Postsynaptic glycine receptor (GlyR) chloride channels mediate inhibitory neurotransmission in the spinal cord and brain stem, although presynaptic and extrasynaptic GlyRs are expressed more widely throughout the brain. In humans, GlyRs are assembled as homo- or heteromeric pentamers of α1-3 and β subunits. GlyR malfunctions have been linked to a range of neurological disorders including hyperekplexia, temporal lobe epilepsy, autism, breathing disorders, and chronic inflammatory pain. Although it is possible that GlyRs may eventually be clinically targeted for a variety of neurological disorders, most research to date has focused on developing GlyR-targeted treatments for chronic pain. Inflammatory pain sensitization is caused by inflammatory mediators downregulating the magnitude of α3 GlyR-mediated inhibitory postsynaptic currents in spinal nociceptive neurons. Consistent with this paradigm, it is now well established that the selective enhancement of α3 GlyR current magnitude is effective in alleviating inflammatory pain. In this review, we briefly describe the physiological roles and pharmacological properties of GlyRs. We then outline the methods commonly used to discover new GlyR-active compounds and review recent progress, in our laboratory and elsewhere, in developing GlyR-targeted analgesics. We conclude that the eventual development of an α3 GlyR-targeted analgesic is an eminently feasible goal. However, in selecting or designing new therapeutic leads, we caution against the automatic exclusion of compounds with potentiating effects on α1 GlyRs. Also, as GlyRs are strongly potentiated by Zn2+ at nanomolar concentrations, we also caution against the identification of false positives caused by contaminating Zn2+ in otherwise pure compound samples.
Keywords: Alcoholism; Autism; Breathing disorders; Glycinergic; Hyperekplexia; Inflammation; Motor neuron disease; Pain; Temporal lobe epilepsy.
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