Arm width and brightness modulation of spontaneous behaviour of two strains of mice tested in the elevated plus-maze

Amongst the nonpharmacological variables that may influence spontaneous behaviour in the elevated plus-maze, at least two (namely, the width and brightness level of the maze arms) have not been evaluated for possible consequences on baseline activity. We therefore investigated the effect of width (5, 7, or 9 cm) and brightness level (grey vs. white) of the maze arms on the activity patterns of NMRI and C57/BL 10j mice in a plus-maze based on that described by Lister. Results indicated a clear strain difference in spontaneous behaviour in the open/closed arms with C57/BL mice making no visits on the open arms of the maze. In the NMRI strain, enlarging the arms resulted in significantly increased running in open arms but brightness level did not affect behavioural parameters. In the C57/BL mice, no significant behavioural changes were detected after increasing the arm width; however, the maze with a white floor significantly increased the latency to move and decreased ambulation. Finally, employing a maze with white closed arms and open grey arms resulted in ambulation by C57/BL mice into the open arms, a behaviour not normally observed in this strain using a uniformly bright maze. The results are discussed in terms of their putative effects in pharmacological testing.