Thymol inhibits [35S]TBPS binding at the GABAA receptor in primary cultures of cortical neurons. Implication of different exposure buffers used.

GARCÍA D.A.; VENDRELL I.; SUÑOL C.

Los Cocos, Cordoba

Congreso; XXII Reunion Anual de la Sociedad Argentina de Investigacion en Neurociencias (SAN); 2007

Sociedad Argentina de Investigacion en Neurociencias (SAN)

Thymol is a monoterpene that specifically interacts with synaptic neural functions in neuronal GABA-operated Cl- channels. Its structural properties, similar to the well-known anaesthetic propofol, suggest a close or common recognition site in the receptor. Here we explore the effects of thymol, with propofol as positive control, on [35S]TBPS binding in primary cultures of cortical neurons, in order to confirm its GABAergic activity. The study includes a meaningful analysis of the effect of various exposure buffers, and thymol’s correlation with GABA released from cells and chloride influx through the GABAA receptor. An inhibitory effect was observed when [35S]TBPS binding was performed in Tris-Citrate-NaCl buffer in the presence of thymol or propofol (IC50: 25 and 5 ìM, respectively), whereas biphasic effects were observed in HEPES buffered solution. The different effects of the two buffers analysed are due to the higher capacity of Tris-citrate-NaCl buffer to induce the release of endogenous GABA (2.5 ìM vs 0.08 ìM in HEPES buffer) facilitating the binding of [35S]TBPS to its recognition site. Tris-citrate-NaCl buffer also induced a chloride influx, which was reverted by picrotoxinin. The results confirm thymol as a positive allosteric modulator of the GABAA receptor, with a specific recognition site. Furthermore, we corroborate [35S]TBPS binding as an important test to verify the capacity of drugs to act on and recognize a specific site in the GABAA receptor. It is emphasized that the correct interpretation of the results depends on the methodology used.