Influences of intraventricular injection of 6-hydroxydopamine on passive-avoidance response, acetylcholine, and muscarinic receptors in mouse brain

In step-through and step-down tasks, icv 6-hydroxydopamine (6-OHDA) 20 micrograms on d 14 before training impaired the learning and memory processes in mice. But the amnesic effects in mice received icv 6-OHDA were overcome by ip scopolamine (Scop) 0.5 mg.kg-1 at 15 min before trial. When mice were pretreated with icv 6-OHDA the content of acetylcholine (ACh) in the brain showed no change, whereas the ACh-depleting action of Scop (2 mg.kg-1) was diminished. [3H]Quinuclidinyl benzilate binding assay indicated that the brain muscarinic receptor density (Bmax) and Kd in the mice after icv 6-OHDA were respectively decreased 48% and 57% as compared to the icv sterile water group. These findings suggested a possible participation of brain cholinergic nervous system in memory impairment induced by icv 6-OHDA in mice.