Elsevier

Physiology & Behavior

Volume 60, Issue 6, December 1996, Pages 1491-1494
Physiology & Behavior

Sex and Intrauterine Position Influence the Size of the Gerbil Hippocampus

https://doi.org/10.1016/S0031-9384(96)00311-3Get rights and content

Abstract

Sex differences in home range size and spatial ability are predictive of sex differences in the relative size of the hippocampus in rodents. Such differences in behavior and hippocampal volume are presumed to be, in part, the result of differences in perinatal exposure to hormones. We predicted from differences in the size of home ranges of male and female Mongolian gerbils (Meriones unguiculatus) in the wild that the hippocampus of male gerbils would be relatively larger than that of females. We examined the effect of prenatal hormonal influences on hippocampal size by comparing hippocampal volume of males and females from 2F and 2M intrauterine positions to that of randomly selected males and females. We found that, as predicted, randomly selected males had a significantly larger hippocampus, relative to telencephalon, than did randomly selected females. However, males and females from 2F and 2M intrauterine positions did not differ in relative hippocampal size. Possible explanations for the absence of a sex difference in hippocampal size in male and female gerbils from 2F and 2M intrauterine positions are discussed.

Section snippets

Subjects

Twenty-six male and 26 female Mongolian gerbils born and reared in the vivarium of the McMaster University Department of Psychology served as subjects. All were second or third generation descendants of breeding stock acquired from Tumblebrook Farms (Brookfield, MA). Seventeen male and 16 female subjects were delivered by cesarian section. The remaining 19 subjects (9 males and 10 females), referred to below as group R, were randomly selected from among males and females used as breeding stock

RESULTS

Volume of the hippocampus and telecephalon for all males and females is shown in Fig. 1. Analysis of covariance was used to examine the effects of sex and intrauterine position on the size of the hippocampus, using size of the telencephalon as a covariate. Homogeneity of the regression of hippocampal volume on telencephalon volume was confirmed for both sexes and for the three intrauterine conditions (2M, 2F, and R) prior to analysis of covariance. Mean residuals from this regression are shown

DISCUSSION

The results provide evidence for a sex difference in relative hippocampal size in a random selection of Mongolian gerbils in the direction expected on the basis of sex differences in home range size in the wild. Like male meadow voles and kangaroo rats 15, 16, male gerbils have a larger home range and a relatively larger hippocampus than do females.

As can be seen most clearly in Fig. 2, gestation in either 2F or 2M intrauterine positions eliminated the sex difference found in randomly selected

Acknowledgements

This research was supported by grants from the Natural Sciences and Engineering Research Council of Canada to D.F.S. and M.M.C. We would like to thank Tammi Ivanco, Karen-Anne Moore, and Miney Ham for assistance in preparing gerbil brains, Richard Cooley for expert histological work, and Mark Sangster for digitizing several thousand brain sections. Elizabeth Hampson and Scott Moffat provided valuable comment and discussion.

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