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Types, Mechanism of action and more of: 5-Hydroxytryptamine receptors, Opioid receptors, GABA receptors - ePharmacology

Updated on September 29, 2015

Today on ePharmacology we will discuss about the following receptors:

  1. 5 Hydroxytryptamine (Serotonin) receptors
  2. Opioid receptors
  3. GABA receptors

Before starting you should review your knowledge of receptors in general.


Structure of 5HT-1B receptor
Structure of 5HT-1B receptor | Source

5-Hydroxytryptamine (Serotonin) receptors

5-Hydroxytryptamine (5-HT) / Serotonin receptors are of seven types. The seven Serotonin receptors are further divided into a total of 14 discovered serotonin receptors.

1) 5HT1 receptor

a) 5HT1A

b) 5HT1B

c) 5HT1D

d) 5HT1E

e) 5HT1F

2) 5HT2 receptors

a) 5HT2A

b) 5HT2B

c) 5HT2C

3) 5HT3 receptors

4) 5HT4 receptors

5) 5HT5 receptors

a) 5HT5A

b) 5HT5B

6) 5HT6 receptors

7) 5HT7 receptors

14 types of 5-HT (Serotonin) receptors and their locations
14 types of 5-HT (Serotonin) receptors and their locations | Source

5-HT 1 and 2 receptor agonists and antagonists

5-HT receptor
Agonist
Antagonist
5-HT1A
F-15,599
BMY 7378
 
Flesinoxan
Cyanopindolol
 
Gepirone
Iodocyanopindolol
 
Haloperidol
Lecozotan
 
Ipsapirone
Mefway
 
Quetiapine
WAY-100,635
 
Trazodone
WAY-100,135
 
Yohimbine
Nefazodone
 
Tandospirone
Nebivolol
 
 
Methiothepin
 
 
NAN-190
 
 
Methysergide
5HT-1B
CP-94,253
Alprenolol
 
Dihydroergotamine
AR-A000002
 
Eltoprazine
Yohimbine
 
Ergotamine
Asenapine
 
Methysergide
SB-216,641
 
RU 24969
Propranolol
 
TFMPP
Pindolol
 
Triptans e.g. Zolmitriptan, Eletriptan, Sumatriptan
Oxprenolol
 
Vortioxetine
Methiothepin
 
CGS-12066A
Metergoline
 
CP-93,129
Isamoltane
 
5-CT
Iodocyanopindolol
 
 
Cyanopindolol
 
 
GR-127,935
5-HT1D
5-CT
BRL-15572
 
Yohimbine
Ziprasidone
 
Triptans
Vortioxetine
 
Methysergide
Ritanserin
 
Ergotamine
Rauwolscine
 
Dihydroergotamine
Methiothepin
 
CP-135,807
Metergoline
 
 
Ketanserin
 
 
GR-127,935
5-HT1E
BRL-54443
 
5-HT1F
Naratriptan
 
 
BRL-54443
 
 
LY-334,370
 
 
Lasmiditan
 
5-HT2A
25I-NBOMe
Atypical antipsychotics Clozapine, Olanzapine, Quetiapine, Risperidone, Ziprasidone
 
TFMPP
Yohimbine
 
Psilocybin
Trazodone
 
Psilocin
Ritanserin
 
PNU-22394
Pizotifen
 
Myristicin
Pimavanserin
 
Mescaline
Nefazodone
 
LSD
Mirtazapine
 
Lisuride
Mianserin
 
Ergonovine
Methysergide
 
DOM
Ketanserin
 
DMT
Iloperidone
 
Bufotenin
Hydroxyzine
 
BZP
Haloperidol
 
5-MeO-DMT
Etoperidone
 
2C-B
Eplivanserin
 
 
Cyproheptadine
 
 
Clomipramine
 
 
Amitriptyline
 
 
Asenapine
 
 
Aripiprazole
5-HT2B
BW-723C86
Agomelatine
 
Ro60-0175
Yohimbine
 
PNU-22394
Tegaserod
 
Norfenfluramine
RS-127,445
 
MDMA
Ritanserin
 
Fenfluramine
Methysergide
 
 
Ketanserin
 
 
BZP
 
 
Asenapine
5-HT2C
A-372,159
Agomelatine
 
YM-348
Ziprasidone
 
Trazodone
Trazodone
 
TFMPP
Tramadol
 
Ro60-0175
Ritanserin
 
PNU-22394
Risperidone
 
Lorcaserin
Quetiapine
 
Ergonovine
Paroxetine
 
Aripiprazole
Olanzapine
 
AL-38022A
Nefazodone
 
 
Mirtazapine
 
 
Mianserin
 
 
Methysergide
 
 
Lisuride
 
 
Ketanserin
 
 
Iloperidone
 
 
Haloperidol
 
 
Fluoxetine
 
 
Etoperidone
 
 
Eltoprazine
 
 
Dimebolin
 
 
Cyproheptadine
 
 
Clozapine
 
 
Clomipramine
 
 
Asenapine
 
 
Amitriptyline
5-HT 1 and 2 receptor agonists and antagonists

5-HT 3, 4, 5, 6 and 7 receptor agonists and antagonists

5-HT Receptor
Agonist
Antagonist
5-HT3
2-Methyl-5-HT
Alosetron
 
RS-56812
Vortioxetine
 
Quipazine
Quetiapine
 
BZP
Olanzapine
 
 
Mirtazapine
 
 
Mianserin
 
 
Metoclopramide
 
 
Memantine
 
 
Clozapine
 
 
Several antiemetics: Dolasetron, Ondansetron, Granisetron, Tropisetron
5-HT4
5-MT
L-Lysine
 
