Strain and sex differences in the rat brain

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Abstract
The brains of female and male Wistar (W) rats were larger than the brains of Long-Evans (LE) rats at all ages and males had larger brains than females (p < 0.001). These differences did not correlate with differences in body weight. Brains of female and male LE and W rats aged 60 days (n = 48) were perfused with 10% neutral formalin and cut and stained with hematoxylin and eosin. Matching sagittal sections were selected for the study of the cerebellum, hippocampus and the olfactory bulbs. Brains from a similar group of 48 animals were prepared according to the Golgi-Cox method and were used for the study of Purkinje cells. Males had a 5.7% larger cerebellar area than females (p < 0.001). This difference was mostly due to a 6.1 % difference in the area of the molecular layer and a 6.2% difference in the granule cell layer (p < 0.001). Males also had more granule cells (8.1%), p < 0.05) and Purkinje cells (7.2%, p < 0.05) than females. The strains were similar in the area of the cerebellum, but LE had more Purkinje cells (9.6%, p < 0.01), packed more densely (11.1%, p < 0.01) than W cells. The results of the Golgi preparation suggest that the dendritic tree of the Purkinje cells was larger in the LE strain (10.5%, p < 0.05). There were no sex differences for the hippocampus and the olfactory bulbs. The area of the hippocampus did not differ between strains but W had a longer and thus thinner granule cell layer (15.2%, p < 0.001). The hippocampal granule cells were packed more densely in W strain (8.9%), p < 0.05). The olfactory bulb granule cell layer of W rats was larger than that of LE rats (14.9%o, p < 0.05). Such anatomical differences may be correlated in subsequent studies with behavioral differences. Indeed, there are indications that the strain LE which possesses a greater number and larger Purkinje cells also perform better in motor tasks.

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