Lack of Sex Differences in Psychostimulant-Induced Locomotor Activity When Comparing Rats From the Same Behavioral Groups

Abstract

Background

We hypothesized that sex differences in baseline-, saline-, and psychostimulant-induced locomotor activity (LMA) would not be observed when we compared males and females that belonged to the same behavioral group(s). Our aim was to determine whether we could detect differences between males and females within a truly distinct behavioral group. To identify behavioral groups, current models use median-split analysis typically of one variable, but this procedure may not be effective. With the rationale that clustering analysis of several variables is a more robust grouping strategy, we developed a new model termed the MISSING (Mapping Intrinsic Sex Similarities as an Integral quality of Normalized Groups) model to test our hypothesis.

Methods

We obtained baseline LMA, drug-induced LMA, and a new variable that integrates both baseline and drug-induced LMA (drug-induced LMA normalized-to-baseline activity-time) from LMA assessments following saline (males n = 12, females n = 11) and cocaine 10 mg/kg (male n = 22, female n = 23) intraperitoneal injections, and intra–nucleus accumbens dopamine 15 μg/side (male n = 20, female n = 17). Using regression analysis and analysis of variance, we compared the MISSING model with the current model for effectiveness in identifying distinct groups.

Results

The MISSING model was superior to the median split in distinct behavioral group identification. For both models, we confirmed that there were no differences in psychostimulant-induced LMA when we compared males and females within the same group/cluster.

Conclusions

There were no sex differences in psychostimulant-induced LMA when we compared rats from the same behavioral group(s).