A shortened Barnes maze protocol reveals memory deficits at 4-months of age in the triple-transgenic mouse model of Alzheimer's disease

Abstract

Alzheimer's disease is a progressive neurodegenerative disease that manifests as memory loss, cognitive dysfunction, and dementia. Animal models of Alzheimer's disease have been instrumental in understanding the underlying pathological mechanism and in evaluation of potential therapies. The triple transgenic (3 × Tg) mouse model of AD is unique because it recapitulates both pathologic hallmarks of Alzheimer's disease--amyloid plaques and neurofibrillary tangles. The earliest cognitive deficits in this model have been shown at 6-m of age by most groups, necessitating aging of the mice to this age before initiating evaluation of the cognitive effects of therapies. To assess cognitive deficits in the 3 × Tg mice, originally we employed a typical Barnes maze protocol of 15 training trials, but found no significant deficits in aged mice. Therefore, we shortened the protocol to include only 5 training trials to increase difficulty. We found cognitive deficits using this protocol using mainly measures from the probe day, rather than the training trials. This also decreased the effort involved with data analysis. We compared 3 × Tg and wild-type mice at 4-m- and 15-m of age using both the original, long training, and the short training paradigms. We found that differences in learning between 3 × Tg and wild-type mice disappeared after the 4(th) training trial. Measures of learning and memory on the probe day showed significant differences between 3 × Tg and wild-type mice following the short, 5-training trial protocol but not the long, 15-training trial protocol. Importantly, we detected cognitive dysfunction already at 4-m of age in 3 × Tg mice using the short Barnes-maze protocol. The ability to test learning and memory in 4-m old 3 × Tg mice using a shortened Barnes maze protocol offers considerable time and cost savings and provides support for the utilization of this model at pre-pathology stages for therapeutic studies.

Figure 1. Barnes maze diagram with quadrants.

The Barnes maze is made up of a circular platform, 48” in diameter, with 20 equally spaced holes around the periphery. The holes are 1” away from the edge and have a 1.75” diameter. The maze is divided into 4 quadrants labeled Target, Positive, Opposite, and Negative with the escape hole being in the center of the Target quadrant.

Figure 2. Primary latency of training trials shows group differences only in first 4 trials.

A) Primary latency, out of 120 s, for 15-m old wild-type (WT) or triple transgenic (3×Tg) mice receiving 15 training trials (WT n = 32, 3×Tg n = 24). Mean and median values given for comparison. Primary latency over 5 training trials for 15-m old (B; WT n = 15, 3×Tg n = 15) and 4-m old (C; WT n = 14, 3×Tg n = 17) mice. *p<0.05, **p<0.01 compare mean values of WT and 3×Tg.

Figure 3. Percent holes searched and time in target quadrant show short training can resolve cognitive deficits.

A) Percent holes searched, on probe day, in each of four quadrants by 15-m old wild-type or triple transgenic mice receiving either short or long training. Chance level of holes searched in each quadrant is 25%. B) Time (s) spent in the Target quadrant by all 6 groups of mice. Chance amount of time spent per quadrant is 30 s out of 120 s. C) Percent holes searched in each of four quadrants by WT or TG and 15-m or 4-m old mice receiving short training. *p<0.05, ***p≦0.001 compare WT and 3×Tg.

Figure 4. Percent of mice being guided to escape hole on training days decreased with training.

Percent of mice being manually guided to the escape hole that did not independently enter in the allotted 2: trials 1–5, 6–10, and 11–15. *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001 compare WT and 3×Tg.