Article

Sexual dimorphism in neuronal number of the posterodorsal medial amygdala is independent of circulating androgens and regional volume in rats

Neuroscience Program, Michigan State University, East Lansing, Michigan 48824-1101, USA.
The Journal of Comparative Neurology (Impact Factor: 3.51). 02/2008; 506(5):851-9. DOI: 10.1002/cne.21536
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ABSTRACT The posterodorsal medial amygdala (MePD) in rodents integrates olfactory and pheromonal information, which, coupled with the appropriate hormonal signals, may facilitate or repress reproductive behavior in adulthood. MePD volume and neuronal soma size are greater in male rats than in females, and these sexual dimorphisms are maintained by adult circulating hormone levels. Castration of adult males causes these measures to shrink to the size seen in females 4 weeks later, whereas testosterone treatment of adult females for 4 weeks enlarges these measures to the size of males. We used stereological methods to count the number of cells in the MePD and found that, in addition to the sex difference in regional volume and soma size, males also have more MePD neurons than do females, yet these numbers are unaffected by the presence or absence of androgen in adults of either sex. Males also have more glial cells than do females, but, in contrast to the effects on neuronal number, the number of glial cells is affected by androgen in the right MePD of both sexes and, therefore, may contribute to regional volume changes in adulthood in that hemisphere. Thus, regional volume, neuronal size, and glial numbers vary in the MePD of adult rats in response to circulating androgens, but neuronal number does not. These results suggest that the sex difference in neuronal number in the rat MePD may be "organized" by androgens prior to adulthood, whereas regional volume, neuronal size, and glial numbers can be altered by androgens in adulthood.

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    • "The MePD is highly sensitive to gonadal hormones action (Simerly et al., 1990; € Osterlund et al., 1998; Cooke et al., 1999; Gr eco et al., 2003). The volume of the MePD (Hines et al., 1992; Cooke et al., 1999), its neuronal (Morris et al., 2008) and glial densities (Johnson et al., 2008), neuronal volume (Hermel et al., 2006), dendritic orientation (Dall'Oglio et al., 2008a,b), and synaptic contacts (Nishizuka and Arai, 1983a) are all sexually dimorphic and/or change along the estrous cycle. In such a manner, the MePD is considered a relevant brain area to promote timely physiological changes in neuroendocrine secretion and behavioral display according to different stimuli and social demands perceived by the animal (Newman, 1999; Choi et al., 2005; Rasia-Filho et al., 2012a,b). "
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    • "The MeA is composed of 4 subnuclei and modulates social and reproductive behaviors [22] [23] [24] [25], among other functions [19] [20] [21]. Several studies indicate that sex steroids can alter the morphology and function of the posterodorsal medial amygdala (MePD) neurons and glial cells [26] [27] [28], thus making the MePD rat sexually dimorphic or modifiable by naturally occurring variations in the level of circulating ovarian steroids [23] [24] [25] [26] [27] [28] [29] [30] [31]. "
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