A new study examines what occurs in the brain at the neuronal level during a concussion and shows just how a hit to the head leads to swelling along the axon of the neuron or nerve cell. The new revelations could potentially help scientists to improve symptoms in people with concussions.
Traumatic brain injury or TBI occurs when an external mechanical force disrupts normal brain function. A sudden blow to the head is most often the cause of TBI.
According to the Centers for Disease Control and Prevention (CDC), 2.5 million emergency department visits and 56,000 deaths were linked to TBI in 2013.
The severity of TBI depends on the symptoms, which range from mild to moderate to severe. When someone experiences a case of mild TBI or concussion, they do not always lose consciousness and if they do, it typically only lasts for a few seconds.
Symptoms of mild TBI include confusion, headache, dizziness, lightheadedness, ringing in the ears, blurred vision, tired eyes, lethargy, fatigue and a bad taste in the mouth, according to the National Institute of Health (NIH). Other symptoms may include alternations in sleep, mood and behavior. The condition can also affect reasoning, concentration and memory.
The study conducted by researchers at the Ohio State University in Columbus examines how “varicosities” form along the axons of a neuron during a concussion. The neuron is made up of three components – axon, the cell body and dendrites. The axon is responsible for sending electrical singles from the cell body to other neurons.
Axons produce “small, bead-like swellings” during a concussion, which is similar to neurodegeneration in Parkinson and Alzheimer’s diseases.
The research team discovered they could create the same affect in neurons of the hippocampus, the brain region that creates and stores new memory.
The axons were injected with liquid from a pipette, creating pressure that is similar to the pressure the neurons may potentially experience following a hit to the head.
Those swellings, specifically concussion-typical varicosities developed quickly and even more rapidly in young neurons, within 5 seconds.
Even more shocking was that the swellings disappeared within a few minutes, which suggests axonal varicosities do not indicate irreversible degeneration of the axons.
The researchers duplicated the induction of axonal varicosities in cultured neurons, emulating the effects of repeated hits to the head. The swellings were then compared to those induced in mice models.
The research team found the method utilized to inject liquid into the axons or “puffing” activated TRPV4, a channel protein in the membrane of neuronal axons. TRPV4 allows calcium ions to penetrate the cell.
The research team identified the mechanism that causes the swelling formation. After the calcium ions penetrate the cell through the activated TRPV4 channel, they prohibit STOP, a type of protein, from disrupting the transfer of cellular materials along the axon. Those materials collect along the axon, leading to the formation of varicosities.
Older neurons contain lower amounts of TRPV4, but higher levels of STOP. However, the older neurons are stronger and more capable of combating the effects of induced puffing.
Leading author Chen Gu said, “Taken together, our findings provide novel mechanistic insights into the initial state of a new type of neuronal plasticity in health and disease.”
“This process may, therefore, play a key role in neural development and central nervous system function in adults, as well as in chronic brain disorders and various acute brain injuries.”