Study of the Interaction of 1,4- and 1,5-Benzodiazepines with GABAA 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 GABAA 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 α6 ß2/3 γ2 and α1 α6 ß2/3 γ2 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 α1 ß2/3 γ2 receptors, while N-desmethyl-diazepam seems to interact with not only α1- but also α6-containing receptors.

GABAA Receptors of Cerebellar Granule Cells in Culture: Interaction with Benzodiazepines.

GABAA receptor mediated inhibition plays an important role in modulating the input/output dynamics of cerebellum. A characteristic of cerebellar GABAA receptors is the presence in cerebellar granule cells of subunits such as α6 and δ which give insensitivity to classical benzodiazepines. In fact, cerebellar GABAA receptors have generally been considered a poor model for testing drugs which potentially are active at the benzodiazepine site. In this overview we show how rat cerebellar granule cells in culture may be a useful model for studying new benzodiazepine site agonists. This is based on the pharmacological separation of diazepam-sensitive α1 ß2/3 γ2 receptors from those which are diazepam-insensitive and contain the α6 subunit. This is achieved by utilizing furosemide/Zn2+ which block α6 containing and incomplete receptors.