Learning and Memory in S100-β Transgenic Mice: An Analysis of Impaired and Preserved Function

Neurobiology of Learning and Memory 75, 230–243 (2001) doi:10.1006/nlme.2000.3961, available online at http://www.idealibrary.com on

Learning and Memory in S100-␤ Transgenic Mice: An Analysis of Impaired and Preserved Function Gordon Winocur,* John Roder,† and Nancy Lobaugh‡ *Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada; Department of Psychology, Trent University, Peterborough, Ontario, Canada; and Departments of Psychology and Psychiatry, University of Toronto, Toronto, Ontario, Canada; †Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Ontario, Canada; ‡Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada

S100-␤, a calcium-binding astrocytic protein from chromosome 21, has been implicated in CNS function generally and the hippocampus in particular. Elevated levels of S100-␤ have been observed reliably in the brains of patients with Alzheimer’s Disease and Down Syndrome. Groups of transgenic mice, carrying multiple S100-␤ gene copies, and nontransgenic controls were administered a series of behavioral tests (delayed spatial and nonspatial non-matching-to-sample, radial arm maze, socially acquired food preference) that assessed a wide range of cognitive functions. Consistent with the widespread presence of S100-␤ throughout the brain, transgenic mice exhibited learning or memory impairment on all tasks. The dementia-like cognitive profile of S100-␤ mice represents a promising model for studying comparable cognitive deficits associated with neurodegenerative diseases. 䉷 2001 Academic Press

Key Words: S100-␤; transgenic mice; learning and memory.

INTRODUCTION S100-␤, an astrocytic, calcium-binding protein from chromosome 21, has been implicated generally in CNS function (Barger & Van Eldik, 1992). The functional significance of this protein is unclear but the discovery that it is found in elevated levels in Alzheimer’s Disease and Down Syndrome generated increased interest in its possible involvement in cognitive abilities (Griffin, Stanley, Ling, White, MacLeod, Perrot, White, & Araoz, 1989; This research was supported by a grant from the Natural Sciences and Engineering Research Council of Canada to G.W. and a grant from the Ontario Mental Health Foundation to J.R. N.L. was supported by a research fellowship from the Rotman Research Institute. The authors gratefully acknowledge the technical assistance provided by Chris Conley, Doug Caruana, Gordon Figuerroa, and Heidi Roesler. Address correspondence and reprint requests to Gordon Winocur, Rotman Research Institute, Baycrest Centre for Geriatric Care, 3560 Bathurst Street, Toronto, Ontario, Canada M6A 2E1. Fax: 416–785–2474. E-mail: [email protected]. 1074-7427/01 $35.00 Copyright 䉷 2001 by Academic Press All rights of reproduction in any form reserved.

