Gamma-aminobutyric acid.
Gamma-aminobutyric acid.

A GABA receptor agonist is a drug that is an agonist for one or more of the GABA receptors, producing typically sedative effects, and may also cause other effects such as anxiolytic, anticonvulsant, and muscle relaxant effects.[1] There are three receptors of the gamma-aminobutyric acid. The two receptors GABA-α and GABA-ρ are ion channels that are permeable to chloride ions which reduces neuronal excitability. The GABA-β receptor belongs to the class of G-Protein coupled receptors that inhibit adenylyl cyclase, therefore leading to decreased cyclic adenosine monophosphate (cAMP). GABA-α and GABA-ρ receptors produce sedative and hypnotic effects and have anti-convulsion properties. GABA-β receptors also produce sedative effects. Furthermore, they lead to changes in gene transcription.

Types

Many commonly used sedative and anxiolytic drugs that affect the GABA receptor complex are not agonists. These drugs act instead as positive allosteric modulators (PAMs) and while they do bind to the GABA receptors, they bind to an allosteric site on the receptor and cannot induce a response from the neuron without an actual agonist being present. Drugs that fall into this class exert their pharmacodynamic action by increasing the effects that an agonist has when potentiation is achieved.

General anaesthetics act primarily as PAMs of GABA-A receptor. Positive allosteric modulators work by increasing the frequency with which the chloride channel opens when an agonist binds to its own site on the GABA receptor. The resulting increase in the concentration of Cl− ions in the postsynaptic neuron immediately hyperpolarizes this neuron, making it less excitable and thus inhibiting the possibility of an action potential. However, some general anaesthetics like propofol and high doses of barbiturates may not only be positive allosteric modulators of GABA-A receptors but also direct agonists of these receptors.

Alcohol is an indirect GABA agonist. GABA is the major inhibitory neurotransmitter in the brain, and GABA-like drugs are used to suppress spasms. Alcohol is believed to mimic GABA's effect in the brain, binding to GABA receptors and inhibiting neuronal signaling.

GABAA

GABAA receptor ligands include:

Agonists

PAMs

Main article: GABAA receptor positive allosteric modulator

GABAB

GABAB receptor ligands include:

Agonists

PAMs

GABAA

GABAA-ρ receptor ligands include:

Agonists

PAMs

References

  1. ^ Brohan J, Goudra BG (October 2017). "The Role of GABA Receptor Agonists in Anesthesia and Sedation". CNS Drugs. 31 (10): 845–856. doi:10.1007/s40263-017-0463-7. PMID 29039138. S2CID 207486777.
  2. ^ a b c d e f g h i Ganellin CR, Triggle DJ, Macdonald F (1996). Dictionary of Pharmacological Agents. Boca Raton: Chapman & Hall/CRC. p. 608. ISBN 9780412466304.
  3. ^ Löscher W, Rogawski MA (December 2012). "How theories evolved concerning the mechanism of action of barbiturates". Epilepsia. 53 Suppl 8: 12–25. doi:10.1111/epi.12025. PMID 23205959. S2CID 4675696.
  4. ^ a b Ruesch D, Neumann E, Wulf H, Forman SA (January 2012). "An allosteric coagonist model for propofol effects on α1β2γ2L γ-aminobutyric acid type A receptors". Anesthesiology. 116 (1): 47–55. doi:10.1097/aln.0b013e31823d0c36. PMC 3261780. PMID 22104494.
  5. ^ Hales TG, Lambert JJ (November 1991). "The actions of propofol on inhibitory amino acid receptors of bovine adrenomedullary chromaffin cells and rodent central neurones". British Journal of Pharmacology. 104 (3): 619–628. doi:10.1111/j.1476-5381.1991.tb12479.x. PMC 1908220. PMID 1665745.