Cholinergic receptor blockade in the rat impairs locale but not taxon strategies for place navigation in a swimming pool.

Normal Long-Evans hooded rats and rats drugged with atropine sulfate (10–200 mg/kg, intraperitoneally), a cholinergic muscarinic blocker, were evaluated in the Morris water task for their use of spatial navigation strategies. Atropine-treated Ss were impaired on a place response of swimming to a platform hidden in a pool filled with opaque water. With extended training, they did learn the place response, though not with the precision of controls. Acquisition could not be accounted for by habituation to the drug. In contrast with the acquisition deficit, pretrained Ss were relatively unimpaired by the drug. Atropine-treated Ss were not impaired in acquisition or retention of a cue task (swimming to a visible platform) or a position response task (turning to locate a platform). Atropine-treated Ss were unable to acquire a place learning set or to perform a learning-set response that they had acquired when undrugged. The impairments following atropine were characteristic of a deficit in the use of a locale strategy (rapid use of relational properties of distal cues), whereas their successes were characteristic of the use of taxon strategies (cue or position responses). Results suggest that locale systems of navigation are more importantly dependent on cholinergic brain mechanisms than taxon strategies. The resistance of preacquired place responses to atropine suggests that normally rats acquire place responses by using a locale strategy but effect rehearsed responses by using taxon strategies. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How do room and apparatus cues control navigation in the Morris water task? Evidence for distinct contributions to a movement vector.

The present study compared the relative influence of location and direction on navigation in the Morris water task. Rats were trained with a fixed hidden or cued platform, and probe trials were conducted with the pool repositioned such that the absolute spatial location of the platform was centered in the opposite quadrant of the pool. Rather than swimming to the platform location, rats swam in the direction that was reinforced during training, resulting in navigation to the relative location of the platform in the pool and search at the appropriate distance from the pool wall. Pool relocation tests revealed disruptions in cued navigation if the cued platform remained at the absolute location, whereas no disruption was observed if the platform remained at the relative location (same direction). The results indicate that direction holds greater influence than does location and further demonstrate that this observation is not altered by the amount of training or time on the platform. The authors propose that navigation in the water task involves a movement vector in which the distal cues and apparatus provide direction and distance information, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholinergic receptor blockade impairs spatial localization by use of distal cues in the rat.

Studied spatial localization in the Morris water maze. 30 male Long-Evans hooded rats were required to escape from cool water by finding a submerged, invisible platform located at a fixed place. The start point randomly varied, and there were no local cues. After training, the platform was moved. Six Ss subjected to central cholinergic receptor blockade with atropine sulfate were compared with normal Ss and with 6 Ss receiving peripheral cholinergic blockade with atropine methylnitrate. The controls were a group of blind Ss and Ss for which the platform was moved from trial to trial. Results show that controls and the atropine methylnitrate Ss used a spatial mapping strategy to locate the platform. The atropine sulfate-treated Ss adopted a search strategy like that of the blind Ss and Ss for which the platform was randomly moved. Results support the idea that central cholinergic systems are important for spatial mapping, which demands the use of distal visual cues. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delayed development of place navigation compared to directional responding in young rats.

Recent work from our laboratory demonstrates that both young and adult rats show a preference for directional responding over place navigation in the Morris water task. Based on these findings, previous studies on the postnatal development of spatial learning have most likely assessed the ontogeny of directional responding instead of true place navigation. Here, we examined the development of directional responding and place navigation among young male and female rats using two variants of the Morris water task that specifically require directional and place responses. In the place variant, the hidden platform remained in the same absolute spatial location regardless of pool position. In the direction variant, the platform remained in the same direction in the room regardless of pool position. We found that ability to solve the direction task emerged around 20 to 21 days of age, whereas ability to solve the place task did not emerge until 26 to 27 days of age. These findings indicate that directional responding and place navigation exhibit different developmental trajectories and suggest that the 2 forms of navigation have different neurobiological bases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preweanling rats solve the Morris water task via directional navigation.

Adult rats show a preference for directional navigation over place navigation in the Morris water task. Here, the authors investigated whether preweanling rats with a newly developed ability to perform the water task also solve the task via directional navigation. After 24-day-old rats were trained to find a hidden platform in a fixed spatial location, a no-platform probe trial was conducted with the pool either in the same position as that used during training (no shift group) or shifted to a new position in the room (shift group). The authors found that rats in the shift group did not search for the platform at its absolute spatial location but rather navigated in the same direction that the platform was located during training and searched at the correct distance from the pool wall, resulting in a search at a location that was never trained. This pattern of results suggests that young rats learn to solve the water task by navigating in a particular direction rather than navigating to a precise place--a finding that may have implications for understanding hippocampal development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative influence of place and direction in the Morris water task.

