Study of the Interaction of 1,4- and 1,5-Benzodiazepines with GABA<inf>A</inf> Receptors of Rat Cerebellum Granule Cells in Culture

The effects of a classical 1,4-benzodiazepine agonist, such as diazepam, its catabolite N-desmethyl-diazepam (nordiazepam), and 1,5-benzodiazepines such as clobazam and RL 214 (a triazolobenzodiazepine previously synthesized in our labs) were evaluated on native GABA(A) receptors of cerebellar granule cells in culture. The parameter studied was the increase of GABA-activated chloride currents caused by these substances. The contributions of alpha 6 beta 2/3 gamma 2 and alpha 1 alpha 6 beta 2/3 gamma 2 receptor subtypes to the increase of GABA-activated chloride current were investigated by comparing the effects of such substances in the presence vs. the absence of furosemide. Furosemide is in fact able to block such receptors. It was found that the percent enhancement of peak GABA-activated current doubled for diazepam, clobazam, and RL 214. However, it did not change for N-desmethyl-diazepam. These results indicate that diazepam, clobazam, and RL 214 interact exclusively with alpha 1 beta 2/3 gamma 2 receptors, while N-desmethyl-diazepam seems to interact with not only alpha 1-but also alpha 6-containing receptors