Morphological and Functional Features of the Sex Steroid-Responsive Posterodorsal Medial Amygdala of Adult Rats

Abstract

The rat posterodorsal medial amygdala (MePD) expresses receptors for gonadal hormones and integrates sex steroid-sensitive subcortical networks. Male-female differences are found in the morphology, connectivity, and local neuropil structure of MePD. For example, dendritic spine density is sexually-dimorphic and changes with the estrous cycle and following gonadal hormones manipulations. Due to its connectivity, the MePD may affect emotionally-loaded social behaviors, according to a former Newman's seminal proposition. Unilateral fiber-sparing ibotenic acid damage of the MePD does not impair male sexual behavior. However, microinjecting glutamate and histamine into the right MePD facilitates ejaculation. Further, MePD-lesioned rats are not different from normal rats in anxiety-like behavior as evaluated by the elevated plus maze test or innate fear test induced by a live cat. In another study, an adapted model for inducing aggressive behavior in rats by a brief period of restraint prior to the resident-intruder paradigm was used to study Fos-immunoreactivity in the MePD. Following stressful stimulation (restraint) or the restraint and fight condition, but not after aggression alone, Fos-immunoreactivity was detected in the MePD. Microinjecting the inhibitory neuropeptide somatostatin into the right MePD notably reduces fighting behavior without affecting locomotion. Overall, these data indicate that sex steroids and local neurochemical stimulatory/inhibitory transmitters modulate the MePD and reinforce the idea that this area is a node for modulating social behavior neural networks.

Inhibitory and multisynaptic spines, and hemispherical synaptic specialization in the posterodorsal medial amygdala of male and female rats

“…In this sense, aromatase activity is lateralized in the MeA, it is higher in the left MeA at gestational day 22, higher in the right MeA at postnatal day 6, and equivalent in both hemispheres at postnatal day 15 (von Ziegler and Lichtensteiger, ). Steroid‐dependent plasticity of adult MePD occurs on synapses already organized into male and female lateralized phenotypes (Cooke and Woolley, ; see also Nishizuka and Arai, ), although morphological changes continue to occur in the MeA during puberty (Zehr et al, ) to reach the complex ongoing scenario of cellular and synaptic organization of the adult rat MePD (Rasia‐Filho et al, ).…”

Remodeling of the number and structure of dendritic spines in the medial amygdala: From prepubertal sexual dimorphism to puberty and effect of sexual experience in male rats

“…The MePD forms a network involving the accessory olfactory bulb and the vomeronasal inputs (Bian, Yanagawa, Chen, & Luo, ; Hashikawa, Hashikawa, Falkner, & Lin, ; Pereno, Balaszczuk, & Beltramino, ), specific parts of the bed nucleus of the stria terminalis (Dong, Petrovich, & Swanson, ) and reproduction‐related hypothalamic nuclei (Choi et al., ; Petrovich, Canteras, & Swanson, ). Then, the MePD can serve as an interface for the processing of chemosignals and the actions of sex steroids to elaborate proper reproductive behavior display (Baum & Bakker, ; Blake & Meredith, ; Petrulis, ; Rasia‐Filho et al., , ; Wood & Coolen, ). Indeed, the MePD has a marked Fos activation after exposure to conspecific pheromones and genital sensory stimuli or the occurrence of intromission, ejaculation and, depending on the species, sexual satiety (Coolen, Peters, & Veening, ; Hashikawa et al., ; Kollack‐Walker & Newman, ; Phillips‐Farfán & Fernández‐Guasti, ).…”

The Cytoarchitecture of the Telencephalon of Betta Splendens Regan 1910 (Perciformes: Anabantoidei) with a Stereological Approach to the Supracommissural and Postcommissural Nuclei

“…This possibility is partly supported by two interesting findings: in goldfish, lesions in the Vs and the adjacent ventral telencephalic areas, besides the POA, resulted in the impairment of the male and female sexual behavior (Kyle and Peter, ; Kyle et al, ; Koyama et al, ) and, in male and female red salmons, electrical stimulation in both the Vs and the POA were able to elicit sexual behavior (Satou et al, ). Interestingly, these results agree with the functions described for the rat MeA (reviewed in Rasia‐Filho et al, ).…”

“…The vomeronasal system and the MeA show a remarkable sexual dimorphism in mammals, including differences in the volume of different nuclei, the number of neurons and the complexity of glial cells (Guillamón and Segovia, ; Rasia‐Filho et al, and references therein; Greenberg and Trainor, ). Considering the fish Vs and Vp an homologous to the mammalian MeA with similar hodology and function (O'Connell and Hofmann, , Teles et al, ; Perathoner et al, ), we tested the presence of a putative sexual dimorphism in these fish telencephalic areas using a stereological approach for estimating the number of neurons and glial cells (Salazar et al, ).…”

“…It is likely that the MeA (or at least part of it) would be homolog to the supracommissural and postcommissural nuclei of the ventral telencephalon (Vs and Vp, respectively) in fishes (Bradford, ; O'Connell and Hofmann, ; Bruce, ; Kress and Wullimann, ; Maximino et al, ). This is interesting because the vomeronasal pathway and the interconnected MeA subnuclei are sexually dimorphic and involved with the display of social behaviors, including reproduction and aggression, in rodents (Guillamón and Segovia, ; De Lorme et al, ; Rasia‐Filho et al, ; Greenberg and Trainor, ).…”