Serotonin is a massively large molecule. In fact, it is so large that it cannot cross the blood brain barrier. We can’t simply take Serotonin orally or eat foods that have high levels of Serotonin- this won’t be able to get to the brain. Serotonin is like Las Vegas- what happens in Las Vegas, stays in Las Vegas….or so I am told. (I actually have never been there.)

Seratonin is a very large molecule. Courtesy of panama-guide.com

All we can do is block or prevent the natural time-course of Serotonin from being reabsorbed by the tissues of the central nervous system. There is a class of antidepressants called selective serotonin reuptake inhibitors, or SSRIs for short.  SSRIs, as the name suggests, inhibit or block the central nervous system’s propensity to wanting to do away with the Serotonin. The result is that more Serotonin is available for the various neurologic and metabolic processes that occur in the brain.

The biochemistry of SSRIs is actually pretty clever- if you can’t add more, then block the re-uptake of it.  SSRIs are a common medication given for people as antidepressants.

 

In a recent study in Cell Reports researchers at the Oregon Health and Science University found that too much Serotonin can be a bad thing, at least when it comes to the treatment of tinnitus. 

Earrings and necklaces have been made out of the Serotonin molecule….. I think that they forgot the double bonded carbon atoms, but then again, its only jewelry. Courtesy of www.etsy.com.

In examining the Dorsal Cochlear Nucleus of mice, the researchers found that a special type of neuron called fusiform cells exhibited hyperactivity and increased sensitivity when exposed to higher levels of Serotonin. This may explain why many people who are prescribed SSRIs as an antidepressant often report an increase in the level of tinnitus.

I should point out that for many people SSRIs are an important tool in the treatment of their depression and despite the increased prevalence of tinnitus that they may experience, the benefits may far outweigh the potential side effects.  

The researchers wanted to better understand the biochemistry and physiology leading to tinnitus.   One of the areas of further study, perhaps the most important area, would be the study of the various ion channels that allow the Serotonin to enter a cell and perhaps by altering this pathway, the benefits of SSRIs may increase or maintain, while minimizing the potential side effects such as tinnitus.

 

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One Response to Despite the benefits of SSRIs, tinnitus may be a side effect

  1. Max Stanley Chartrand, Ph.D. says:

    Thank you, Marshall covering an important aspect of ototixicty that is often passed over in the literature. Too much serotonin and, from synaptic dilation, which holds back ALL of the hormones, both, are areas needing more attention in medical research. Overlaid with other drugs, such as caffeine, and certain other psychoactive substances, aberrations in serotonin secretion present even more challenges, many of which are behavioral as well as ototoxic.

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