Previous work from our laboratory has demonstrated that rats display a preference for directional responding over true place navigation in the Morris water task. The present study evaluated the range of situations in which this preference is observed and attempted to identify methods that favor navigation to the precise location of the escape platform in the room. A preference for directional responding over place navigation was observed in a wide range of procedures that included providing extensive training (Experiment 1), providing only platform placement experience in the absence of active swim training (Experiment 2), training navigation to multiple platform locations in a moving platform variant of the task (Experiment 3), and explicitly training navigation to a precise location in the room, versus navigation in a particular direction, regardless of the pool's position in the room (Experiments 4-5). A modest preference for navigation to the precise spatial location of the platform was observed when the pool wall was virtually eliminated as a source of control by filling it to the top with water (Experiment 6). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of spatial learning in woodmice (Apodemus sylvaticus) and hooded rats (Rattus norvegicus).

The spatial learning of woodmice and rats was examined in two different experiments. In the Morris place navigation task, the woodmice were slower to escape and took more circuitous routes than did the rats. However, in a special probe trial their accuracy in swimming repetitively through the position of the absent training platform was comparable to that of the rats. In the second experiment, subjects were allowed to escape from a large arena through a hole connected with their home cage. Rats and woodmice learned this task in few trials. In a special trial with no connected hole, subjects of both species showed accurate searching behavior in and around the hole of the training location. However, only the rats developed direct approaches in a systematic manner. These differences are discussed in the contexts of the species specific constraints that might affect the acquisition of direct approaches in a wild species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visits to starts, routes, and places by rats (Rattus norvegicus) in swimming pool navigation tasks.

In 2 studies, 40 young adult female Sprague-Dawley rats were trained to escape to visible or to hidden platforms in a swimming pool and then given probe trials, which required that they searched for a platform that had been removed or repositioned. Results indicate that to solve the tasks, Ss simultaneously used a number of behavioral strategies including position responses, cue responses, and place responses. On the probe trials, they not only displayed behaviors that were reinforced during training but also displayed novel behaviors. Ss trained on the place task (hidden platform) made more swims across the platform's previous location, whereas Ss trained on the cue task (visible platform) made more returns to previously used start points. Increases in the number of start points produced more returns to start points, whereas increases in the number of platform locations produced more searches for platforms. It is concluded that rats make coextensive use of all relevant strategies to solving spatial navigation tasks and that their search patterns on probe trials reflect both previously reinforced behaviors and novel unconditioned search behaviors. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cholinergic receptor blockade produces impairments in a sensorimotor subsystem for place navigation in the rat: Evidence from sensory, motor, and acquisition tests in a swimming pool.

In Experiment 1, control rats and rats treated with atropine sulfate or atropine methyl nitrate (50 mg/kg) were trained to escape to a visible platform from different starting points in a swimming pool. All groups learned the task by concomitantly developing position responses, by orienting according to room cues, and by orienting to the platform, but probe trials showed that the atropine-sulfate group made more use of the platform as a local cue and made less use of distal cues than did the other groups. The atropine-sulfate group also made fewer searches during acquisition, made fewer searches when the platform was removed on probe trials, and were less responsive to novel cues placed above and around the pool. Swim speed, as estimated by the distance swum on probe trials, was also greater in atropine-sulfate-treated rats. The postulate that rats treated with atropine sulfate preferentially guide swimming by using position responses and local cues was tested in Experiment 2 by comparing their performance with that of control rats in a place task in which the target platform was hidden (no local cues present) and in a similar place task in which the target platform was visible, as was a second incorrect platform that sank when climbed upon (two competing local cues present). Although both tasks were acquired by the control and drugged rats, the two-platform task, as predicted, was comparatively more difficult for the atropine-treated rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Active preexposure enhances attention to the landmarks surrounding a Morris swimming pool.

