Handling and environmental enrichment do notrescue learning and memory impairments inaCamKIIT286A mutant mice

A. C. Need and K. P. Giese*

Wolfson Institute for Biomedical Research, University College

London, Gower Street, London, UK

*Corresponding author: K. P. Giese, Wolfson Institute for Biome-

dical Research, University College London, Gower Street, Lon-

don, WC1E 6BT, UK. E-mail: p.giese@ucl.ac.uk

Environmental enrichment and postnatal handling have

been shown to improve learning and memory in the

Morris water maze, and to rescue impairments caused

by genetic modification, age or genetic background.

Mice with a targeted point mutation that prevents

autophosphorylation at threonine-286 of the a-isoformof the Ca2+/calmodulin-dependent kinase II have

impaired hippocampus-dependent and -independent

strategy learning and memory in the water maze. We

have investigated whether these impairments can be

rescued with a combination of postnatal handling and

environmental enrichment in a hybrid genetic back-

ground. Severe impairments were seen in acquisition

and probe trials in both enriched and nonenriched

mutants, indicating that enrichment did not rescue the

learning and memory impairments. However, enrich-

ment did rescue a specific performance deficit; enhanced

floating behaviour, in the mutants. In summary, we have

shown the lack of autophosphorylation of the a-isoformof the Ca2+/calmodulin-dependent kinase II prevents

enrichment-induced rescues of strategy learning and

memory impairments. Furthermore, we have estab-

lished that there are enrichment mechanisms that are

independent of this autophosphorylation.

Keywords: Calcium/ calmodulin-dependent kinase II, environ-

mental enrichment, hippocampus, learning and memory,

postnatal handling

Received 26 March 2003, revised 2 May 2003, accepted for

publication 2 May 2003

One of the most intensively investigated signalling mole-

cules in learning and memory (L & M) is the Ca2þ/calmodu-

lin-dependent kinase II (CaMKII). A key feature of CaMKII is

that it can undergo autophosphorylation so that its activity is

switched from Ca2þ-dependence to Ca2þ-independence

(Miller & Kennedy 1986). In the a-isoform this autophos-

phorylation occurs at threonine 286 (Fong et al. 1989;

Hanson et al. 1989; Miller et al. 1988; Ohsako et al. 1991;

Waxham et al. 1990). Computational models suggest that

the autophosphorylation of CaMKII could act as a memory

switch at synapses (Lisman et al. 2002). Consistent with

this idea, spatial learning increases the Ca2þ-independent

activity of CaMKII in the hippocampus (Tan & Liang 1996).

Furthermore, aCaMKIIT286A (T286A) mutant mice, with a

targeted point mutation that inactivates the aCaMKII auto-

phosphorylation, are impaired in learning in the hidden-

platform version of the Morris water maze (MWM) (Giese

et al. 1998), a hippocampus-dependent L & M task (Morris

et al. 1982).

L & M in the MWM task can be improved by rearing

the animals in an enriched environment (Duffy et al.

2001; Faverjon et al. 2002; Pham et al. 1999; Tees 1999;

Williams et al. 2001). Environmentally enriched animals

are housed in larger groups with more space and stimuli

than under standard laboratory conditions. Environmental

enrichment can rescue impairments in the MWM such as

the ectopia-induced deficits in the NZB mouse strain

(Schrott et al. 1992) and in female Ts65Dn mice, which

are partially trisomic for chromosome 16 (Martinez-Cue

et al. 2002).

Another treatment that can improve performance in hippo-

campus-dependent L & M tasks is postnatal handling (Tang

2001). During postnatal handling the pups are removed from

the nursing mother for a short period of time every day.

Postnatal handling rescues MWM deficits in BALB/c mice

(Zaharia et al. 1996) and in aged rats (Meaney et al. 1988;

Tremml et al. 2002).

