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Abstract
Several classes of nonbenzodiazepine compounds, including imidazopyridines such as
alpidem and zolpidem and cyclopyrrolones, e.g., zopiclone, have effects similar to
benzodiazepines and may act at the benzodiazepine receptor in brain. We characterized
the binding of these compounds to the benzodiazepine site in three brain regions using
specific uptake of the high-affinity ligand [3H]Ro15-1788 (flumazenil). For alpidem,
benzodiazepine binding was decreased in cortex and hippocampus with increasing drug
dose. For zolpidem, receptor binding was reduced in cortex without a dose-response
effect and no effect was observed on cerebellar binding. Zopiclone did not alter binding
except for a decrease in binding at the lowest dose evaluated and an increase in binding
above control at the highest dose. These data corroborate prior studies indicating
that the imidazopyridines appear to act at the benzodiazepine receptor, but do not
support receptor subtype selectivity of zolpidem. The limited effect of zopiclone
except for increased binding at high doses is also consistent with prior studies suggesting
that zopiclone acts at a site distinct from the benzodiazepine receptor.