Gustatory nucleus

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Gustatory nucleus
Details
PartsA component of the solitary nucleus
FunctionAssisting in food identification.
Identifiers
NeuroNames 1386
Anatomical terms of neuroanatomy
Location of structures connected to the gustatory nucleus Blausen 0115 BrainStructures.png
Location of structures connected to the gustatory nucleus
Basic neuroanatomy of the gustatory system. Basic neuroanatomy of the gustatory system.jpg
Basic neuroanatomy of the gustatory system.
Different taste receptors in the tongue and their connections to afferent neurons. Taste cells - Type I II III Receptors grey.png
Different taste receptors in the tongue and their connections to afferent neurons.

The gustatory nucleus is the rostral part of the solitary nucleus located in the medulla. The gustatory nucleus is associated with the sense of taste [1] and has two sections, the rostral and lateral regions. [2] A close association between the gustatory nucleus and visceral information exists for this function in the gustatory system, assisting in homeostasis - via the identification of food that might be possibly poisonous or harmful for the body. [3] There are many gustatory nuclei in the brain stem. Each of these nuclei corresponds to three cranial nerves, the facial nerve (VII), the glossopharyngeal nerve (IX), and the vagus nerve (X) [3] and GABA is the primary inhibitory neurotransmitter involved in its functionality. [4] All visceral afferents in the vagus and glossopharyngeal nerves first arrive in the nucleus of the solitary tract and information from the gustatory system can then be relayed to the thalamus and cortex. [5]

Contents

The central axons on primary sensory neurons in the taste system in the cranial nerve ganglia connect to lateral and rostral regions of the nucleus of the solitary tract which is located in the medulla and is also known as the gustatory nucleus. [3] The most pronounced gustatory nucleus is the rostral cap of the nucleus solitarius which is located at the ponto-medullary junction. Afferent taste fibers from the facial and from the facial and glossopharyngeal nerves are sent to the nucleus solitarius. The gustatory system then sends information to the thalamus which ultimately sends information to the cerebral cortex.

Each nucleus from the gustatory system can contain networks of interconnected neurons that can help regulate the firing rates of one another. [6] Fishes (specifically channel catfish), have been used to study the structure, mechanism for activation and its integrated with the solitary nucleus. The secondary gustatory nucleus contains three subnucleic structures: a medial, central and dorsal subnucleus (with the central and dorsal positioned in the rostral area of the secondary gustatory nucleus). [7]

Furthermore, the gustatory nucleus is connected via the pons to the thalamocortical system consisting of the hypothalamus and the amygdala. [6] These connections can stimulate appetite, satisfaction, and other homeostatic responses that have to do with eating. [3] Distributed throughout the dorsal epithelium of the tongue, soft palate, pharynx, and upper part of the esophagus are taste buds that contain taste cells, which are peripheral receptors involved in gustatory system and react to chemical stimuli. [3] Different sections of the tongue are innervated with the three cranial nerves. The facial nerve (VII) innervates the anterior two-thirds of the tongue, the glossopharyngeal nerve (IX) innervates the posterior one-third and the vagus nerve (X) innervates the epiglottis. [8]

The study of the nucleus usually involves model organisms like fish, hamsters, and mice. [7] [9] [10] Studies with humans involve MRIs and PET scan. [2] [11] A study done on monkeys found that when a given food is consumed to the point that a monkey is full and satisfied, specific orbitofrontal neurons in the monkey direct their firing towards that stimulus which indicates that these neurons are used in motivating one to eat as well as not to eat. In addition, the gustatory system has been greatly studied in some cyprinoid and cobitoid fish species because of their enormously hypertrophied peripheral gustatory nerves. The major difference between the gustatory neural structure of the fish and the rat is that the secondary gustatory nucleus of the fish projects to the interior lobe's lateral lobule of the diencephalon, while in the rat, the secondary gustatory nucleus projects to a specific thalamic area in the ventrobasal complex and to the ventral forebrain and rostroventral diencephalon. [5]

Mechanism

Three of the twelve cranial nerves send input to the Gustatory nucleus: the facial nerve (VII), the glossopharyngeal nerve (IX), and the vagus nerve (X). 1320 The Cranial Nerves.jpg
Three of the twelve cranial nerves send input to the Gustatory nucleus: the facial nerve (VII), the glossopharyngeal nerve (IX), and the vagus nerve (X).