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Rabe, Wisniewski, Schapf, & Wisniewski, 1990). This issue has been addressed further in studies with animal models that have focused largely on the overexpression of S100␤ in the hippocampus, a structure that is widely identified with learning and memory functions (Milner, 1966; Squire, 1992) Several lines of evidence suggest that transgenic mice, carrying multiple copies of the human S100-␤ gene, exhibit abnormal hippocampal function. For example, Gerlai, Wojtowicz, Marks, and Roder (1995) compared long-term potentiation (LTP), a measure of synaptic activity thought to mediate hippocampus-controlled memory processes (Bliss & Collingridge, 1993), in hippocampal (CA1) slices of normal and age-matched S100-␤ transgenic mice. Electrical stimulation (100 Hz) of afferent pathways to CA1 yielded a substantially reduced excitatory postsynaptic response in the slices of transgenic mice. Of particular interest, this abnormal response correlated with impaired spatial memory in the Morris Water Maze, a task that is highly sensitive to hippocampal dysfunction (Morris, Garrud, Rawlins, & O’Keefe, 1982). Other forms of behavior associated with the hippocampus (e.g., spontaneous alternation, exploratory behavior) are also impaired in S100␤ transgenic mice (Gerlai, Marks, & Roder, 1994; Janus, Janus, & Roder, 1995; Roder, Roder, & Gerlai, 1996). Although the S100-␤ protein can be linked to hippocampus-controlled cognitive processes, the evidence is based on a limited sample of behavioral tests. Moreover, in almost every case, investigators included only tasks that required an intact hippocampus for successful performance (but see Gerlai et al., 1995). Consequently, it is not known if S100-␤ participates in a broader range of hippocampal functions or if its involvement is specific to this structure. The latter question is important because S100-␤ is widely distributed throughout the CNS and is found in other brain regions that participate in cognitive function (Friend, Clapoff, Landry, Becker, O’Hanlon, Allore, Brown, Marks, Roder, & Dunn, 1992). Such issues need to be addressed in order to assess the limits of S100-␤ transgenic mice as a model for studying related cognitive changes in humans. Accordingly, the aim of the present research was to broaden the behavioral assessment of S100-␤ transgenic mice and improve the description of their cognitive profile. Groups of S100-␤ and control mice were administered a series of tasks that included spatial and nonspatial tests of learning and memory. The tests assessed a range of functions in different paradigms and included measures of rule (procedural) learning, short- and long-term memory, and forgetting rates. Of the various processes sampled, several are reliably associated with the hippocampus, while others are controlled by other brain regions. The spatial tests were Olton’s radial arm maze (RAM) and a test of spatial non-matchingto-sample (SNMTS) learning. Both are diagnostic of hippocampal impairment (Olton, Becker, & Handelmann, 1979; Shaw & Aggleton, 1993) but, apart from their reliance on spatial cues, assess quite different behavioral processes. A test of non-spatial, non-matching-to-sample (NSNMTS) learning, which is not sensitive to effects of hippocampal damage (Aggleton, Hunt, & Rawlins, 1986; Gagnon & Winocur, in preparation), was also included to compare NMTS rule-learning with spatial or nonspatial cues. In both versions, following acquisition training on the basic NMTS task, a variable interval was introduced between study and test trials to assess retention of trial-specific information over relatively short delays. Extensive work in our lab has shown that rats with hippocampal damage perform normally at short delays on NSNMTS and related nonspatial rule-learning tasks (e.g., Go/No-go response alternation, Winocur, 1985; matching-to-sample, Winocur, 1992;

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conditional associative learning, Winocur, 1991), but they are severely impaired when required to retain trial-specific information over long delays between critical trials. By comparison, the pattern of deficits observed in rats with lesions to other brain regions (e.g., prefrontal cortex, Winocur, 1991; thalamus, Winocur, 1985; caudate nucleus, Winocur & Eskes, 1998) are quite different and can include disruption of rule-learning and/or short-term memory. Finally, S100-␤ and control mice were administered a food-preference task that has been used successfully to test long-term forgetting rates in normal and brain-damaged rats (Winocur, 1990). Previous research has shown that acquisition of the preference is highly resistant to various types of restricted brain damage, but that the ability to remember it over several days requires an intact hippocampus. METHOD Animals and Housing S100-␤ transgenic male and nontransgenic control mice of the CD-1 strain served as subjects in all behavioral tests. The transgenic mice, all of which were males, carried approximately 70 copies of the human S100-␤ gene (Line 8) and were born from the stock originally derived by Friend et al. (1992). Breeding mice were originally obtained from the Samuel Lunenfield Research Institute, Mt. Sinai Hospital, Toronto, Ontario, and transferred to the Trent University Breeding Centre, Peterborough, Ontario. All mice tested in this study were born, raised, and tested at Trent University. For several months after weaning, transgenic and control mice were housed in groups of four mice in standard plastic cages that contained sawdust bedding. All cages were located in the same room that was centrally illuminated according to a 12-h, light–dark schedule, in which lights were on between 8:00 PM and 8:00 AM. This schedule was maintained throughout the study to ensure that mice, which are nocturnal animals, would be tested during times of optimal alertness. During this period, food and water were available on an ad-lib. basis. Mice were examined regularly by a veterinarian and especially before behavioral testing to ensure that there were no health-related reasons for excluding them. At least 2 weeks before testing, mice assigned to their respective tasks were marked for identification and, depending on the task, were placed on a restricted food schedule. Under these conditions, 20 g of standard lab chow was placed in the cage. Since this procedure did not ensure that all mice ate precisely the same amount of food, feeding was monitored and, in the few cases where there was some concern that mice were not feeding well in the group situations, they were removed from the cages and fed separately. Water was available at all times. During this pretest period, mice were regularly handled by the experimenter. Mice were between 6 and 8 months old when they were tested. Each mouse was tested on only one of the behavioral tests, with the exception of the foodpreference test. All the mice administered the latter test had also been tested previously on one of the other tests. Behavioral Tests and Procedures RAM. This test was adapted from the eight-arm radial maze, developed originally by Olton and Samuelson (1976) for the rat. The present apparatus, which was constructed