Postnatal handling and environmental enrichment have a

variety of neurological effects including enhancement of

long-term potentiation and increases in synapse density in

the hippocampus (Fernandez-Teruel et al. 2002; van Praag

et al. 2000). However, the underlying molecular mechanisms

are not well understood. Here we have studied whether

enrichment can rescue the L & M deficits in the MWM of

the T286A mutants. These experiments address whether

aCaMKII autophosphorylation is essential for L & M in the

MWM or whether alternative enrichment-induced L & M

mechanisms exist.

Genes, Brain and Behavior (2003) 2: 132–139 Copyright # Blackwell Munksgaard 2003

ISSN 1601-1848

132

Materials and methods

Animals

The subjects were housed in a 12-h light-dark cycle with food

and water ad libitum. Homozygous aCamKIIT286A (T286A)

mutants and control wild-type (WT) littermates were

obtained in the 129B6F2,3 background by intercrosses of

heterozygous mutants. Genotyping was carried out with

PCR analysis, as described previously (Giese et al. 1998),

with DNA obtained from tail biopsies on postnatal day 21

(P21), the day of weaning. Heterozygous mice were

removed immediately after genotyping and all following pro-

cedures were carried out blind to genotype. When all mice

from a cage had completed the testing, they were culled and

regenotyped. Nonenriched mice were housed in groups of

2–4 in standard transparent mouse cages with sawdust and

bedding material changed weekly. All experiments were

undertaken in accordance with the UK Animals (Scientific

Procedures) Act 1986.

Postnatal handling

Handling took place from P1-P18 and was modified from

methods used by Meaney and colleagues (Meaney et al.

1988). Once daily the parents were removed from the cage

and the entire litter was removed. The parents were then

returned to the home cage. The litter was placed in a clean

cage in a separate room. The floor of the new cage was

covered with clean tissue and from P1-P10 a heat pad was

placed underneath the cage to prevent cooling of pups. After

20min the pups were returned to the home cage.

Enrichment

Litters were weaned at P21 into Plexiglass rat cages, in

single-sex groups, where they were housed for a minimum

of five weeks before testing. Litters of the same age were

combined where possible to provide maximum social enrich-

ment in group sizes of 5–15 (excluding heterozygotes, who

were removed after genotyping, at P23). The rat cages con-

tained an assortment of toys, exercise wheels, tubes,

‘houses’ and different bedding types (Fig. 1) Each group of

mice was moved to a new cage, with different contents and

bedding, on a daily basis.

Morris water maze

Mice were between the ages of two and four months when

tested, and equal numbers of males and females were used.

Before training, the animals were handled for two minutes

daily for five days, in order to reduce anxiety levels. Mice

were acclimatised to the dim light conditions for 10 minutes

before testing began. During the testing the mice remained

in their home cage, positioned in the water maze room in

such a way that the maze itself and all relevant cues were

not visible. The pool was 1.5 m in diameter, with a white

platform of 10 cm diameter positioned 0.5 cm below the sur-

face of the water. The water was maintained at 24–27 �C

throughout the trials, and made opaque with non-toxic white

paint so the platform was not visible. The animals received

12 training trials per day, in blocks of four, with one hour in

between each block. Each trial started from a pseudorandom

selection of four different starting positions. Each starting

position was in a different quadrant and each position was

used only once in a block. If the animal had not found the

platform within 90 seconds it was removed and placed back

onto the platform. The mouse was placed on the platform for

one minute before and after each trial. On days three and

five a probe trial was given, in which the platform was

removed and the animal was allowed to swim for 90 seconds

before being removed from the pool. The movement of the

animals whilst in the pool was video-taped and recorded by

a computer tracking system (HVS Image, Hampton, UK). This

water maze set-up has previously been shown to be

hippocampus-dependent (Angelo et al. in press). After

completion of hidden-platform training some enriched mice

(six T286A mutants and eight WT mice) were tested in the

visible platform version. The swimming pool was surrounded

by a white curtain to hide cues and the platform was marked

with a flag. Two 90 second trials were given with a one

minute intertrial interval.

