Genetic Analysis Of Brainbehavior Relationships

So far, we have not dealt with the intermediate neuronal structures through which genes modulate aggressive behavior. Results from knockout studies have certainly identified a wealth of brain receptors that might be involved in aggressive behavior. However, do they also represent naturally occurring variation in behavior and underlying neuronal structures?

One of the more eye-catching products of genetic analyses of brain and behavior comes from studies on the hippocampal intra- and infrapyramidal mossy fiber (IIPMF) terminal fields. Also, this research clearly demonstrates the importance and strength of classic behavioral genetical techniques.

The hippocampus has been shown by means of lesion studies to be involved in learning and memory. Subsequently, it was shown that the performance of mice in learning tasks dependent on hippocampal integrity is correlated with heritable variations in the size of the IIPMF. Animals with larger IIPMF projections perform better on spatial learning tasks.

However, several mossy fiber studies also indicate hippocampal involvement in the regulation of intermale aggression.

The first indication for the involvement of genetics and the IIPMF sizes in the development of aggression came from the two selection lines previously mentioned. (Aggressive) SAL males had shorter IIPMF terminal fields than (nonaggressive) LAL males. Soon after, a study that compared multiple inbred strains for both the sizes of the IIPMF terminal fields and aggressive behavior clearly demonstrated that the SAL-LAL difference was no coincidence. In fact, a strong negative genetic correlation was observed between these two variables: The shorter the IIPMF sizes, the more aggressive the behavior (Fig. 2). These findings strongly suggest that hereditary neuroanato-mical variations in a defined brain structure, the hippocampus, may influence intermale attack behavior.

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