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of wood and painted flat gray, consisted of eight arms (30 ⫻ 5 cm) radiating horizontally from a central cylindrical platform (18 cm in diameter). The entire apparatus was elevated (120 cm) above the floor. Recessed food cups with rims that hid the contents of the cup from the animal’s sight were placed in the floor at the end of each arm. The maze was placed in the center of a small testing room which was illuminated by fluorescent lighting. Eight S100-␤ and 8 control mice were administered the RAM. Food-deprived mice received 5 days of preliminary training in which pieces of Froot Loop cereal were scattered throughout the apparatus, including the central platform, each arm, and the food cups. Mice were placed in pairs and allowed to explore the apparatus for about 15 min. Testing began on the sixth day. For the test trials, each food cup was baited with a small amount of Froot Loop cereal, and the mouse was placed individually on the central platform. The mouse was removed after all eight arms had been entered or after 10 min had elapsed. An arm was recorded as having been entered when a mouse reached and ate the cereal in the food cup. An error was scored whenever a mouse reentered an arm that had been previously scored as entered. An arm was considered reentered when all four of the mouse’s paws were in the previously entered arm. One such trial was administered daily for 15 consecutive days. SNMTS. This test was adapted from one devised by Gagnon and Winocur (1995) for rats. The apparatus, which was painted flat gray, was an elevated Y-maze that consisted of a start box (5 ⫻ 5 cm) and two identical arms (25 ⫻ 5 cm). Guillotine doors separated the start box from the two arms. A recessed food cup was located at the end of each arm. The start box was covered by a hinged Plexiglas roof in which several holes had been drilled. The apparatus was placed on a table which was illuminated by overhead fluorescent lighting. Ten S100-␤ mice and 9 control mice received the SNMTS test. Mice were familiarized with the task over a 10-day period. In the first 3 days, bits of Froot Loop cereal were scattered throughout the Y-maze. Mice were placed individually in the start box, the Plexiglas roof lowered, and the guillotine doors raised. Mice had access to the entire apparatus and were free to eat the cereal. The session ended when all the cereal was eaten or after 15 min had elapsed. On Days 4–6, Froot Loop bits were placed only in the two food cups at the ends of the arms and mice had 15 min to find and eat them. On Days 7–10, one piece of Froot Loop was placed in each food cup, and the mouse was allowed to visit both arms and eat the cereal. The mice were then returned to the start box, and the procedure was repeated for a total of five trials each day. SNMTS training was initiated on Day 11. A complete trial consisted of a forced-choice study run followed by a test run. On the study run, the mouse was placed in the start box, the roof lowered, and the guillotine door of one of the arms raised (the guillotine door at the entrance to the other arm remained lowered throughout the study run). As soon as the mouse’s four paws were in the open arm, the guillotine door was lowered and the mouse was allowed to run down the arm and eat the cereal. After eating the cereal in the study run, the mouse was returned to the start box for the test run, which was initiated immediately. For the test run, both arms were open but only the arm that the mouse had not visited on the preceding study run was baited. As soon as the mouse entered one of the arms (all four paws in the arm), the guillotine door was lowered. If the selection was correct, the mouse was allowed to eat the cereal and

