When old is not old enough: the challenges of using aging pigs in preclinical neuro studies

Abstract

Many brain disorders emerge in old age, making it essential to use aged laboratory animals to obtain reliable and translatable research outcomes. While this is feasible in rodent models, such as mice and rats, due to their short lifespan, accessing aged animals poses a significant challenge in large experimental animal models like pigs. In this study, we compared volumes of whole brains and selected brain structures from young adult Göttingen minipigs (7 months-1 year; N=4) with brains from aging minipigs (4-11 years; N=4), in addition to a single old Ossabaw pig (8 years; N=1). All nine pigs were females, and the aging pigs were the oldest we had access to. Brains were removed and stored in formalin until they were structurally scanned in a preclinical magnetic resonance imaging (MRI) scanner. The total volumes of each brain were determined, in addition to the volumes of three structures, namely the hippocampus, striatum, and amygdala (the volume of the striatum decreases with age in humans, and the same may also be true for the amygdala). The mean volume of the old Göttingen minipig brains (78,770 mm³ +/- 3,331 mm³) were 19 percent larger than for the young minipig brains (65,990 mm³ +/- 1,346 mm³) (p=0.002), while the Ossabaw pig's brain was significantly larger (85 percent, 121,767 mm³) than both the young and aging Göttingen minipig brains reflecting the bigger body size of the Ossabaw pig. The average volume fractions of the structures analyzed were slightly lower for the old minipigs compared to the young, although not significant for either the hippocampus (p=0.299), striatum (p=0.149), or amygdala (p=0.406). Qualitative MRI assessment did not reveal brain atrophy or ventricle enlargement in the old pig brains. The average volume fractions in the Ossabaw pig were comparable to those observed in the Göttingen minipigs. Even the oldest pig brains in this study showed no clear MRI-based indicators of aging-related neurodegeneration. These findings, therefore, highlight the challenges of obtaining truly aged pig brains and address a real, practical challenge for future aging research using large animal models.