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Factor Analysis Shows That Female Rat Behaviour Is Characterized Primarily by Activity, Male Rats Are Driven by Sex and Anxiety

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Abstract

This experiment explored sex differences in behaviour using factor analysis to describe the relationship between different behavioral variables. A principal component solution with an orthogonal rotation of the factor matrix was used, ensuring that the extracted factors are independent of one another, and thus reflect separate processes. In the elevated plus-maze test of anxiety, in male rats factor 1 accounted for 75% of the variance and reflected anxiety, factor 2 represented activity, and accounted for 24% of the variance. This contrasted with the finding in female rats in which factor 1 was activity, accounting for 57% of the variance, with the anxiety factor accounting for only 34% of the variance. When behaviour in both the plus-maze and holeboard were analysed, a similar sex difference was found with anxiety emerging as factor 1 in males and holeboard activity as factor 1 in females. Locomotor activity in the inner portion of the holeboard loaded on the anxiety factor for males, but on activity for females. When behaviours in the plus-maze and sexual orientation tests were analysed, anxiety emerged as factor 1 in males, sexual preferences factor 2, and activity factor 3. In females, activity was factor 1, sexual preference factor 2, anxiety factor 3, and social interest factor 4. These results suggest caution should be exercised in interpreting the results from female rats in tests validated on males because the primary controlling factor may be different.

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Animals

Male (n = 57) and female (n = 59) Wistar rats (bred at St. George's Hospital Medical School), were housed in same-sex groups of five or six from weaning. All animals were housed in the same animal room, maintained at 22°C, in a reversed light regimen 12 h on:12 h off (lights off 0800 h). Food and water were freely available. The animals were tested at approximately 90 days of age. The experimental procedures carried out in this study were in compliance with the UK Animal Scientific Procedures

Factor Analysis on the Measures of Behavior in the Holeboard

In both sexes, two clear independent factors emerged from a factor analysis of the holeboard data—factor 1 reflecting exploration, and factor 2 reflecting motor activity (see Table 1). There were no sex differences in the factor analyses of holeboard data.

Factor Analysis on the Measures of Behaviour in the Elevated Plus-Maze

As can be seen from Table 2, two independent factors were extracted from the analysis of the elevated plus-maze measures in male and female rats.

In male rats, factor 1, on which open-arm activity loaded highly, was considered to be an index of

Discussion

Head-dipping is considered to be a measure of directed exploration in the holeboard because it reflects novel aspects of the environment, manipulated by placing objects under the holes, and results in information storage, indicated by habituation on repeated exposures (15). There is also pharmacological and factor analytical evidence for a separation of head-dipping and locomotor activity 12, 13, 15. Far greater variability between the scores of different sample groups from the same population

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