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was then returned to a holding cage for a 30-s intertrial interval. If the mouse selected an unbaited arm, it was immediately placed in the holding cage to await the next trial, which began 30 s later. Mice were administered 10 such trials over 20 consecutive days. After 20 sessions, the mice received an additional 5 days of testing in which the amount of time that the mouse waited in the start box for the beginning of a test run was increased to 15 s. This was followed by a final block of 5 test days in which the delay between study and test runs was extended to 30 s. In all other respects, the procedure on the last two blocks of trials was identical to that during SNMTS training NSNMTS. This test was conducted in a Y-maze that, in terms of dimensions and design, was identical to that used in the SNMTS test. A major difference was that, for this task, the start box was painted flat gray, while the arms were painted black or white. The arms were interchangeable and could be easily attached to the start box. As well, two arms, painted flat gray, were used during the familiarization stage of training. Nine S100-␤ mice and 9 control mice were administered the NSNMTS test. The familiarization stage was identical to that followed in the SNMTS test, except that the Y-maze was fitted with the gray arms. For NSNMTS training, which was initiated the day after the last familiarization day, the apparatus was fitted with a black arm and a white arm. Each NSNMTS training trial consisted of a forced-choice study run followed by a test run. On the study run, the mouse was placed in the start box, the roof lowered, and the guillotine door of one of the arms raised to allow the mouse to enter a black or white arm. As soon as the mouse’s four paws were in the open arm, the guillotine door was lowered and the mouse was allowed to run down the arm and eat the cereal. After eating the cereal in the study run, the mouse was returned for a few seconds to a holding cage. This allowed the experimenter to reposition the black and white arms on those trials where that was necessary. The mouse was then replaced in the start box and both guillotine doors were immediately raised. For the test runs, only the arm that contrasted to the one that the mouse had not visited on the immediately preceding study run was baited. Thus, if the mouse was allowed to enter and feed in the black arm during the study trial, it was rewarded with food if it entered the white arm on the test run. The opposite was the case if the animal had been forced to enter the white arm in the study run. As soon as the mouse entered one of the arms in a test run (all four paws in the arm), the guillotine door was lowered. If the selection was correct, the mouse ate the cereal and was then returned to a holding cage for a 30-s intertrial interval. If the mouse selected an unbaited arm, it was immediately placed in the holding cage to await the next trial, which began 30 s later. The positions of the black and white arms during the study and test runs, as well as the baiting of arms, were all determined randomly. Mice were administered 10 such trials over 20 consecutive days. After 20 sessions, the mice received 5 more days of testing in which the interval between the study and test runs was increased to 15 s. As in the SNMTS task, the mouse waited in the start box during the extended interval. This was followed by a final block of 5 test days in which the interval was extended to 30 s. In all other respects, the procedure on the last two blocks of trials was identical to that during training. Food-preference test. The procedure for this test was adapted from Galef and Wigmore (1983) and similar to that followed by Winocur (1990). Two weeks prior to the test, mice

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were placed on a 23.5-h food-deprivation schedule. The testing procedure involved five discrete stages: (1) Mice were transferred individually to new wire-mesh cages that were divided into two compartments by a wire-mesh partition. A subject mouse (S) was placed in one of the compartments and an unfamiliar demonstrator mouse (D) was placed in the other. Typically, 12 pairs of mice were studied at one time. The pairs of mice were left undisturbed for 2 days, during which they were fed standard chow on an ad-lib. basis. (2) Food was removed from both compartments for 23 h. (3) D was removed to another room and, for 60 min, was allowed to eat powdered chow that was flavored with commercially prepared sifted cocoa (2% by weight) or commercially ground cinnamon (1% by weight). (4) D was returned to its compartment and allowed to interact with its S partner across the partition for 20 min. (5) D was removed from the cage and, under the 0-delay condition, S was offered two weighed food cups, one containing the cocoa-flavored food and the other containing the cinnamon-flavored food. After 1 h, both food cups were weighed and the amount of food eaten was calculated. In addition to the 0-delay condition, different groups of S mice were tested at delays of 1, 3, or 5 days following acquisition training. During these delays, Ss were returned to their home cages where they given daily rations of standard chow in pellet form. After the appropriate delay, each was returned individually to the test compartment and given the choice of cinnamon- and cocoa-flavored food in the usual manner. RESULTS RAM Records were kept of the total number of errors made before all arms were entered at least once and the number of errors made in the first eight responses. Since the two scores were highly correlated in both groups, only the total-error measure is reported here. As can be seen in Fig. 1, the S100-␤ group consistently made more errors than the control

