5HT receptor
5-HT receptors, 5-hydroxytryptamine receptors, or serotonin receptors, are a group of G protein-coupled receptor and ligand-gated ion channels found in multiple tissues including the central and peripheral nervous systems. They mediate both ex ...
that binds the
endogenous
Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell.
For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...
neurotransmitter
A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell.
Neurotra ...
serotonin
Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...
(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 ...
excitatory
In neuroscience, an excitatory postsynaptic potential (EPSP) is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential. This temporary depolarization of postsynaptic membrane potential, caused by the ...
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'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
encoding for the
receptor
Receptor may refer to:
* Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and respond ...
.
Distribution
The 5HT6 receptor is expressed almost exclusively in the
brain
The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
. 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. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...
entorhinal
The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in th ...
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 hypo ...
,
striatum
The striatum (: striata) or corpus striatum is a cluster of interconnected nuclei that make up the largest structure of the subcortical basal ganglia. The striatum is a critical component of the motor and reward systems; receives glutamat ...
,
caudate nucleus
The caudate nucleus is one of the structures that make up the corpus striatum, which is part of the basal ganglia in the human brain. Although the caudate nucleus has long been associated with motor processes because of its relation to Parkinso ...
,
hippocampus
The hippocampus (: hippocampi; via Latin from Ancient Greek, Greek , 'seahorse'), also hippocampus proper, is a major component of the brain of humans and many other vertebrates. In the human brain the hippocampus, the dentate gyrus, and the ...
, and the molecular layer of 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 ...
limbic
The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''P ...
, 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 movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxes.
To control ...
,
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 is 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, thought, ...
, 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 remembe ...
.
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 agonist ...
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 cation ...
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 gamma-aminobutyric acid (GABA). For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic ...
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. It is an amine synthesized ...
and
norepinephrine
Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic compound, organic chemical in the catecholamine family that functions in the brain and human body, body as a hormone, neurotransmitter and neuromodulator. The ...
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
Latrepirdine ( INN, also known as dimebolin and sold as Dimebon) is an antihistamine drug which has been used clinically in Russia since 1983.
Research was conducted in both Russia and western nations into potential applications as a neuroprotec ...
,
idalopirdine
Idalopirdine (INN; development code Lu AE58054) is a potent and selective 5-HT6 receptor antagonist under development by Lundbeck as an augmentation therapy for the treatment of cognitive deficits associated with Alzheimer's disease and schiz ...
(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 and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...
and other forms of
dementia
Dementia is a syndrome associated with many neurodegenerative diseases, characterized by a general decline in cognitive abilities that affects a person's ability to perform activities of daily living, everyday activities. This typically invo ...
. 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 reg ...
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 conn ...
, 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, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...
anxiety
Anxiety is an emotion characterised by an unpleasant state of inner wikt:turmoil, turmoil and includes feelings of dread over Anticipation, anticipated events. Anxiety is different from fear in that fear is defined as the emotional response ...
, 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
antidepressant
Antidepressants are a class of medications used to treat major depressive disorder, anxiety disorders, chronic pain, and addiction.
Common side effects of antidepressants include Xerostomia, dry mouth, weight gain, dizziness, headaches, akathi ...
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 primarily work by blo ...
s (SSRIs) and
tricyclic antidepressant
Tricyclic antidepressants (TCAs) are a class of medications that are used primarily as antidepressants. TCAs were discovered in the early 1950s and were marketed later in the decade. They are named after their chemical structure, which contains ...
s (TCAs).
Ligands
A large number of selective 5HT6 ligands have now been developed.
* 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
Lysergic acid diethylamide, commonly known as LSD (from German ; often referred to as acid or lucy), is a semisynthetic, hallucinogenic compound derived from ergot, known for its powerful psychological effects and serotonergic activity. I ...
Cerlapirdine
Cerlapirdine (USAN; SAM-531, WAY-262,531, PF-05212365) is a drug which was under development by Wyeth/Pfizer for the treatment of cognitive disorders associated with Alzheimer's disease and schizophrenia. In a phase II clinical trial it demonstr ...
Idalopirdine
Idalopirdine (INN; development code Lu AE58054) is a potent and selective 5-HT6 receptor antagonist under development by Lundbeck as an augmentation therapy for the treatment of cognitive deficits associated with Alzheimer's disease and schiz ...
antagonist
An antagonist is a character in a story who is presented as the main enemy or rival of the protagonist and is often depicted as a villain.Landipirdine (RO-5025181, SYN-120)
*
Latrepirdine
Latrepirdine ( INN, also known as dimebolin and sold as Dimebon) is an antihistamine drug which has been used clinically in Russia since 1983.
Research was conducted in both Russia and western nations into potential applications as a neuroprotec ...
(non-selective) and analogues
* Maritupirdine (AVN-101) – selective
Atypical antipsychotics
The atypical antipsychotics (AAP), also known as second generation antipsychotics (SGAs) and serotonin–dopamine antagonists (SDAs), are a group of antipsychotic drugs (antipsychotic drugs in general are also known as tranquilizers and neuro ...
(
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, ...
,
olanzapine
Olanzapine, sold under the brand name Zyprexa among others, is an atypical antipsychotic primarily used to treat schizophrenia and bipolar disorder. It is also sometimes used off-label for treatment of chemotherapy-induced nausea and vomitin ...
,
asenapine
Asenapine, sold under the brand name Saphris among others, is an atypical antipsychotic medication used to treat schizophrenia and acute mania associated with bipolar disorder as well as the medium to long-term management of bipolar disorder.
I ...
,
clozapine
Clozapine, sold under the brand name Clozaril among others, is a psychiatric medication and was the first atypical antipsychotic to be discovered. It is used primarily to treat people with schizophrenia and schizoaffective disorder who have ...
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 ...
neuropsychiatric disorder
A mental disorder, also referred to as a mental illness, a mental health condition, or a psychiatric disability, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. A mental disorder is ...
s. For example, an association between the C267T ( rs1805054) polymorphism and
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...
has been shown.
Others have studied the polymorphism in relation to
Parkinson's disease
Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...
.
See also
*
5-HT receptor
5-HT receptors, 5-hydroxytryptamine receptors, or serotonin receptors, are a group of G protein-coupled receptor and ligand-gated ion channels found in multiple tissues including the Central nervous system, central and peripheral nervous systems ...