Mariana Zancan and Alberto A. Rasia-Filho130
elements that modulate mainly the excitatory neurotransmission. These
findings indicate that the female rat MePD modulates the synaptic input
in a complex and dynamic way prior to influencing other interconnected
brain areas relevant for the neuroendocrine secretion needed for the
ovulation and the display of proceptive behavior. Furthermore,
substitutive hormonal therapy to adult ovariectomized females do not
resemble the physiological variations in the normally cycling rat. This
synaptic organization changes once more when females have the
experience of motherhood. In mothers, the reduced density of dendritic
spines is likely involved with less avoidance behavior toward pups and
for other adaptive skills developed for the new demands from the
environment, for nursing behavior and memory elaboration about this life
event. These data provide additional insights about the important role of
the rat MePD as a model for the study of the link between sex steroids,
the cellular specializations for synaptic processing, and the functional
organization of the nervous tissue in females.INTRODUCTION
The medial nucleus of the amygdala (MeA) is a subcortical component of
the extended amygdala in the ventral forebrain of rats (de Olmos et al., 2004).
According to morphological, neurochemical, hodological, and functional
criteria, the MeA can be divided into the anterodorsal, anteroventral,
posterodorsal (MePD), and posteroventral subnuclei (Canteras et al., 1995;
Petrovich et al., 2001; Dall ́Oglio et al., 2008a,b). The MePD contains one of
the highest expression of gonadal hormone receptors in the rat brain, which is
comparable to some hypothalamic nuclei that control neuroendocrine secretion
for reproduction. The MePD has both estrogen receptors α (ER-α) and β (ER-
β), progesterone receptors, and androgen receptors (Simerly, 1990; Gréco et
al., 1998, 2001; De Vries and Simerly, 2002). These receptors have a complex
interaction and dynamics along the estrous cycle and/or after ovariectomy
(OVX). As reviewed in Rasia-Filho et al. (2012a), “In the MePD of female
rats there were high concentrations of both ER-a and ER-ß (Simerly et al.,
1990; Shughrue et al., 1997; Gréco et al., 1998, 2001, 2003). Different
regional distribution of these ERs occurs in the dorsal and in the ventral parts
of this subnucleus, but both ERs can be co-localized in the same neurons
(Gréco et al., 2001, 2003). The replacement treatment with estradiol to
castrated females decreased the number of MePD cells immunoreactive to ER-
α and those co-expressing ER-α and ER-ß (Gréco et al., 2001). In castrated
and hormone primed female rats, the early gene activation expression of Fos-