3046
Hyperactivity of hippocampus-amygdala network during cue-reward association learning of APP/PS1 Alzheimer’s disease model mice detected by 14T-fMRI1Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan
Synopsis
Dys-regulation of neural network is a biomarker for neurodegenerative disease, such as Alzheimer’s disease. We prepared numbers of 12-month-old APP/PS1 Alzheimer’s disease (AD) model mice and obtained series of BOLD fMRI (SE-EPI) data during cue-reward association learning. We pointed out hyperactivity of amygdala as well as hippocampus in the AD mice, which may involve in a cause for alteration of behavior phenotype in the AD.
Introduction
In AD, brain functions are damaged not only memory but also other cognitive abilities, for example executive function. AD patients usually exhibit executive dysfunction, which is serious obstacles to daily living1, 2. Therefore, in the studies of AD model mouse, it had been required to establish an experimental behavioral system analyzing cognitive properties in addition to the memory function. Here, we utilized non-magnetic learning device3 which can measure cognitive properties in AD model mouse. In this study, fMRI was performed on the AD model mouse during operant learning in order to elucidate mechanism of cognitive dysfunction in AD.Methods
We utilized the 12-month-old APP/PS1 transgenic mice as AD model mice (n=3) and the 12-month-old wild-type mice as normal control (n=3). We designed operant learning task for fMRI consisted of 4 phases; surgery, 3-day rest, 3-day licking training and 4-day Go task (Fig. 1). First, we conducted a surgery to mice and fix a plate to their head for head fixation to the operant device. After that, mice were rested to recovery for 3 days. After the rest, mice were restricted to take water (2 mL/day) and subjected to licking training for 3 days as a habituation phase. After that, mice were subjected to cue-reward association Go task (Fig. 2) for 4 days. We performed fMRI during association learning on the 4th day of Go task. fMRI scanning was performed first 15 trials (7 times per 1 trial). The MRI apparatus used in this study has very high magnetic field (14T) as compared with the MRI apparatus currently used in fMRI of experimental animals. We used SE-EPI (TR: 2000ms, TE: 30ms, FOV: 1.72x1.72 cm2, Matrix: 64x64, 6 slices, slice width: 0.75 mm). fMRI data was pretreated by using spm12 in the order of slice timing, realign, co-registration to C57BL/6 template4, normalization, and smoothing. After that, statistical fMRI data analysis was performed.Results
As a result of the neural activity comparison between the baseline and the immediate after reward (0-2s after the light stimulation) in the WT and the AD, activation area could rarely detected in all WT. Meanwhile, in all AD, activation of amygdala and hippocampus was observed (Fig. 3). We selected representative slices of each mouse (slices surrounded by a blue square in Fig. 3), and aligned with image of SPMMouse5 (Fig. 4). To determine time course of BOLD response during operant learning in the AD, we computed fMRI data sets from reward trials in a 1st-level analysis and plotted time course of BOLD signal in the amygdala. As a result, about 5% activation relative to the baseline was observed (Fig. 5).Discussion
Elevated hippocampal activation is observed in human AD patients, including mild cognitive impairment (MCI)6. Studies in both human and animal studies have indicated that hyperactivity in specific hippocampal circuits contributes to cognitive impairment6, 7. These results have shown that hippocampus was hyperactivated in Alzheimer's disease model mice as well as humans Therefore, it was suggested that the hippocampal hyperactivity occurred due to the influence of AD, and cognitive impairment occurred, in the rodent model. In addition, hyperactivation of the amygdala was observed in AD model mice in this study. The amygdala is associated with emotional memory and learning8, and it is also a region of the brain with high functional association with the hippocampus9. Also, it is known that deficit in cognitive function such as impulsive behavior increases in AD2, and amygdala is reported to be involved in this impulsivity10. Therefore, hyper-activation of the amygdala may be the cause of this behavioral alteration in the AD.Conclusion
In this study, we were able to visualize the brain activity of the AD model mouse under execution for the first time by fMRI. Since the mouse is a basic animal model and the cognitive function cannot be evaluated unless it is in an awake state, the devices and systems we developed can advance fundamental research in AD. Moreover, our designed operant experimental system is expected to apply to all the preclinical researches of cerebral cognitive functions in various disease model mice.Acknowledgements
The authors acknowledge continuous encouragements and supports from Drs. Hitoshi Wada, Seong-Gi Kim, and Seiji Ogawa.References
