Triazolam-induced modulation of muscarinic acetylcholine receptor in living brain slices as revealed by a new positron-based imaging technique

Summary.

The effect of triazolam, a potent benzodiazepine (BZ) agonist, on muscarinic acetylcholinergic receptor (mAChR) binding was investigated in living brain slices by use of a novel positron-based imaging technique. Fresh rat brain slices were incubated with [¹¹C]N-methyl-4-piperidylbenzilate ([¹¹C]NMPB), a mAChR antagonist, in oxygenated Krebs-Ringer solution at 37°C. During incubation, time-resolved imaging of [¹¹C]NMPB binding in the slices was constructed on the storage phosphor screens. Addition of triazolam (1 μM) plus muscimol (30 μM), a GABA_A receptor agonist, to the incubation mixture decreased the specific binding of [¹¹C]NMPB. Ro15-1788, a BZ receptor antagonist, prevented this effect, indicating that the effect was exerted through the GABA_A/BZ receptor complex. These results demonstrated that stimulation of the GABA_A/BZ receptor lowers the affinity of the mAChR for its ligand, which may underlie the BZ-induced amnesia, a serious clinical side effect of BZ. No such effect in the P2-fraction instead implies that the integrity of the neuronal cells and/or their environment is prerequisite for the modulation of mAChR by GABA_A/BZ stimulation.