The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ajai Vyas - One of the best experts on this subject based on the ideXlab platform.
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testosterone acts within the Medial Amygdala of rats to reduce innate fear to predator odor akin to the effects of toxoplasma gondii infection
Frontiers in Psychiatry, 2020Co-Authors: Dhiraj Kumar Singh, Shantala Hari A Dass, Samira Abdulaisaiku, Ajai VyasAbstract:Rats infected with the protozoan Toxoplasma gondii exhibit a reduced aversion to cat odor. This behavioral change is thought to increase trophic transmission of the parasite. Infected male rats also show a greater testicular synthesis of testosterone and epigenetic change in arginine vasopressin within the Medial Amygdala. Here, we show that exogenous supply of testosterone within MeA of uninfected castrates recapitulates reduction in innate fear akin to behavioral change attributed to the parasite. We also show that castration post establishment of chronic infection precludes changes in fear and Medial Amygdala arginine vasopressin in the infected male rats. These observations support the role of gonadal hormones and pursuant neuroendocrine changes in mediating the loss of fear in the infected rats. This work also demonstrates that testosterone acting specifically within the Medial Amygdala sufficiently explains reduced defensive behaviors often observed during the appetitive component of reproductive behaviors.
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Testosterone Reduces Fear and Causes Drastic Hypomethylation of Arginine Vasopressin Promoter in Medial Extended Amygdala of Male Mice
Frontiers Media S.A., 2019Co-Authors: Wen Han Tong, Samira Abdulai-saiku, Ajai VyasAbstract:Testosterone reduces anxiety-like behaviors in rodents and increases exploration of anxiogenic parts of the environment. Effects of testosterone on innate defensive behaviors remain understudied. Here, we demonstrate that exogenous testosterone reduces aversion to cat odor in male mice. This is reflected as increased exploration of area containing cat urine when castrated male mice are supplied with exogenous testosterone. We also report that exogenous testosterone leads to DNA hypomethylation of arginine vasopressin (AVP) promoter in posterodorsal Medial Amygdala (MePD) and Medial bed nucleus of stria terminalis (BNST). Our observations suggest that testosterone acting on AVP system within extended Medial Amygdala might regulate defensive behaviors in mice
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toxoplasma gondii infection reduces predator aversion in rats through epigenetic modulation in the host Medial Amygdala
Molecular Ecology, 2014Co-Authors: Shantala Arundhati Hari Dass, Ajai VyasAbstract:Male rats (Rattus novergicus) infected with protozoan Toxoplasma gondii relinquish their innate aversion to the cat odours. This behavioural change is postulated to increase transmission of the parasite to its definitive felid hosts. Here, we show that the Toxoplasma gondii infection institutes an epigenetic change in the DNA methylation of the arginine vasopressin promoter in the Medial Amygdala of male rats. Infected animals exhibit hypomethylation of arginine vasopressin promoter, leading to greater expression of this nonapeptide. The infection also results in the greater activation of the vasopressinergic neurons after exposure to the cat odour. Furthermore, we show that loss of fear in the infected animals can be rescued by the systemic hypermethylation and recapitulated by directed hypomethylation in the Medial Amygdala. These results demonstrate an epigenetic proximate mechanism underlying the extended phenotype in the Rattus novergicus-Toxoplasma gondii association.
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copulation or sensory cues from the female augment fos expression in arginine vasopressin neurons of the posterodorsal Medial Amygdala of male rats
Frontiers in Zoology, 2014Co-Authors: Shantala Hari A Dass, Ajai VyasAbstract:Background: The posterodorsal part of the Medial Amygdala is essential for processing reproductively salient sensory information in rodents. This is the initial brain structure where information from olfactory system and male hormones intersect. The neurochemical identity of the neurons participating in the sensory processing in Medial Amygdala remains presently undetermined. Many neurons in this brain structure express arginine vasopressin in a testosterone-dependent manner, suggesting that this neuropeptide is maintained by the androgenic milieu. Method: Here we use Fos, a protein expressed by recently active neurons, to quantify activation of arginine vasopressin neurons after exposure to odor from physically inaccessible female. We compare it to mating with accessible female and to reproductively innocuous odor. Results: We show that inaccessible female activate arginine vasopressin neurons in the male posterodorsal Medial Amygdala. The magnitude of activation is not further enhanced when physical access with resultant mating is granted, even though it remains undetermined if same population of AVP neurons is activated by both inaccessible female and copulation. We also show that arginine vasopressin activation cannot be fully accounted for by mere increase in the number of Fos and AVP neurons. Conclusion: These observations posit a role for the Medial Amygdala arginine vasopressin in reproductive behaviors, suggesting that these neurons serve as integrative node between the hormonal status of the animal and the availability of reproductive opportunities.
