Behaviors in Elevated Plus Mazes

We'd noted that Rats and Mice are observed to behave quite differently when put in the same elevated plus maze. Our rodent guru tells us that while superficially similar norway rats and lab mice, Rattus rattus, and Mus musculus are not even generically similar. Even at quite a coarse scale, norway rats have 22 chromosome pairs, lab mice have 20 (Levan 1991) and the common ancestor is at least 8 million years ago - as far back as humans are separated from Great Apes. The Rat Genome Sequencing Consortium 2004 tells us that Norway rats have 2.75 million base pairs while mice have 2.6 million so we'd expect significant differences.

I'd noted that with the HVS Image 2012 series Elevated Plus Maze the physical mazes are actually provided in different sizes for the two animals - for example the width is 50mm in the HVS Image Mouse Maze and 100mm in the HVS Image Rat maze so it's possible that its just a question of scaling.

Rats vs Mice in the Elevated Plus Maze.

One of our colleagues was discussing the big differences in control behaviors that experimenters observe between rats and mice in the  Elevated Plus Maze. We are planning to write that up here in due course, but in the meanwhile we'd certainly welcome your observations.

The elevated plus maze (EPM)

The elevated plus maze (EPM) is a rodent model of anxiety that is used as a screening test for putative anxiolytic or anxiogenic compounds and as a general research tool in neurobiological anxiety research.



The test setting consists of a cross (or plus) -shaped apparatus. Two of the arms are open and two are enclosed. Each has an open roof, elevated above the floor. In a typical set-up like the mouse version of the HVS Image Elevated plus maze the mice are 50 centimetres above the floor. In the rat version of the HVS Image Elevated plus maze the rodents are 80 centimetres above the floor.

The model is based on rodents' aversion of open spaces. This aversion leads to the behavior termed thigmotaxis, which involves avoidance of open areas by confining movements to enclosed spaces or to the edges of a bounded space. In elevated plus maze this is manifested as a restriction of movement of the rodent to the enclosed arms.