Data analysis

Animals were excluded from the analysis if they never found

the platform position (n¼ 1, nonenriched mutant), or if they

floated in more than 75% of the trials for more than 20

seconds (n ¼ 1 nonenriched mutant, 1 enriched mutant), or

spent more than 75% of their search time in the thigmotaxis

zone in more than 85% of trials (n ¼ 2 enriched mutants).

The behavioural data were analysed with HVS water program

and Sigmastat (SYSTAT Software, SSPS Science Inc., Chicago,

IL). Additionally, to examine the effects of enrichment on WT

mice, the first three training blocks were analysed using

WINTRACK software (http://www.dpwolfer.ch/wintrack) (Wolfer

et al. 2001), and two-way ANOVAs with repeated measures.

Latency

The scores for each of four training trials were averaged to

form a mean score for each block. The maximum score for

each trial was 91 seconds, and was recorded if the mouse

did not find the platform. For the statistical analysis, three-

way between-within ANOVAS were conducted, with genotype

and enrichment as the between-subject effects, and training

as the within-subject effect. A two-way ANOVA was used to

analyse the first block of training.

Path length

The distance covered in 90 seconds at the average swim

speed of the slowest group (nonenriched T286A mutants)

was taken as the maximum path length for this data (18.5m).

This was recorded every time the path length was greater

than 18.5m, and every time the mouse failed to find the

Enrichment effects on aCamKIIT286A L & M impairments

Genes, Brain and Behavior (2003) 2: 132–139 133

platform in a trial. Statistical analysis was the same as that

for the latency.

Cumulative proximity and platform crossings

Proximity data were normally distributed and one-way ANOVAs

were performed. Platform crossings were not normally dis-

tributed, so the non-parametric Kruskal–Wallis one-way

ANOVA on ranks was used. To compare target quadrant data,

two way ANOVAs were used. Tukey post hoc analysis was

performed where significance was found.

Thigmotaxis and slow-swim

Thigmotaxis was defined by the HVS water software as

swimming in the outer 0.9% of the pool. The random level

of thigmotaxis was calculated to be 19%, as this outer 0.9%

comprised 19% of the total pool area. Slow swim time was

defined as the percent of time swimming at less than 5 cm/

second. Because the raw data were not normally distributed,

they were transformed into square routes which were nor-

mally distributed for parametric statistics. Two-way ANOVAs

were performed, with Tukey post hoc analyses.

Results

To investigate the impact of enrichment on the T286A

mutants, enriched mutants (n¼ 12), enriched WT mice

(n¼ 12), nonenriched mutants (n¼ 9) and nonenriched WT

mice (n¼ 9) were studied in the hidden-platform version of a

MWM task.

Acquisition in the MWM

Since the swim speeds differed between the groups (see

below), both latency and path length to reach the hidden

platform were analysed (Fig. 2).

For both latency and path length, there was a significant

training� genotype interaction (F1/38¼ 3.42, P<0.001 and F1/38

Figure 1: Protocol for the enrichment of mice. (a) Litters were handled from postnatal day (P) 1 to P18. At P21 they weregenotyped and weaned into an enriched environment. After the age of 8weeks they were handled for one week and then testedin the hidden-platform version of the Morris water maze. (b) Photograph of enriched cages.

Need and Giese

134 Genes, Brain and Behavior (2003) 2: 132–139

¼ 3.58, P <0.001, respectively), since the WT mice improved

across the training trials and the T286A mutants did not.

However, there was no training� enrichment interaction for

either latency or path length (F1/38¼ 0.73, P ¼ 0.66 and

F1/38¼ 0.88, P ¼ 0.53, respectively) indicating that enrichment

did not have an effect on learning.

