Brainstem and cerebellar variations in cheetahs (Acinonyx jubatus)

The cheetah is a species known for its high-speed hunting, requiring sophisticated visuomotor and vestibulomotor skills. A recent study showed cheetahs have enlarged semicircular canals, suggesting enhanced vestibular information processing. We asked if the semicircular canal specializations might be reflected in the brainstem targets of vestibular input and in related cerebellar structures. We studied blocks of brain tissue with the medulla and pons from five US zoo-bred cheetahs (three different zoos), and one brainstem of an animal from a zoo in Sweden. We compared the cheetah brainstems with each other, and with the brainstem of the domestic cat. We found variations in several structures, most consistently in the cochlear nuclei, in the brains of the US zoo-bred cheetahs. There were differences among these brains in the nature and extent of these variations. Despite the unusual structural characteristics of the cochlear nuclei, no impairments in auditory function had been noted by the home zoos. The brain of the Swedish zoo cheetah did not show these atypical features. We also saw consistent differences between the US cheetahs and cats in the sizes of the cerebellar peduncles, the pyramidal tracts and the medial longitudinal fasciculus. The low genetic diversity of cheetahs, a consequence of one or more population bottlenecks, may underlie the persistence of genetic changes causing atypical brainstem development.