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Involvement of cAMP-guanine nucleotide exchange factor II in hippocampal long-term depression and behavioral flexibility.

Lee K, Kobayashi Y, Seo H, Kwak JH, Masuda A, Lim CS, Lee HR, Kang SJ, Park P, Sim SE, Kogo N, Kawasaki H, Kaang BK, Itohara S - Mol Brain (2015)

Bottom Line: Although cAMP-GEF II is expressed abundantly in several brain areas including the cortex, striatum, and hippocampus, its specific function and possible role in hippocampal synaptic plasticity and cognitive processes remain elusive.We found that deletion of cAMP-GEF II induced moderate decrease in long-term potentiation, although this decrease was not statistically significant.We concluded that cAMP-GEF II plays a key role in hippocampal functions including behavioral flexibility in reversal learning and in mechanisms underlying induction of long-term depression.

View Article: PubMed Central - PubMed

Affiliation: Behavioral Neural Circuitry and Physiology Laboratory, Department of Anatomy, Brain Science & Engineering Institute, Kyungpook National University Graduate School of Medicine, 2-101, Dongin-dong, Jung-gu, Daegu, 700-842, Korea. irislkm@knu.ac.kr.

ABSTRACT

Background: Guanine nucleotide exchange factors (GEFs) activate small GTPases that are involved in several cellular functions. cAMP-guanine nucleotide exchange factor II (cAMP-GEF II) acts as a target for cAMP independently of protein kinase A (PKA) and functions as a GEF for Rap1 and Rap2. Although cAMP-GEF II is expressed abundantly in several brain areas including the cortex, striatum, and hippocampus, its specific function and possible role in hippocampal synaptic plasticity and cognitive processes remain elusive. Here, we investigated how cAMP-GEF II affects synaptic function and animal behavior using cAMP-GEF II knockout mice.

Results: We found that deletion of cAMP-GEF II induced moderate decrease in long-term potentiation, although this decrease was not statistically significant. On the other hand, it produced a significant and clear impairment in NMDA receptor-dependent long-term depression at the Schaffer collateral-CA1 synapses of hippocampus, while microscopic morphology, basal synaptic transmission, and depotentiation were normal. Behavioral testing using the Morris water maze and automated IntelliCage system showed that cAMP-GEF II deficient mice had moderately reduced behavioral flexibility in spatial learning and memory.

Conclusions: We concluded that cAMP-GEF II plays a key role in hippocampal functions including behavioral flexibility in reversal learning and in mechanisms underlying induction of long-term depression.

No MeSH data available.


