Acute CNS axonal injury models a subtype of dystrophic neurite in Alzheimer's disease

The morphological and neurochemical sequelae of physical injury to cortical axons were investigated for their similarity to a subtype of dystrophic ne urite in Alzheimer's disease (AD). A 25 gauge needle was inserted into the cortex of anaesthetised rats for 10 min. At 1 day post-injury, neurofilamen t-immunoreactive bulb- and ring-like abnormal neurites were present along t he needle tract edge. Double labelling immunohistochemistry demonstrated co localisation of neurofilament subunits with different phosphorylation state s within the same reactive axonal structures. Ultrastructurally, bulb-like axons contained neurofilaments and abnormal structures such as dense-core v esicles and multilamellar bodies. Ring-like structures corresponded to coll apsed myelinated axons or axon terminals, with bands of neurofilaments surr ounding central mitochondria and/or other organelles, All of these reactive axons lacked microtubules. The morphological, neurochemical and ultrastruc tural features of axons responding to physical trauma resemble the cellular alterations within a subset of dystrophic neurites in AD, particularly in the early stages of the condition.