FIG. 1. Radial arm maze. The mean number of errors per trial for S100-␤ and Control groups, averaged over five blocks of three trials, is shown. Bars indicate ⫾1 SEM.

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group across the 15 trials. Analysis of variance (ANOVA) confirmed a highly significant group difference, F(1, 14) ⫽ 217.08, p ⬍ .00001; the Group x Block interaction was not statistically significant, F ⬍ 1. SNMTS Figure 2a provides learning rates for S100-␤ and control groups under the 0-delay condition of the SNMTS task, where delays between study and test runs were minimal. The data are averaged over five blocks of four trials each. It is apparent that both groups displayed substantial learning but, by the end of training, the control group was making more correct responses than the S100-␤ group. ANOVA performed on these data confirmed the significant Group effect, F(1, 17) ⫽ 154.55, p ⬍ .00001. The main effect of Blocks, F(3, 51) ⫽ 34.76, p ⬍ .0001, and the Group x Block interaction, F(4, 68) ⫽ 5.55, p ⬍ .001, were also highly significant. Figure 2b provides the mean percentage of correct responses for the S100-␤ and control groups, averaged over the last 5 training trials and over the 5 trials of the 15- and 30-s delay conditions. The group difference in performance that was evident at the end of training clearly persisted under the delay conditions. ANOVA performed on these scores

FIG. 2. Spatial non-matching-to-sample. (a) The mean percentage of correct responses by S100-␤ and Control groups during 0–delay, acquisition training, averaged over five blocks of 4 trials and (b) over the last 5 acquisition-training trials and the 5 trials of the 15- and 30-s delay conditions. Bars indicate ⫾ 1 SEM.

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yielded a highly significant main effect of group, F(1, 17) ⫽ 87.70, p ⬍ .00001. The Group x Delay interaction (F ⬍ 1), was not significant. NSNMTS As with the SNMTS task, the S100-␤ group exhibited a clear learning deficit on the NSNMTS task (see Fig. 3a). Analysis of the percentage of correct responses over the 20 days of training under the 0-delay condition revealed a significant group difference, F(1, 16) ⫽ 29.85, p ⬍ .0001. The Block effect, F(3, 48) ⫽ 164.92, p ⬍ .00001, and the Group x Block interaction, F(4, 64) ⫽ 6.12, p ⬍ .001, were also statistically significant. The main effect of Group persisted at the longer delays (Fig. 3b), F(1, 16) ⫽ 34.97, p ⬍ .0001. The Group x Delay interaction was also statistically significant, F(1, 16) ⫽ 9.87, p ⬍ .006, indicating that, for the NSNMTS task, the S100-␤ group was more affected than controls by increases in the interval between study and test runs. Food-Preference Test As in previous experiments with rats, none of the groups displayed a preference for either the cocoa or cinnamon in any of the tests. Accordingly, the data for each food as

FIG. 3. Nonspatial non-matching-to-sample. (a) The mean percentage of correct responses by S100-␤ and Control groups during 0–delay, acquisition training, averaged over five blocks of 4 trials and (b) over the last 5 acquisition-training trials and the 5 trials of the 15- and 30-s delay conditions. Bars indicate ⫾1 SEM.