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cAMP-GEF II−/− mice showed impaired reversal learning in the place preference learning task. a, Novel location recognition test. Left panel, experimental design. Right panel, no difference between genotypes in the discrimination index, which indicates that spatial memory is normal in cAMP-GEF II−/− mice (6-month-old male mice; wild-type (WT) = 10 mice; cAMP-GEF II−/− (KO) = 12 mice; unpaired t-test, p = 0.63). The discrimination index was calculated as follows: discrimination index = (contact duration for object B)/(total contact duration for objects). b, There were no differences in escape latency between genotypes in the Morris water maze test during training days from day 1 to 13 (6-month-old male mice; 12 mice per genotype; Two-way RM ANOVA, F(1, 22) = 0.20, p = 0.66 for genotype; F(13,286) = 11.28, p < 0.00001 for day; F(13,286) = 0.60, p = 0.85 for genotype and day interaction). c, Stay time (WT = 34.54 ± 2.85 s; KO = 32.25 ± 2.69 s) in the initial target quadrant during a probe trial on day 14 showed that cAMP-GEF II−/− mice have similar spatial memory to wild-type mice (Two-way ANOVA; F(1, 66) = 0.94, p = 0.33 for genotype; F(2,66) = 17.76, p < 0.00001 for quadrant; F(2,66) = 0.41, p = 0.66 for genotype and quadrant interaction). d, Wild-type and cAMP-GEF II−/− mice crossed more frequently the platform position in the target quadrant where the platform was located than pseudo-positions in other quadrants (Two-way ANOVA; F(2,90) = 19.71, p < 0.00001 for position; F(1,90) = 0.25, p = 0.62 for genotype; F(2,90) = 1.28, p = 0.28 for genotype and position interaction; post-hoc Bonferroni test p = 0.001 between positions in WT and p = 0.004 between positions in KO) during a probe trial after initial learning. e, Escape latency to the new platform during reversal training was not different between genotypes (two-way RM ANOVA; F(1, 22) = 0.27, p = 0.61 for genotype; F(4,88) = 14.92, p < 0.00001 for day; F(4,88) = 0.95, p = 0.44 for genotype and day interaction). f, Stay time in the new target quadrant during a reversal probe trial on day 19. Wild-type and cAMP-GEF II−/− mice showed significant preference for the new target quadrant compared to opposite or adjacent quadrants, resulting in no difference between genotypes (Two-way ANOVA; F(1, 90) = 0.1, p = 0.75 for genotype; F(2,90) = 21.84, p < 0.00001 for quadrant; F(2,90) = 1.27, p = 0.29 for genotype and quadrant interaction). g,cAMP-GEF II−/− mice crossed less frequently the platform position in the new target quadrant during the reversal probe trial (Two-way ANOVA; F(1,92) = 5.48, p = 0.021 for position; F(1,92) = 1.5, p = 0.22 for genotype; F(1,92) = 1.24, p = 0.27 for genotype and position interaction; post-hoc Bonferroni test p = 0.015 between positions in WT and p = 0.39 between positions in KO). h, Experimental scheme for place preference and reversal learning test in IntelliCage. Performance was quantified as the percentage of correct corner visits (4-month-old female mice; 12 mice per genotype). i, There was no difference in spatial memory between the two genotypes in the place preference learning test (Two-way RM ANOVA; F(1, 22) = 2.35, p = 0.14 for genotype; F(2,44) = 71.2, p < 0.00001 for day; F(2,44) = 0.55, p = 0.58 for genotype and day interaction). j, The percentage of correct corner visits in the reversal learning test was significantly reduced in cAMP-GEF II−/− mice, indicating a deficit in behavioral flexibility (Two-way RM ANOVA; F(1, 22) = 6.03, p = 0.022 for genotype; F(2,44) = 64.0, p < 0.0001 for day; F(2,44) = 0.84, p = 0.43 for genotype and day interaction; post-hoc unpaired t-test, day 8 ( p = 0.0298), day 11 (p = 0.1376), day 14 (p = 0.0306). k and l, Learning speeds in the first days of the place preference (k, day 1) and reversal learning (l, day 8) tests. The slope of the learning curve in each mouse was determined by the least squares analysis. Black dashed lines indicate the chance level. Thin and thick blue lines represent wild-type mice and average, respectively. Thin and thick red lines represent cAMP-GEF II−/− mice and average, respectively. The slope was significantly decreased in cAMP-GEF II−/− mice in both place preference (PP) and place preference reversal (PPR) tests (for PP: WT, slope = 0.57 ± 0.03; cAMP-GEF II−/−, slope = 0.49 ± 0.022; Unpaired t-test, p = 0.048; for PPR, WT, slope = 0.64 ± 0.036; KO, slope = 0.53 ± 0.024; Unpaired t-test, p = 0.026). All data are shown as mean ± SEM