Taste cells synapse with primary sensory axons of three cranial nerves; the facial nerve, glossopharyngeal nerve, and the vagus nerve. These cranial nerves innervate the taste buds in the tongue, palate, epiglottis, and esophagus. The primary sensory neurons of these central axons are in the cranial nerve ganglia of each respective cranial nerve. To produce the sense of taste, these neurons project to the gustatory nucleus, or the rostral and lateral regions of the nucleus of the solitary tract, and are ultimately projected to the cerebral cortex. [3]

The tongue contains taste receptors, that sends sensory information via action potential to the solitary nucleus. Then, such signal is directed towards the gustatory nucleus, which is located within the Thalamus. [12] Topography on the tongue doesn't determine the arrangement and processing of input within this nucleus. Instead, individual gustatory nuclei processing information is influenced by separate taste bud populations. Some examples of gustatory cranial nerves, that innervate the taste buds and are connected to this nucleus include the chorda tympani and lingual branch of the glossopharyngeal nerves. [13]

Tastants are the chemical molecules that provide the stimulus for taste perception. The concentration of this taste stimulus is what dictates the intensity of the taste sensation that is perceived. [14] Furthermore, the threshold concentration for a required degree of sensation varies depending on the specific tastant. However, in general, threshold concentrations for tastants are very high relative to other sensory stimuli such as odorants. [15]

Gustatory Nucleus and Obesity

Numerous studies have investigated the connection between the gustatory nucleus and obesity; an increase in visceral fat is negatively correlated with taste function. In both humans and rats, taste sensitivity changes with body weight, especially sweet and fat taste qualities that signal high energy availability. The nucleus tractus solitarii (NTS), which includes the gustatory nucleus, has neurons that express many different receptors that inform organisms of their internal state and are involved in the homeostatic regulation of ingestion. This shows the role of taste as a sensory regulator of food consumption that produces different responses depending on the chemical composition of a food. However, in rats and humans with obesity, there is a reduction in taste receptor cell expression as well as reduced activation of taste receptor cells. [16]

In one study, the effect of obesity on responses to taste stimuli in the NTS was investigated by recording taste responses from single cells in this sensory region of rats with diet induced obesity due to a high energy diet and lean rats fed a normal diet. Results of the study showed that rats with diet induced obesity produce a more prevalent response to taste in the gustatory nucleus of the NTS as well as a weakened association between taste responses and ingestive behavior compared to lean rats. In addition, it was also discovered that the responses to taste stimuli in rats with obesity were smaller, shorter, and occur at longer latencies compared to those of lean rats. These electrophysiological recordings create a connection between the gustatory nucleus and obesity as exposure to a high energy diet can alter how taste is encoded by the nervous system. In both humans and rats with obesity, taste responses are shorter and weaker and can have a large impact on how the brainstem represents taste stimuli. This ultimately effects food choice and body weight, resulting in a possible increase in consumption of high energy foods, such as sugars and fats. [16]

Related Research Articles

<span class="mw-page-title-main">Cranial nerves</span> Nerves that emerge directly from the brain and the brainstem

Cranial nerves are the nerves that emerge directly from the brain, of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck, including the special senses of vision, taste, smell, and hearing.

<span class="mw-page-title-main">Vagus nerve</span> Cranial nerve X, for visceral innervation

The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right vagus nerves—but they are typically referred to collectively as a single subsystem. The vagus is the longest nerve of the autonomic nervous system in the human body and comprises both sensory and motor fibers. The sensory fibers originate from neurons of the nodose ganglion, whereas the motor fibers come from neurons of the dorsal motor nucleus of the vagus and the nucleus ambiguus. The vagus was also historically called the pneumogastric nerve.

<span class="mw-page-title-main">Autonomic nervous system</span> Division of the nervous system supplying internal organs, smooth muscle and glands

The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that supplies internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.

<span class="mw-page-title-main">Parasympathetic nervous system</span> Division of the autonomic nervous system

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Facial nerve</span> Cranial nerve VII, for the face and tasting

The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue. The nerve typically travels from the pons through the facial canal in the temporal bone and exits the skull at the stylomastoid foramen. It arises from the brainstem from an area posterior to the cranial nerve VI and anterior to cranial nerve VIII.

<span class="mw-page-title-main">Brainstem</span> Posterior part of the brain, adjoining and structurally continuous

The brainstem 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 continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

<span class="mw-page-title-main">Trigeminal nerve</span> Cranial nerve responsible for the faces senses and motor functions

In neuroanatomy, the trigeminal nerve (lit. triplet nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name (trigeminal, from Latin tri- 'three', and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

<span class="mw-page-title-main">Glossopharyngeal nerve</span> Cranial nerve IX, for the tongue and pharynx

The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.