Two-way ANOVA showed that for both latency and path

length there was no effect of genotype (F1/38¼ 2.85, P ¼

0.10 and F1/38¼ 2.70, P ¼ 0.11, respectively) or enrichment

(F1/38¼ 0.90, P ¼ 0.35 and F1/38¼ 0.33, P ¼ 0.57, respect-

ively) on performance in the first training block.

Effects of enrichment on acquisition in WT miceduring training day 1

Both enriched and nonenriched WT mice had reached

asymptote by the end of the first training day, showing no

further improvement in acquisition after block 3 (data not

shown). In order to determine if the enrichment had an

effect, the 12 training trials of day 1 were analyzed with WIN-

TRACK software and the results are summarized in Table 1.

The enriched WT mice needed less time to find the platform

(P< 0.05), had a lower average distance to the platform

(P< 0.05) and showed a lower cumulative search error

(P< 0.05). Thus, enrichment improved acquisition in WT

mice.

Visible platform version of the MWM

We tested enriched T286A mutants and WT mice in the

visible platform version of the MWM in order to determine

any possible motivational, visual or motor differences

between the genotypes. Consistent with previous findings

in nonenriched mice (Giese et al. 1998), the genotypes did

not differ in latency to find the platform (F1/24¼ 0.02, P ¼0.89, Fig. 2c). Neither was any difference seen in swim

speed (F1/24¼ 0.04, P ¼ 0.84), or path length (F1/24¼ 0.02,

P ¼ 0.88) (data not shown).

Spatial learning in the MWM

To assess spatial learning, probe trials were performed after

training days three and five. During probe trials the platform

was removed and the mice were allowed to swim for 90

seconds. Because analyses of days three and five probe trial

data revealed similar results, only day five probe trial data are

presented.

Cumulative proximity measures the distance of the mouse

from the centre of the four platform positions (Gallagher et al.

1993). Two-way ANOVA revealed an effect of genotype on the

proximity to the target quadrant (F1/38¼ 27.3, P <0.001), but

no effect of enrichment (F1/38¼ 0.03, P ¼ 0.86; Fig. 3a). One-

way ANOVA revealed that both enriched and nonenriched WT

mice searched selectively (F3/32¼ 35.0, P <0.001 and F3/44

¼ 64.2, P <0.001, respectively), and both showed lower

proximity to the target quadrant than to any other, indicating

that they had developed a spatial learning strategy. Consist-

ent with the impairment in acquisition, the T286A mutants

were also impaired in spatial learning, as one-way ANOVA

showed that neither the enriched nor the nonenriched

T286A mutants searched selectively (F3/52¼ 0.78, P ¼ 0.27

and F3/32¼ 1.72, P ¼ 0.18, respectively).

As a measure of search accuracy, platform crossings were

analysed. In agreement with the proximity data, two-way

ANOVA revealed an effect of genotype on the number of cross-

ings of the target platform (F1/38¼ 26.2, P <0.001), but no

Figure 2: Enrichment did not rescue the learning deficits in

the Morris water maze of the T286A mutants. Means(�SEM) of scores recorded over five days of training in a12 trial/day protocol of the hidden platform version of theMorris water maze. (a) Latency to find the platform. Thenonenriched mutants were impaired in comparison tocontrol littermates and did not improve with training.Importantly, the mutants were normal in the first trainingblock. Overall there was no significant effect of enrichmenton either the T286A mutant mice or on the WT mice. (b) Pathlength to find platform. The same results as for the latencymeasure were obtained. (c) Latency to find visible platform.No difference was observed between the enriched T286Amutants and the enrichedWTmice when tested in the visibleplatform version of the MWM.