Zacopride
Piboserod
 
Tegaserod
 
 
Renzapride
 
 
RS-67333
 
 
Prucalopride
 
 
Mosapride
 
 
Metoclopramide
 
 
Dazopride
 
 
Cisapride
 
 
Cinitapride
 
 
BIMU-8
 
5-HT5A
5-CT
Asenapine
 
Valerenic Acid
SB-699,551-A
 
Ergotamine
SB-699,551
 
 
Ritanserin
 
 
Methiothepin
 
 
Dimebolin
5-HT5B
 
 
5-HT6
EMD-386,088
Amitriptyline
 
EMDT
SB-399,885
 
 
SB-357,134
 
 
SB-271,046
 
 
SB-258,585
 
 
Ro04-6790
 
 
Olanzapine
 
 
MS-245
 
 
Iloperidone
 
 
Haloperidol
 
 
EGIS-12233
 
 
Dimebolin
 
 
Clozapine
 
 
Clomipramine
 
 
Asenapine
 
 
Aripiprazole
5-HT7
5-CT
Amitriptyline
 
RA-7
Vortioxetine
 
E-55888
SB-269,970
 
AS-19
Risperidone
 
Aripiprazole
Ritanserin
 
8-OH-DPAT
Olanzapine
 
 
Mirtazapine
 
 
Ketanserin
 
 
Imipramine
 
 
Iloperidone
 
 
Haloperidol
 
 
EGIS-12233
 
 
Clozapine
 
 
Clomipramine
 
 
Asenapine
5-HT 3, 4, 5, 6 and 7 receptor agonists and antagonists

Type 1, 2, 4, 5, 6, and 7 are G-coupled receptors and type 3 is a Ligand-gated Na+ and K+ cation channel. These receptors are present in the CNS and vascular smooth muscle.

Specific agonists for 5HT1 receptors are sumatriptan and buspirone. Spiperone, methiothepin and quipazine are the 5HT1 receptor antagonists.

Methysergide, ketanserin and cyproheptadine are the examples of 5HT2 receptor antagonists.

Specific agonist for 5HT3 receptor is 2-methyl-5-HT. Ondansetron and tropisetron are the 5HT3 receptor antagonists.

Metoclopramide is the specific agonist for 5HT4 receptor.

Opioid receptors

Morphine and related drugs produce their responses by acting on their specific receptors which are called opioid receptors. There are 3 well defined or classical subtypes of opioid receptor:

  • μ (Mu) opioid receptor
  • κ (Kappa) opioid receptor
  • δ (Delta) opioid receptor

More recently, cDNA encoding an orphan receptor was identified which has a high degree of homology to the classical opioid receptors. On structural grounds this receptor is an opioid receptor and has been named ORL1 (opioid receptor-like). Later an endogenous ligand was discovered for this receptor which is called Nociceptin. So ORL1 is now an adopted receptor.

Subtypes of opioid receptors and their locations
Subtypes of opioid receptors and their locations | Source

Opioid receptors are G-protein coupled receptors. All of the opioid receptors possess the same general structure of an extracellular N-terminal region, seven transmem­brane domains and intracellular C-terminal tail structure.

Different agonists act on different subtypes of receptor. For example, morphine predominantly acts on μ and κ opioid receptors. Enkephalins mainly bind with δ opioid receptors but have weak affinity to μ opioid receptors. Dynorphin preferentially binds with κ opioid receptors.

Selective and non-selective antagonists for opioid receptors:

Opioid Receptor
Selective Antagonist
Non-selective (for all opioid receptors) antagonists
Mu (μ) receptor
Cyprodime
Naloxone
Delta (δ) receptor
Naltrindole
Naltrexone
Kappa (κ) receptor
Norbinaltorphimine
Nalorphine
Nociceptin receptor
J-113,397
Levallorphan
 
 
AT-076

GABA receptors

GABA receptors are of two types:

  • GABAA
  • GABAB

Both types of recep­tors are present in the CNS. However, the concentration of GABA A receptors is more than that of GABAB receptors. GABAA receptors are widely distributed in the granular cell layers of the cerebellum and are directly associated with a Cl- channel (pore size ~5 Å). The concentration of GABAB receptor in the interpeduncular nucleus is far greater than the concentration of GABAA receptors and it appears to be linked to calcium and potassium channels via GTP-binding proteins.

GABA receptors appear to exist as pentamers of three distinct subunits in the arrangement αmβnγ. The β subunit appears to have the recognition capacity for GABA and related agonists. GABAA receptor agonists are GABA, muscimol, and isoguvacine. GABAB receptor agonists are GABA and baclofen. GABAA receptor antagonists are bicuculline and picrotoxin. GABAB receptor antagonist is phaclofen.

Recently a third type of GABA receptor, named GABAC is reported to be distrib­uted in the mammalian CNS which has central chloride pore and is insensitive to both bicuculline and baclofen. GABAC receptors are composed of p-subunits. cis-4-aminocrotonic acid (CACA) is the selective agonist for GABAC receptor. Although the term GABAС receptor is frequently used, GABAС may be viewed as a variant within the GABAA receptor family

GABA receptor agonists and antagonists

GABA receptor
Agonists
Antagonists
GABA-A
GABA
Bicuculline
 
Isoguvacine
Picrotoxin
 
Muscimol
 
GABA-B
GABA
Phaclofen
 
Baclofen
 
GABA-C
cis-4-aminocrotonic acid (CACA)
 

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© 2015 Oyon B

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