Changes in GABA receptor (GABAAR) gene expression are detected in animal models of epilepsy, anxiety and in post‐mortem schizophrenic brain, suggesting a role for GABAAR regulation in neurological disorders. Persistent (48 h) exposure of brain neurons in culture to GABA results in down‐regulation of GABAAR number and uncoupling of GABA and benzodiazepine (BZD) binding sites. Given the central role of GABAARs in fast inhibitory synaptic transmission, GABAAR down‐regulation and uncoupling are potentially important mechanisms of regulating neuronal excitability, yet the molecular mechanisms remain unknown. In this report we show that treatment of brain neurons in culture with tetrodotoxin, glutamate receptor antagonists, or depolarization with 25 mm K+ fails to alter GABAAR number or coupling. Changes in neuronal activity or membrane potential are therefore not sufficient to induce either GABAAR down‐regulation or uncoupling. Nifedipine, a voltage‐gated Ca2+ channel (VGCC) blocker, inhibits both GABA‐induced increases in [Ca2+]i and GABAAR down‐regulation, suggesting that VGCC activation is required for GABAAR down‐regulation. Depolarization with 25 mm K+ produces a sustained increase in intracellular [Ca2+] without causing GABAAR down‐regulation, suggesting that activation of VGCCs is not sufficient to produce GABAAR down‐regulation. In contrast to GABAAR down‐regulation, nifedipine and 25 mm K+ fail to inhibit GABA‐induced uncoupling, demonstrating that GABA‐induced GABAAR down‐regulation and uncoupling are mediated by independent molecular events. Therefore, GABAAR activation initiates at least two distinct signal transduction pathways, one of which involves elevation of intracellular [Ca2+] through VGCCs.

Benzodiazepines (BZDs), barbiturates, ethanol, and general anesthetics potentiate the action of gamma-aminobutyric acid (GABA) at the type A GABA receptor (GABA(A)R) and have profound effects on mood, arousal, and susceptibility to seizures. GABA(A)R number and subunit mRNA levels change in animal models of epilepsy and anxiety and following exposure to GABA(A)R agonists and positive modulators, but the mechanism of receptor down-regulation remains unknown. Persistent exposure (48 h) of brain neurons in primary culture to GABA results in a 30% decrease in the levels of mRNA encoding the alpha1, beta2S, and gamma1 GABA(A)R subunit isoforms, which form a receptor enhanced by nonselective BZDs. Down-regulation of alpha1 mRNA (t1/2 = 8 h) precedes down-regulation of receptor number (t1/2 = 25 h), suggesting that GABA-induced GABA(A)R down-regulation is a consequence of decreased mRNA levels. The apparent half-life of the alpha1 mRNA in the presence of alpha-amanitin (9 h) is consistent with the time course of alpha1 mRNA down-regulation. Moreover, the stability of the alpha1, beta2S, and gamma1 subunit mRNAs is not altered by chronic GABA exposure. The results demonstrate that GABA(A)R subunit mRNA down-regulation is not a consequence of accelerated mRNA degradation and argue that GABA-induced GABA(A)R down-regulation is due to inhibition of transcription.

Benzodiazepines (BZDs), barbiturates, ethanol, and general anesthetics potentiate the action of gamma-aminobutyric acid (GABA) at the type A GABA receptor (GABA(A)R) and have profound effects on mood, arousal, and susceptibility to seizures. GABA(A)R number and subunit mRNA levels change in animal models of epilepsy and anxiety and following exposure to GABA(A)R agonists and positive modulators, but the mechanism of receptor down-regulation remains unknown. Persistent exposure (48 h) of brain neurons in primary culture to GABA results in a 30% decrease in the levels of mRNA encoding the alpha 1, beta 2S, and gamma 1 GABA(A)R subunit isoforms, which form a receptor enhanced by nonselective BZDs, Down-regulation of alpha 1 mRNA(t1/2 = 8 h) precedes down-regulation of receptor number (t1/2 = 25 h), suggesting that GABA-induced GABA(A)R down-regulation is a consequence of decreased mRNA levels, The apparent half-life of the al mRNA in the presence of alpha-amanitin (9 h) is consistent with the time course of alpha 1 mRNA down-regulation. Moreover, the stability of the alpha 1, beta 2S, and gamma 1 subunit mRNAs is not altered by chronic GABA exposure. The results demonstrate that GABA(A)R subunit mRNA down-regulation is not a consequence of accelerated mRNA degradation and argue that GABA-induced GABA(A)R down-regulation is due to inhibition of transcription.