The GABAA receptor (GABAAR) is an ionotropic receptor and ligand-gated ion channel. Its endogenous ligand is γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system. Upon opening, the GABAA receptor on the postsynaptic cell is selectively permeable to chloride ions (Cl−) and, to a lesser extent, bicarbonate ions (HCO3−). Depending on the membrane potential and the ionic concentration difference, this can result in ionic fluxes across the pore. If the membrane potential is higher than the equilibrium potential (also known as the reversal potential) for chloride ions, when the receptor is activated Cl− will flow into the cell. This causes an inhibitory effect on neurotransmission by diminishing the chance of a successful action potential occurring at the postsynaptic cell. The reversal potential of the GABAA-mediated inhibitory postsynaptic potential (IPSP) in normal solution is −70 mV, contrasting the GABAB IPSP (-100 mV).
Fenobam is an imidazole derivative developed by McNeil Laboratories in the late 1970s as a novel anxiolytic drug with an at-the-time-unidentified molecular target in the brain. Subsequently, it was determined that fenobam acts as a potent and selective negative allosteric modulator of the metabotropic glutamate receptor subtype mGluR5, and it has been used as a lead compound for the development of a range of newer mGluR5 antagonists.
Desformylflustrabromine (dFBr) is a monomethyltryptamine derivative which was first isolated as a secondary metabolite of the marine bryozoan Flustra foliacea.
The human muscarinic acetylcholine receptor M5, encoded by the CHRM5 gene, is a member of the G protein-coupled receptor superfamily of integral membrane proteins. It is coupled to Gq protein. Binding of the endogenous ligand acetylcholine to the M5 receptor triggers a number of cellular responses such as adenylate cyclase inhibition, phosphoinositide degradation, and potassium channel modulation. Muscarinic receptors mediate many of the effects of acetylcholine in the central and peripheral nervous system. The clinical implications of this receptor have not been fully explored; however, stimulation of this receptor is known to effectively decrease cyclic AMP levels and downregulate the activity of protein kinase A (PKA).
The muscarinic acetylcholine receptor M1, also known as the cholinergic receptor, muscarinic 1, is a muscarinic receptor that in humans is encoded by the CHRM1 gene. It is localized to 11q13.
The muscarinic acetylcholine receptor M4, also known as the cholinergic receptor, muscarinic 4 (CHRM4), is a protein that, in humans, is encoded by the CHRM4 gene.
Metabotropic glutamate receptor 2 (mGluR2) is a protein that, in humans, is encoded by the GRM2 gene. mGluR2 is a G protein-coupled receptor (GPCR) that couples with the Gi alpha subunit. The receptor functions as an autoreceptor for glutamate, that upon activation, inhibits the emptying of vesicular contents at the presynaptic terminal of glutamatergic neurons.
Metabotropic glutamate receptor 4 is a protein that in humans is encoded by the GRM4 gene.
Metabotropic glutamate receptor 5 is an excitatory Gq-coupled G protein-coupled receptor predominantly expressed on the postsynaptic sites of neurons. In humans, it is encoded by the GRM5 gene.
The alpha-7 nicotinic receptor, also known as the α7 receptor, is a type of nicotinic acetylcholine receptor implicated in long-term memory, consisting entirely of α7 subunits. As with other nicotinic acetylcholine receptors, functional α7 receptors are pentameric [i.e., (α7)5 stoichiometry].
Himbacine is an alkaloid isolated from the bark of Australian magnolias. Himbacine has been synthesized using a Diels-Alder reaction as a key step. Himbacine's activity as a muscarinic receptor antagonist, with specificity for the muscarinic acetylcholine receptor M2, made it a promising starting point in Alzheimer's disease research. The development of a muscarinic antagonist based on himbacine failed but an analog, vorapaxar, has been approved by the FDA as a thrombin receptor antagonist.
Xanomeline is a small molecule muscarinic acetylcholine receptor agonist that was first synthesized in a collaboration between Eli Lilly and Novo Nordisk as an investigational therapeutic being studied for the treatment of central nervous system disorders.
PHCCC is a research drug which acts as a glutamate receptor ligand, particularly being a positive allosteric modulator at the mGluR4 subtype, as well as an agonist at mGluR6. It has anxiolytic effects in animal studies. PHCCC and similar drugs have been suggested as novel treatments for Parkinson's disease.
ADX-47273 is a research pharmaceutical developed by Addex Therapeutics which acts as a positive allosteric modulator (PAM) selective for the metabotropic glutamate receptor subtype mGluR5. It has nootropic and antipsychotic effects in animal studies, and has been used as a lead compound to develop improved derivatives.
CDPPB is a drug used in scientific research which acts as a positive allosteric modulator selective for the metabotropic glutamate receptor subtype mGluR5. It has antipsychotic effects in animal models, and mGluR5 modulators are under investigation as potential drugs for the treatment of schizophrenia, as well as other applications.
Ro67-4853 is a drug used in scientific research, which acts as a selective positive allosteric modulator for the metabotropic glutamate receptor subtype mGluR1. It was derived by modification of the simpler compound Ro01-6128, and has itself subsequently been used as a lead compound to develop a range of potent and selective mGluR1 positive modulators.
LY-487,379 is a drug used in scientific research that acts as a selective positive allosteric modulator for the metabotropic glutamate receptor group II subtype mGluR2. It is used to study the structure and function of this receptor subtype, and LY-487,379 along with various other mGluR2/3 agonists and positive modulators are being investigated as possible antipsychotic and anxiolytic drugs.
PD-102,807 is a drug which acts as a selective antagonist for the muscarinic acetylcholine receptor M4. It is used in scientific research for studying the effects of the different muscarinic receptor subtypes in the body and brain.
AFDX-384 (BIBN-161) is a drug which acts as a selective antagonist of the muscarinic acetylcholine receptors, with selectivity for the M2 and M4 subtypes. It is used mainly for mapping the distribution of M2 and M4 muscarinic receptors in the brain, and studying their involvement in the development and treatment of dementia and schizophrenia.
Ro4938581 is a nootropic drug invented in 2009 by a team working for Hoffmann-La Roche, which acts as a subtype-selective inverse agonist at the α5 subtype of the benzodiazepine binding site on the GABAA receptor. It has good selectivity for the α5 subtype and did not produce convulsant or anxiogenic effects in animal studies, making it a promising potential nootropic. Ro4938581 and a related derivative basmisanil have subsequently been investigated for the alleviation of cognitive dysfunction in Down syndrome.
