Background: Changes in levels of estradiol and progesterone that occur with the transition to reproductive senescence may influence nociception or affect.
Objective: To ascertain whether nociceptive and affective processes change with reproductive senescence, this study examined pain and anxiety-like behaviors in middle-aged female rats that were reproductively competent, transitioning to reproductive senescence, or reproductively senescent.
Methods: Middle-aged (12-14 months old) female rats (N = 46) were tested in the following tasks to assess pain and anxiety-like behavior: tail flick, elevated plus maze, elevated zero maze, mirror maze, Vogel punished drinking, and defensive burying. For the tail-flick task, the latency for rats to move their tail from a heat source, as an indication of pain sensitivity, was determined. In the elevated plus and elevated zero mazes, the time spent on the open arms or quadrants, respectively, were determined as measures of reduced anxiety behavior. In the mirror maze, the time spent in the mirrored portion of the chamber was used as an indicator of anxiety-like responding. In the Vogel task, the number of punished licks made was determined as a measure of reduced anxiety-like behavior. In the defensive burying task, the duration spent by rats burying an electrified prod postfootshock was utilized as an index of anxietylike responding. All rats were experimentally naive, retired breeders from our colony and had not had a litter or been lactating for 1 to 4 weeks before behavioral testing.
Results: Although tail-flick latencies were not significantly different among rats that were reproductively competent or senescent, reproductively competent rats had less anxiety-like behavior in the elevated plus maze (more time spent on the open arms: F(2,43) = 5.93; P < 0.01), elevated zero maze (more time spent on the open quadrants: F(2,43) = 4.62; P = 0.01), and Vogel punished drinking task (more punished licks made: F(2,43) = 3.76; P = 0.03). There were no statistically significant differences in the mirror maze and defensive burying task.
Conclusion: In this study of adult female rats, nociceptive behavior did not vary significantly with reproductive senescence, but anxiety-like behavior of rats did.