CELLULAR PROLIFERATION IN THE RAT PINEAL-GLAND DURING POSTNATAL-DEVELOPMENT

To establish a possible correlation between the rate of cellular proli feration and already documented functional and morphological character istics of the rat pineal gland during postnatal development, the bromo deoxyuridine labelling method was used to evaluate the fraction of cel ls at the S phase of the cell cycle in paraffin sections from 1-, 7-, 14- and 28-day-old rats. Numerical density, taken as an indirect measu re of cell hypertrophy, was also evaluated. During the first week afte r birth the percentage of S phase-cells in the rat pineal gland sharpl y decreased from around 9% to 1.3%. A smaller but also significant dec rease was found from the 7th to the 14th postnatal day where S phase c ells were less than 0.5% of all pineal cells. A very low percentage wa s also seen in samples from 28-day-old rats. Numerical density, namely , the total number of cells per surface unit of pineal section, decrea sed from birth to the end of the first month. This decrease was also s teeper from birth to the 7th postnatal day than at any other period of the study. These results support the idea that a strong expansion of the cellular population of the rat pineal gland precedes morphological and functional maturation and opens the way to further exploration of the relationship between functional and proliferative responses of th e pineal gland.