Hemispheric control of territorial aggression in Anolis carolinensis: effects of mild stress

Previous work has demonstrated that the brain of Anolis carolinensis is functionally split, in that the left and right eyes project predominantly to the contralateral hemisphere, and as there are minimal connections between the left and right hemispheres. Using this model, the current experiment examined the effect of mild acute stress on hemispheric regulation of territorial aggression. Thirteen adult male Anolis were paired with an antagonistic males, and eye use and behavioral responses were repeatedly measured during 3 minute behavioral trials. Trials were conducted either after exposure to mild stress, produced by handling the subject, or without stress, and they were run either in the subject's home cage or in a cage foreign to the subject. Left eye preference for aggressive movements was found during the trials run in the non-stressed conditions (p < 0.05). Conversely, stressed subjects showed a reduction in left eye/right hemisphere mediated aggressive movements relative to the non-stressed subjects but no changes in right eye/left hemisphere aggression. This effect was independent of whether or not the subject was in its home or a foreign cage. No laterality in aggressive responding was found when the subjects were placed in separate cages with visual contact. These findings suggest that territorial aggression in Anolis is preferentially initiated and processed by the left eye/right hemisphere but is subject to right-hemispheric inhibition following exposure to acute mild stress.