The 5HT₆ receptor is a subtype of 5HT receptor that binds the

endogenous Endogenous substances and processes are those that originate from within a living system such as an organism, tissue, or cell. In contrast, exogenous substances and processes are those that originate from outside of an organism. For example, ...

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neu ...

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 va ...

(5-hydroxytryptamine, 5HT). It is a

G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related p ...

(GPCR) that is coupled to G_s and mediates excitatory

neurotransmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...

. ''HTR6'' denotes the

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

encoding for the

receptor Receptor may refer to: *Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...

Distribution

The 5HT₆ receptor is expressed almost exclusively in the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

. It is distributed in various areas including, but not limited to, the

olfactory tubercle The olfactory tubercle (OT), also known as the tuberculum olfactorium, is a multi-sensory processing center that is contained within the olfactory cortex and ventral striatum and plays a role in reward cognition. The OT has also been shown to ...

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

(

frontal Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music *The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...

and entorhinal regions),

nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hyp ...

striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives gluta ...

caudate nucleus The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's d ...

hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic syste ...

, and the molecular layer of the

cerebellum The cerebellum (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 or even larger. In humans, the cerebe ...

. Based on its abundance in extrapyramidal, limbic, and cortical regions it can be suggested that the 5HT₆ receptor plays a role in functions like

motor control Motor control is the regulation of movement in organisms that possess a nervous system. Motor control includes reflexes as well as directed movement. To control movement, the nervous system must integrate multimodal sensory information (both ...

emotionality Emotionality is the observable behavioral and physiological component of emotion. It is a measure of a person's emotional reactivity to a stimulus. Most of these responses can be observed by other people, while some emotional responses can only ...

cognition Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, though ...

, and

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...

Function

Blockade of central 5HT₆ receptors has been shown to increase

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 agonis ...

and

cholinergic Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word " choline" describes the various quaternary ammonium salts containing the ''N'',''N'',''N''-trimethylethanolammonium cati ...

neurotransmission in various brain areas, whereas activation enhances

GABAergic In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter GABA. For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic neuron produces GABA. A ...

signaling in a widespread manner. Antagonism of 5HT₆ receptors also facilitates

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. Dopamine constitutes about 80% o ...

and

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad ...

release in the frontal cortex, while stimulation has the opposite effect.

As a drug target for antagonists

Despite the 5HT₆ receptor having a functionally excitatory action, it is largely co-localized with GABAergic neurons and therefore produces an overall inhibition of brain activity. In parallel with this, 5HT₆ antagonists are hypothesized to improve cognition, learning, and memory. Agents such as latrepirdine, idalopirdine (Lu AE58054), and intepirdine (SB-742,457/RVT-101) were evaluated as novel treatments for

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...

and other forms of

dementia Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...

. However, phase III trials of latrepirdine, idalopirdine, and intepirdine have failed to demonstrate efficacy. 5HT₆ antagonists have also been shown to reduce

appetite Appetite is the desire to eat food items, usually due to hunger. Appealing foods can stimulate appetite even when hunger is absent, although appetite can be greatly reduced by satiety. Appetite exists in all higher life-forms, and serves to regu ...

and produce

weight loss Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, by a mean loss of fluid, body fat ( adipose tissue), or lean mass (namely bone mineral deposits, muscle, tendon, and other co ...

, and as a result, PRX-07034, BVT-5,182, and BVT-74,316 are being investigated for the treatment of

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

As a drug target for agonists

Recently, the 5HT₆ agonists WAY-181,187 and WAY-208,466 have been demonstrated to be active in rodent models of depression,

anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...

