The first test was the radial arm maze (RAM), a navigational test frequently used in animal models. The second test was a subtest from the Kaufman assessment battery for children (K-ABC). The IUGR group comprised 28 children aged 6 years. The control group comprised 29 appropriate-for-gestational age children. The performance of the IUGR children was significantly inferior to controls in both tests. In the RAM test, the ratio between the correct entrances to the total entrances was significantly lower in the IUGR group than in the control group (P<0.001). In the K-ABC, the IUGR group could not perform as well as control children (P<0.001). These results suggest that spatial orientation in IUGR children is inferior to their age-matched controls, possibly contributing to their potential learning difficulties. The present results also suggest that the RAM can be potentially used to test spatial orientation of children at-risk.

Exploring the limits of spatial memory in rats, using very large mazes

In Experiment 1, rats foraged for food in six successive phases with 8, 16, 24, 32, 40, and 48 arms attached in random locations to a large radial maze. The percentage of novel choices appeared to be determined more by spatial proximity than by number of arms. In Experiment 2, rats foraged for food in four successive phases with 8, 16, 24, and 48 arms attached to the maze in spread-out or tight configurations. Performance was poor in the tight configurations regardless of the number of arms. Performance was excellent in the 8-arm spread-out condition but declined as 16 and, then again, 24 arms were added. Thus, spatial separation, not number of locations, was the chief determinant of performance in the first two experiments. In Experiment 3, in successive phases, 8, 16, 24, 32, 40, 48, 16, and 8 food towers were set in a circle on the floor, with the spatial separation between adjacent towers held constant at 33 cm. The percentage of novel choices declined as 8 towers became 16 and did not change again with 24, 32, 40, or 48 towers in place but then increased again as 16 towers became 8. In Experiment 4, in successive phases, 8, 16, 24, and 32 food towers were set in a circle, with the spatial separation between adjacent towers held constant at 66 cm. The percentage of novel choices declined as 8 towers became 16 and again as 16 towers became 24 but did not decline further. These data were discussed in terms of the fundamental problems posed by variations in the number of food locations in the pursuit of the limit of spatial memory in rats.

Behavioral phenotyping of mice in pharmacological and toxicological research

The evaluation of behavioral effects is an important component for the in vivo screening of drugs or potentially toxic compounds in mice. Ideally, such screening should be composed of monitoring general health, sensory functions, and motor abilities, right before specific behavioral domains are tested. A rational strategy in the design and procedure of testing as well as an effective composition of different well-established and reproducible behavioral tests can minimize the risk of false positive and false negative results in drug screening. In the present review we describe such basic considerations in planning experiments, selecting strains of mice, and propose groups of behavioral tasks suitable for a reliable detection of differences in specific behavioral domains in mice. Screening of general health and neurophysiologic functions (reflexes, sensory abilities) and motor function (pole test, wire hang test, beam walking, rotarod, accelerod, and footprint) as well as specific hypothesis-guided testing in the behavioral domains of learning and memory (water maze, radial maze, conditioned fear, and avoidance tasks), emotionality (open field, hole board, elevated plus maze, and object exploration), nociception (tail flick, hot plate), psychiatric-like conditions (porsolt swim test, acoustic startle response, and prepulse inhibition), and aggression (isolation-induced aggression, spontaneous aggression, and territorial aggression) are described in further detail. This review is designed to describe a general approach, which increases reliability of behavioral screening. Furthermore, it provides an overview on a selection of specific procedures suitable for but not limited to behavioral screening in pharmacology and toxicology.

Learning and memory in two different reward tasks in a radial arm maze in rats

In an eight-arm radial maze, working and reference memory can be assessed simultaneously in the fixed position of reward task (FPRT) in which half of the arms are baited and their positions are fixed throughout the training trails. We characterized performance of rats in the variable position of reward task (VPRT), in which four out of eight arms were baited, but the positions were varied in every training trial. In the VPRT, the rats learned to choose all arms without any discrimination between baited and non-baited arms and the memory retention was time-dependent. The performance of rats in the FPRT was impaired by altering the spatial organization of the extramaze cues while it was not affected in the VPRT. The number of Fos-positive cells transiently increased in the cerebral cortex and hippocampus of both groups of animals during the training. Finally, bilateral lesions of the dorsal hippocampus resulted in an impairment of working memory in the FPRT and the performance of the rats in the VPRT. These results suggest that different strategies are used between the FPRT and VPRT but the hippocampus plays an important role in performance of rats trained for the VPRT as well as FPRT.

