Researchers at Ohio State University (OSU) examined the effects of concussions on “sub-cellular levels,” possibly pointing the way for new treatments to be developed for concussions.
According to Science Daily, the OSU researchers discovered that blows to the head cause numerous small swellings along the length of neuronal axons. The study, published in The Journal of Cell Biology, observes the swelling process in live cultured neurons and could lead to new ways of limiting the symptoms associated with concussive brain injuries.
The researchers induced “mild traumatic brain injury” (mTBI) on rodents and found that part of a nerve cell swells within a matter of seconds, much faster than previously believed. The injury activated a protein that caused a chain reaction. Suppressing the protein prevented swelling. Such a finding is highly relevant to mild traumatic brain injury (mTBI), or concussion as it is more commonly known, researcher Chen Gu reports.
According to the researchers, one effect of mTBI is the development of “axonal varicosities,” small, bead-like swellings appear along the length of neuronal axons, which are the parts of neurons that transmit electrical and chemical signals to neighboring nerve cells. Similar swellings are seen in the brains of people with Alzheimer’s disease or Parkinson’s disease.
In the study, the axonal varicosities formed rapidly; in younger neurons they swelled up within five seconds of being puffed. The researchers were surprised to see that the varicosities disappeared several minutes after puffing, indicating that they are not indicative of irreversible degeneration.
The researchers found that puffing activated a mechanosensitive channel protein called TRPV4. Inhibiting this channel blocked the formation of axonal varicosities. After entering axons through activated TRPV4 channels, calcium ions disrupt the microtubule cytoskeleton by inhibiting a microtubule-stabilizing protein called STOP. This interrupts the transport of cellular materials along axonal microtubules, causing these materials to accumulate along the axon where they may give rise to varicosities.
Older neurons are more resistant to the effects of puffing and express lower levels of TRPV4 and higher levels of STOP. Gu noted that this raises the question whether a mature brain is more resistant to mild traumatic brain injury than a young brain.
Gu points out that axonal varicosities have also been observed in healthy brains and may play a key role in neural development and central nervous system function, as well as in brain disorders and injuries.