Dear Melanie,

on average rats enter the open arm in 30 to 80 seconds and spend on average 25-30% of time on the open arms. Of course, there is a large inter-individual variability with animals entering within few second or not entering the open at all during the given 5 min (in this case animals are scored with the maximal time give, namely 300 s). And there are, indeed, differences depending on gender, age, housing conditions, illumination (e.g., we perform the elevated plus maze under darkness using an infrared camera) and so on. If many of "your" control rats do not enter the open arms within 5 min, then you should check that the protocol and experimental conditions are correct (as ell as the housing conditions and handling of the rats).

Best regards,

Fabio

Dear Melanie, 

This paper may help you: 

Nat Protoc. 2007; 2(2): 322–328.

The use of the elevated plus maze as an assay of anxiety-related behavior in rodents

Alicia A Walf1 and Cheryl A Frye

Dear Melanie,

on average rats enter the open arm in 30 to 80 seconds and spend on average 25-30% of time on the open arms. Of course, there is a large inter-individual variability with animals entering within few second or not entering the open at all during the given 5 min (in this case animals are scored with the maximal time give, namely 300 s). And there are, indeed, differences depending on gender, age, housing conditions, illumination (e.g., we perform the elevated plus maze under darkness using an infrared camera) and so on. If many of "your" control rats do not enter the open arms within 5 min, then you should check that the protocol and experimental conditions are correct (as ell as the housing conditions and handling of the rats).

Best regards,

Fabio

Dear Melanie,

In a long-term study we performed elevated plus maze experiment on rats three times. Between two consecutive sessions, more than 3 months ellapsed. However, we clearly observed a "training-effect" in the behavior of the rats, namely, the time spent in the open arm decreased in all of the experimental groups. It was annoying because in the last session, a lot of animals did not enter the open arm at all, so we were confused how to compare the results.

I have no idea, why a trained rat spend less time in the open arm (maybe, this is not typically habituation). Maybe they learn that nothing interesting can be found in the open arm, but it is scary, so they prefer to stay in the closed arms. :)

So, I think, habituation and training is an important factor that must be considered, if you want to perform multiple EPM sessions on the same animals. I think, a long time ago I've read a paper, which suggested some kind of solution for this problem, but unfortunately I can't remember this paper... :(

Hi Melanie and Zsolt: Please refer to Carobrez and Bertoglio, 2005 (Neuroscience and Behavioral Reviews) for a great report on protocols to overcome confounding results associated with habituation to the EPM. Best, Johnny.

Hi Melanie,

The question was posted some time ago but I hope that others can still benefit from the answer.

According to Pellow and al.  (1987), habituation to EPM has no effect on later testing and EPM can be repeated twice on the same animals. However, the authors suggest to not go for more than twice, as this can lead to unreliable results.

Pellow and al. (1987).Validation of open: closed arm entries in an elevated plus-maze as a measure of anxiety in the rat. J Neurosci Methods. Best,Hassiba