Serotonergic pathways

The Clusters of serotonin neurons (chosen B1–B9) are scattered throughout the brain stem, generally towards the midline in the raphe nuclei. The Projections into the spinal cord which terminate in the dorsal horn decrease nociceptor input into the spinothalamic tract. The Forward projections run into the medial forebrain bundle to go to the hypothalamus, striatum, amygdala, thalamus, hippocampus, and neocortex as shown in figure. A few of these serotonergic neurons might be included in the expression of anxiety. They are reserved by GABAergic neurons, enhancing the activity of which decreases the anxiety. Numerous potent anxiolytic drugs are 5-HT receptor ligands. The Serotonin transmission is modulated by social status; that is, by how dominant an animal is within its social assembly. This might underlie the effect of serotonin on mood. The Deficits are related with depression and increased risk of suicide. The Serotonin is also included in satiety, sleep, and regulation of the CSF secretion and cerebral blood flow.

Figure: Major serotonin (5-HT) pathways in a sagittal part of the rat brain. The cell groups B1–B8 communicate to the 5-HT having raphe nuclei (except B4 & B6). Here, MFB=medial forebrain bundle; ST=stria terminalis.