Glutamate-induced asymmetry in the sexual and aggressive behavior of young chickens

A unilateral injection of monosodium glutamate (MSG) into the left hemisphere of the forebrain, at doses of either 50 nmol or 500 nmol per hemisphere on day 2 post-hatch, resulted in a marked and long lasting elevation of attack and copulatory behavior in cockerels. This was not observed when MSG was injected into the right hemisphere or both hemispheres, and further demonstrates functional brain asymmetry in lower vertebrates. A similar asymmetry was observed after administering the higher dose of MSG to females on day 2. A significant change in copulatory performance was observed when the higher dose was injected into the left hemisphere on day 11, compared to the controls, without affecting attack behavior, whereas, the lower dose failed to induce any changes. This may be due to the development of efficient brain uptake mechanisms for glutamate. The possibility that the behavioral changes were induced indirectly via increased secretion of plasma androgen, which then stimulates the appropriate brain centres, was found not to be the case.