AVERSIVE-STIMULATION DURING THE STRESS-HYPORESPONSIVE PERIOD DOES NOTAFFECT THE NUMBER OF CORTICOTROPH CELLS IN NEONATAL MALE RATS

Immunohistochemistry was used to evaluate the effects of neonatal hand ling and aversive stimulation during the first 10 days of life on the number of corticotrophs in the anterior lobe of the pituitary of 11-da y-old male Wistar rats. Since adult rats handled during infancy respon d with reduced corticosterone secretion in response to stressors and w ith less behavior inhibition in novel environments, we assumed that ne onatal stimulation could affect pituitary morphology during this criti cal period of cell differentiation. Three groups of animals were studi ed: intact(no manipulation, N = 5), handled (N = 5) and stimulated (su bmitted to 3 different aversive stimuli, N = 5). The percentage of ACT H-immunoreactive cells in the anterior lobe of the pituitary (number o f ACTH-stained cells divided by total number of cells) was determined by examining three slices per pituitary in which a minimum of 200 cell s were counted by two independent researchers. Although animals during the neonatal period are less reactive to stress-like stimulation in t erms of ACTH and corticosterone secretion, results showed that the rel ative number of ACTH-stained cells of neonatal handled (0.25 +/- 0.01) and aversive stimulated (0.29 +/- 0.03) rats was not significantly di fferent from intact (0.30 +/- 0.03) animals. Neonatal stimulation may have a differential effect on the various subpopulations of corticotro ph cells in the anterior pituitary.