New understanding of the opposite action of serotonin will help treat depression and addictions

(ORDO NEWS) — Japanese scientists have discovered a new pathway in the brainstem in which serotonin mediates the signaling of unpleasant signals.

This system operates in reverse of another previously studied pathway, in which an increase in serotonin levels, on the contrary, serves as a signal of pleasure.

This information may lead to the development of new drugs for the treatment of depression and drug addiction.

Scientists from the University of Hokkaido and Kyoto University (Japan) have identified a previously unknown neural pathway involved in the processing of unpleasant external stimuli in mice.

It originates in a bundle of nerve fibers in the brainstem known as the median raphe nucleus.

It also turned out that signaling through this pathway acts in contrast to the previously discovered reward/disgust pathway, which originates in the adjacent dorsal raphe nucleus.

The results of the study, have implications for the treatment of various mental disorders, including addiction and depression.

Activation of serotonin-producing nerve fibers in the dorsal raphe nucleus in mice results in a sense of pleasure associated with reward.

However, the most common antidepressants, selective serotonin reuptake inhibitors (SSRIs), which increase levels of this neurotransmitter in the brain, do not produce this kind of reward.

Therefore, they do not treat the loss of pleasure associated with depression. This suggests that there are other serotonin pathways in the brain associated with feelings of reward and aversion.

The authors of the new work focused on the median raphe nucleus, which also contains serotonin-producing nerve cells.

The researchers used a variety of tests to measure the activity of serotonin neurons in mice.

To do this, they used fluorescent proteins, which make it possible to detect the penetration of calcium ions into neurons, which accompanies their activation.

It turned out that such an unpleasant stimulus as pinching the tail increased the activity of neurons. In contrast, giving mice a treat, such as sugar, reduced it.

In addition, direct stimulation or inhibition of neurons in the midnucleus using developmental technology resulted in aversion or reward-seeking behavior, respectively.

The team also ran tests to find out where these cells send signals and found their connection to another nucleus, which has serotonin receptors involved in responding to unpleasant stimuli.

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