Michael J Baum - One of the best experts on this subject based on the ideXlab platform.
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disruption of urinary odor preference and lordosis behavior in female mice given lesions of the Medial Amygdala
Physiology & Behavior, 2012Co-Authors: Brett T Dibenedictis, Michael J Baum, Kaitlin L Ingraham, James A CherryAbstract:Previous research showed that axonal inputs to both anterior and posterior subdivisions of the Medial Amygdala from the main and accessory olfactory bulbs of female mice, respectively, process volatile and non-volatile pheromonal signals from male conspecifics. In the present study we found that bilateral electrolytic lesions that included posterior portions, but not the anterior subdivision alone of the Medial Amygdala (Me) blocked the preference of estrous female mice to investigate volatile urinary odors from testes-intact vs. castrated males. Similar results were obtained in separate tests in which nasal contact with urinary stimuli was permitted. In addition, total time investigating volatile urinary stimuli was reduced in subjects with posterior Me lesions. Subjects were able to discriminate volatile urinary odors from testes-intact vs. castrated male mice, suggesting that this disruption of odor preference did not result from the inability of females given amygdaloid lesions to discriminate these male urinary odors. Bilateral lesions of the Me that were either restricted to the anterior or posterior subdivisions, or included areas of both regions, caused significant reductions in the display of lordosis behavior in estrous female mice. Our results suggest that the Me is a critical segment of the olfactory circuit that controls both mate recognition and mating behavior in the female mouse.
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a sex comparison of the anatomy and function of the main olfactory bulb Medial Amygdala projection in mice
Neuroscience, 2011Co-Authors: Ningdong Kang, James A Cherry, Elizabeth A Mccarthy, Michael J BaumAbstract:We previously reported that some main olfactory bulb (MOB) mitral/tufted (M/T) cells send a direct projection to the "vomeronasal" Amygdala in female mice and selectively respond to volatile male mouse urinary odors. We asked whether MOB M/T cells that project to the vomeronasal Amygdala exist in male mice and whether there is a sexually dimorphic response of these neurons to volatile male urinary pheromones. Gonadectomized male and female mice received bilateral injections of the retrograde tracer, Cholera toxin-B (CTb) into the Medial Amygdala (Me), which is part of the vomeronasal Amygdala. All subjects were then treated with estradiol benzoate and progesterone before being exposed to volatile male urinary odors whereupon they were sacrificed 90 min later. Sections of the MOB were immunostained for Fos protein and/or CTb. Male mice, like females, displayed a small population of MOB M/T cells that project to the Me. While the general localization of these cells was similar in the two sexes, there were statistically significant sex differences in the percentage of MOB M/T cells in the anterior and posterior Medial segments of the MOB that were retrogradely labeled by CTb. Male urinary volatiles stimulated equivalent, significant increases in Fos expression by MOB M/T neurons projecting to the Me in the two sexes. By contrast, in the same mice exposure to male urinary volatiles stimulated a significant increase in Fos expression by mitral cells in the accessory olfactory bulb (AOB) only in female subjects. Thus any sexually dimorphic behavioral or neuroendocrine responses to male urinary volatiles likely depend on the differential processing of these odor inputs in the AOB and/or other downstream forebrain structures after their detection by the main olfactory system.
