Impaired discriminative avoidance and increased plasma corticosterone levels induced by vaginal lavage procedure in rats

Abstract

Historically, females have been neglected in behavioral neuroscience research due to the alleged increased variability caused by hormonal fluctuations. More recently, there has been a tendency to include female subjects in the studies, in a majority of those cases with the condition that the hormonal variation is controlled. In rodent studies, the vaginal lavage procedure is a common method of collecting smears and determining the estrous cycle phase. However, little is known regarding the consequences of the procedure, although stress is often mentioned as a concern. Within the neuroscience field, spatial memory has been a relevant subject in terms of sex differences. The plus-maze discriminative avoidance task (PMDAT) allows for the concomitant evaluation of spatial memory, anxiety-like behavior, and locomotion, as well as possible interactions between these behaviors. The aim of the present study was to investigate the effects of the vaginal lavage procedure (VLP) on the performance of female rats in the PMDAT. We submitted adult female Wistar rats to VLP for 14 straight days and then to training and test sessions in the PMDAT. Additionally, another set of animals was submitted to the VLP procedure for determination of plasma corticosterone levels. Rats submitted to the vaginal lavage procedure did not discriminate the enclosed arms of the PMDAT apparatus, indicating impaired performance, but no anxiety-like alterations were found. VLP also resulted in a higher corticosterone level, suggesting it is a stressful manipulation. As such, the use of this method to control for hormonal variation should be restricted in behavioral studies.

Keywords: Aversive memory; Corticosterone; Estrous cycle; Female behavior; Spatial memory.