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Fig5: cAMP-GEF II−/− mice showed impaired reversal learning in the place preference learning task. a, Novel location recognition test. Left panel, experimental design. Right panel, no difference between genotypes in the discrimination index, which indicates that spatial memory is normal in cAMP-GEF II−/− mice (6-month-old male mice; wild-type (WT) = 10 mice; cAMP-GEF II−/− (KO) = 12 mice; unpaired t-test, p = 0.63). The discrimination index was calculated as follows: discrimination index = (contact duration for object B)/(total contact duration for objects). b, There were no differences in escape latency between genotypes in the Morris water maze test during training days from day 1 to 13 (6-month-old male mice; 12 mice per genotype; Two-way RM ANOVA, F(1, 22) = 0.20, p = 0.66 for genotype; F(13,286) = 11.28, p < 0.00001 for day; F(13,286) = 0.60, p = 0.85 for genotype and day interaction). c, Stay time (WT = 34.54 ± 2.85 s; KO = 32.25 ± 2.69 s) in the initial target quadrant during a probe trial on day 14 showed that cAMP-GEF II−/− mice have similar spatial memory to wild-type mice (Two-way ANOVA; F(1, 66) = 0.94, p = 0.33 for genotype; F(2,66) = 17.76, p < 0.00001 for quadrant; F(2,66) = 0.41, p = 0.66 for genotype and quadrant interaction). d, Wild-type and cAMP-GEF II−/− mice crossed more frequently the platform position in the target quadrant where the platform was located than pseudo-positions in other quadrants (Two-way ANOVA; F(2,90) = 19.71, p < 0.00001 for position; F(1,90) = 0.25, p = 0.62 for genotype; F(2,90) = 1.28, p = 0.28 for genotype and position interaction; post-hoc Bonferroni test p = 0.001 between positions in WT and p = 0.004 between positions in KO) during a probe trial after initial learning. e, Escape latency to the new platform during reversal training was not different between genotypes (two-way RM ANOVA; F(1, 22) = 0.27, p = 0.61 for genotype; F(4,88) = 14.92, p < 0.00001 for day; F(4,88) = 0.95, p = 0.44 for genotype and day interaction). f, Stay time in the new target quadrant during a reversal probe trial on day 19. Wild-type and cAMP-GEF II−/− mice showed significant preference for the new target quadrant compared to opposite or adjacent quadrants, resulting in no difference between genotypes (Two-way ANOVA; F(1, 90) = 0.1, p = 0.75 for genotype; F(2,90) = 21.84, p < 0.00001 for quadrant; F(2,90) = 1.27, p = 0.29 for genotype and quadrant interaction). g,cAMP-GEF II−/− mice crossed less frequently the platform position in the new target quadrant during the reversal probe trial (Two-way ANOVA; F(1,92) = 5.48, p = 0.021 for position; F(1,92) = 1.5, p = 0.22 for genotype; F(1,92) = 1.24, p = 0.27 for genotype and position interaction; post-hoc Bonferroni test p = 0.015 between positions in WT and p = 0.39 between positions in KO). h, Experimental scheme for place preference and reversal learning test in IntelliCage. Performance was quantified as the percentage of correct corner visits (4-month-old female mice; 12 mice per genotype). i, There was no difference in spatial memory between the two genotypes in the place preference learning test (Two-way RM ANOVA; F(1, 22) = 2.35, p = 0.14 for genotype; F(2,44) = 71.2, p < 0.00001 for day; F(2,44) = 0.55, p = 0.58 for genotype and day interaction). j, The percentage of correct corner visits in the reversal learning test was significantly reduced in cAMP-GEF II−/− mice, indicating a deficit in behavioral flexibility (Two-way RM ANOVA; F(1, 22) = 6.03, p = 0.022 for genotype; F(2,44) = 64.0, p < 0.0001 for day; F(2,44) = 0.84, p = 0.43 for genotype and day interaction; post-hoc unpaired t-test, day 8 ( p = 0.0298), day 11 (p = 0.1376), day 14 (p = 0.0306). k and l, Learning speeds in the first days of the place preference (k, day 1) and reversal learning (l, day 8) tests. The slope of the learning curve in each mouse was determined by the least squares analysis. Black dashed lines indicate the chance level. Thin and thick blue lines represent wild-type mice and average, respectively. Thin and thick red lines represent cAMP-GEF II−/− mice and average, respectively. The slope was significantly decreased in cAMP-GEF II−/− mice in both place preference (PP) and place preference reversal (PPR) tests (for PP: WT, slope = 0.57 ± 0.03; cAMP-GEF II−/−, slope = 0.49 ± 0.022; Unpaired t-test, p = 0.048; for PPR, WT, slope = 0.64 ± 0.036; KO, slope = 0.53 ± 0.024; Unpaired t-test, p = 0.026). All data are shown as mean ± SEM

