A part of the brain stem with important functions for our survival.
Serotonin is a brain neurotransmitter highly involved in emotional regulation and aggressive behavior. The nuclei of the Rafe, located in the brainstem, is the area with the most serotonin in the brain, and where it is secreted.
In this article we will know in detail these nuclei at the anatomical level, their functions and how serotonin affects our behavior.
What are the Rafe cores?
The word “Rafe” comes from the Greek, and refers to a ridge that separates two symmetrical areas of an organ or tissue. The nucleus or nuclei of the Rafe is a set of groups of neurons found in the midline of the brainstem.
Specifically, the nuclei of the Rafe are a region of the human brain where serotonin is synthesized and flows, a brain neurotransmitter with an inhibitory effect on the brain; Serotonin acts on the receptors located at the level of the amygdala and contributes to curbing aggressive behavior. Its decrease implies an increase in the aggressive response in humans.
Thus, the serotonergic system originates in the nuclei of the Rafe; These nuclei make up a vast network organized in the brain stem.
On the other hand, the nuclei of the Rafe are part of the reticular formation, one of the most primitive areas of the brain, responsible for controlling sleep rhythms.
Where are they found?
Each of the serotonergic Rafe nuclei is located adjacent to the midline of the brainstem. Let’s get to know this area of the brain:
The nuclei of the Rafe are found in the brain stem. The brain stem is the region responsible for human “emotional reactions” and includes other structures such as the pons, cerebellum, reticular formation, and locus coeruleus. In humans, these primitive structures remain active as vital alert mechanisms for survival, and also to maintain the sleep-wake cycle and respiration.
The brain stem, in turn, is made up of several very important areas such as the midbrain, the pons, and the medulla oblongata. In addition to the above, it is also responsible for communicating the spinal cord and the nerves of the periphery with the different areas of the brain.
As we have already seen, the main function of the Rafe nuclei is the synthesis of serotonin, the main neurotransmitter for the nervous system to function properly. We are going to see some of the most important functions of these cores:
1. Mood regulation: serotonin (SA)
Serotonin regulates mood, and it does so by controlling negative emotions such as fear, aggressiveness or anxiety. On the other hand, its lack or reduction can trigger disorders such as depression.
Once serotonin is synthesized in the nuclei of the Rafe, it is sent to the rest of the nervous system, where it performs its functions. Serotonin maintains and regulates mood, and controls certain aggressive behaviors (also in animals). Some medications, such as SSRIs (antidepressants), inhibit the reuptake of serotonin, causing it to increase its concentration levels in the brain; All this implies that depressive states improve (that is, they improve the mood). This is why they are often used to treat depression (along with other serotonin enhancers such as tricyclic antidepressants, MAOIs, etc.).
On the other hand, we must know that the nuclei of the Rafe contain other types of neurons, not only serotonergic ones.
2. Sleep-wake cycles
The nuclei of the Rafe are also involved in the regulation of sleep-wake cycles, working in a synchronized way with the hypothalamus, with which they will carry out a feedback on alert and wakefulness levels, consequently producing more or less serotonin.
3. Inhibition of pain
Furthermore, the nuclei of the Rafe (especially the nucleus magnus and the nucleus dorsalis) are involved in the processes of pain inhibition.
4. Aggressive behavior
As we have seen, aggressive behavior has to do with serotonin levels (the more serotonin, the less aggressive behavior). Numerous structures are involved in the deployment and control of such behavior, such as the sensory systems (initially), the thalamus (which receives the information) and the amygdala (where the information culminates).
Anatomy of the Rafe nuclei
The nuclei of the Rafe are divided into six small nuclei. Some of them are located in the rostral zone (closer to the upper area of the brainstem), while others are located in the caudal area (the lowest area).
Specifically, 85% of brain serotonergic neurons are found in the rostral zone. This area is composed of the nucleus of the Rafe pontis and the upper central nucleus, in the area of the bridge, and by the nucleus of the Rafe dorsalis, in the area of the midbrain.
All these nuclei connect with the areas of the brain where higher functions are carried out (such as the frontal areas), although the neurons of the nucleus dorsalis connect with numerous brain areas such as the orbitofrontal cortex or the hypothalamus (the latter controls the functioning of the nervous system, among other functions).
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- Carlson, NR (2005). Physiology of behavior. Madrid: Pearson Education.