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a direct main olfactory bulb projection to the vomeronasal Amygdala in female mice selectively responds to volatile pheromones from males
European Journal of Neuroscience, 2009Co-Authors: Ningdong Kang, Michael J Baum, James A CherryAbstract:The main olfactory system, like the accessory olfactory system, responds to pheromones involved in social communication. Whereas pheromones detected by the accessory system are transmitted to the hypothalamus via the Medial (‘vomeronasal’) Amygdala, the pathway by which pheromones are detected and transmitted by the main system is not well understood. We examined in female mice whether a direct projection from mitral/tufted (M/T) cells in the main olfactory bulb (MOB) to the Medial Amygdala exists, and whether Medial Amygdala-projecting M/T cells are activated by volatile urinary odors from conspecifics or a predator (cat). Simultaneous anterograde tracing using Phaseolus vulgaris leucoagglutinin and Fluoro-Ruby placed in the MOB and accessory olfactory bulb (AOB), respectively, revealed that axons of MOB M/T cells projected to superficial laminae of layer Ia in anterior and posterodorsal subdivisions of the Medial Amygdala, whereas projection neurons from the AOB sent axons to non-overlapping, deeper layer Ia laminae of the same subdivisions. Placement of the retrograde tracer cholera toxin B into the Medial Amygdala labeled M/T cells that were concentrated in the ventral MOB. Urinary volatiles from male mice, but not from female conspecifics or cat, induced Fos in Medial Amygdala-projecting MOB M/T cells of female subjects, suggesting that information about male odors is transmitted directly from the MOB to the ‘vomeronasal’ Amygdala. The presence of a direct MOB-to-Medial Amygdala pathway in mice and other mammals could enable volatile, opposite-sex pheromones to gain privileged access to diencephalic structures that control mate recognition and reproduction.
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increased expression of c fos in the Medial preoptic area after mating in male rats role of afferent inputs from the Medial Amygdala and midbrain central tegmental field
Neuroscience, 1992Co-Authors: Michael J Baum, Barry J EverittAbstract:Abstract Immunocytochemical methods were used to localize the protein product of the immediate-early gene, c-fos , in male rats after exposure to, or direct physical interaction with, oestrous females. Increasing amounts of physical contact with a female, with resultant olfactory-vomeronasal and/or genitalsomatosensory inputs, caused corresponding increments in c-fos expression in the Medial preoptic area, the caudal part of the bed nucleus of the stria terminalis, the Medial Amygdala, and the midbrain central tegmental field. Males bearing unilateral electrothermal lesions of the olfactory peduncle showed a significant reduction in c-fos expression in the ipsilateral Medial Amygdala, but not in other structures, provided their coital interaction with oestrous females was restricted to mount-thrust and occasional intromissive patterns due to repeated application of lidocaine anaesthetic to the penis. No such lateralization of c-fos expression occurred in other males with unilateral olfactory lesions which were allowed to intromit and ejaculate with a female. These results suggest that olfactory inputs, possibly of vomeronasal origin, contribute to the activation of c-fos in the Medial Amygdala. However, lesion-induced deficits in this type of afferent input to the nervous system appear to be readily compensated for by the genital somatosensory input derived from repeated intromissions. Unilateral excitotoxic lesions of the Medial preoptic area, made by infusing quinolinic acid, failed to reduce c-fos expression in the ipsilateral or contralateral Medial Amygdala or central tegmental field following ejaculation. By contrast, combined, unilateral excitotoxic lesions of the Medial Amygdala and the central tegmental field significantly reduced c-fos expression in the ipsilateral bed nucleus of the stria terminalis and Medial preoptic area after mating; no such assymetry in c-fos expression occurred when lesions were restricted to either the Medial Amygdala or central tegmental field. This suggests that afferent inputs from the central tegmental field (probably of genital-somatosensory origin) and from the Medial Amygdala (probably of olfactory-vomeronasal origin) interact to promote cellular activity, and the resultant induction of c-fos , in the ipsilateral bed nucleus of the stria terminalis and Medial preoptic area. The monitoring of neuronal c-fos expression provides an effective means of studying the role of sensory factors in governing the activity of integrated neural structures which control the expression of a complex social behaviour.
Kevin T Obyrne - One of the best experts on this subject based on the ideXlab platform.