Mentions: We examined whether deficits of hippocampal synaptic plasticity in the cAMP-GEF II−/− mice are accompanied by alterations of hippocampal-dependent cognitive functions. Unfortunately, we could not use a contextual fear conditioning test because cAMP-GEF II−/− mice were less sensitive to foot shock stimuli compared to wild-type mice (Fig. 4). Therefore, we used the novel location recognition test, Morris water maze task, and IntelliCage test [13, 14]. In the novel location recognition test, which is a simple assay for hippocampal-dependent spatial memory [15], we found that both genotypes of mice equally exhibited a preference for novel location of an identical object, which resulted in a similar discrimination index (Fig. 5a). In the Morris water maze task we also found that there was no difference in performance during training from day 1 to day 14 (Fig. 5b), or in a probe trial on day 14 (Fig. 5c, d) between wild-type and cAMP-GEF II−/− mice, which indicates normal spatial learning and memory in cAMP-GEF II−/− mice. We then tested reversal learning by changing the position of the hidden platform to the opposite of the initial quadrant in the pool, and found that both wild-type and cAMP-GEF II−/− mice equally learned the new target position (Fig. 5e). Additionally, both genotypes of mice did not show any significant differences in the preference for the new target quadrant during the probe trial of reversal learning on day 19 (Fig. 5f). To evaluate the accuracy of spatial memory, we analyzed the crossing numbers of the platform position in both of the probe tests. We found no differences between genotypes in the first probe test after initial learning. However, cAMP-GEF II−/− mice tended to cross the target platform position less frequently than wild-type mice in the second probe test after reversal learning (Fig. 5g), suggesting a low accuracy of reversal memory in cAMP-GEF II−/− mice. As mentioned above, since cAMP-GEF II−/− mice showed less sensitivity to painful or aversive stimuli such as foot shock compared to wild-type mice, we wanted to confirm hippocampal cognitive functions using preference behavior rather than avoidance behavior in cAMP-GEF II−/− mice. In contrast to the Morris water maze task, which is based on the avoidance behavior of mice escaping from water, the automated IntelliCage apparatus enabled us to measure spatial memory and reversal learning using preference behavior to reward, without the intervention of experimenters. Therefore, we performed the place preference learning test using the IntelliCage system for 7 days for spatial memory, and for the next 7 days for reversal learning (Fig. 5h). We found that initial spatial memory was normal (Fig. 5i), while reversal learning was significantly impaired (Fig. 5j) in cAMP-GEF II−/− mice. We also measured the learning speeds of each mouse in the first days of the place preference and reversal learning tests. We found significant differences in the learning speeds between genotypes in both tests (Fig. 5k, l for place preference and reversal learning test, respectively). The difference was, however, more significant in the reversal learning test. These results indicate that cAMP-GEF II−/− mice showed slower learning than WT especially in the case of the reversal learning. Taken together, these findings from the Morris water maze and IntelliCage tests suggest that deletion of cAMP-GEF II may affect spatial learning and memory acquisition, and it may contribute to impairment of hippocampal-dependent reversal learning with a reduction in behavioral flexibility. These results are consistent with previous reports showing that hippocampal LTD is related to memory processes [16] and behavioral flexibility in spatial learning [17, 18].Fig. 4


