rTMS Modulation of Behavioral and Biological Measures in 3xTg-AD Mice

Abstract

Background/objectives: The biological basis for behavioral manifestations of Alzheimer's disease remains unclear. Emotional and behavioral alterations of Alzheimer's disease can result in substantial caregiver burden and lack effective management. This study expands upon previous work investigating behavioral alterations in mice with Alzheimer's disease and a potential treatment of increasing brain-derived neurotrophic factor (BDNF) using repetitive transcranial magnetic stimulation (rTMS).

Methods: A total of 47 3xTg-AD (Alzheimer's) and 53 B6 (wildtype) mice were administered ANA12 (an antagonist of TrkB receptor) or Vehicle (saline) and then rTMS or Sham treatment daily. After 14 days of treatments and injections, mouse behavior was assessed under various behavioral cognitive tests. Mice were then perfused, and brain samples were processed for histology and protein assays. Brain homogenates were analyzed for BDNF and its downstream signaling molecules.

Results: Open field testing demonstrated that 3xTg-AD mice spent more time in the center than B6 mice. 3xTg-AD-Sham mice injected with ANA12 were the only group to travel significantly less distance than B6-ANA12-Sham or B6-Vehicle-Sham mice (p < 0.05), while 3xTg-AD-rTMS mice (irrespective of injection) were not significantly different from B6 mice. 3xTg-AD mice had significantly greater measured levels of BDNF and TrkB than the wild-type mice.

Conclusions: Treatment of Alzheimer's disease using rTMS positively affects elements of hypoactivity, but not all behavioral abnormalities. rTMS shifted 3xTg-AD open field behavioral test measures, generating significant differences between untreated 3xTg-AD and B6 genotypes. Despite its benefit, further investigation of rTMS as a treatment for Alzheimer's disease as well as its biological underpinnings are needed.

Keywords: ANA12; Alzheimer’s disease; disinhibition-like behavior; rTMS.

Figure 1

Representative stain of AD pathology in 3× mouse.

Figure 2

Lower exploratory activity in 3× mice was shown in the distance travelled in the Open Field Test (A), in the total object exploration in the familiarization phase of the Object Recognition Test (B) and in the total entries into arms in the Y Maze (C). Annotations in bars are the n in each group and the Tukey or genotype effect p values of significant results are shown.

Figure 3

Behavioral disinhibition phenotype was present in the 3× mice. In the center 3× spent more time (A) and had a slower velocity (B) than B6 mice; however, these differences were not present in the periphery (C) for the Open Field Test. Number of entries into the center zone between conditions (D). Represented trace images of activity from one 3× and one B6 mouse are shown (E). Annotations in bars are the n in each group and the Tukey p values of significant results are shown.

Figure 4

Genotype and ANA12 injections had differing effects on BDNF (A), TrkB (B) and downstream BDNF-TrkB pathway protein AKT (C). Example Western blot bands from TrkB and AKT (D). For full unaltered images of Westerns, see Supplementary Figure S1. Annotations in bars are the n in each group and the Tukey or genotype effect p values of significant results are shown.