Serotonin is a neurotransmitter in the brain that is highly involved in emotional regulation and aggressive behavior. The nuclei of the rafe , located in the brain stem, 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 an anatomical level, their functions and how serotonin affects our behavior.
What are the Rafe’s 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 brain stem .
Specifically, the nuclei of the rafe are a region of the human brain where serotonin, a brain neurotransmitter with an inhibitory effect on the brain, is synthesized and flows; serotonin acts on receptors located at the level of the amygdala and helps to stop aggressive behavior. Its decrease implies an increase in the aggressive response in the human being.
Thus, the serotoninergic system originates in the nuclei of the rafe; these nuclei form a wide organized network in the brain stem.
On the other hand, the nuclei of the rafe are part of the reticular formation , one of the most primitive zones of the brain, in charge of controlling the rhythms of sleep.
Where are they?
Each of the nuclei of the serotonergic rafe are located next to the midline of the brain stem. Let’s get to know this area of the brain:
1. Brain stem
The nuclei of the rafe are located in the brain stem. The brain stem is the region responsible for the “emotional reactions” of the human being, and includes other structures such as the bridge, the cerebellum, the reticular formation and the locus coeruleus. In humans, these primitive structures remain active as vital warning mechanisms for survival, and also for maintaining the sleep-wake cycle and breathing .
The brain stem, in turn, is made up of several very important areas such as the midbrain, the bridge and the spinal cord. In addition to the above, it is also responsible for communicating the spinal cord and peripheral nerves with the different areas of the brain.
Functions of the cores
As we have already seen, the main function of the Rafe’s nuclei is the synthesis of serotonin, the main neurotransmitter for the nervous system to function properly. Let’s see some of the most important functions of these nuclei:
1. Mood regulation: serotonin (SA)
Serotonin regulates mood , and does so by controlling negative emotions such as fear, aggression or anxiety. On the other hand, its lack or reduction can trigger disorders such as depression.
Once the serotonin is synthesized in the nuclei of the rafe, it is sent to the rest of the nervous system, where it fulfills 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 of which means that depressive states improve (i.e., mood improves). 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 another type of neurons, not only the serotonergic ones.
2. Sleep-wake cycles
The nuclei of Rafe are also involved in the regulation of sleep-wake cycles , working in synchronization with the hypothalamus, with which they will carry out a feedback on the levels of alertness and wakefulness, consequently producing more or less serotonin.
3. Pain Inhibition
In addition, the nuclei of the rafe (especially the magnus nucleus and the dorsal nucleus), 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 display and control of this behaviour, such as the sensory systems (initially), the thalamus (which receives the information) and the amygdala (where the information ends).
Anatomy of the Rafe’s nuclei
The Rafe’s cores are divided into six small cores. Some of them are located in the rostral zone (closer to the upper part of the brain stem), while others are located in the caudal zone (the lower zone).
Specifically, 85% of the brain’s serotoninergic neurons are found in the rostral area. This area is composed of the nucleus of the Rafe pontis and the upper central nucleus, in the area of the bridge, and the nucleus of the Rafe dorsalis, in the midbrain area.
All these nuclei connect with the areas of the brain where higher functions are performed (such as the frontal areas), although the neurons of the dorsalis nucleus 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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