Cohort Removal Induces Changes in Body Temperature, Pain Sensitivity, and Anxiety-Like Behavior

Keizo Takao,Satoko Hattori,Tsuyoshi Miyakawa,Hirotaka Shoji

doi:10.3389/fnbeh.2016.00099

Abstract

Mouse behavior is analyzed to elucidate the effects of various experimental manipulations, including gene mutation and drug administration. When the effect of a factor of interest is assessed, other factors, such as age, sex, temperature, apparatus, and housing, are controlled in experiments by matching, counterbalancing, and/or randomizing. One such factor that has not attracted much attention is the effect of sequential removal of animals from a common cage (cohort removal). Here we evaluated the effects of cohort removal on rectal temperature, pain sensitivity, and anxiety-like behavior by analyzing the combined data of a large number of C57BL/6J mice that we collected using a comprehensive behavioral test battery. Rectal temperature increased in a stepwise manner according to the position of sequential removal from the cage, consistent with previous reports. In the hot plate test, the mice that were removed first from the cage had a significantly longer latency to show the first paw response than the mice removed later. In the elevated plus maze, the mice removed first spent significantly less time on the open arms compared to the mice removed later. The results of the present study demonstrated that cohort removal induces changes in body temperature, pain sensitivity, and anxiety-like behavior in mice. Cohort removal also increased the plasma corticosterone concentration in mice. Thus, the ordinal position in the sequence of removal from the cage should be carefully counterbalanced between groups when the effect of experimental manipulations, including gene manipulation and drug administration, are examined using behavioral tests.

Highlights

Mice are subjected to behavioral tests in laboratories to examine the effects of gene mutations, drug treatments, and other experimental manipulations on brain function
The order of the sequential removal from the home cage significantly influenced the rectal temperature of mice (Figure 1, one-way ANOVA, position effect, F(4,1695) = 52.29, p < 0.0001)
The significance of these differences among the positions all survived the Benjamini and Hochberg false discovery rate (FDR) procedure (Benjamini-Hochberg Critical Value; q = 0.05; Benjamini and Hochberg, 1995; Verhoeven et al, 2005). These results suggest that cohort removal induced hyperthermia in mice in a manner dependent on the number of mice removed from their cage before the test

Summary

Introduction

Mice are subjected to behavioral tests in laboratories to examine the effects of gene mutations, drug treatments, and other experimental manipulations on brain function. Various factors must be taken into account in addition to the main effects under study The impact of those factors on the analyses should be minimized in the experiments by matching, counterbalancing, and/or randomizing. Some of these factors have not drawn much attention of the researchers in the field, their effects should not be ignored. The effect of cohort removal on anxiety-like behaviors of mice assesed in the elevated plus maze, may not be large enough to detect using a small number of subjects. We combined data collected using our behavioral test battery to examine the effect of cohort removal on mouse behavior with a much larger number of subjects

Methods

Results

Conclusion