Effects of Scopolamine, Pilocarpine, and Oxotremorine on the Exploratory Behavior of Two Psychogenetically Selected Lines of Rats in a Complex Maze

Rats of two psychogenetically selected lines received pretest IP injections of scopolamine hydrobromide (0.25, 1.0, or 4.0 mg/kg), pilocarpine hydrochloride (3.0, 6.0, or 12.0 mg/kg) or oxotremorine sesquifumarate (0.2, 0.4 or 0.8 mg/kg) and were subsequently placed in a complex enclosed maze of the Dashiell type that included a small, central, illuminated arena. Animals receiving pilocarpine or oxotremorine injections were pretreated with methscopolamine to counter the peripheral actions of these muscarinic cholinergic agonists. Following vehicle injections, Roman High-Avoidance rats (RHA/Verh) were significantly more active, explored more maze sectors, and required less time to activate the initial 24 different photocell units uniformly distributed throughout the maze than Roman Low-Avoidance rats (RLA/Verh). Scopolamine, pilocarpine, and oxotremorine depressed locomotor activity, reduced the explored area, and increased the time required to activate the initial 24 different photocell units within this complex maze for both RHA/Verh and RLA/Verh rats. Although the doses of scopolamine injected were approximately equally effective in both rat lines (except for total maze activity), the RHA/Verh rats exhibited significant alterations in several measures of maze patrolling after treatment with the lowest dose of pilocarpine, whereas the RLA/Verh rats did not. In contrast, most of the RLA/Verh rats exhibited very pronounced tremors following treatment with the highest dose of oxotremorine, but none of the RHA/Verh rats did. These results demonstrate that manipulation of the central cholinergic system with scopolamine, pilocarpine, or oxotremorine, despite their different pharmacological mechanisms, impair maze patrolling. Furthermore, the results suggest that the two psychogenetically bred lines of rats investigated are differentially sensitive to central cholinergic manipulation with the muscarinic receptor agonists pilocarpine and oxotremorine.