IN-VIVO AND IN-VITRO FLOW-CYTOMETRY COMPARATIVE-ANALYSIS OF SOMATOSTATIN-POSITIVE CELLS IN THE PINEAL-GLAND OF THE NEONATAL RAT

Flow cytometry was used for comparative in vivo and in vitro analysis of cell populations staining positively for somatostatin. Experiments were carried out with pineals obtained from neonatal, 8- and 15-day-ol d rats. Pineal cells were obtained by dispersion with collagenase and then processed in a flow cytometer or maintained in culture for 1 or 2 weeks. Identification of somatostatin-immunopositive cell populations was performed using a polyclonal somatostatin antibody and confirmed by indirect immunostaining of cytospun smears with the avidin-biotin-p eroxidase method. In vivo, the percentage of somatostatin-positive cel ls was 60.6+/-4% in neonatal pineals and declined to 22.2+/-11% in 15- day-old animals (p < 0.04). The density of peptide immunostaining decr eased in 8-day-old animals but recovered to the neonate levels in 15 d ay-old animals; homogeneity in the immunopositive population increased with age. Maintenance in culture for 1 week resulted in an increase i n positive somatostatin staining in animals of 8 and 15 days with no c hanges in neonates; however, after 2 weeks of culture, the percent of immunopositive cells decreased from 53.3+/-6 to 12.2+/-4% in the older animals and remained unchanged in neonates. We conclude that somatost atin is found in pinealocytes and shows a declining pattern during the perinatal period; this probably implies that the peptide plays a para crine role important for cell differentiation in these young animals, since maximal cellularity and a high mitotic index occur within the fi rst 3 days of life, and pineal cell differentiation is completed befor e the end of the third week of extrauterine life.