<span class="mw-page-title-main">Taste bud</span> Taste receptor cells

Taste buds contain the taste receptor cells, which are also known as gustatory cells. The taste receptors are located around the small structures known as papillae found on the upper surface of the tongue, soft palate, upper esophagus, the cheek, and epiglottis. These structures are involved in detecting the five elements of taste perception: saltiness, sourness, bitterness, sweetness and umami. A popular myth assigns these different tastes to different regions of the tongue; in fact, these tastes can be detected by any area of the tongue. Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with the taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves.

<span class="mw-page-title-main">Solitary nucleus</span> Sensory nuclei in medulla oblongata

In the human brainstem, the solitary nucleus, also called nucleus of the solitary tract, nucleus solitarius, and nucleus tractus solitarii, is a series of purely sensory nuclei forming a vertical column of grey matter embedded in the medulla oblongata. Through the center of the SN runs the solitary tract, a white bundle of nerve fibers, including fibers from the facial, glossopharyngeal and vagus nerves, that innervate the SN. The SN projects to, among other regions, the reticular formation, parasympathetic preganglionic neurons, hypothalamus and thalamus, forming circuits that contribute to autonomic regulation. Cells along the length of the SN are arranged roughly in accordance with function; for instance, cells involved in taste are located in the rostral part, while those receiving information from cardio-respiratory and gastrointestinal processes are found in the caudal part.

<span class="mw-page-title-main">Nucleus ambiguus</span>

The nucleus ambiguus is a group of large motor neurons, situated deep in the medullary reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innervate the muscles of the soft palate, pharynx, and larynx which are associated with speech and swallowing. As well as motor neurons, the nucleus ambiguus contains preganglionic parasympathetic neurons which innervate postganglionic parasympathetic neurons in the heart.

<span class="mw-page-title-main">Corticobulbar tract</span> Motor pathway in the brain connecting the motor cortex to the medullary pyramids

In neuroanatomy, the corticobulbartract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata region, and are primarily involved in carrying the motor function of the non-oculomotor cranial nerves. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

<span class="mw-page-title-main">Chorda tympani</span> Nerve carrying taste sensations

Chorda tympani is a branch of the facial nerve that carries gustatory (taste) sensory innervation from the front of the tongue and parasympathetic (secretomotor) innervation to the submandibular and sublingual salivary glands.

<span class="mw-page-title-main">Cranial nerve nucleus</span>

A cranial nerve nucleus is a collection of neurons in the brain stem that is associated with one or more of the cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei except that of the trochlear nerve supply nerves of the same side of the body.

<span class="mw-page-title-main">Inferior ganglion of glossopharyngeal nerve</span>

The inferior ganglion of the glossopharyngeal nerve is a sensory ganglion. It is larger than and inferior to the superior ganglion of the glossopharyngeal nerve. It is located within the jugular foramen.

<span class="mw-page-title-main">Inferior ganglion of vagus nerve</span> Ganglion of the peripheral nervous system

The inferior ganglion of the vagus nerve is a sensory ganglion of the peripheral nervous system. It is located within the jugular foramen where the vagus nerve exits the skull. It is larger than and below the superior ganglion of the vagus nerve.

<span class="mw-page-title-main">Solitary tract</span>

The solitary tract, is a compact fiber bundle that extends longitudinally through the posterolateral region of the medulla oblongata. The solitary tract is surrounded by the solitary nucleus, and descends to the upper cervical segments of the spinal cord. It was first named by Theodor Meynert in 1872.

A Special visceral afferent fibers (SVA) is a afferent fiber that develop in association with the gastrointestinal tract. They carry the special sense of taste (gustation). The cranial nerves containing SVA fibers are the facial nerve (VII), the glossopharyngeal nerve (IX), and the vagus nerve (X). The facial nerve receives taste from the anterior 2/3 of the tongue; the glossopharyngeal from the posterior 1/3, and the vagus nerve from the epiglottis. The sensory processes, using their primary cell bodies from the inferior ganglion, send projections to the medulla, from which they travel in the tractus solitarius, later terminating at the rostral nucleus solitarius.

<span class="mw-page-title-main">Salivatory nuclei</span>

The salivatory nuclei are the superior salivatory nucleus, and the inferior salivatory nucleus that innervate the salivary glands. They are located in the pontine tegmentum in the brainstem. They both are examples of cranial nerve nuclei.

The primary gustatory cortex is a brain structure responsible for the perception of taste. It consists of two substructures: the anterior insula on the insular lobe and the frontal operculum on the inferior frontal gyrus of the frontal lobe. Because of its composition the primary gustatory cortex is sometimes referred to in literature as the AI/FO(Anterior Insula/Frontal Operculum). By using extracellular unit recording techniques, scientists have elucidated that neurons in the AI/FO respond to sweetness, saltiness, bitterness, and sourness, and they code the intensity of the taste stimulus.