Involvement of cAMP-guanine nucleotide exchange factor II in hippocampal long-term depression and behavioral flexibility.

Lee K, Kobayashi Y, Seo H, Kwak JH, Masuda A, Lim CS, Lee HR, Kang SJ, Park P, Sim SE, Kogo N, Kawasaki H, Kaang BK, Itohara S - Mol Brain (2015)

cAMP-GEF II−/− mice showed impaired reversal learning in the place preference learning task. a, Novel location recognition test. Left panel, experimental design. Right panel, no difference between genotypes in the discrimination index, which indicates that spatial memory is normal in cAMP-GEF II−/− mice (6-month-old male mice; wild-type (WT) = 10 mice; cAMP-GEF II−/− (KO) = 12 mice; unpaired t-test, p = 0.63). The discrimination index was calculated as follows: discrimination index = (contact duration for object B)/(total contact duration for objects). b, There were no differences in escape latency between genotypes in the Morris water maze test during training days from day 1 to 13 (6-month-old male mice; 12 mice per genotype; Two-way RM ANOVA, F(1, 22) = 0.20, p = 0.66 for genotype; F(13,286) = 11.28, p < 0.00001 for day; F(13,286) = 0.60, p = 0.85 for genotype and day interaction). c, Stay time (WT = 34.54 ± 2.85 s; KO = 32.25 ± 2.69 s) in the initial target quadrant during a probe trial on day 14 showed that cAMP-GEF II−/− mice have similar spatial memory to wild-type mice (Two-way ANOVA; F(1, 66) = 0.94, p = 0.33 for genotype; F(2,66) = 17.76, p < 0.00001 for quadrant; F(2,66) = 0.41, p = 0.66 for genotype and quadrant interaction). d, Wild-type and cAMP-GEF II−/− mice crossed more frequently the platform position in the target quadrant where the platform was located than pseudo-positions in other quadrants (Two-way ANOVA; F(2,90) = 19.71, p < 0.00001 for position; F(1,90) = 0.25, p = 0.62 for genotype; F(2,90) = 1.28, p = 0.28 for genotype and position interaction; post-hoc Bonferroni test p = 0.001 between positions in WT and p = 0.004 between positions in KO) during a probe trial after initial learning. e, Escape latency to the new platform during reversal training was not different between genotypes (two-way RM ANOVA; F(1, 22) = 0.27, p = 0.61 for genotype; F(4,88) = 14.92, p < 0.00001 for day; F(4,88) = 0.95, p = 0.44 for genotype and day interaction). f, Stay time in the new target quadrant during a reversal probe trial on day 19. Wild-type and cAMP-GEF II−/− mice showed significant preference for the new target quadrant compared to opposite or adjacent quadrants, resulting in no difference between genotypes (Two-way ANOVA; F(1, 90) = 0.1, p = 0.75 for genotype; F(2,90) = 21.84, p < 0.00001 for quadrant; F(2,90) = 1.27, p = 0.29 for genotype and quadrant interaction). g,cAMP-GEF II−/− mice crossed less frequently the platform position in the new target quadrant during the reversal probe trial (Two-way ANOVA; F(1,92) = 5.48, p = 0.021 for position; F(1,92) = 1.5, p = 0.22 for genotype; F(1,92) = 1.24, p = 0.27 for genotype and position interaction; post-hoc Bonferroni test p = 0.015 between positions in WT and p = 0.39 between positions in KO). h, Experimental scheme for place preference and reversal learning test in IntelliCage. Performance was quantified as the percentage of correct corner visits (4-month-old female mice; 12 mice per genotype). i, There was no difference in spatial memory between the two genotypes in the place preference learning test (Two-way RM ANOVA; F(1, 22) = 2.35, p = 0.14 for genotype; F(2,44) = 71.2, p < 0.00001 for day; F(2,44) = 0.55, p = 0.58 for genotype and day interaction). j, The percentage of correct corner visits in the reversal learning test was significantly reduced in cAMP-GEF II−/− mice, indicating a deficit in behavioral flexibility (Two-way RM ANOVA; F(1, 22) = 6.03, p = 0.022 for genotype; F(2,44) = 64.0, p < 0.0001 for day; F(2,44) = 0.84, p = 0.43 for genotype and day interaction; post-hoc unpaired t-test, day 8 ( p = 0.0298), day 11 (p = 0.1376), day 14 (p = 0.0306). k and l, Learning speeds in the first days of the place preference (k, day 1) and reversal learning (l, day 8) tests. The slope of the learning curve in each mouse was determined by the least squares analysis. Black dashed lines indicate the chance level. Thin and thick blue lines represent wild-type mice and average, respectively. Thin and thick red lines represent cAMP-GEF II−/− mice and average, respectively. The slope was significantly decreased in cAMP-GEF II−/− mice in both place preference (PP) and place preference reversal (PPR) tests (for PP: WT, slope = 0.57 ± 0.03; cAMP-GEF II−/−, slope = 0.49 ± 0.022; Unpaired t-test, p = 0.048; for PPR, WT, slope = 0.64 ± 0.036; KO, slope = 0.53 ± 0.024; Unpaired t-test, p = 0.026). All data are shown as mean ± SEM
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Fig5: cAMP-GEF II−/− mice showed impaired reversal learning in the place preference learning task. a, Novel location recognition test. Left panel, experimental design. Right panel, no difference between genotypes in the discrimination index, which indicates that spatial memory is normal in cAMP-GEF II−/− mice (6-month-old male mice; wild-type (WT) = 10 mice; cAMP-GEF II−/− (KO) = 12 mice; unpaired t-test, p = 0.63). The discrimination index was calculated as follows: discrimination index = (contact duration for object B)/(total contact duration for objects). b, There were no differences in escape latency between genotypes in the Morris water maze test during training days from day 1 to 13 (6-month-old male mice; 12 mice per genotype; Two-way RM ANOVA, F(1, 22) = 0.20, p = 0.66 for genotype; F(13,286) = 11.28, p < 0.00001 for day; F(13,286) = 0.60, p = 0.85 for genotype and day interaction). c, Stay time (WT = 34.54 ± 2.85 s; KO = 32.25 ± 2.69 s) in the initial target quadrant during a probe trial on day 14 showed that cAMP-GEF II−/− mice have similar spatial memory to wild-type mice (Two-way ANOVA; F(1, 66) = 0.94, p = 0.33 for genotype; F(2,66) = 17.76, p < 0.00001 for quadrant; F(2,66) = 0.41, p = 0.66 for genotype and quadrant interaction). d, Wild-type and cAMP-GEF II−/− mice crossed more frequently the platform position in the target quadrant where the platform was located than pseudo-positions in other quadrants (Two-way ANOVA; F(2,90) = 19.71, p < 0.00001 for position; F(1,90) = 0.25, p = 0.62 for genotype; F(2,90) = 1.28, p = 0.28 for genotype and position interaction; post-hoc Bonferroni test p = 0.001 between positions in WT and p = 0.004 between positions in KO) during a probe trial after