Abstract
After an initial increase, repeated exposure to a particular stimulus or familiarity with an event results in lower immediate early gene expression levels in relevant brain structures. We predicted that similar effects would occur in Japanese quail after repeated sexual experience within brain areas involved in sexual behavior, namely, the medial preoptic nucleus (POM), the bed nucleus of stria terminalis (BST), and the nucleus taeniae of the amygdala (TnA), an avian homolog of medial amygdala. High experience subjects copulated with a female once on each of 16 consecutive days, whereas low experience subjects were allowed to copulate either once or twice. Control subjects were never exposed to a female. High experience subjects were faster to initiate sexual interaction, performed more cloacal contacts, and completed each cloacal contact faster than low experience subjects. Low experience subjects showed an increase in egr-1 (ZENK) expression, an immediate early gene product used as marker of neural activation in birds, in the areas of interest. In contrast, in high experience animals, egr-1 expression in the POM, BST, and the periaqueductal gray (PAG) was not different than the level of expression in unmated controls. These results show that experience modulates the level of immediate early gene expression in the case of sexual behavior. Our results also indicate that immediate early gene expression in specific brain areas is not necessarily related to behavioral output but depends on the behavioral history of the subjects.