EFFECTS OF NEONATAL TREATMENT WITH 1-(2,5-DIMETHOXY-4-IODOPHENYL)-2 AMINOPROPANE HCL(DOI) AND RITANSERIN ON AGONISTIC BEHAVIOR IN ADULT MALE AND FEMALE RATS

The role played by the neonatal 5-hydroxytryptamine (5HT) system in th e organization and sexual differentiation of adult agonistic behavior was investigated in rats. Focus was on the 5HT2 receptor subtype, whic h has been demonstrated to be involved in agonism control in the adult . 5HT2 activity was experimentally manipulated by ad ministration of a specific agonist [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl ( DOI)] or antagonist (ritanserin) during the second week of life, when serotonin is known to concur to anatomical and behavioral sexual diffe rentiation. Interactions between early 5HT2 activity, genetic sex, and neonatal circulating testosterone (T) were studied by administering t he ligands to males, females, and androgenized females. At adulthood, the animals were tested for both aspects of agonism, i.e., aggression and defense, in a 20-min confrontation with an unfamiliar conspecific of the same sex, age, body weight, and social experience. Neonatal adm inistration of the 5HT2 antagonist ritanserin increased aggression ind ependently of sex; it also increased defense, but this effect was conf ined to males. The agonist DOI had no effect on aggression, but enhanc ed defense in males and androgenized females, with an effect which dep ended therefore more on neonatal T than genetic sex. Females appeared in general less sensitive to neonatal 5HT2 manipulation than both andr ogenized females and males; this suggests that neonatal T is crucial f or experimental modifications of neonatal 5HT2 activity to have any co nsistent effect on adult agonistic behavior. On the other hand, effect s observed in males and androgenized females were dependent on the beh avior considered and the drug administered. This was especially eviden t for defense, enhanced by ritanserin in males only, and in both males and androgenized females by DOI. Neonatal 5HT2 activity seems therefo re to play a role in the modulation of adult agonistic behaviors, whic h depends on the behavior considered and is under multiple control of genetic sex and hormonal neonatal substrate. (C) 1994 Wiley-Liss, Inc.