Mechanism of action of the hypnotic zolpidem in vivo

Zolpidem is a widely used hypnotic agent acting at the GABA(A) receptor ben zodiazepine site. On recombinant receptors, zolpidem displays a high affini ty to alpha1-GABA(A) receptors, an intermediate affinity to alpha (2)- and alpha (3)-GABA(A) receptors and fails to bind to alpha (5)-GABA(A) receptor s. However, it is not known which receptor subtype is essential for mediati ng the sedative-hypnotic action in vivo. Studying alpha1(H101R) mice, which possess zolpidem-insensitive alpha (1)-GABA(A) receptors, we show that the sedative action of zolpidem is exclusively mediated by alpha (1)-GABA(A) r eceptors. Similarly, the activity of zolpidem against pentylenetztrazole-in duced tonic convulsions is also completely mediated by alpha (1)-GABA(A) re ceptors. These results establish that the sedative-hypnotic and anticonvuls ant activities of zolpidem are due to its action on alpha (1)-GABA(A) recep tors and not on,or alpha (3)-GABA(A) receptors.