Effect of novel allosteric modulators of metabotropic glutamate receptors on drug self-administration and relapse: a review of preclinical studies and their clinical implications
Results from preclinical rodent studies during the last 20 years implicated glutamate neurotransmission in different
brain regions in drug self-administration and rodent models of relapse. These results, along with evidence for druginduced
neuroadaptations in glutamatergic neurons and receptors, suggested that addiction might be treatable by
medications that inhibit glutamatergic responses to drugs of abuse, drug-associated cues, and stressors. This idea is
supported by findings in rodent and primate models that drug self-administration and relapse are reduced by systemic
injections of antagonists of ionotropic glutamate receptors or metabotropic glutamate receptors (mGluRs) or
orthosteric agonists of mGluR2/3. However, these compounds have not advanced to clinical use because of potential
side effects and other factors. This state of affairs has led to the development of positive allosteric modulators (PAMs)
and negative allosteric modulators (NAMs) of mGluRs. PAMs and NAMs of mGluRs, either of which can inhibit evoked
glutamate release, may be suitable for testing in humans. We reviewed results from recent studies of systemically
injected PAMs and NAMs of mGluRs in rodents and monkeys, focusing on whether they reduce drug selfadministration,
reinstatement of drug seeking, and incubation of drug craving. We also review results from rat
studies in which PAMs or NAMs of mGluRs were injected intracranially to reduce drug self-administration and
reinstatement. We conclude that PAMs and NAMs of mGluRs should be considered for clinical trials.