Neurotransmitters and Post-Concussion Symptoms

What are Neurotransmitters?

Neurotransmitters are chemical messengers used by the nervous system in the body. These messengers transmit messages between nerve cells or between nerve cells and organs, muscles, or other tissues. 

Neurotransmitters are grouped into different categories, based on their chemical structures.

  • Amino Acids: e.g., glutamic acid, GABA (γ-aminobutyric acid), glycine and aspartic acid.
  • Biogenic Amines: e.g., serotonin, dopamine, norepinephrine, epinephrine, acetylcholine, and histamine. 
  • Peptides: e.g., enkephalines, neurotensin, somatostatin, and vasopressin.
  • Gaseous Neurotransmitters:  e.g., carbon monoxide, hydrogen sulfide and nitric oxide. 

Major Neurotransmitters

 

  • Glutamate: Glutamate is important for learning, cognition, perception of pain, and memory. Neuroplasticity also requires glutamate because the brain uses glutamate to help build neural pathways.  Glutamate imbalance is detrimental as it can lead to several neurological diseases. 
  • GABA (γ-aminobutyric acid): GABA is an inhibitory neurotransmitter in the central nervous system (CNS). In other words, GABA decreases the activity in the CNS and blocks specific signals from the brain. Research has shown that abnormal GABA regulation is associated with sleep and eating disorders. Low levels of GABA have also been linked to anxiety disorders. 
  • Dopamine: Dopamine is responsible for feelings of joy or pleasure by triggering the brain. Dopamine also plays a role in executive function, attention, and memory. Dysfunctions in dopamine-responsive neurons are linked to many diseases, such as hypertension, schizophrenia, Parkinsonism and pheochromocytoma. 
  • Serotonin: Serotonin has an important role in several behavioural and cognitive functions, such as learning, pain, mood, anxiety, and depression. Specifically, serotonin helps regulate emotions, stress, and mood. Serotonin imbalance is harmful to the body as it may lead to brain fog, confusion, sleeplessness, and lower moods. Additionally, too much serotonin in the brain can negatively impact memory, create paranoia, and impair judgement. 

Impacts of Concussions on Neurotransmitters

 


Excessive Neurotransmitter Release 

Concussions can cause excessive neurotransmitter release. This is harmful as it can result in permanent damage and/or functional impairment. Research has found that concussions can specifically cause an excessive release of glutamate. In extreme cases, excessive neurotransmitter release can cause cell death, which is linked to neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease. 

 

Serotonin Disturbance 

The frontal lobes are a major area for the serotonin neurotransmitter system. However, injury to the left frontal lobe is associated with depression after a concussion. Therefore, it is not surprising that post-concussion depression is very common. Depression is also linked to serotonin disturbance post-concussion because depression impacts the serotonin neurotransmitter system. Serotonin dysfunction or imbalance may also be caused through prolonged stress, which is also commonly experienced among concussion survivors. Research has also found that there are differences in serotonin function between non-depressed vs. depressed concussion survivors.

 

Dopamine Fluctuations 

Following a concussion, dopamine levels will substantially fluctuate. Increases in dopamine are linked to the induction of inflammatory signals and increased oxidative stress, whereas decreases in dopamine are linked to executive functions, attention, and memory deficits. Research has also shown that dopamine dysfunction may also contribute to other post-concussion deficits. 

 

Written by Dorothy Dinh


References 

Bales, J. W., Wagner, A. K., Kline, A. E., & Dixon, C. E. (2009). Persistent cognitive dysfunction after traumatic brain injury: A dopamine hypothesis. Neuroscience and Biobehavioral Reviews, 33(7), 981-1003. https://doi.org/10.1016/j.neubiorev.2009.03.011

 

Lan, Y., Li, S., Lou, J., Ma, X., & Zhang, B. (2019). The potential roles of dopamine in traumatic brain injury: A preclinical and clinical update. American Journal of Translational Research, 11(5), 2616-2631.

 

MacFarlane, M. P., & Glenn, T. C. (2015). Neurochemical cascade of concussion. Brain Injury, 29(2), 139-153. https://doi.org/10.3109/02699052.2014.965208

 

Pradhan, T., Jung, H. S., Jang, J. H., Kim, T. W., Kang, C., & Kim, J. S. (2014). Chemical sensing of neurotransmitters. Chemical Society Reviews, 43(13), 4684-4713. https://doi.org/10.1039/c3cs60477b

  

Smyth, K., Sandhu, S. S., Crawford, S., Dewey, D., Parboosingh, J., & Barlow, K. M. (2014). The role of serotonin receptor alleles and environmental stressors in the development of post‐concussive symptoms after pediatric mild traumatic brain injury. Developmental Medicine and Child Neurology, 56(1), 73-77. https://doi.org/10.1111/dmcn.12263

 

Steenerson, K., MD, & Starling, A. J., MD. (2017). Pathophysiology of sports-related concussion. Neurologic Clinics, 35(3), 403-408. https://doi.org/10.1016/j.ncl.2017.03.011