Effects of experience and novelty on sexual behavior and associated neuronal activity in male Japanese quail
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In many behavioral paradigms, repeated exposures to a particular stimulus or event results in lower immediate early gene (IEG) expression. First, it was investigated if a similar reduction in IEG expression in the brain areas controlling male sexual behaviors would be observed after repeated copulation experiences in male Japanese quail. The results showed that IEG expression, as assessed by egr-1 immunoreactivity, did not increase in the POM, the BST, or the PAG after a copulation episode in highly sexually experienced subjects. One possibility was that the pattern of initial elevation of neuronal activity during the early trials of sexual interactions and the lack of increase in IEG expression later was associated with the novelty of sexual stimuli. While early exposures to certain stimuli constitute a new learning experience, the significance of such exposures would be lower as the level of experience increases. It was hypothesized that the introduction of a novel stimulus would increase the IEG expression in the POM, the BST and the PAG of experienced subjects. To evaluate this prediction, subjects were tested to see if they learn to respond to females decorated with distinct novel artificial cues after repeated exposures. The results showed that control subjects that did not have sexual experiences with decorated females discriminate against such females and directed their responses to normal females. Trained subjects did not show such preferences and responded to both types of females. In the next experiment, contrary to the prediction, no increase in IEG expression was observed after the introduction of the novel stimulus. This might be due to lower sexual motivation in subjects exposed to novel females. Effects of sexual experience were also tested in the catecholaminergic system. It was hypothesized that TH innervation in the POM and the BST would increase as a result of sexual experience. IEG expression in the catecholaminergic areas was predicted to be lower after repeated sexual experiences. The results showed no effect of experience in either tyrosine hydroxylase (TH) innervation, nor TH-egr-1 colocalization. These findings suggest that experience-related changes in male sexual behavior may be mediated by a different neurotransmitter system.