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Behavioural effects of scopolamine and the TRH analogue RX77368 on radial arm maze performance in the rat

Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham University, Nottingham NG7 2UH

M.J. Hewitt

Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham University, Nottingham NG7 2UH

K.C.F. Fone

Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham University, Nottingham NG7 2UH

S.L. Dickinson

Reckitt & Colman Psychopharmacology Unit, School of Medical Sciences, University Walk, Bristol University, Bristol BS8 1TD, UK

G.W. Bennett

Department of Physiology and Pharmacology, Medical School, Queen's Medical Centre, Nottingham University, Nottingham NG7 2UH

Effects of repeated intracerebroventricular administration of the thyrotrophin-releasing hormone (TRH) analogue, RX77368 (3,3'-dimethyl-TRH, 2 µg, 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 the number of unrepeated arm entries and total arm entries and increased the percentage of incorrect arm entries and the total time on the maze, compared with saline-treated controls. Prior treatment with RX77368 (40 min before maze testing) produced a partial but significant attenuation of the scopolamine-induced performance deficit on the maze during the first five trials but RX77368 also enhanced maze performance during the same period when given alone. These results suggest that the observed scopolamine-induced performance deficit on the radial arm maze partly results from a reduction in locomotion and maze exploration rather than solely impairment of memory, and that RX77368 treatment may improve radial maze performance by increasing arousal and exploratory behaviour in rats rather than directly enhancing cognition.

Key Words: thyrotrophin-releasing hormone • cognition • scopolamine • radial maze • behaviour • motivation

Journal of Psychopharmacology, Vol. 8, No. 2, 88-93 (1994)
DOI: 10.1177/026988119400800203


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