BEHAVIORAL-EFFECTS OF SCOPOLAMINE AND THE TRH ANALOG RX77368 ON RADIAL-ARM MAZE PERFORMANCE IN THE RAT

Effects of repeated intracerebroventricular administration of the thyr otrophin-releasing hormone (TRH) analogue, RX77368 (S,S'-dimethyl-TRH, 2 mu g, once daily), on a scopolamine-induced performance deficit in an eight-arm radial maze were evaluated in adult rats. Scopolamine (0. 3 mg/kg i.p.-30 min) pre-treatment produced a significant deficit in t he number of unrepeated arm entries and total arm entries and increase d the percentage of incorrect arm entries and the total time on the ma ze, compared with saline-treated controls. Prior treatment with RX7736 8 (40 min before maze testing) produced a partial but significant atte nuation of the scopolamine-induced performance deficit on the maze dur ing the first five trials but RX77368 also enhanced maze performance d uring the same period when given alone. These results suggest that the observed scopolamine-induced performance deficit on the radial arm ma ze partly results from a reduction in locomotion and maze exploration rather than solely impairment of memory, and that RX77368 treatment ma y improve radial maze performance by increasing arousal and explorator y behaviour in rats rather than directly enhancing cognition.