Serotonergic cell groups refer to collections of

neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

in the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

that have been demonstrated by histochemical

fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

to contain the neurotransmitter

serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...

(5-hydroxytryptamine). Since they are for the most part localized to classical

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...

nuclei, particularly the raphe nuclei, they are more often referred to by the names of those nuclei than by the B1-9 nomenclature. These cells appear to be common across most mammals and have two main regions in which they develop; one forms in the mesencephlon and the rostral pons and the other in the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

and the caudal pons.R. Nieuwenhuys, J. Voogd, C. Van Huijzen, The human central nervous system: a synopsis and atlas (Springer Science & Business Media, 2007). Nine serotonergic cell groups have been identified.

B1 cell group

Cell group B1 occupies the midline nucleus raphes pallidus and adjacent structures in the caudal

of the rodent and the primate.

B2 cell group

Cell group B2 occupies the midline nucleus raphes obscurus and adjacent structures in the caudal medulla oblongata of the rodent and the primate.

B3 cell group

Cell group B3 occupies the midline

nucleus raphes magnus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

and adjacent structures in the caudal medulla oblongata of the rodent and the primate. Its boundary with the serotonergic group B1 is indistinct.

B4 cell group

Cell group B4 is located in the floor of the

fourth ventricle The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ve ...

, in the vicinity of the

vestibular nuclei The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica they are grouped in both the pons and the medulla in the brainstem. Structure Path The fibers of the vestibular nerve ...

and

abducens nucleus The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the Anatomical terms of location, caudal portion of the pons, Anatomical t ...

in the rat and in the caudal interstitial nucleus of the medial longitudinal fasciculus of the mouse. A comprehensive study of monoaminergic cell groups in the macaque and the squirrel monkey did not identify a B4 cell group distinct from other groups in the region.

B5 cell group

Cell group B5 is located in the midline pontine raphe nucleus and adjacent areas in the rodent and the primate.

B6 cell group

Cell group B6 is located in the floor of the

dorsal to, and between, the right and left

medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is an area of crossed over tracts, on each side of the brainstem. These bundles of axons are situated near the midline of the brainstem. They are made up of both ascending and descending fibers that ari ...

of the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Va ...

in the primate and the rodent. and forms the caudal portion of the

dorsal raphe nucleus The dorsal raphe nucleus is located on the midline of the brainstem and is one of the raphe nuclei. It has rostral and caudal subdivisions. * The rostral aspect of the ''dorsal'' raphe is further divided into interfascicular, ventral, ventrolatera ...

B7 cell group

Cell group B7 is a group of cells located in the central

gray Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...

of the pons, the dorsal raphe nucleus and adjacent structures in the primate and the rodent.

B8 cell group

Cell group B8 is located in the dorsal part of the

median raphe nucleus The median raphe nucleus (MRN or MnR), also known as the nucleus raphes medianus (NRM)Federative Committee on Anatomical Terminology (FCAT) (1998). ''Terminologia Anatomica''. Stuttgart: Thieme or superior central nucleus, is a brain region compos ...

(superior central nucleus) and adjacent structures of the

pontine reticular formation The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation ...

of the rodent and the primate.

B9 cell group

Cell group B9 is a group of cells located in the

pontine tegmentum Pontine may refer to: * Having to do with the pons, a structure located in the brain stem (from ''pons'', "bridge") * Pontine Marshes, a region of Italy near Rome * Pontine Islands The Pontine Islands (, also ; it, Isole Ponziane ) are an ar ...

, ventral to serotonergic group B8. In the nonhuman primate they are found in the ventral part of the superior central nucleus and adjacent structures. In the rodent they have a more lateral location within the

medial lemniscus In neuroanatomy, the medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist Johann Christian Reil), is a large ascending bundle of heavily myelinated axons that decussate (cross) in the brainstem, specifically in the m ...

of the pons and dorsal and medial to it.,

References

External links

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