, and obsessive-compulsive disorder (OCD), and such agents may be useful treatments for these conditions. Additionally, indirect 5HT₆ activation may play a role in the therapeutic benefits of

serotonergic Serotonergic () or serotoninergic () means "pertaining to or affecting serotonin". Serotonin is a neurotransmitter. A synapse is serotonergic if it uses serotonin as its neurotransmitter. A serotonergic neuron ''produces'' serotonin. A substance is ...

antidepressant Antidepressants are a class of medication used to treat major depressive disorder, anxiety disorders, chronic pain conditions, and to help manage addictions. Common Side effect, side-effects of antidepressants include Xerostomia, dry mouth, weig ...

s like the

selective serotonin reuptake inhibitor Selective serotonin reuptake inhibitors (SSRIs) are a class of drugs that are typically used as antidepressants in the treatment of major depressive disorder, anxiety disorders, and other psychological conditions. SSRIs increase the extracellul ...

s (SSRIs) and

tricyclic antidepressant Tricyclic antidepressants (TCAs) are a class of medications that are used primarily as antidepressants, which is important for the management of depression. They are second-line drugs next to SSRIs. TCAs were discovered in the early 1950s and wer ...

s (TCAs).

Ligands

A large number of selective 5HT₆ ligands have now been developed.

Agonists

Full agonists

* 2-Ethyl-5-methoxy-N,N-dimethyltryptamine (EMDT) * WAY-181,187 * WAY-208,466 * ''N''-(inden-5-yl)imidazothiazole-5-sulfonamide (43): ''K''_i = 4.5nM, EC₅₀ = 0.9nM, E_max = 98% * E-6837 - Full agonist at human 5HT₆ receptors

Partial agonists

* E-6801 * E-6837 - partial agonist at rat 5-HT₆ receptors. Orally active in rats, and caused weight loss with chronic administration * EMD-386,088 - potent partial agonist (EC₅₀ = 1 nM) but non-selective * LSD - E_max = 60%

Antagonists and inverse agonists

* ALX-1161 * AVN-211 * BVT-5182 * BVT-74316 * Cerlapirdine - selective * EGIS-12233 - mixed 5HT₆ / 5HT₇ antagonist * Idalopirdine (Lu AE58054) - selective * Intepirdine (SB-742,457/RVT-101) - selective

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, ri ...

* Landipirdine (RO-5025181, SYN-120) * Latrepirdine (non-selective) and analogues * MS-245 * PRX-07034 * SB-258,585 * SB-271,046 * SB-357,134 * SB-399,885 * SGS 518 Fb: 45441-26-9* Ro 04-6790 * Ro-4368554 * Atypical antipsychotics (

sertindole Sertindole, sold under the brand name Serdolect among others, is an antipsychotic medication. Sertindole was developed by the Danish pharmaceutical company Lundbeck and marketed under license by Abbott Labs. Like other atypical antipsychotics, i ...

olanzapine Olanzapine (sold under the trade name Zyprexa among others) is an atypical antipsychotic primarily used to treat schizophrenia and bipolar disorder. For schizophrenia, it can be used for both new-onset disease and long-term maintenance. It is t ...

, asenapine,

clozapine Clozapine is a psychiatric medication and is the first atypical antipsychotic (also called second-generation antipsychotic). It is primarily used to treat people with schizophrenia and schizoaffective disorders who have had an inadequate respo ...

) * WAY-255315 / SAM-315: K_i = 1.1 nM, IC₅₀ = 13 nM *

Rosa rugosa ''Rosa rugosa'' (rugosa rose, beach rose, Japanese rose, Ramanas rose, or letchberry) is a species of rose native to eastern Asia, in northeastern China, Japan, Korea and southeastern Siberia, where it grows on beach coasts, often on sand dunes ...

extract

Genetics

Polymorphisms in the HTR6 gene are associated with

neuropsychiatric disorder A mental disorder, also referred to as a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may be persistent, relapsing and remitt ...

s. For example, an association between the C267T ( rs1805054) polymorphism and

has been shown. Others have studied the polymorphism in relation to

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms beco ...

References

External links

* * * {{DEFAULTSORT:5-HT6 Receptor Serotonin receptors