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sample were combined and are presented in Fig. 4. The scores represent the amount of sample food eaten, expressed as a percentage of the total amount consumed. As can be seen in Fig. 4, at 0-delay, S100-␤ and control groups displayed an equally strong preference for the sample food. Although the preference decreased over time in both groups, the rate of decline was faster in the S100-␤ group. These observations were confirmed by ANOVA in which Group and Days were treated as between-subject variables. The Group x Day interaction was significant, F(3, 72) ⫽ 6.58, p ⬍ .001, due to the smaller percentage of the sample food eaten by the S100-␤ group at the 3- and 5 day tests. Posthoc t tests indicated highly significant differences between the groups on these days ( p’s ⬍ .0001) but not at the 0- and 1-day delays. DISCUSSION S100-␤ mice exhibited wide-ranging behavioral deficits indicative of hippocampal as well as nonhippocampal dysfunction. These deficits included impaired spatial memory on the RAM and, relative to controls, poor learning of a non-matching-to-sample rule using spatial or nonspatial cues. As well, in the nonspatial version of the NMTS task, the deficit of the S100-␤ group increased disproportionately with the length of the interval between study and test trials. The groups did not differ on a test of food-preference acquisition but, over several days, S100-␤ rats forgot the learned preference at a significantly faster rate. A major purpose of the present research was to improve our understanding of lost and spared function in S100-␤ transgenic mice. Since the S100-␤ protein is associated with hippocampal function, as well as that of other brain regions, it was of interest to determine if behavioral deficits associated with overexpression of the gene were restricted to hippocampus-sensitive tasks. The present results confirmed that S100-␤ mice are impaired on

FIG. 4. Food-preference task. The amount of sample food consumed by S100-␤ and Control groups, expressed as the mean percentage of the total amount of food consumed, at the various delays. Bars indicate ⫾ 1 SEM.

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tests of hippocampal function (Gerlai et al., 1994, 1995; Janus et al., 1995; Roder et al., 1996) and, indeed, extended the range of tasks on which such effects can be observed. The RAM and SNMTS tasks, which are dependent on spatial information processing, are extremely sensitive to hippocampal impairment (Olton et al., 1979; Shaw & Aggleton, 1993). As well, the temporally graded deficits of S100-␤ mice in the NSNMTS test and the socially acquired, food-preference test are probably the result of hippocampal dysfunction. In related work, rats with hippocampal lesions exhibited similar deficits on both tasks (Gagnon & Winocur, in preparation; Winocur, 1990). The hippocampus-based, time-dependent memory deficits in the two nonspatial tasks are noteworthy in that they represent two distinct types of memory loss. In the NSNMTS task, the intervals between study and test trials ranged between 0 and 30 s and involved memory for trial-specific information. While incorporating characteristics of working memory, this task appears to challenge an intermediate-memory system that retains information for periods longer than can normally be held in short-term storage (Rawlins, 1985). By comparison, the food-preference test measured long-term memory for invariant information that is not necessarily contextually bound. While both are legitimately identified with hippocampal function, they represent quite different memory processes and serve different purposes. A potentially important indication of the present research, consistent with the widespread expression of S-100 throughout the CNS, is that the behavioral deficits of S100-␤ mice may extend to functions controlled by other brain regions. For example, S100-␤ mice were impaired in learning the NSNMTS rule, a task that does not appear to be sensitive to hippocampal impairment. In previous work with this and other nonspatial matching and non-matching-to sample tasks where study–test intervals were minimal, rats with hippocampal lesions consistently performed as well as normal controls (Aggleton et al., 1986; Gagnon & Winocur, in preparation; Rawlins, Lyford, Seferiades, Deacon, & Cassaday, 1993; Winocur, 1992). On the other hand, such tasks, because of their conditional rule-learning learning component, are extremely sensitive to frontal lobe and striatal damage (Kolb, 1990; Petrides, 1994; Winocur, 1992; Winocur & Eskes, 1998). The present findings are significant in providing evidence that S100-␤ mice are impaired in behavioral processes that are controlled by nonhippocampal areas that are also affected by S100-␤ overexpression (Friend et al., 1992). The impaired performance of S100-␤ mice on the RAM test may also reflect involvement of nonhippocampal areas. Accurate performance on this task requires spatial and memoryrelated hippocampal functions and deficits observed in other populations, including aged rats (De Toledo-Morrell & Morrell, 1985), drug-treated rats (White, Simson, & Best, 1997), and rats fed high-fat diets (Greenwood & Winocur, 1990), have been interpreted in these terms. In fact, the RAM is a multidimensional task and deficits have also been observed in rats with encoding deficits resulting from thalamic lesions (Stokes & Best, 1988) and procedural learning problems following striatal lesions (Packard, Winocur, & White, 1992). A similar point can be made with respect to the food-preference task, where it has been shown that, under certain conditions, the frontal lobes, as well as the hippocampus, are involved in long-term retrieval of a learned preference (Winocur & Moscovitch, 1999). Taken together, the present findings, along with evidence of overexpression of S100-␤ in several brain regions, underscore the need for a fuller description of the functional impairments of S100-␤ transgenic mice. One strategy for determining

