ARM WIDTH AND BRIGHTNESS MODULATION OF SPONTANEOUS BEHAVIOR OF 2 STRAINS OF MICE TESTED IN THE ELEVATED PLUS-MAZE

Amongst the nonpharmacological variables that may influence spontaneou s behaviour in the elevated plus-maze, at least two (namely, the width and brightness level of the maze arms) have not been evaluated for po ssible consequences on baseline activity. We therefore investigated th e 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 mic e 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. I n the NMRI strain, enlarging the arms resulted in significantly increa sed running in open arms but brightness level did not affect behaviour al 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 brig ht maze. The results are discussed in terms of their putative effects in pharmacological testing.