Traumatic brain injury in Picidae avian species: the neuropathology of woodpeckers
Woodpeckers can withstand 1200-1400 g of force during repetitive pecking. The forces a woodpecker’s skull and brain are subjected to warrants an in-depth investigation for the possible existence of neuro-trauma. Dr. Philip May and colleagues in 1976 published a paper titled “Woodpeckers and Head Injury” detailing two woodpeckers and one toucan control. The group utilized ferrocyanide staining, a general stain used for detecting iron deposits, on the sections. The results of these stains were not reported in Dr. May’s paper, yet he and his colleagues conclude that “clearly the woodpecker’s brain is protected somehow from impact and vibration injury.” Close to 115 journal articles have cited this one paper as the standard for woodpeckers not incurring brain injury during pecking. Due to limited studies on the woodpecker brain and the fact the woodpecker is a model for advancing helmet technology, we set out to study the woodpecker’s brain for signs of injury. Taking 10 different ethanol preserved woodpeckers from all parts of the world in different climates, and five non-woodpecker, ethanol preserved red-winged black bird experimental controls, paraffin embedded sections were cut and stained. A piece of human Alzheimer’s disease cortex was also used as a positive control. We utilized Gallyas silver stain for the study of neurofibrillary tangles and tauopathies as well as anti-phospho-tau and anti-glial fibrillary acidic protein (GFAP) immunostaining to detect tau protein and GFAP respectively. The results demonstrated perivascular silver-positive deposits in the superficial cortex and axonal tract injury of eight out of the 10 woodpeckers. The anti-phospho-tau immunostaining stained axonal tract injury in two of the three woodpeckers studied. The red-winged back birds demonstrated no positivity for all three stains. The Alzheimer’s positive control showed silver positive and phospho-tau positive staining as expected. This is the first study of this kind to discover and label potential brain injury in the woodpecker model. The negative staining of the red-winged black bird controls contrasted with the positive staining woodpecker sections suggest pecking in the woodpecker may induce brain injury. When addressing the development of safety equipment, the use of the woodpecker model should be approached with caution. Moving forward, research into different immunostaining molecular targets and an age controlled woodpecker and experimental control study should be performed to determine if the brain injury seen with our research is age-dependent.