Rats were required to swim to a hidden platform in order to escape from a Morris pool, after they had been exposed to the landmarks around the pool by swimming to a platform that had a beacon attached to it. The platform occupied a different place for the test trials than for the preexposure trials. Escape from the pool was facilitated if the landmarks remained in the same place throughout preexposure, but if their positions were changed during preexposure, then subsequent escape from the pool was disrupted (Experiment 2). Escape learning was also disrupted if the rats were placed on the platform for their preexposure treatment (Experiment 3). The results indicate that the associability of the cues around a Morris pool may be enhanced when they are in a stable spatial relationship with the platform throughout each preexposure session. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for a shift from place navigation to directional responding in one variant of the Morris water task.

Previous work from our laboratory has demonstrated that rats display a preference for directional responding over place navigation in a wide range of procedural variants of the Morris water task (Hamilton, Akers, Weisend, & Sutherland, 2007; Hamilton et al., 2008). A preference for place navigation has only been observed when the pool is reduced as a cue by filling it with water. Studies using dry land mazes have suggested that rats place navigate early in training and later switch to other forms of responding (e.g., motor). The present study evaluated whether rats switch from place navigation to directional responding in the “full-pool” variant of the water task. Rats were given 12, 24, or 36 hidden platform training trials. Probe trials with the pool repositioned in the room revealed a preference for place navigation in rats given 12 trials, an equal division of response preferences in rats given 24 trials, and a preference for directional responding in rats given 36 trials. These results indicate that the early preference for place navigation in the full-pool water task is transient and yields to a preference for directional responding with continued training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An evaluation of spatial information processing in aged rats.

The spatial learning abilities of young, middle-age, and senescent rats were investigated in 2 experiments using several versions of the Morris water maze task. In Exp I, Long-Evans hooded rats were trained to find a submerged escape platform hidden within the water maze. Aged Ss exhibited acquisition deficits compared with either young or middle-age Ss. With continued training, all age groups eventually achieved comparable asymptotic levels of performance. To identify the basis of the age-related impairments observed in Exp I, naive young and aged Ss in Exp II were initially tested for their ability to locate a cued escape platform in the water maze. The escape latencies of both young and aged Ss rapidly decreased to equivalent asymptotic levels. Following cue training, young Ss exhibit a significant spatial bias for the region of the testing apparatus where the platform was positioned during training. In contrast, aged Ss showed no spatial bias. Training was continued in Exp II using a novel submerged platform location for each S. During these place training trials, the escape latencies of senescent Ss were longer than those of young Ss. These impairments were also accompanied by a lack of spatial bias among aged Ss relative to young controls. Results indicate that age-related impairments in water maze performance reflect a specific deficit in the ability of aged rats to utilize spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial septal lesions disrupt spatial mapping ability in rats.

Rats with lesions of the medial septum were more likely to begin swimming in the wrong direction, swim farther, and, therefore, require more time to find a platform hidden in a Morris water tank than were control rats. Although the performance of the rats with medial septal lesions did improve over trials, their asymptotic performance also failed to equal that of the controls. Movement of the platform to a new position in the tank disrupted the performance of both groups, and, again, the rats with medial septal lesions were slower to locate the moved platform. However, this deficit was completely eliminated when a visual cue indicating the location of the moved platform was introduced. We suggest that these data indicate that damage to the septo-hippocampal cholinergic projection system produces a deficit in the formation or utilization of a spatial map (reference memory) that represents the location of a place with respect to the surrounding distal cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial behavior in the Brazilian short-tailed opossum (Monodelphis domestica): Comparison with the Norway rat (Rattus norvegicus) in the Morris water maze and radial arm maze.

The spatial behavior displayed in a swimming pool and radial arm maze by the Brazilian gray, short-tailed opossum (Monodelphis domestica) was compared with that of the laboratory rat (Rattus norvegicus). The performance of the 6 opossums was clearly different from that of the 6 rats in both tasks. The opossums failed to learn to find a hidden platform in the swimming pool (place task), but they did learn to swim to a visible platform. The opossums did learn working and reference memory components of the radial arm maze but showed different search strategies in this situation. The results are discussed with reference to possible species differences in motor behavior, ecology, brain structure and evolution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of passive preexposure on escape from a Morris pool.