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optogenetic stimulation of kisspeptin neurones within the posterodorsal Medial Amygdala increases luteinising hormone pulse frequency in female mice
Journal of Neuroendocrinology, 2020Co-Authors: Geffen Lass, William H Colledge, Stafford L Lightman, Ross A De Burgh, Yanping Kang, Lydia Sinnettsmith, Shel Hwayeo, Stephen M Manchishi, Kevin T ObyrneAbstract:Kisspeptin within the arcuate nucleus of the hypothalamus is a critical neuropeptide in the regulation of reproduction. Together with neurokinin B and dynorphin A, arcuate kisspeptin provides the oscillatory activity that drives the pulsatile secretion of gonadotrophin-releasing hormone (GnRH), and therefore luteinising hormone (LH) pulses, and is considered to be a central component of the GnRH pulse generator. It is well established that the Amygdala also exerts an influence over gonadotrophic hormone secretion and reproductive physiology. The discovery of kisspeptin and its receptor within the posterodorsal Medial Amygdala (MePD) and our recent finding showing that intra-MePD administration of kisspeptin or a kisspeptin receptor antagonist results in increased LH secretion and decreased LH pulse frequency, respectively, suggests an important role for Amygdala kisspeptin signalling in the regulation of the GnRH pulse generator. To further investigate the function of Amygdala kisspeptin, the present study used an optogenetic approach to selectively stimulate MePD kisspeptin neurones and examine the effect on pulsatile LH secretion. MePD kisspeptin neurones in conscious Kiss1-Cre mice were virally infected to express the channelrhodopsin 2 protein and selectively stimulated by light via a chronically implanted fibre optic cannula. Continuous stimulation using 5 Hz resulted in an increased LH pulse frequency, which was not observed at the lower stimulation frequencies of 0.5 and 2 Hz. In wild-type animals, continuous stimulation at 5 Hz did not affect LH pulse frequency. These results demonstrate that selective activation of MePD Kiss1 neurones can modulate hypothalamic GnRH pulse generator frequency.
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optogenetic stimulation of kisspeptin neurones within the posterodorsal Medial Amygdala increases lh pulse frequency in female mice
bioRxiv, 2018Co-Authors: Geffen Lass, William H Colledge, Stafford L Lightman, Ross A De Burgh, Yanping Kang, Sh Yeo, Lydia Sinnettsmith, Kevin T ObyrneAbstract:Abstract Kisspeptin within the arcuate nucleus of the hypothalamus is a critical neuropeptide in the regulation of reproduction. Together with neurokinin B and dynorphin A, arcuate kisspeptin provides the oscillatory activity that drives the pulsatile secretion of GnRH, and therefore LH pulses, and is believed to be a central component of the GnRH pulse generator. It is well established that the Amygdala also exerts an influence over gonadotrophic hormone secretion and reproductive physiology. The discovery of kisspeptin and its receptor within the posterodorsal Medial Amygdala (MePD), and our recent finding showing that intra-MePD administration of kisspeptin or a kisspeptin receptor antagonist results in increased LH secretion and decreased LH pulse frequency, respectively, suggests an important role for Amygdala kisspeptin signalling in the regulation of the GnRH pulse generator. To further investigate the function of Amygdala kisspeptin, the present study used an optogenetic approach to selectively stimulate MePD kisspeptin neurones and examine the effect on pulsatile LH secretion. MePD kisspeptin neurones in conscious Kiss1-CRE mice were virally infected to express a channelrhodopsin protein and selectively stimulated by light via a chronically implanted fibre optic cannula. Continuous stimulation using 5 Hz resulted in an increased LH pulse frequency, which was not observed at the lower stimulation frequencies of 0.5 and 2 Hz. In wild-type animals, continuous stimulation at 5 Hz did not affect LH pulse frequency. These results demonstrate that selective activation of MePD Kiss1 neurons can modulate hypothalamic GnRH pulse generator frequency.
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kisspeptin neurones in the posterodorsal Medial Amygdala modulate sexual partner preference and anxiety in male mice
Journal of Neuroendocrinology, 2018Co-Authors: Daniel Adekunbi, Geffen Lass, K Shetty, O A Adegoke, Shelhwa Yeo, William H Colledge, Stafford L Lightman, Kevin T ObyrneAbstract:The posterodorsal Medial Amygdala (MePD) is a neural site in the limbic brain involved in regulating emotional and sexual behaviours. There is, however, limited information available on the specific neuronal cell type in the MePD functionally mediating these behaviours in rodents. The recent discovery of a significant kisspeptin neurone population in the MePD has raised interest in the possible role of kisspeptin and its cognate receptor in sexual behaviour. The present study therefore tested the hypothesis that the MePD kisspeptin neurone population is involved in regulating attraction towards opposite sex conspecifics, sexual behaviour, social interaction and the anxiety response by selectively stimulating these neurones using the novel pharmacosynthetic DREADDs (designer receptors exclusively activated by designer drugs) technique. Adult male Kiss-Cre mice received bilateral stereotaxic injections of a stimulatory DREADD viral construct (AAV-hSyn-DIO-hM3 D(Gq)-mCherry) targeted to the MePD, with subsequent activation by i.p. injection of clozapine-N-oxide (CNO). Socio-sexual behaviours were assessed in a counter-balanced fashion after i.p. injection of either saline or CNO (5 mg kg-1 ). Selective activation of MePD kisspeptin neurones by CNO significantly increased the time spent by male mice in investigating an oestrous female, as well as the duration of social interaction. Additionally, after CNO injection, the mice appeared less anxious, as indicated by a longer exploratory time in the open arms of the elevated plus maze. However, levels of copulatory behaviour were comparable between CNO and saline-treated controls. These data indicate that DREADD-induced activation of MePD kisspeptin neurones enhances both sexual partner preference in males and social interaction and also decreases anxiety, suggesting a key role played by MePD kisspeptin in sexual motivation and social behaviour.
