GABAB receptors (GABABR) are G-protein coupled receptors for gamma-aminobutyric acid (GABA), therefore making them metabotropic receptors, that are linked via G-proteins to potassium channels. The changing potassium concentrations hyperpolarize the cell at the end of an action potential. The reversal potential of the GABAB-mediated IPSP is –100 mV, which is much more hyperpolarized than the GABAA IPSP. GABAB receptors are found in the central nervous system and the autonomic division of the peripheral nervous system.
The metabotropic glutamate receptors, or mGluRs, are a type of glutamate receptor that are active through an indirect metabotropic process. They are members of the group C family of G-protein-coupled receptors, or GPCRs. Like all glutamate receptors, mGluRs bind with glutamate, an amino acid that functions as an excitatory neurotransmitter.
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.
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 3 (mGluR3) is an inhibitory Gi/G0-coupled G-protein coupled receptor (GPCR) generally localized to presynaptic sites of neurons in classical circuits. However, in higher cortical circuits in primates, mGluR3 are localized post-synaptically, where they strengthen rather than weaken synaptic connectivity. In humans, mGluR3 is encoded by the GRM3 gene. Deficits in mGluR3 signaling have been linked to impaired cognition in humans, and to increased risk of schizophrenia, consistent with their expanding role in cortical evolution.
Metabotropic 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.
Metabotropic glutamate receptor 7 is a protein that in humans is encoded by the GRM7 gene.
Cyclothiazide, sometimes abbreviated CTZ, is a benzothiadiazide (thiazide) diuretic and antihypertensive that was originally introduced in the United States in 1963 by Eli Lilly and was subsequently also marketed in Europe and Japan. Related drugs include diazoxide, hydrochlorothiazide, and chlorothiazide.
Biphenylindanone A is a research agent which acts as a potent and selective positive allosteric modulator for the group II metabotropic glutamate receptor subtype mGluR2.
2-Methyl-6-(phenylethynyl)pyridine (MPEP) is a research drug which was one of the first compounds found to act as a selective antagonist for the metabotropic glutamate receptor subtype mGluR5. After being originally patented as a liquid crystal for LCDs, it was developed by the pharmaceutical company Novartis in the late 1990s. It was found to produce neuroprotective effects following acute brain injury in animal studies, although it was unclear whether these results were purely from mGluR5 blockade as it also acts as a weak NMDA antagonist, and as a positive allosteric modulator of another subtype mGlu4, and there is also evidence for a functional interaction between mGluR5 and NMDA receptors in the same populations of neurons. It was also shown to produce antidepressant and anxiolytic effects in animals, and to reduce the effects of morphine withdrawal, most likely due to direct interaction between mGluR5 and the μ-opioid receptor.
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.
Ro01-6128 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 a lead compound found via high-throughput screening, and was further developed to give the improved compound Ro67-4853.
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.
RO-4491533 is a drug developed by Hoffmann-La Roche which acts as a potent and selective negative allosteric modulator for group II of the metabotropic glutamate receptors (mGluR2/3), being equipotent at mGluR2 and mGluR3 but without activity at other mGluR subtypes. In animal studies, RO-4491533 produced antidepressant effects and reversed the effects of the mGluR2/3 agonist LY-379,268 with similar efficacy but slightly lower potency than the mGluR2/3 antagonist LY-341,495. A number of related compounds are known, with similar effects in vitro and a fairly well characterized structure-activity relationship.
AZD 9272 is a drug which acts as a selective antagonist for the metabotropic glutamate receptor subtype mGluR5. It was unsuccessful in human trials as an analgesic, but continues to be widely used in research especially as its radiolabelled forms.
AZ-12216052 is a drug which acts as a potent and selective positive allosteric modulator of the metabotropic glutamate receptor 8, and is used for research into the role of this receptor subtype in various processes including anxiety and neuropathic pain.
XAP044 is a drug which acts as a potent and selective antagonist of the metabotropic glutamate receptor 7 (mGluR7). It inhibits long-term potentiation in the amygdala and inhibits responses associated with stress and anxiety in animal models, as well as being used to study the role of mGluR7 in various other processes.
LSP2-9166 is a drug which acts as a selective agonist for the group III metabotropic glutamate receptors, with a reasonably potent EC50 of 70nM at mGluR4 and 220nM at mGluR7, and weaker activity of 1380nM at mGluR6 and 4800nM at mGluR8. It has anticonvulsant effects in animal studies, and reduces self-administration of various addictive drugs.
