The parabrachial nuclei, also known as the parabrachial complex, are a group of nuclei in the dorsolateral

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, 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 ...

that surrounds the

superior cerebellar peduncle In the human brain, the superior cerebellar peduncle (brachium conjunctivum) is one of the three paired cerebellar peduncles of bundled fibers that connect the cerebellum to the brainstem. The superior cerebellar peduncle connects to the midbrain. ...

as it enters the

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 conti ...

from the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

. They are named from the Latin term for the superior cerebellar peduncle, the ''brachium conjunctivum''. In the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

, the expansion of the superior cerebellar peduncle expands the parabrachial nuclei, which form a thin strip of

grey matter Grey matter, or gray matter in American English, is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axons), glial cells ( astrocytes and oligodendrocytes), synapses, ...

over most of the peduncle. The parabrachial nuclei are typically divided along the lines suggested by Baxter and Olszewski in humans, into a medial parabrachial nucleus and lateral parabrachial nucleus. These have in turn been subdivided into a dozen subnuclei: the superior, dorsal, ventral, internal, external and extreme lateral subnuclei; the lateral crescent and subparabrachial nucleus (Kolliker-Fuse nucleus) along the ventrolateral margin of the lateral parabrachial complex; and the medial and external medial subnuclei

Anatomy

Structure

The main parabrachial nuclei are the medial parabrachial nucleus, the lateral parabrachial nucleus, and the subparabrachial nucleus. They are located at the junction of the

midbrain The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

and pons.

Medial parabrachial nucleus

The medial parabrachial nucleus relays information from the taste area of the

solitary nucleus The solitary nucleus (SN) (nucleus of the solitary tract, nucleus solitarius, or nucleus tractus solitarii) is a series of neurons whose cell bodies form a roughly vertical column of grey matter in the medulla oblongata of the brainstem. Their a ...

to the

ventral posteromedial nucleus The ventral posteromedial nucleus (VPM) is a nucleus within the ventral posterior nucleus of the thalamus and serves an analogous somatosensory relay role for the ascending trigeminothalamic tracts as its lateral neighbour the ventral posterolat ...

of the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

Lateral parabrachial nucleus

The lateral parabrachial nucleus receives information from the caudal solitary tract and transmits signals mainly to the

medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repr ...

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

but also to the lateral

and many of the nuclei targeted by the medial parabrachial nucleus.

Subparabrachial nucleus

The subparabrachial nucleus (also known as the Kölliker-Fuse nucleus, or diffuse reticular nucleus) regulates the

breathing rate The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute. Measurement The respiratory rate in humans is me ...

. It receives signals from the caudal, cardio-respiratory part of the

and sends signals to the lower

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 ...

, the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

, the

amygdala The amygdala (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...

and the

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

Afferents and efferents

The parabrachial nuclei receive visceral afferent information from a variety of sources in the brainstem, including much from the

, which brings

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

information and information about the remainder of the body. The external, dorsal, internal and superior lateral subnuclei also receive input from the spinal and trigeminal dorsal horn, mainly concerned with pain and other visceral sensations. Outputs from the parabrachial nucleus originate from specific subnuclei and target forebrain sites involved in autonomic regulation, including the lateral hypothalamic area, ventromedial, dorsomedial, and arcuate hypothalamic nuclei, the median and lateral preoptic nuclei, the substantia innominate, the ventroposterior parvicellular and

intralaminar thalamic nuclei The intralaminar thalamic nuclei (ITN) are collections of neurons in the medullary laminae of thalamus, internal medullary lamina of the thalamus.Mancall, E., Brock, D. & Gray, H. (2011). Gray's clinical neuroanatomy the anatomic basis for clinical ...

, the central nucleus of the amygdala, and the insular and infralimbic cortex. The subparabrachialnucleus and lateral crescent send efferents to the nucleus of the solitary tract,

ventrolateral medulla The ventrolateral medulla, part of the medulla oblongata of the brainstem, plays a major role in regulating arterial blood pressure and breathing. It regulates blood pressure by regulating the activity of the sympathetic nerves that target the hear ...

, and spinal cord, where they target many respiratory and autonomic cell groups. Many of these same brainstem and forebrain areas send efferents back to the parabrachial nucleus as well.

