Abstract
Muscimol conjugated with fluorescent or MRI-contrast agents may be useful for visualizing inactivated brain areas if they act as agonists of GABA-A receptor. Recently, some N-acyl muscimol conjugated with a marker molecule have been reported to bind to GABA receptors. However, it remains unclear whether they can activate the GABA-A receptor. In this study, we synthesized two N-acyl muscimol derivatives and purified them thoroughly. Their pharmacological effects on neurons were examined by whole-cell patch clamp in vitro and extracellular recording in vivo. Muscimol (m.w. 114.1) and the smallest derivative N-acetylmuscimol (m.w. 156.1) evoked inward currents with the threshold concentrations of 0.05 and 200 µM, respectively. Evoked currents were potentiated by diazepam and inhibited by SR-95531, indicating that the GABA-A receptor was activated. On the other hand, a more bulky derivative N-biotin-6-aminohexanoylmuscimol (m.w. 453.6) did not evoke any currents even at concentrations up to 1 mM. Although a previous study (Biomaterials 26, 1895-1903, 2005) showed that N-biotin-6-aminohexanoylmuscimol activates GABA-A receptor, we failed to confirm this observation. This discrepancy might arise from the difference in the grade of purification to remove residual unreacted muscimol. Our experiments suggest that N-acylation impaired the agonistic property of muscimol on the GABA-A receptor. Supported by MEXT18500311 (HI), MEXT19390055 (JN), and MEXT19002010 (YM) [J Physiol Sci. 2008;58 Suppl:S83]