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kisspeptin in the Medial Amygdala and sexual behavior in male rats
Neuroscience Letters, 2016Co-Authors: Rebecca Gresham, Daniel Adekunbi, Shengyun Li, Minghan Hu, Xiao Feng Li, Kevin T ObyrneAbstract:The Medial Amygdala (MeA) is crucial for sexual behavior; kisspeptin (Kiss1) also plays a role in sexual function. Kisspeptin receptor (Kiss1r) knockout mice display no sexual behavior. Recently Kiss1 and Kiss1r have been discovered in the posterodorsal subnucleus of the Medial Amygdala (MePD). We hypothesised that Kiss1 in the MePD may have an influence on male sexual behavior. To test this we bilaterally cannulated the MePD and infused kisspeptin-10 in male rats. This caused the rats to have multiple erections, an effect specific to Kiss1 receptor activation, because Kiss1r antagonism blocked the erectile response. When Kiss1 was infused into the lateral cerebroventricle, there were no observed erections. We also measured the plasma levels of LH when Kiss1 is infused into the MePD or lateral cerebroventricle; Kiss1 increased plasma LH to comparable levels when infused into both sites. We conclude that Kiss1 has a role in male sexual behavior, which is specific to the MePD.
Catherine Dulac - One of the best experts on this subject based on the ideXlab platform.
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oxytocin signaling in the Medial Amygdala is required for sex discrimination of social cues
eLife, 2017Co-Authors: Shenqin Yao, Joseph F Bergan, Anne Lanjuin, Catherine DulacAbstract:Oxytocin is a hormone that promotes milk production, contractions during childbirth, and many social interactions in humans and other creatures. It has also been implicated in conditions like autism or schizophrenia, which show altered social interactions. Oxytocin is made and released by cells in the brain called neurons. The oxytocin-producing neurons are clustered in a brain region called the hypothalamus, and oxytocin can act over a long distance in the brain or in the body. Many mammals detect chemical signals called pheromones that are involved in social interactions. These chemicals are detected by neurons in a structure within the cartilage of the nose called the vomeronasal organ. Pheromone-sensing neurons in the vomeronasal organ connect with another part of the brain called the Medial Amygdala. The Medial Amygdala, in turn, connects with regions of the brain that control behavior. Mice in particular rely on pheromones for social communication. Male and female mice respond differently to pheromones. Male mice prefer to investigate female mice to other males. The neurons in Medial Amygdala of male mice also become more active in response to scents from females than from males. Oxytocin is known to act on the Medial Amygdala, but its exact role in the male’s preference for females and their scents is not known. Now, Yao et al. show that oxytocin controls male preference for interacting with females and their scents by turning on neurons in the Medial Amygdala. In the experiments, male mice genetically engineered to lack oxytocin do not prefer female mice to other males, and they also appear unable to distinguish male and female scents. These mice also have less activity in the neurons of the Medial Amygdala when exposed to females and their scents. Directly manipulating these neurons and the oxytocin receptors on them also altered sex-preferences in male mice. The experiments show that oxytocin alters the behaviors of male mice in response to females or their scents by manipulating a specific set of brain cells. More studies of these cells or their interactions with oxytocin might help scientists understand oxytocin-liked diseases that impair social interactions or develop new treatments for conditions like autism or schizophrenia.