Radial arm maze performance in rats following gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Recently, we reported that in utero and lactational exposure to 2,3, 7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a task-specific reduction of errors on the radial arm maze (RAM), without similar improvements on other spatial learning tasks including the Morris water maze. The effect was more pronounced in males than in females. This study further investigated the effects of in utero and lactational exposure to TCDD on RAM performance by testing male and female TCDD-exposed rats on either an eight-arm RAM with all arms baited or a 12-arm RAM with 8 of the 12 arms baited. If the rats have improved spatial learning or memory on the RAM, then they should be improved on both RAM tasks; whereas, if they are using adjacent arm selection or some other response strategy to solve the task, they should not show enhanced performance on the 12-arm RAM where not all the arms are rewarded. Time-mated Sprague-Dawley dams were gavaged with corn oil vehicle or one of two doses of TCDD in vehicle (0.1 or 0.2 microg/kg body weight) on gestational days 10 to 16. Litters were culled to eight on day 2 and weaned on day 21. Beginning on day 80, one male and female from each litter was tested on the eight-arm RAM with all arms baited. As in our previous studies, the 0.1-microg/kg TCDD-exposed male rats showed a significant decrease in the number of errors. However, the 0.2-microg/kg males did not differ from the controls. Neither group of TCDD-exposed females differed from the controls. None of the TCDD-exposed rats differed from the controls in adjacent arm selection behavior. An additional male and female from each litter were tested on the 12-arm RAM with only 8 of the 12 arms baited. In this task, neither TCDD group differed from the controls. These results suggest that the reduction of errors on the eight-arm RAM may be due to increased response patterning or use of intramaze cues rather than to improved spatial learning or memory. Also, the reduction in errors was only present at the lower dose of TCDD suggesting that the improvement in performance is only present at very low, nonovertly toxic doses of TCDD.

Algorithmic behaviour and spatial memory are used by two intertidal fish species to solve the radial maze

We used an eight-arm radial maze to assess the relative contributions of learned patterns of movement (algorithmic behaviour) and spatial memory to the foraging efficiency of two sympatric rocky-shore fish, fifteen-spined stickleback, Spinachia spinachia, and corkwing wrasse, Crenilabrus melops, exploiting nonrenewable food sources. To forage efficiently, subjects had to avoid arms already depleted within a trial. In the absence of spatial cues, sticklebacks and wrasse improved their foraging efficiency by developing the algorithm of visiting every third arm. In the presence of spatial cues (coloured tiles) algorithmic behaviour was largely subsumed by the use of spatial memory. Imposition of a delay within trials reset the behavioural algorithm, so depressing foraging efficiency in the absence of cues, but not in their presence when memory could be used to guide behaviour. Memory retention for previous choices (working memory) lay within the range 0.5-5.0 min, consistent with the characteristic timescale expected for habitats where prey distribution changes rapidly during the tidal cycle. We considered two hypotheses on the type of information memorized: the cue list hypothesis and the spatial configuration hypothesis. The cue list hypothesis predicts that neither random repositioning nor fixed rotation of spatial cues should impair foraging efficiency, whereas the spatial configuration hypothesis predicts that efficiency should be impaired by random repositioning of cues but not by rotation. Data supported the spatial configuration hypothesis. Copyright 1999 The Association for the Study of Animal Behaviour.

Reference memory and allocentric spatial localization deficits after unilateral cortical brain injury in the rat

Traumatic brain injury (TBI) produces learning and memory impairments in humans. This study investigated the effects of TBI on memory and spatial localization strategies in rats. Prior to TBI, separate groups of rats were trained in an 8-arm radial maze with either all 8 arms baited (Expt. 1) or only 4 of the 8 arms baited (Expt. 2). TBI was produced by a controlled pneumatic impactor striking the entire right sensorimotor cortex of the anesthetized rat. Rats used in Expt. 1 were selected because they did not use a stereotypic response strategy (going to adjacent arms) in performing the maze before injury. After TBI the rats were not different from control rats in the number of working memory (WM) errors made. They did, however, display a distinct propensity to go to adjacent arms, i.e., exhibit stereotypic behavior, with a right-handed (ipsiversive) bias (P < 0.005). After TBI, rats which were trained with only 4 of 8 arms baited committed more reference memory (RM) errors than control rats (P < 0.05). They did not differ from controls on WM errors. Injured rats took longer to re-attain criteria than controls (P < 0.0001). Injured rats also initially displayed a propensity to enter the adjacent arm sequentially before re-attaining criteria. Further analysis indicated that injured rats re-learned the maze with a right-hand bias (P < 0.0001). The results of both experiments suggest that after TBI, rats shifted from an allocentric to an egocentric strategy to re-learn the maze. It was suggested that damage to the parietal cortex may have been responsible for both RM errors and the shift away from an allocentric strategy to an egocentric strategy. Possibly, the ipsiversive (right-hand) bias may be the result of a behaviorally or injury-induced neurochemical asymmetry within the motor system.