In 3 experiments rats were preexposed to the landmarks that surround a Morris pool by being placed on a submerged platform within the pool. They were then required to escape from the pool by swimming to the platform, which was in a location that had not been used during preexposure. Preexposure facilitated subsequent escape from the pool, provided that the platform was not moved during preexposure and the relative position of the landmarks to each other remained constant throughout preexposure. In contrast, if during preexposure the platform was moved from session to session (Experiment 1), or the array of landmarks was altered unsystematically from trial to trial (Experiments 2 and 3), then subsequent learning to escape from the pool was disrupted. These findings suggest that the effects of preexposure to the landmarks in a Morris pool is determined by whether or not they are of relevance for identifying the location of the platform. When they are relevant, then subsequent learning is facilitated, but when they are irrelevant, then subsequent learning is disrupted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in learning and memory in mice: Effects of sequence of testing and cholinergic blockade.

Sexual dimorphism in spatial and cued navigation using the Morris water maze was examined in C57BL/6 mice both with and without administration of scopolamine, a cholinergic blocker. In Exp 1, female and male mice learned to perform first a spatial, then a cued, navigation task. Both performed a spatial task similarly; males, however, performed a cued task better than females. In Exp 2, the sequence of navigation testing was reversed. Both performed similarly on a cued task; however, males performed a spatial task better than females. In both experiments, females were more sensitive than males to the effects of scopolamine. No significant confounding sex differences were found in either spontaneous activity or passive avoidance retention. These data indicate that sex differences in spatial and cued tasks are dependent on the sequence of task presentation and implicate a role for the cholinergic system in these differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of low-intensity hippocampal stimulation on spatial versus working memory in rats.

Investigated differing predictions from the spatial mapping hypothesis of hippocampal function proposed by O'Keefe and Nadel (1978) and the working memory hypothesis proposed more recently by Olton and colleagues (Olton, Becker, & Handelmann, 1979). Each of 2 groups of rats was trained to use a different strategy to locate a submerged platform in opaque water. The MAP group used a spatial mapping strategy to reach a platform in a fixed location, whereas the CUE group used a guidance strategy, which involved following a cue that signaled the location of a randomly placed platform. Half of each group was given low-level unilateral electrical stimulation of the dentate gyrus and immediately tested on the water maze task. Results of Exp 1 show that both the MAP and CUE groups were impaired by stimulation. However, there was an inadvertent spatial element involved in the CUE task. When this element was eliminated in Exp 3, the same CUE Ss were unaffected by a 2nd series of stimulation trials, whereas the MAP Ss continued to show impairment. Results strongly support the cognitive mapping hypothesis and provide little support for the working memory hypothesis of hippocampal function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A deficit in ambient visual guidance following superior colliculus lesions in rats.

21 male black-hooded rats were tested for their ability to locate a hidden platform in the Morris swimming pool, in which extrapool cues are required to guide locomotion. At the end of each trial, Ss were either removed immediately or allowed to remain on the platform for 60 sec. As in a previous experiment by the present authors (see record 1984-06177-001), bilateral lesions of the superior colliculus (SC) produced a severe deficit. Permitting the Ss to stay on the platform did not significantly affect performance in either Ss with SC lesions or sham-operated controls. Results indicate that the reduced orienting behavior on the platform observed in the rats with lesions in the previous experiment was not the cause of their navigational impairment. It is concluded that the impairment following SC lesions came about during the swimming itself; therefore, it may be attributed to a disturbance of, or a failure to utilize, ambient vision. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats repeatedly placed on a hidden platform learn but quickly forget its location.

Retracted July 1989. (See record 1989-35458-001.) Rats were pretrained to escape from cool water by swimming to a platform hidden at a fixed location in a swimming pool. They were then placed a number of times on a platform at a new location in another pool in a new room. Rats placed on the platform subsequently swam to it more quickly than rats that were not placed or rats placed in inappropriate locations. Rats required 10–25 placements on the platform before swimming directly to it on a test trial. An interval of as little as 2 hr between placement and testing eliminated the advantage of previous placement. These results unambiguously demonstrate that rats can latently acquire spatial information, and they disclose some performance features of latent spatial learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absence of an Interaction Between Navigational Strategies Based on Local and Distal Landmarks.

In 3 experiments, rats were required to escape from a Morris pool by swimming to a submerged platform that was located at the apex of a notional, equilateral triangle with 2 different landmarks occupying the corners at the base. Training for 1 group was always conducted in view of the landmarks surrounding the pool and with the triangular array in a fixed orientation. Subjects could therefore identify the direction of the platform from a single landmark within the pool by reference to cues outside the pool or to the other landmark within the pool. Both strategies were used, and the results from additional groups revealed that the first of these strategies did not affect the acquisition of the second one. (PsycINFO Database Record (c) 2010 APA, all rights reserved)