The possible role of hypoxia in the formation of axonal bulbs

Aims - To assess the possible role of hypoxia in the formation of axonal bu lbs. Methods - Study material comprised sections from 28 brains showing evidence of cerebral hypoxia with no history of head injury, four with a history of head trauma but no evidence of hypoxic change, eight with a history of hea d trauma and hypoxic change, and four from control brains originally descri bed as "diffuse axonal injury." These were subjected to microwave antigen r etrieval and immunohistochemistry using monoclonal antibodies to beta amylo id precursor protein (beta APP), glial fibrillary acid protein (GFAP;), and CD68-PGM1. Results - Positive staining for beta APP was seen in all four controls, all four cases of head injury only, seven of eight cases of head injury and hy poxic changes, and 12 of 28 cases of hypoxia without history of head injury ; 22 of 25 cases who had been ventilated showed positive staining. The majo rity of cases showed evidence of cerebral swelling. Conclusions - Axonal bulbs staining positively for beta APP may occur in th e presence of hypoxia and in the absence of head injury. The role of hypoxi a, raised intracranial pressure, oedema, shift effects, and ventilatory sup port in the formation of axonal bulbs is discussed. The presence of axonal bulbs cannot necessarily be attributed to shearing forces alone.