Function

Arousal

Many subsets of neurons in the parabrachial complex that target specific

forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain controls body temperature, reproductive functions, eating, sleeping, and the display of emotions. Ve ...

or brainstem cell groups contain specific

neuropeptide Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

s, and appear to carry out distinct functions. For example, a population of neurons in the external lateral parabrachial subnucleus that contain the neurotransmitter

calcitonin gene-related peptide Calcitonin gene-related peptide (CGRP) is a neuropeptide that belongs to the calcitonin family. Human CGRP consists of two Protein isoform, isoforms, CGRP alpha (α-CGRP, also known as CGRP I) and CGRP beta (β-CGRP, also known as CGRP II). α-C ...

(CGRP) appears to be critical for relaying information about hypoxia (low blood oxygen) and/or

hypercapnia Hypercapnia (from the Greek ''hyper'', "above" or "too much" and ''kapnos'', "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...

(high blood ) to forebrain sites to “wake up the brain” (arouse) when breathing is inadequate to meet physiological demands during sleep. This resulting “wakefulness drive to breath” contributes to prevention of

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects all the tissues and organs, some more rapidly than others. There are m ...

. Recent data indicate that

glutamatergic Glutamatergic means "related to glutamate". A glutamatergic agent (or drug) is a chemical that directly modulates the excitatory amino acid (glutamate/aspartate) system in the body or brain. Examples include excitatory amino acid receptor agonist ...

neurons in the medial and lateral parabrachial nuclei, along with glutamatergic neurons in the pedunculopontine tegmental nucleus, provide a critical node in the brainstem for producing a waking state. Lesions of these neurons cause irreversible

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

Blood sugar control

Other neurons in the superior lateral parabrachial nucleus that contain cholecystokinin have been found to prevent hypoglycemia.

Thermoregulation

In 2008, neurons in the external lateral parabrachial nucleus were found to mediate

cold Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjectivity, subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute t ...

sensory transmission from the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

to the

preoptic area The preoptic area is a region of the hypothalamus. MeSH classifies it as part of the anterior hypothalamus. TA lists four nuclei in this region, (medial, median, lateral, and periventricular). Functions The preoptic area is responsible for the ...

, a thermoregulatory center in the

, to stimulate heat production in the cold. Warm sensory transmission to the preoptic area to avoid

hyperthermia Hyperthermia, also known as overheating, is a condition in which an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat than it dissipates. When extreme te ...

in hot environments is mediated by another group of neurons in the dorsal lateral parabrachial nucleus, which contain dynorphin or

cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat a ...

. A study in 2017, has shown this thermosensory information to be relayed through the lateral parabrachial nucleus rather than the thalamus, which drives thermoregulatory behavior. A thermosensory neural pathway from the lateral parabrachial nucleus to the preoptic area induces heat avoidance behavior, and another pathway to the central amygdaloid nucleus induces cold avoidance behavior.

Taste

Parabrachial neurons in rodents that relay taste information to the ventroposterior parvocellular (taste) nucleus of the

are mainly CGRP neurons in the external medial parabrachial nucleus and they project predominantly

contralateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

ly, as well as a smaller number in the ventral lateral nucleus, which project mainly

ipsilateral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

ly. Neurons that mediate the sensation of

itching An itch (also known as pruritus) is a sensation that causes a strong desire or reflex to scratch. Itches have resisted many attempts to be classified as any one type of sensory experience. Itches have many similarities to pain, and while both ...

, connect to the parabrachial nucleus by way of glutamatergic spinal projection neurons. This pathway triggers scratching in mice.

Pleasure

The parabrachial nucleus relays satiety and pain-related signals to higher brain regions; when inhibited, this can produce "liking" responses to certain pleasurable stimuli, such as sweet taste.

Wet dog shakes

The lateral parabrachial nucleus integrates sensory signals, primarily, but not exclusively, from low-threshold mechanoreceptors to initiate the wet dog shake behavior by which mammals remove water and irritants from their back and neck fur. It receives this mechanoreceptor input from group C nerve fibers that connect to spinoparabrachial neurons in the

References

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