BRIEF EXPOSURE TO GABA INDUCES DELAYED ONSET OF GABA/BENZODIAZEPINE RECEPTOR UNCOUPLING WITHOUT DOWN-REGULATION OF RECEPTOR NUMBER

MARIA CLARA GRAVIELLE

Nueva Orleans

Congreso; XXXIII Reunión Anual de la Society for Neurocience; 2003

Society for Neurocience

Chronic exposure of neurons to GABA induces a downregulation of type-A GABA receptor (GABAAR) number (t1/2=25h) and a reduction of allosteric interactions between binding sites on the receptor complex (t1/2=24h), a phenomenon called uncoupling (1, 2). The molecular mechanism underlying this regulation is not understood. In the present study we were surprised to find that brief exposure (5-10min) of rat cortical neurons to GABA (half-maximal concentration ~ 250mM) induces a decrease in the potentiation of [3H]flunitrazepam binding by GABA (46.6 ± 6.1 % uncoupling at 1mM GABA) when measured 24h later. Delayed uncoupling occurs without a change in receptor number or affinity. As a first step to determine whether transcriptional regulation may play a role in delayed uncoupling, the effect of brief exposure to GABA on receptor subunit mRNA levels was determined using real-time PCR. The results reveal a differential response of GABAAR subunit genes: a significant decrease in a1, a3, b1, b2, b3 and g3 was observed, with no change in a2, a4, a5, g1 and g2S. To determine whether changes in mRNA levels were predictive of a corresponding change in subunit protein expression, Western blot was performed with antibodies specific to a1, b2 and b3 subunits. Results are consistent with a direct relationship between changes in mRNA and protein levels for the a1 and b2/3 subunits. In conclusion, the results indicate that brief activation of GABAAR(s) induces a delayed uncoupling with a slow time course that is completed in 24h and may involve regulation of transcription. 1        Roca DJ, Schiller GD, Farb DH. Mol. Pharmacol. 30: 481-485, 1988. 2        Roca DJ, Rozenberg I, Farrant M, Farb DH. Mol. Pharmacol. 37: 37-43, 1990 Funded by NIAAA 11697.