Ontogenetic and seasonal changes in immunoreactive vasotocin in the canary brain.

Using immunocytochemistry the central VT system of the canary was examined during ontogeny and throughout the season. At 4 weeks of age no VT-immunoreactive staining in the bed nucleus of the stria terminalis and lateral septum was present, but VT-containing cells and fibers were clearly visible in the nucleus paraventricularis of the hypothalamus. At 13 weeks of age a weak VT immunoreactivity appeared in the bed nucleus of the stria terminalis and lateral septum. This VT immunostaining increased progressively till at the age of 28 weeks adult levels were reached. In adulthood, cells and fibers in the lateral septum and the bed nucleus of the stria terminalis contained the highest amounts of immunoreactive VT during the breeding season, whereas during the molt, in august, a decreased VT immunostaining was noted. These seasonal changes in VT immunostaining coincided with variations in circulating testosterone level, which is high during the breeding season and low during the molt. In the ventral capsular region surrounding the nucleus robustus archistriatalis a clear VT-immunoreactive fiber pattern was demonstrated at the age of 8 and 13 weeks in both female and male canaries. Although the size of this nucleus varies during the season no seasonal changes in the VT-immunoreactive pattern surrounding the RA were detected. The data suggest that the activity of the VT system slowly increases during development. At adulthood seasonal and gonadal hormone-dependent changes occur in the limbic VT system only. The VT immunostaining associated with the nucleus robustus archistriatalis however, is resistant to seasonal and gonadal influences.