Enrichment effects on aCamKIIT286A L & M impairments

Genes, Brain and Behavior (2003) 2: 132–139 135

effect of enrichment (F1/38¼ 0.51, P ¼ 0.48, Fig. 3b). One-

way ANOVA showed that both nonenriched and enriched WT

mice crossed selectively (H¼ 22.05, P <0.001 and H ¼23.46, P <0.001, respectively), with post hoc analysis show-

ing more crossings of the target platform than any other

(H¼ 22.046, P <0.05 for both). The nonenriched T286A

mutants showed selective crossing (H¼ 13.16, P <0.01),

and post hoc analysis showed that the number of target

platform crossings was significantly higher than the cross-

ings of the opposite (P< 0.05) and adjacent left (P< 0.05)

platform positions, but not different from those of the adja-

cent right platform position. The enriched T286A mutants did

not cross selectively (H¼ 3.93, P ¼ 0.27).

Thigmotaxis

Two-way ANOVA of thigmotaxis measurements showed an

effect of genotype (F1/38¼ 30.9, P <0.001), but no effect of

enrichment (F1/38¼ 0.145, P ¼ 0.71, Fig. 4a). Post hoc analy-

sis revealed that the T286A mutants showed significantly

more thigmotaxis than their WT littermates, regardless of

whether they had been reared in an enriched or standard

environment (P< 0.001 for both). Notably, the level of thig-

motaxis in the T286A mutants was not significantly different

from that calculated if the animals were swimming randomly

about the pool (one-way ANOVA enriched: F1/22¼ 2.525, P ¼0.126; nonenriched: F1/16¼ 3.955, P ¼ 0.064). In contrast

with the mutants, the WT mice spent significantly less time

in the thigmotaxis zone than that calculated for a random

swim (enriched: F1/20¼ 34.451, P <0.001; nonenriched: F1/16

¼ 14.825, P ¼ 0.001).

Swim speed

Two-way ANOVA on average swim speed during the probe

trial demonstrated that there was a significant effect of

environment (F1/38¼ 4.96, P <0.05), but not genotype

(F1/38¼ 3.89, P ¼ 0.06). Post hoc analyses showed

that nonenriched T286A mutants swam significantly

more slowly than enriched T286A mutants (nonenriched

Table 1: Assessment of enrichment effects on WT mice during the first training day

Task WT nonenriched

(n¼ 9)

WT enriched

(n¼ 12)

ANOVA F-value ANOVA P-value

mean�SEM mean�SEM environment training interaction environment training interaction

Latency (s) 50.9�4.70 34.1�3.92 5.06 28.62 0.36 < 0.05 < 0.001 0.7

Average distance to target 0.6�0.02 0.5�0.02 4.65 23.74 0.43 < 0.05 < 0.001 0.65

Cumulative search error 33.1�3.82 20.4�2.95 4.89 37.9 0.37 < 0.05 < 0.001 0.69

Path length (m) 13.1�1.41 9.3�1.13 2.82 35.67 0.02 0.11 < 0.001 0.98

Failure index (% of trials) 37.8�6.19 18.1�4.74 3.94 7.72 0.75 0.06 < 0.05 0.48

% time in wall zone* 23.7�5.70 33.3�3.40 3.58 32.49 1.33 0.07 < 0.001 0.28

Time target quad 34.5�2.06 40.6�2.27 2.95 6.31 0.03 0.1 < 0.005 0.97

% path parallel to wall 30.7�1.60 28.4�1.48 0.53 2.93 1.19 0.45 0.07 0.32

*Data was transformed to square routes before analysis to obtain normal distribution

Figure3: Enrichment did not rescue the spatial learning

deficits in the T286A mutants. Means (�SEM) of scoresrecorded in a probe trial after training day 5 in the Morriswater maze. *, P<0.05; ***, P<0.001. (a) Using thecumulative proximity measure enriched and nonenrichedT286A mutants searched randomly in the four quadrants[target quadrant (TQ), adjacent left (AL), adjacent right (AR)and opposite (OP)], whereas both enriched and nonenrichedWT mice searched selectively in TQ. Furthermore, for bothenriched and nonenriched groups the cumulative proximity inTQ was significantly lower for WT vs. T286A mutant mice.(b) The number of times the mice crossed the platformposition in the TQ, as compared to equivalent positions in theother three quadrants. Both enriched and nonenriched WTmice selectively crossed the missing platform position in TQ.The enriched T286A mutants did not selectively cross anyplatform position, whereas the nonenriched T286A mutantsshowed some selectivity. For both enriched and nonenrichedgroups the number of platform crossings in TQ wassignificantly higher for WT vs. T286A mutant mice.