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the full extent of brain dysfunction in S100-␤ mice would be to assess these animals on tests that measure dissociable cognitive processes associated with different brain regions. Such tests are increasingly available for rats (Kesner, Bolland, & Dakis, 1993; McDonald & White, 1994; Winocur, 1990) and can be readily adapted for use with mice. Despite the generally poor performance of S100-␤ mice, they were capable of considerable learning. In both the SNMTS and NSNMTS tasks S100-␤ groups improved over the course of training under the 0-delay conditions. In the food-preference test, S100-␤ mice acquired preferences for sample foods as well as controls and retained them normally for up to 48 h. These results and the latter, in particular, point to the presence of residual cognitive abilities in S100-␤ mice and underscore the need for additional research to identify other examples of partially or fully spared function. In assessing the widespread impairments of S100-␤ mice, it is important to consider the possibility that noncognitive performance deficits contributed to their poor performance. In fact, several points argue against this interpretation. The ability of transgenic mice to normally acquire food preferences and the learning they displayed in the spatial and nonspatial NMTS tests indicate that they were motivated to perform the tasks. As well, in the latter tasks, the S100-␤ mice progressed normally through the shaping and training procedures and there was no indication of difficulty in mastering the sensorimotor requirements (see also Gerlai et al., 1995). On the other hand, the performance of the transgenic mice on the RAM raises some concern in this regard. On this task, the S100-␤ mice made substantially more errors than controls on the initial trials, raising the possibility of a generalized performance deficit. On the other hand, our extensive training procedure typically enables normal animals to readily acquire the win-shift strategy, resulting in differences with impaired groups early in testing (Winocur, 1982; Packard et al., 1992). Although it is impossible to rule out noncognitive factors, there was no indication that S100-␤ mice were hyperactive (as has been reported in female S100-␤ mice—Gerlai, Friend, Becker, O’Hanlon, Marks, & Roder, 1993) or exhibited other behavior differences that may have affected performance on the RAM. Rather, the differences appear related to the failures of transgenic mice in learning and remembering appropriate responses. In summary, the present results extend previous research in showing that S100-␤ transgenic mice are impaired on a broad range of spatial and nonspatial learning and memory tasks that require the hippocampus for successful performance. As such, they are consistent with anatomical and physiological evidence that the S100-␤ protein contributes to normal hippocampal function. The results also show that overexpression of the S100-␤ gene can affect performance on tasks that do not involve the hippocampus. The latter finding undoubtedly reflects the widespread presence of S100-␤ throughout the brain. S100-␤ is found in abnormally high levels in the brains of patients with Alzheimer’s Disease and Down Syndrome, two conditions associated with dementia and general mental retardation. Significantly, most of the learning and memory deficits observed in the present research have been reported in analogous form in such patients (Adelstein, Kesner, & Strassberg, 1992; Brugge et al., 1994; Dulaney, Raz, & Devine, 1996; Irle, Kessler, Markowitsch, & Hofmann, 1987; Nadel, 1996; Sahakian et al., 1988). Thus, the results take on added significance in that the dementia-like cognitive profile of S100-␤ mice may represent a promising model for studying comparable cognitive deficits in neurodegenerative diseases. Future studies that investigate the progression of cognitive changes in

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