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. 2021 May:204:173168.
doi: 10.1016/j.pbb.2021.173168. Epub 2021 Mar 5.

Sex differences in the elevated plus-maze test and large open field test in adult Wistar rats

Parker Knight  1 , Ranjithkumar Chellian  1 , Ryann Wilson  1 , Azin Behnood-Rod  1 , Stefany Panunzio  1 , Adriaan W Bruijnzeel  2
Affiliations

Sex differences in the elevated plus-maze test and large open field test in adult Wistar rats

Parker Knight et al. Pharmacol Biochem Behav. 2021 May.

Abstract

There is a growing need for a better understanding of sex differences in animal models of psychiatric disorders. The elevated plus-maze (EPM) test and large open field (LOF) test are widely used to study anxiety-like behavior in rodents. Our studies explored sex differences in anxiety and activity parameters in the LOF and EPM and determined whether these parameters correlate within and between tests. Drug naïve adult male and female Wistar rats (n = 47/sex) were used for the studies, and the rats were tested for 5 min in the EPM and 10 min in the LOF. The females spent more time on the open arms of the EPM and made more open arms entries than the males. The females also spent more time in the center zone of the LOF and made more center zone entries. The females traveled a greater distance in the LOF and EPM. There was a moderate positive correlation between time on the open arms of the EPM and time in the center zone of the LOF. There was also a moderate positive correlation between open arms entries in the EPM and center zone entries in the LOF. A hierarchical cluster analysis revealed one cluster with LOF parameters, one cluster with EPM parameters, and one cluster with parameters related to the avoidance of open spaces. In conclusion, these findings indicate that female rats display less anxiety-like behavior in the EPM and LOF. Furthermore, there are sex differences for almost all behavioral parameters in these anxiety tests.

Keywords: Anxiety; Dendrogram; Elevated plus-maze; Hierarchical cluster analysis; Open field; Sex.

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Conflict of interest statement

Conflict of Interest: The authors declare that they have no conflict of interest.

Figures

Figure 1.
Figure 1.. Decreased anxiety-like behavior in female rats compared to male rats in the elevated plus-maze test.
The figure shows open arm entries (A), closed arm entries (B), center entries (C), percentage open arm entries (D), open arm duration (E), closed arm duration (F), center duration (G), percentage open arm duration (H), and total distance traveled (I). The females were more active and displayed less anxiety-like behavior. N=47/group. *p<0.05, *** p<0.001, **** p<0.0001. Data are expressed as means ± SEM.
Figure 2.
Figure 2.. Automated tracking in the large open field and the elevated plus-maze test.
Representative figures of one male (A) and one female (B) rat in the EPM, and one male (C) and one female (D) rat in the LOF. The figures were generated with the EthoVision video tracking system. A–D, N=1.
Figure 3.
Figure 3.. Sex differences in exploratory behavior in the large open field test and the elevated plus-maze test.
The figures show that the males (A) spent less time in the open arms of the EPM and more time in the closed arms of the EPM compared to the females (B). The males (C, E) spent less time in the middle/center zone than the females (D, F) in the LOF. Figs. 3A–D were generated with EthoVision software, and 3E and F were generated with COLORcation software. All track data were obtained with the EthoVision system. Warmer colors indicate more time in spent in a specific area. A and B, N=12/group; C–F, N=47/group.
Figure 4.
Figure 4.. Decreased anxiety-like behavior in female rats compared to male rats in the large open field test.
The figure shows entries into the outer (A), middle (B), and center (C) zone, latency to enter the middle (D) and center zone (E), duration in the outside (F), middle (G), and center zone (H), and total distance traveled. The females were more active and displayed less anxiety-like behavior. N=47/group. **** p<0.0001. Data are expressed as means ± SEM.
Figure 5:
Figure 5:. Correlation heatmap of behavioral parameters in the large open field and elevated plus-maze test.
The heatmap shows the three clusters. One cluster contains LOF parameters, one cluster contains EPM parameters, and one cluster contains a mixture of LOF and EPM parameters. N=47/group. The degree of correlation is indicated by the intensity of the colors (red is indicative of a positive correlation and blue of a negative correlation). The Pearson correlation values are shown in the heatmap. N=47/group.
Figure 6.
Figure 6.. Relationship between behavioral parameters in the large open field test and the elevated plus-maze test.
The linear regression analysis shows the relationship between various behavioral parameters in the LOF and EPM. Relationship between total distance in the LOF and EPM (A), entries into the center zone of the EPM and the open arms of the EPM (B), time in the center zone of the LOF and open arms of the EPM (C), and entries into the middle zone of the EPM and open arms of the EPM (D). N=47/group.
Figure 7.
Figure 7.. Detailed hierarchical clustering dendrogram of behavioral parameters in the large open field test and the elevated plus-maze test.
The length of the vertical lines reflects the similarity between the groups (short lines are indicative of greater similarity). N=47/group.
See this image and copyright information in PMC

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