LOCOMOTION AND STEREOTYPY INDUCED BY SCOPOLAMINE - CONTRIBUTIONS OF MUSCARINIC RECEPTORS NEAR THE PEDUNCULOPONTINE TEGMENTAL NUCLEUS

In this study, we test whether blockade of muscarinic receptors near m esopontine cholinergic cell groups may contribute to locomotor activat ion induced by scopolamine. Unilateral or bilateral injections of scop olamine (10-150 mu g) into the pedunculopontine tegmental nucleus (PPT ) increased horizontal locomotion by 2-15 times in a dose-related way. Unilateral or bilateral injections of scopolamine into the PPT increa sed stereotypic behaviors (such as sniffing in one location or over la rge areas), self-biting and grooming. Carbachol (4 mu g) injected into PPT reduced locomotion for 20 min, followed by 70 min of increased lo comotion. When carbachol (4 mu g) was injected into the PPT before sco polamine (3 mg/kg, i.p.), the activating effect of scopolamine was att enuated, but not when carbachol was injected after scopolamine. Theref ore, carbachol appears to compete with scopolamine for muscarinic rece ptors near the PPT that mediate locomotor activating effects of system ic scopolamine. Haloperidol (0.1 mg/kg, i.p.) also attenuated the ster eotypy and locomotion induced by scopolamine in the PPT. We hypothesiz e that scopolamine acts by blocking muscarinic receptors on mesopontin e cholinergic neurons, thereby disinhibiting cholinergic neurons that can activate dopamine neurons. (C) 1997 Elsevier Science B.V.