initial learning. e, Escape latency to the new platform during reversal training was not different between genotypes (two-way RM ANOVA; F(1, 22) = 0.27, p = 0.61 for genotype; F(4,88) = 14.92, p < 0.00001 for day; F(4,88) = 0.95, p = 0.44 for genotype and day interaction). f, Stay time in the new target quadrant during a reversal probe trial on day 19. Wild-type and cAMP-GEF II−/− mice showed significant preference for the new target quadrant compared to opposite or adjacent quadrants, resulting in no difference between genotypes (Two-way ANOVA; F(1, 90) = 0.1, p = 0.75 for genotype; F(2,90) = 21.84, p < 0.00001 for quadrant; F(2,90) = 1.27, p = 0.29 for genotype and quadrant interaction). g,cAMP-GEF II−/− mice crossed less frequently the platform position in the new target quadrant during the reversal probe trial (Two-way ANOVA; F(1,92) = 5.48, p = 0.021 for position; F(1,92) = 1.5, p = 0.22 for genotype; F(1,92) = 1.24, p = 0.27 for genotype and position interaction; post-hoc Bonferroni test p = 0.015 between positions in WT and p = 0.39 between positions in KO). h, Experimental scheme for place preference and reversal learning test in IntelliCage. Performance was quantified as the percentage of correct corner visits (4-month-old female mice; 12 mice per genotype). i, There was no difference in spatial memory between the two genotypes in the place preference learning test (Two-way RM ANOVA; F(1, 22) = 2.35, p = 0.14 for genotype; F(2,44) = 71.2, p < 0.00001 for day; F(2,44) = 0.55, p = 0.58 for genotype and day interaction). j, The percentage of correct corner visits in the reversal learning test was significantly reduced in cAMP-GEF II−/− mice, indicating a deficit in behavioral flexibility (Two-way RM ANOVA; F(1, 22) = 6.03, p = 0.022 for genotype; F(2,44) = 64.0, p < 0.0001 for day; F(2,44) = 0.84, p = 0.43 for genotype and day interaction; post-hoc unpaired t-test, day 8 ( p = 0.0298), day 11 (p = 0.1376), day 14 (p = 0.0306). k and l, Learning speeds in the first days of the place preference (k, day 1) and reversal learning (l, day 8) tests. The slope of the learning curve in each mouse was determined by the least squares analysis. Black dashed lines indicate the chance level. Thin and thick blue lines represent wild-type mice and average, respectively. Thin and thick red lines represent cAMP-GEF II−/− mice and average, respectively. The slope was significantly decreased in cAMP-GEF II−/− mice in both place preference (PP) and place preference reversal (PPR) tests (for PP: WT, slope = 0.57 ± 0.03; cAMP-GEF II−/−, slope = 0.49 ± 0.022; Unpaired t-test, p = 0.048; for PPR, WT, slope = 0.64 ± 0.036; KO, slope = 0.53 ± 0.024; Unpaired t-test, p = 0.026). All data are shown as mean ± SEM
Mentions: We examined whether deficits of hippocampal synaptic plasticity in the cAMP-GEF II−/− mice are accompanied by alterations of hippocampal-dependent cognitive functions. Unfortunately, we could not use a contextual fear conditioning test because cAMP-GEF II−/− mice were less sensitive to foot shock stimuli compared to wild-type mice (Fig. 4). Therefore, we used the novel location recognition test, Morris water maze task, and IntelliCage test [13, 14]. In the novel location recognition test, which is a simple assay for hippocampal-dependent spatial memory [15], we found that both genotypes of mice equally exhibited a preference for novel location of an identical object, which resulted in a similar discrimination index (Fig. 5a). In the Morris water maze task we also found that there was no difference in performance during training from day 1 to day 14 (Fig. 5b), or in a probe trial on day 14 (Fig. 5c, d) between wild-type and cAMP-GEF II−/− mice, which indicates normal spatial learning and memory in cAMP-GEF II−/− mice. We then tested reversal learning by changing the position of the hidden platform to the opposite of the initial quadrant in the pool, and found that both wild-type and cAMP-GEF II−/− mice equally learned the new target position (Fig. 5e). Additionally, both genotypes of mice did not show any significant differences in the preference for the new target quadrant during the probe trial of reversal learning on day 19 (Fig. 5f). To evaluate the accuracy of spatial memory, we analyzed the crossing numbers of the platform position in both of the probe tests. We found no differences between genotypes in the first probe test after initial learning. However, cAMP-GEF II−/− mice tended to cross the target platform position less frequently than wild-type mice in the second probe test after reversal learning (Fig. 5g), suggesting a low accuracy of reversal memory in cAMP-GEF II−/− mice. As mentioned above, since cAMP-GEF II−/− mice showed less sensitivity to painful or aversive stimuli such as foot shock compared to wild-type mice, we wanted to confirm hippocampal cognitive functions using preference behavior rather than avoidance behavior in cAMP-GEF II−/− mice. In contrast to the Morris water maze task, which is based on the avoidance behavior of mice escaping from water, the automated IntelliCage apparatus enabled us to measure spatial memory and reversal learning using preference behavior to reward, without the intervention of experimenters. Therefore, we performed the place preference learning test using the IntelliCage system for 7 days for spatial memory, and for the next 7 days for reversal learning (Fig. 5h). We found that initial spatial memory was normal (Fig. 5i), while reversal learning was significantly impaired (Fig. 5j) in cAMP-GEF II−/− mice. We also measured the learning speeds of each mouse in the first days of the place preference and reversal learning tests. We found significant differences in the learning speeds between genotypes in both tests (Fig. 5k, l for place preference and reversal learning test, respectively). The difference was, however, more significant in the reversal learning test. These results indicate that cAMP-GEF II−/− mice showed slower learning than WT especially in the case of the reversal learning. Taken together, these findings from the Morris water maze and IntelliCage tests suggest that deletion of cAMP-GEF II may affect spatial learning and memory acquisition, and it may contribute to impairment of hippocampal-dependent reversal learning with a reduction in behavioral flexibility. These results are consistent with previous reports showing that hippocampal LTD is related to memory processes [16] and behavioral flexibility in spatial learning [17, 18].Fig. 4

