Immunohistochemical localization of serotonin in the pineal gland of the chicken during post-hatching development in relation to light-dark cycle.

In the present immunohistochemical study using an antiserum against serotonin, the localization of serotonin was demonstrated in the pineal gland of the chickens from 1 day to 3 years of age. Serotonin-like immunoreactivity was located in the supranuclear region of the follicular cells and in the perikaryon of the parafollicular cells in the pineal gland, exhibiting distinct changes during post-hatching development. The reactivity reached its peak in 1-year-old chicken. Moreover, diurnal changes in immunoreactivity also existed after 1 day of age, being high in the light period and low in the dark period. Occasionally in 1-3-year-old chickens, a part of granular-shaped reactive products observed in the light period appear to be diffused in the cytoplasm in the dark period. In addition, a number of immunoreactive fibers were shown in the pineal parenchyma, exhibiting a slight increase in number and in reactivity at 40 days of age.