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neuronal representation of social information in the Medial Amygdala of awake behaving mice
Cell, 2017Co-Authors: Alexander Mathis, Catherine Dulac, Benjamin F Grewe, Jessica A Osterhout, Biafra Ahanonu, Mark J Schnitzer, Venkatesh N MurthyAbstract:The Medial Amygdala (MeA) plays a critical role in processing species- and sex-specific signals that trigger social and defensive behaviors. However, the principles by which this deep brain structure encodes social information is poorly understood. We used a miniature microscope to image the Ca2+ dynamics of large neural ensembles in awake behaving mice and tracked the responses of MeA neurons over several months. These recordings revealed spatially intermingled subsets of MeA neurons with distinct temporal dynamics. The encoding of social information in the MeA differed between males and females and relied on information from both individual cells and neuronal populations. By performing long-term Ca2+ imaging across different social contexts, we found that sexual experience triggers lasting and sex-specific changes in MeA activity, which, in males, involve signaling by oxytocin. These findings reveal basic principles underlying the brain's representation of social information and its modulation by intrinsic and extrinsic factors.
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oxytocin signaling in the Medial Amygdala is required for sex discrimination of social cues
bioRxiv, 2017Co-Authors: Shenqin Yao, Joseph F Bergan, Anne Lanjuin, Catherine DulacAbstract:The neural control of social behaviors in rodents requires the encoding of pheromonal cues by the vomeronasal system. Here we show that the typical preference of male mice for females is eliminated in mutants lacking oxytocin, a neuropeptide modulating social behaviors in many species. Ablation of the oxytocin receptor in aromatase expressing neurons of the Medial Amygdala (MeA) fully recapitulates the elimination of female preference in males. Further, single unit recording in the MeA uncovered significant changes in the sensory representation of conspecific cues in the absence of oxytocin signaling. Finally, acute manipulation of oxytocin signaling in adults is sufficient to alter social interaction preferences in males as well as responses of MeA neurons to chemosensory cues. These results uncover the critical role of oxytocin signaling in a molecularly defined neuronal population in order to modulate the behavioral and physiological responses of male mice to females on a moment-to-moment basis.
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sex specific processing of social cues in the Medial Amygdala
eLife, 2014Co-Authors: Joseph F Bergan, Yoram Benshaul, Catherine DulacAbstract:Many animals emit and detect chemicals known as pheromones to communicate with other members of their own species. Animals also rely on chemical signals from other species to warn them, for example, that a predator is nearby. Many of these chemical signals—which are present in sweat, tears, urine, and saliva—are detected by a structure called the vomeronasal organ, which is located at the base of the nasal cavity. When this organ detects a particular chemical signal, it broadcasts this information to a network of brain regions that generates an appropriate behavioral response. Two structures within this network, the accessory olfactory bulb and the Medial Amygdala, play an important role in modifying this signal before it reaches its final destination—a region of the brain called the hypothalamus. Activation of the hypothalamus by the signal triggers changes in the animal's behavior. Although the anatomical details of this pathway have been widely studied, it is not clear how information is actually transmitted along it. Now, Bergan et al. have provided insights into this process by recording signals in the brains of anesthetized mice exposed to specific stimuli. Whereas neurons in the accessory olfactory bulb responded similarly in male and female mice, those in the Medial Amygdala showed a preference for female urine in male mice, and a preference for male urine in the case of females. This is the first direct demonstration of differences in sensory processing in the brains of male and female mammals. These differences are thought to result from the actions of sex hormones, particularly estrogen, on brain circuits during development. Consistent with this, neurons in the Medial Amygdala of male mice with reduced levels of estrogen showed a reduced preference for female urine compared to control males. Similarly, female mice that had been previously exposed to high levels of estrogen as pups showed a reduced preference for male urine compared to controls. In addition to increasing understanding of how chemical signals—including pheromones—influence the responses of rodents to other animals, the work of Bergan et al. has provided clues to the neural mechanisms that underlie sex-specific differences in behaviors.
Marc S Breedlove - One of the best experts on this subject based on the ideXlab platform.
