The Involvement of Neonatal 5HT Receptor-Mediated Effects on Sexual Dimorphism of Adult Behavior in the Rat
Catherine A. Wilson, M. Isabel Gonzalez, M. Emmanuella Albonetti, and Francesca Farabollini
The brain is sexually dimorphic and this leads to the sexual differences in centrally controlled physiological functions and behaviors ( MacLusky & Naftolin, 1981). This differentiation of the brain is under the control of testosterone secreted by the fetal/neonatal testicles over a critical period which, in the rat, extends over the last days in utero and the first two weeks postpartum ( MacLusky & Naftolin, 1981; Wilson, George, & Griffin, 1981). In the presence of androgens, the brain is masculinized and, compared to the female, some brain areas develop differently in size, neuronal population, synaptic connections, and neurotransmitter concentrations and activity ( Breedlove, 1994; de Vries, 1990). It seems likely that the steroid-induced differences in neurotransmitter activity occurring early in life are the links between the neonatal hormone and the sex differences in adulthood.
Among the various transmitters, 5-hydroxytryptamine (serotonin; 5HT) is an important candidate for causing sexual differences in brain functioning and behavior ( Jacobs & Azmitia, 1992). 5HT, like the androgens, has organizational effects over the neonatal period and can promote the development of its own system ( Whitaker-Azmitia & Azmitia, 1986) as well as stimulate the growth and differentiation of other neuronal systems ( Lauder, 1990; Whitaker- Azmitia , 1992). The actions of 5HT are mediated by at least seven receptor subtypes (5HT-1, 5HT-2, etc.), with further divisions within each subtype; so far, for instance, 5HT-1 receptors are further classified as 5HT-1A, -1B, up to -1F ( Watson & Girdlestone, 1995). Both 5HT-1A and 5HT-2 receptors in-