Neural correlates and modulators of social plasticity
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Phenotypic plasticity is the process by which external and internal factors alter the phenotype of the individual, and such factors include social experience and hormonal milieu. For example, sociosexual experience in adulthood can increase the retention of sexual behavior following gonadectomy. Though there exists substantial documentation of the various types of social plasticity, few studies highlight the neural correlates of these changes. Here I present a series of experiments linking social experience to changes in cytochrome oxidase activity and in social behavior in male rats, leopard geckos and whiptail lizards. Cytochrome oxidase (CO) is a rate-limiting enzyme in oxidative phosphorylation and a valuable marker of metabolic capacity. I focused on species differences in the degree to which social experience in adulthood changes the retention of courtship behavior following gonadectomy and CO activity. I found that social experience in adulthood enhanced retention of courtship behavior following castration in male whiptail lizards but not in male geckos. In other words, whiptail lizards resemble rats in this behavioral plasticity. I also found that species that show experience-dependent increases in the retention of courtship behavior following castration also show experience-dependent increases in CO activity in the preoptic area and medial amygdala. Cytochrome oxidase activity decreases following castration in limbic brain areas, and this decrease is likely to be linked to the post-castration decline in sexual behavior. Therefore, I propose that experience-dependent elevations in CO activity in the limbic system allow for the greater display of sexual behavior following castration. In summary, increases in CO activity in the preoptic area and amygdala are neural correlates of social plasticity. With regard to species and individual differences in social plasticity, I found that experience-dependent changes in post-castration behavior were correlated with the capacity for progesterone (P) to induce sexual behavior (i.e., P-sensitivity). I also found that, in male leopard geckos, embryonic incubation temperature can affect behavioral change following social experience. In other words, both P-sensitivity and embryonic incubation temperature were found to modulate social plasticity. Finally, these modulators are also likely to affect the degree to which CO activity changes following social experience.