Hemispheric specialization for the control of copulation in the young chick and effects of 5 alpha-dihydrotestosterone and 17 beta-oestradiol.

After intramuscular treatment with either oestradiol (1 mg/day for 4 days) or 5 alpha-dihydrotestosterone (0.5 mg/day for 7 days) the copulatory behaviour of young male chicks was tested monocularly using removable eye-patches. From day 11 to 14 copulation scores were significantly elevated in chicks treated with oestradiol or 5 alpha-dihydrotestosterone (5 alpha-DHT) and tested either binocularly or monocularly using the left eye. There was no elevation of copulation when the treated chicks were tested monocularly using the right eye. Thus, in the binocular condition neural circuits receiving input from the left eye, and therefore likely to be on the right side of the brain, are specialized for the activation of copulation. This result confirms previous findings using chicks treated with testosterone. On day 14 the eye-patches were changed to the other eye. For chicks treated with oestradiol, those now tested using the left eye showed significantly higher levels of copulation than those now using the right. In other words, there was very little interocular transfer from left eye to right eye. However, after transferring the eye patches, the chicks treated with 5 alpha-DHT had high copulation scores irrespective of the eye used. This suggests that there may be an interaction between prior copulatory experience and 5 alpha-DHT levels which leads to either interocular transfer of copulation behaviour or equal access of both eyes to the brain regions which control copulation.