A detailed ethological analysis of the mouse open field test: effects of diazepam, chlordiazepoxide and an extremely low frequency pulsed magnetic field

The open field test (OFT) is a widely used procedure for examining the beha vioral effects of drugs and anxiety. Detailed ethological assessments of an imal behavior are lacking. Here we present a detailed ethological assessmen t of the effects of acute treatment with the benzodiazepines, diazepam (DZ, 1.5 mg/kg) and chlordiazepoxide (CDP, 5.0 and 10.0mg/kg), as well as expos ure to a non-pharmacological agent, a specific pulsed extremely low frequen cy magnetic field (MAG) on open field behavior. We examined the duration, f requency and time course of various behaviors (i.e. exploration, walk, rear , stretch attend, return, groom, sit, spin turn, jump and sleep) exhibited by male mice in different regions of a novel open field. Both DZ and CDP co nsistently reduced the typical anxiety-like behaviors of stretch attend and wall-following (thigmotaxis), along with that of an additional new measure :'returns', without producing any overall effects on total locomotion. The drugs also differed in their effects. CDP elicited a shift in thr locomotor pattern from a 'high explore' to a 'high walk', while DZ mainly elicited a lterations in sit and groom. The MAC treatment was repeated twice with both exposures reducing horizontal and vertical (rearing) activity and increasi ng grooming and spin turns. However. the anxiety-like behaviors of stretch attend and return were marginally reduced by only the first exposure. We co nclude that a detailed ethological analysis of the OFT allows not only the detection of specific effects of drugs and non-pharmacological agents (i.e. pulsed magnetic field) on anxiety-like behaviors, but also permits the exa mination of non-specific effects, in particular those on general activity. (C) 2001 Elsevier Science Ltd. Ail rights reserved.