Bottom Line: Although cAMP-GEF II is expressed abundantly in several brain areas including the cortex, striatum, and hippocampus, its specific function and possible role in hippocampal synaptic plasticity and cognitive processes remain elusive.We found that deletion of cAMP-GEF II induced moderate decrease in long-term potentiation, although this decrease was not statistically significant.We concluded that cAMP-GEF II plays a key role in hippocampal functions including behavioral flexibility in reversal learning and in mechanisms underlying induction of long-term depression.

View Article: PubMed Central - PubMed

Affiliation: Behavioral Neural Circuitry and Physiology Laboratory, Department of Anatomy, Brain Science & Engineering Institute, Kyungpook National University Graduate School of Medicine, 2-101, Dongin-dong, Jung-gu, Daegu, 700-842, Korea. irislkm@knu.ac.kr.

ABSTRACT

Background: Guanine nucleotide exchange factors (GEFs) activate small GTPases that are involved in several cellular functions. cAMP-guanine nucleotide exchange factor II (cAMP-GEF II) acts as a target for cAMP independently of protein kinase A (PKA) and functions as a GEF for Rap1 and Rap2. Although cAMP-GEF II is expressed abundantly in several brain areas including the cortex, striatum, and hippocampus, its specific function and possible role in hippocampal synaptic plasticity and cognitive processes remain elusive. Here, we investigated how cAMP-GEF II affects synaptic function and animal behavior using cAMP-GEF II knockout mice.

Results: We found that deletion of cAMP-GEF II induced moderate decrease in long-term potentiation, although this decrease was not statistically significant. On the other hand, it produced a significant and clear impairment in NMDA receptor-dependent long-term depression at the Schaffer collateral-CA1 synapses of hippocampus, while microscopic morphology, basal synaptic transmission, and depotentiation were normal. Behavioral testing using the Morris water maze and automated IntelliCage system showed that cAMP-GEF II deficient mice had moderately reduced behavioral flexibility in spatial learning and memory.

Conclusions: We concluded that cAMP-GEF II plays a key role in hippocampal functions including behavioral flexibility in reversal learning and in mechanisms underlying induction of long-term depression.

No MeSH data available.


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