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

Neuroscience Program, Michigan State University, East Lansing, Michigan 48824-1101, USA.
The Journal of Comparative Neurology (Impact Factor: 3.23). 02/2008; 506(5):851-9. DOI: 10.1002/cne.21536
Source: PubMed


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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Available from: Stephen Marc Breedlove
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    • "The vast bibliography regarding sex dimorphic expression and regulation of aromatase in the brain is based on studies in the hypothalamus and the preoptic area (Beyer et al., 1994b; Hutchinson et al., 1997, 1999; Negri-Cesi et al., 2001) and very little is known about factors that control aromatase expression during development in other brain regions with high aromatase levels, such as stria terminalis and amygdala regions. The regions of interest for the present study were the medial preopticoamygdaloid neuronal arc that involves areas known to be sexually dimorphic and sensitive to organizational actions of steroid hormones (Forger et al., 2004; Morris et al., 2008). Taking into account that recent findings suggest that in addition of gonadal hormones, the sex chromosome complement is also involved in the generation of specific traits in the brain (Arnold, 2009; Scerbo et al., 2014) in this study we have tested the hypothesis that sex chromosome complement influences the expression of aromatase in the stria terminalis and amygdala regions. "
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    ABSTRACT: Aromatase, which converts testosterone in estradiol, is involved in the generation of brain sex dimorphisms. Here we used the "four core genotypes" mouse model, in which the effect of gonadal sex and sex chromosome complement is dissociated, to determine if sex chromosomes influence the expression of brain aromatase. The brain of 16 days old XY mouse embryos showed higher aromatase expression in the stria terminalis and the anterior amygdaloid area than the brain of XX embryos, independent of gonadal sex. Furthermore, estradiol or dihydrotestosterone increased aromatase expression in cultures of anterior amygdala neurons derived from XX embryos, but not in those derived from XY embryos. This effect was also independent of gonadal sex. The expression of other steroidogenic molecules, estrogen receptor-α and androgen receptor was not influenced by sex chromosomes. In conclusion, sex chromosomes determine sex dimorphisms in aromatase expression and regulation in the developing mouse brain. Copyright © 2015. Published by Elsevier Ireland Ltd.
    Full-text · Article · Jul 2015 · Molecular and Cellular Endocrinology
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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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    ABSTRACT: The density of dendritic spines is sexually dimorphic and variable throughout the female estrous cycle in the rat posterodorsal medial amygdala (MePD), a relevant area for the modulation of reproductive behavior in rats. The local synaptic activity differs between hemispheres in prepubertal animals. Here, we used serial section transmission electron microscopy to produce three-dimensional reconstructions of dendritic shafts and spines to characterize synaptic contacts on MePD neurons of both hemispheres in adult males and in females along the estrous cycle. Pleomorphic spines and non-synaptic filopodia occur in the MePD. On average, 8.6% of dendritic spines received inputs from symmetric GABA-immunoreactive terminals, whereas 3.6% received two synaptic contacts on the spine head, neck or base. Presynaptic terminals in females right MePD had a higher density of synaptic vesicles and docked vesicles than the left MePD, suggesting a higher rate of synaptic vesicle release in the right MePD of female rats. In contrast, males did not show laterality in any of those parameters. The proportion of putative inhibitory synapses on dendritic shafts in the right MePD of females in proestrus was higher than in the left MePD, and higher than in the right MePD in males, or in females in diestrus or estrus. This work shows synaptic laterality depending on sex and the estrous cycle phases in mature MePD neurons. Most likely, sexual hormones effects are lateralized in this brain region, leading to higher synaptic activity in the right than in the left hemisphere of females, mediating timely neuroendocrine and social/reproductive behavior. J. Comp. Neurol., 2013. © 2013 Wiley Periodicals, Inc.
    Full-text · Article · Jun 2014 · The Journal of Comparative Neurology
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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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    ABSTRACT: Central oxytocin (OT) and arginine-vasopressin (AVP) have been shown to play an important role in sexual behavior and neuroendocrine secretion in rodents. The results of exogenous OT administration on sexual behaviors in male and female mice are controversial. This study aimed to analyze the role of OT in sexual behavior, the number of oocytes and the density of dendritic spines in the posterodorsal medial amygdala (MePD) of female mice with selective deletion of the OT gene (OTKO). Female C57BL/6 mice were genotyped and divided into control (WT) and OTKO groups (n= 11 each). All experiments were performed in the proestrus phase. Compared to WT data, our results showed that the OTKO group had a significant increase in the latency for the display of lordosis behavior (490.8±113.8 and 841.9±53.9, respectively) and a decrease in both the frequency (6.3±2.4 and 0.5±0.4) and duration (49.3±19.9 and 7.2±7.1) of lordosis and a reduction in the number of oocytes (12.2±0.8 and 9.9± 0.6). However, the OTKO group showed a higher density of proximal dendritic spines in the MePD compared to the WT group (2.4±0.1 and 1.9±0.1 spines/dendritic μm, respectively). No significant difference was observed in the plasma levels of AVP between the groups (OTKO: 617.1±96.0 and WT: 583.3±112.0pg/mL). Our data suggest that OT plays a crucial role in the sexual behavior display, number of released oocytes and density of dendritic spines in the MePD of female mice. The AVP plasma concentration was not affected in the OTKO animals.
    Full-text · Article · Jul 2013 · Behavioural brain research
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