Punishing headbutts damage the brains of musk oxen. That observation, made for the first time and reported May 17 in ACTA Neuropathologica, suggests that a life full of bell-ringing clashes is not without consequences, even in animals built to bash.
Although a musk ox looks like a dirty dust mop on four tiny hooves, it’s formidable. When charging, it can reach speeds up to 60 kilometers an hour before ramming its head directly into an oncoming head. People expected that musk oxen brains could withstand these merciless forces largely unscathed, that they were magically perfect. In fact, the brains of three wild musk oxen (two females and one male) showed signs of extensive damage, Ackerman
and her colleagues found. The damage was similar to what’s seen in people with chronic traumatic encephalopathy, a disorder known to be caused by repetitive head hits (SN: 12/13/17). In the musk ox brains, a form of a protein called tau had accumulated in patterns that suggested brain bashing was to blame. The microglial clumps seen in human samples were rare in the animals’ brains, other similarities were present. Specifically, in the muskoxen samples, the authors noted the presence of axon clusters packed with phosphorylated tau, which were especially prevalent on the outer edges of the cerebral cortex—a distribution pattern “reminiscent of mild TBI or early-stage CTE cases,” the authors write. They also detected approximately eight times the number of these clusters in the oldest muskox brain than in a middle-aged one (both were female animals, which would be expected to engage in less headbutting than males). Less pathology was evident in the sheep brains, which the authors suggest could be because the animals were captive and younger, limiting their headbutting experience. Still, the team notes, “a human specimen with the same tau pathology present in the male bighorn sheep would have likely been diagnosed with mild CTE.” “Death and disability caused by traumatic brain injury is a widespread problem that needs better solutions,” said Nicole Ackerman, PhD, postdoctoral fellow at Icahn Mount Sinai and the study leader. “We showed that animals which regularly engage in headbutting may actually suffer the kind of traumatic brain injury seen in humans. This opens the possibility that by studying these animals we could learn a lot about traumatic brain injury.”Part of the reason for obtaining brains from these horned animals is that they are known to engage in violent head-to-head collisions, usually in mating and social hierarchy rituals. For instance, male muskoxen often reach speeds of up to 30 miles an hour before impact. Although a few studies have observed symptoms of traumatic brain injury (TBI), such as acting dazed, none have directly tested whether the brains of muskoxen and other ramming animals show any damage.To look for signs of TBI damage, the researchers then cut the brains into thin slices and treated the slices with antibodies made to detect phosphorylated tau proteins found in humans or mice. This form of tau is a hallmark of damage that is often seen in the brains of Alzheimer’s disease patients, or in people who have suffered TBIs, including chronic traumatic encephalopathy (CTE).When they looked at the brains under a microscope, they saw that one of the antibodies stained muskoxen brains at easily detectable levels, whereas the bighorn sheep brains had lightly detectable levels of staining by a different antibody.
In an unexpected twist, the brains of the females, who hit heads less frequently than males, were worse off than the male’s. The male body, with its heavier skull, stronger neck muscles and forehead fat pads, may cushion the blows to the brain, the researchers suspect. If musk ox do get brain trauma at all, the older males would have it the worst because they headbutt more often and harder than females. The results may highlight an evolutionary balancing act; the animals can endure just enough brain damage to allow them to survive and procreate.
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