References

  1. ↑ "Anatomy 530a at UWO (Functional Neuroanatomy)".
  2. 1 2 Purves, Dale; Augustine, George; Fitzpatrick, David; Hall, William; LaMantia, Anthony-Samuel; White, Leonard (2012). Neuroscience Fifth Edition. Sunderland, Massachusetts: Sinauer Associates, Inc. p. 341. ISBN   978-0-87893-695-3.
  3. 1 2 3 4 5 6 Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark (2001). "The Organization of the Taste System". Neuroscience. 2nd Edition.
  4. ↑ Grabauskas G, Bradley RM (November 1998). "Ionic mechanism of GABAA biphasic synaptic potentials in gustatory nucleus of the solitary tract". Ann. N. Y. Acad. Sci. 855 (1): 486–487. Bibcode:1998NYASA.855..486G. doi:10.1111/j.1749-6632.1998.tb10610.x. PMID   9929643. S2CID   27455499.
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  6. 1 2 Katz, Donald B; Nicolelis, Miguel A L; Simon, Sidney A (2002-08-01). "Gustatory processing is dynamic and distributed". Current Opinion in Neurobiology. 12 (4): 448–454. doi:10.1016/S0959-4388(02)00341-0. ISSN   0959-4388. PMID   12139994. S2CID   17044328.
  7. 1 2 Lamb, Charles F.; Finger, Thomas E. (1996). "Axonal projection patterns of neurons in the secondary gustatory nucleus of channel catfish". Journal of Comparative Neurology. 365 (4): 585–593. doi:10.1002/(sici)1096-9861(19960219)365:4<585::aid-cne6>3.0.co;2-0. ISSN   1096-9861. PMID   8742304. S2CID   19083368.
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  9. ↑ Whitehead, Mark C. (1986). "Anatomy of the gustatory system in the hamster: Synaptology of facial afferent terminals in the solitary nucleus". Journal of Comparative Neurology. 244 (1): 72–85. doi:10.1002/cne.902440106. ISSN   1096-9861. PMID   3950091. S2CID   24265928.
  10. ↑ Shipley, Michael T.; Geinisman, Yuri (1984-03-01). "Anatomical evidence for convergence of olfactory, gustatory, and visceral afferent pathways in mouse cerebral cortex". Brain Research Bulletin. 12 (3): 221–226. doi:10.1016/0361-9230(84)90049-2. ISSN   0361-9230. PMID   6722597. S2CID   4776024.
  11. ↑ Zald, D. H.; Lee, J. T.; Fluegel, K. W.; Pardo, J. V. (1998-06-01). "Aversive gustatory stimulation activates limbic circuits in humans". Brain. 121 (6): 1143–1154. doi: 10.1093/brain/121.6.1143 . ISSN   0006-8950. PMID   9648549.
  12. ↑ Watson, Charles; Kirkcaldie, Matthew; Paxinos, George (2010-01-01), Watson, Charles; Kirkcaldie, Matthew; Paxinos, George (eds.), "Chapter 6 - Gathering information–the sensory systems", The Brain, Academic Press, pp. 75–96, doi:10.1016/B978-0-12-373889-9.50006-1, ISBN   9780123738899 , retrieved 2019-09-24
  13. ↑ Davis, Barry J.; Jang, Taichang (1988). "A Golgi analysis of the gustatory zone of the nucleus of the solitary tract in the adult hamster". Journal of Comparative Neurology. 278 (3): 388–396. doi:10.1002/cne.902780308. ISSN   1096-9861. PMID   2464006. S2CID   26097891.
  14. ↑ Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark (2001). "Taste Receptors and the Transduction of Taste Signals". Neuroscience. 2nd Edition.
  15. ↑ Satoh-Kuriwada, Shizuko; Shoji, Noriaki; Miyake, Hiroyuki; Watanabe, Chiyo; Sasano, Takashi (2018). "Effects and Mechanisms of Tastants on the Gustatory-Salivary Reflex in Human Minor Salivary Glands". BioMed Research International. 2018: 3847075. doi: 10.1155/2018/3847075 . ISSN   2314-6141. PMC   5832054 . PMID   29651428.
  16. 1 2 Weiss, Michael S.; Hajnal, Andras; Czaja, Krzysztof; Di Lorenzo, Patricia M. (2019). "Taste Responses in the Nucleus of the Solitary Tract of Awake Obese Rats Are Blunted Compared With Those in Lean Rats". Frontiers in Integrative Neuroscience. 13: 35. doi: 10.3389/fnint.2019.00035 . ISSN   1662-5145. PMC   6683675 . PMID   31417373.
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