Need and Giese

136 Genes, Brain and Behavior (2003) 2: 132–139

T286A mutants ¼ 0.20� 0.02m/second; enriched T286A

mutants ¼ 0.24� 0.01m/second; P <0.05).

We then investigated the slow swim measure, the percent

of time spent swimming below 5 cm/second, which

accounted for floating behaviour. Two-way ANOVA found a

significant effect of both genotype (F1/38¼ 19.6, P <0.001)

and environment (F1/38¼ 5.427, P <0.05). There was also a

significant interaction (genotype� enrichment, F1/38¼ 6.00,

P <0.05), since the nonenriched T286A mutants had an

increased slow swim level that was rescued by enrichment

(P< 0.01; Fig. 4b).

Analysis of swim speed during the first training block also

revealed the difference in swim speed and the effect of

enrichment on the T286A mutants (data not shown).

Discussion

Here we have investigated whether enrichment can rescue

the L & M deficits in the MWM of T286A mutants. We

tested two groups of mice, each consisting of T286A

mutants and their WT littermates. The control group was

reared under standard laboratory conditions with no postnatal

handling, whereas the second group underwent intense

enrichment with a combination of postnatal handling and

environmental enrichment.

We confirmed the previous finding (Giese et al. 1998) that

the loss of aCaMKII autophosphorylation leads to L & M

impairments in the MWM, with the L & M deficits apparent

in both acquisition and probe trials. The random searching in

the probe trials indicated that the loss of aCaMKII auto-

phosphorylation impaired hippocampus-dependent spatial

L & M. Although the MWM is generally considered to be

a hippocampus-dependent L & M task, it also contains

hippocampus-independent forms of L & M. Mice with hippo-

campal lesions show an improvement across training trials

as they use alternative strategies to locate the hidden plat-

form, such as egocentric navigation (Angelo et al. in press;

Gerlai et al. 2002). However, the T286A mutants show no

improvement across the training trials. This indicates that

the T286A mutants are impaired in both hippocampus-

dependent and -independent L & M in the MWM task.

Nonenriched (Giese et al. 1998) and enriched T286A mutants

did not differ in the visible platform version of the MWM,

indicating that they do not suffer from any motivational,

visual or motor difficulties that could affect performance in

this task.

Postnatal handling and environmental enrichment have

been shown to improve MWM performance in rodents

(Faverjon et al. 2002; Pham et al. 1999; Schrijver et al.

2002; Tang 2001; Tees 1999; Williams et al. 2001). In our

study both the enriched and the nonenriched WT mice have

reached asymptote by the end of the first training day (trial

12). If the first 12 training trials are analysed independently, it

can be seen that the enrichment in WT mice reduced the

latency to find the hidden platform, shortened the average

distance to platform, and reduced the cumulative error rate.

However, enrichment had no effect on acquisition when all

trials were analysed, nor in the probe trials. It is possible that

with the intense training protocol used in this study (12 trials

per day), in the superior-learning hybrid genetic background

(Owen et al. 1997) the level of WT performance cannot be

much improved after the first training day. Consistent with

this idea, other studies in a superior-learning mouse genetic

Figure 4: T286A mutants had non-spatial learning deficits

which were partially rescued by enrichment. Means(�SEM). **, P<0.01. (a) Percentage of time spent inthigmotaxis area. The dotted line represents the calculatedlevel of thigmotaxis if mice swim randomly in the pool. TheT286A mutants showed significantly more thigmotaxis thanWT mice, regardless of whether they had been reared in anenriched or standard environment. Enrichment had no effecton the level of thigmotaxis in either T286A mutant or WTmice. The level of thigmotaxis in the T286A mutants is notsignificantly different than the calculated random value,where WT mice had a significantly lower value. (b) Thepercent time spent swimming at a speed less than 5 cm/second (slow swim speed measure) differed betweennonenriched T286A mutants and nonenriched WT mice.However, this was not the case for the enriched mice.