1. Ritchie, K., and Lovestone, S. The dementias. The Lancet. 2002; 360: 1759-66.
2. Rochat, L., et al. Assessing impulsivity changes in Alzheimer disease. Alzheimer Disease & Associated Disorders. 2008; 22: 278-83.
3. Jomura, N., Shintani, T., Sakurai, K., Kaneko, J., and Hisatsune, T. Mouse BOLD fMRI imaging during operant learning at ultra-high field (14 T). Proc. Intl. Soc. Mag. Reson. Med. 2017; 25, 5365.
4. Hikishima, K., et al. In vivo microscopic voxel-based morphometry with a brain template to characterize strain specific structures in the mouse brain. Scientific Reports. 2017; 7: 85.
5. Sawiak, S.J., Wood, N.I., Williams, G.B., Morton, A.J., Carpenter, T.A. Voxel-based morphometry with templates and validation in a mouse model of Huntington's disease. Magn Reson Imaging. 2013; 31(9): 1522-31.
6. Bakker, A., et al. Reduction of hippocampal hyperactivity improves cognition in amnestic mild cognitive impairment. Neuron. 2012; 74(3):467-74
7. Wilson, A., et al. Age-associated alterations of hippocampal place cells are subregion specific. J Neurosci. 2005; 25(29):6877-86.
8. Guzmán-Vélez, E., et al. Feelings without memory in Alzheimer disease. Cognitive and Behavioral Neurology. 2014; 27:117-29.
9. LaBar, S., and Cabeza, R. Cognitive neuroscience of emotional memory. Nature Reviews Neuroscience. 2006; 7:54-64. Davidson, J. Anxiety and affective style: role of prefrontal cortex and amygdala. Biological Psychiatry. 2002; 51:68-80.
10. Davidson, J. Anxiety and affective style: role of prefrontal cortex and amygdala. Biological Psychiatry. 2002; 51:68-80.
Figures
Fig 1. Experimental design of the operant initial and reversal learnings
First, surgery to attach a plate to head of mouse was performed. After that, mice were rested for 3 days. After the rest, licking training (habituation) was conducted for 3 days. After the habituation, mice were subjected to the cue (light)-reward (water) association Go task. fMRI was conducted on the fourth day of the Go task.
Fig 2. Detail of cue (light)-reward (water) association Go task
In the Go task, mice were provided water (8µL/correct licking action) with a water-supplying nozzle only by sticking out the tongue within 2 seconds after the last of a light stimulus. The light stimulus is given to both eyes of mice from 2 lighting bulbs in front of the face.
Fig 3. Activation area of the WT and the AD model mice after the light stimulation (0s-2s)
p<0.05, FWE corrected, threshold k=20, scale bar represents T-score. In all AD model mice, activation of amygdala and hippocampus was observed. On the other hand, the activation of amygdala was not observed in all WT type mice.
Fig 4. Activation area of the representative slices of WT and AD mouse
Representative slices were shown on the super-imposed image with SPMMouse template. p<0.05, FWE corrected, threshold k=20, scale bar represents T-score. Activation of the hippocampus was observed in the WT mouse. On the other hand, in the AD model mice, robust activation of the amygdala as well as the hippocampal formation was noted.
Fig 5. Elevation of BOLD signal in the amygdala of Alzheimer's disease model mouse
We computed fMRI data sets from all reward trials (14/15 total trials) from AD#2, by spm 12 1st-level analysis. We plotted a time course of BOLD signal (percentage of increase) at the peak voxel in the right amygdala.