γ‐Aminobutyric Acid_A Receptor Function Is Desensitised in Rat Cultured Cerebellar Granule Cells Following Chronic Flunitrazepam Treatment

<jats:p><jats:bold>Abstract:</jats:bold> This study examined γ‐aminobutyric acid<jats:sub>A</jats:sub> (GABA<jats:sub>A</jats:sub>) receptor function in cultured rat cerebellar granule cells by using microphysiometry following chronic flunitrazepam exposure, and correlated the findings with the α1 and β2/3 subunit protein expression and [<jats:sup>3</jats:sup>H]muscimol binding after the same treatment paradigm. Flunitrazepam treatment reduced (<jats:italic>p</jats:italic> &lt; 0.05) the maximal GABA‐stimulated increase in extracellular acidification rate (<jats:italic>E</jats:italic><jats:sub>max</jats:sub>) (16.5 ± 1.2% and 11.3 ± 1.0%, 2‐day control and treated cells, respectively; 17.4 ± 1.0% and 9.9 ± 0.7%, 7‐day control and treated cells, respectively; best‐fit <jats:italic>E</jats:italic><jats:sub>max</jats:sub>± SEM, n = 7), without affecting the GABA concentration required to elicit 50% of maximal response (EC<jats:sub>50</jats:sub>) (1.2 ± 1.7 and 2.3 ± 1.8 µ<jats:italic>M</jats:italic>, 2‐day control and treated cells, respectively; 1.7 ± 1.5 and 1.5 ± 1.5 µ<jats:italic>M</jats:italic>, 7‐day control and treated cells, respectively; best‐fit EC<jats:sub>50</jats:sub>± SEM, n = 7). Flunitrazepam exposure also abolished the flunitrazepam potentiation of the GABA response, caused a transient reduction of the GABA<jats:sub>A</jats:sub> receptor α1 and β2/3 subunit proteins over the initial 2 days, but did not alter [<jats:sup>3</jats:sup>H]muscimol binding compared with vehicle‐treated cells. The results suggest that changes in GABA<jats:sub>A</jats:sub> receptor subunit protein expression, rather than loss of [<jats:sup>3</jats:sup>H]muscimol binding sites, underlie the chronic flunitrazepam‐mediated desensitisation of GABA<jats:sub>A</jats:sub> receptor function.</jats:p>