Enrichment effects on aCamKIIT286A L & M impairments

Genes, Brain and Behavior (2003) 2: 132–139 137

background did not reveal L & M improvements in the MWM

with postnatal handling (Zaharia et al. 1996) or environmental

enrichment (Prusky et al. 2000; Williams et al. 2001).

The T286A mutants remained impaired in acquisition and

probe trial performance after enrichment. Thus, the enrich-

ment rescued neither the hippocampus-dependent nor -

independent L & M impairments in the T286A mutants.

However, enrichment-induced rescues of L & M impair-

ments have been described for other mutant mice (Martinez-

Cue et al. 2002; Rampon et al. 2000; Tang et al. 2001).

For example, Wolfer and colleagues found that MWM

impairments in both acquisition and probe trials in mice

with a hypomorphic mutation of the b-APP gene were res-

cued by postnatal handling (Tremml et al. 2002). Importantly,

our findings cannot be explained by deficiencies in the

enrichment protocol, because an effect of enrichment was

observed (see below).

The T286A mutants are specifically impaired in strategy L

& M, because they were able to use the platform as an

escape but they could not use a strategy to locate the plat-

form. Our finding that enrichment could not rescue the

impairments in strategy L & M suggests that aCaMKII

autophosphorylation may be essential for strategy L & M in

the MWM. Alternatively, aCaMKII autophosphorylation may

be required for enrichment-induced mechanisms facilitating

L & M.

Consistent with an impairment in locating the platform, the

T286A mutants had a higher level of thigmotaxis than the WT

mice. However, the amount of thigmotaxis did not differ

from the calculated amount of time that would be spent in

the thigmotaxis zone if the mouse was swimming randomly.

The high levels of thigmotaxis in the T286A mutants may

be a result of the L & M impairments, as the mutants

cannot learn a search strategy so they continue to swim

randomly.

We found that the nonenriched T286A mutants are not

only impaired in strategy L & M, but also have a specific

performance deficit. They had a reduced swimming speed,

resulting mostly from floating behaviour, which is accounted

for in the slow swim speed measure. In the original study

(Giese et al. 1998), the T286A mutants had a normal swim

speed and this may be attributed to differences in genetic

background between the mouse strains used in the two

studies. Although both studies used mice in the 129B6

hybrid background, the 129 substrain in our study was

129S2/SvHsd, and that used in the original study was

F1(129/Sv� 129/Sv-CP). The 129 substrains can vary signifi-

cantly in their genetic background (Simpson et al. 1997;

Threadgill et al. 1997) and this can translate into behavioural

differences among the substrains (Cook et al. 2002; Rodgers

et al. 2002).

The causes underlying floating behaviour are not under-

stood but interestingly this performance deficit was rescued

by enrichment. Thus, there are enrichment mechanisms that

do not require aCaMKII autophosphorylation.

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Acknowledgments

We wish to thank Keiko Mizuno, Katalin Bartus and Laura von

Hertzen for assistance with genotyping and Elaine Irvine for

instruction on the Morris water maze. We are grateful to Elaine

Irvine and John O’Keefe for reading the manuscript. This work

was supported by a Medical Research Council studentship and a

Neurone grant from the Biotechnology and Biological Sciences

Research Council.

Enrichment effects on aCamKIIT286A L & M impairments

Genes, Brain and Behavior (2003) 2: 132–139 139