Age-related brain atrophy and the positive effects of behavioral enrichment in middle-aged beagles.

Aging dogs serve as a valuable preclinical model for Alzheimer's disease (AD) due to their natural age-related development of beta-amyloid (Aβ) plaques, human-like metabolism, and large brains that are ideal for studying structural brain aging trajectories from serial neuroimaging. Here we examined the effects of chronic treatment with the calcineurin inhibitor (CNI) tacrolimus or the nuclear factor of activated T cells (NFAT)-inhibiting compound Q134R on age-related canine brain atrophy from a longitudinal study in middle-aged beagles (36 females, 7 males) undergoing behavioral enrichment. Annual MRI was analyzed using modern, automated techniques for region-of-interest -based and voxel-based volumetric assessments. We found that the frontal lobe showed accelerated atrophy with age, while the caudate nucleus remained relatively stable. Remarkably, the hippocampus increased in volume in all dogs. None of these changes were influenced by tacrolimus or Q134R treatment. Our results suggest that behavioral enrichment can prevent atrophy and increase the volume of the hippocampus but does not prevent aging-associated prefrontal cortex atrophy.Significance Statement Aging canines naturally show significant neuropathological similarities to human aging and AD, making them valuable translational models for testing disease-modifying treatments. We applied modern, state-of-the-art longitudinal volumetric analysis approaches to evaluate treatment effects from structural MRI in a large cohort of middle-aged beagles treated with the FDA approved calcineurin inhibitor, tacrolimus, or the experimental NFAT inhibitor, Q134R, while undergoing extensive behavioral enrichment. We show increased hippocampal volumes across all dogs, even control placebo dogs, compelling evidence for a strong enrichment-related benefit on hippocampal structural integrity. Our findings are the first of its kind to demonstrate benefits of behavioral intervention on longitudinal structural brain changes in a higher mammalian model of aging and AD.