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androgen receptors mediate masculinization of astrocytes in the rat posterodorsal Medial Amygdala during puberty
The Journal of Comparative Neurology, 2013Co-Authors: Ryan T Johnson, Marc S Breedlove, Cynthia L JordanAbstract:Astrocytes in the posterodorsal portion of the Medial Amygdala (MePD) are sexually dimorphic in adult rats: males have more astrocytes in the right MePD and more elaborate processes in the left MePD than do females. Functional androgen receptors (ARs) are required for masculinization of MePD astrocytes, as these measures are demasculinized in adult males carrying the testicular feminization mutation (Tfm) of the AR gene, which renders AR dysfunctional. We now report that the number of astrocytes is already sexually dimorphic in the right MePD of juvenile 25-day-old (P25) rats. Because Tfm males have as many astrocytes as wild-type males at this age, this prepubertal sexual dimorphism is independent of ARs. After P25, astrocyte number increases in the MePD of all groups, but activation of ARs augments this increase in the right MePD, where more astrocytes are added in males than in Tfm males. Consequently, by adulthood, females and Tfm males have equivalent numbers of astrocytes in the right MePD. Sexual dimorphism in astrocyte arbor complexity in the left MePD arises after P25, and is entirely AR-dependent. Thus, masculinization of MePD astrocytes is a result of both AR-independent processes before the juvenile period and AR-dependent processes afterward. J. Comp. Neurol. 521:2298–2309, 2013. © 2012 Wiley Periodicals, Inc.
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sexual dimorphism in neuronal number of the posterodorsal Medial Amygdala is independent of circulating androgens and regional volume in adult rats
The Journal of Comparative Neurology, 2008Co-Authors: John A Morris, Cynthia L Jordan, Marc S BreedloveAbstract: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. J. Comp. Neurol. 506:851– 859, 2008. © 2007 Wiley-Liss, Inc.
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both estrogen receptors and androgen receptors contribute to testosterone induced changes in the morphology of the Medial Amygdala and sexual arousal in male rats
Hormones and Behavior, 2003Co-Authors: Bradley M Cooke, Marc S Breedlove, Cynthia L JordanAbstract:Abstract In male rats, a steroid-sensitive circuit in the forebrain regulates mating behavior. The masculine phenotype in one component of the circuit, the posterodorsal nucleus of the Medial Amygdala (MePD), depends on the level of circulating androgens in the adult. To investigate which gonadal steroid receptor(s) mediate sexual arousal and MePD plasticity, adult male rats were castrated and given Silastic capsules containing the nonaromatizable androgen 5α-dihydrotestosterone (DHT), 17β-estradiol (E2), both steroids, or nothing. A fifth group was sham-castrated and treated with blank capsules. DHT treatment was necessary and sufficient to maintain the expression of noncontact penile erections and ultrasonic vocalizations in castrates. E2 had no significant effect on these measures. Both DHT and E2 increased olfactory investigation (“nosepokes”) during the noncontact penile erection test. E2, but not DHT, maintained intromission patterns, while either steroid, alone or in combination, maintained ejaculatory behavior. Regional volume and cell soma size of the MePD both decreased following castration. Additionally, MePD cell size was lateralized, with left hemisphere neurons larger than those on the right, an effect that appeared independent of steroid manipulations. DHT and E2 each maintained neuronal soma size. E2 maintained MePD regional volume more effectively in the left MePD than in the right, which may have been due to a greater sensitivity of the left to both castration and hormone treatment. Thus, both androgen receptors and estrogen receptors appear to participate in sexual behaviors that may be mediated by the MePD in adult rats, and both receptors contribute to the steroid-regulated structural plasticity in this brain region.
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photoperiod and social cues influence the Medial Amygdala but not the bed nucleus of the stria terminalis in the siberian hamster
Neuroscience Letters, 2001Co-Authors: Brandley M Cooke, Annalise Keen, Carol D Hegstrom, Marc S BreedloveAbstract:Abstract We investigated whether the posterodorsal nucleus of the Medial Amygdala (MePD) and the posteroMedial nucleus of the bed nucleus of the stria terminalis (BSTpm) undergo structural changes in response to photoperiod or social environment in the Siberian hamster, a seasonally breeding rodent. Adult male hamsters were either kept in long days (LD; 15:9 h light:dark) from birth or were transferred at 12–16 weeks of age to short days (SD; 8:16) and housed with a male conspecific for 11 weeks. Other males were transferred to SD but were housed with an unrelated female conspecific from LD. Males transferred to SD without a female cagemate displayed testicular regression, but males transferred to SD with a female cagemate did not. The regional volume and average soma size of the BSTpm and the MePD were estimated using Nissl-stained brain sections. Neither photoperiod nor social condition modified either of the BSTpm measures. Among males housed in same-sex groups, the average soma size in the MePD was significantly smaller in SD males than in LD males. Cohabitation with a female resulted in MePD volumes indistinguishable from LD males. These results indicate that the MePD, a nucleus implicated in socio-sexual behavior, can respond to photoperiodic as well as to social cues.