Reproduction-related behaviors of Swiss-Webster female mice living in a cold environment

Abstract

Based on a molecular neuroendocrine theory about cold environments, thyroid hormone levels, and liganded thyroid hormone receptor interference with estrogen receptor function, experiments were designed to test female mouse reproductive behaviors in the cold. Because natural seasonal temperature declines would usually be associated with decreased photoperiods and reduced food supplies, we combined cold temperatures with short days and metabolic challenge. The simplest hypothesis was that lordosis quotients would be significantly reduced as a result of cold temperatures. That hypothesis was denied. Instead, female approaches to the stud male declined. Because cold temperatures also led to significant reductions of activity in locomotor wheels, a straightforward reduction of activity could explain the female's behavior during mating tests. We suggest that cold temperatures accompanied by reduced photoperiod and reduced metabolic fuel can reduce overall activity in female mice, thus indirectly blocking untimely reproductive behaviors.

Figure 1

Total numbers of female approaches to the male were significantly less (*, P < 0.01) in both groups given cold environmental exposure than in the controls (NORM). †, In lordosis strength calculations, zeros were not included.

Figure 2

In the second experiment, female approaches to the male occurred significantly less frequently (*, P < 0.01) in the COLD/SD/2DG group than in the controls (NORM). In lordosis strength calculations, zeros were not included.

Figure 3

Locomotor activity in wheels attached to each mouse's home cage was significantly depressed (**, P < 0.005) when the animals were living in a cold environment.

Figure 4

Revolutions per day in the locomotor wheels attached to the home cage, plotted here for two representative mice. (A) One started at normal room temperature (NORM) and was then switched to the cold (COLD) living environment (without being removed from her home cage). (B) The other was measured in the reverse order. Time of switching is shown by a small arrow below the abscissa.