Atrx Deletion in Neurons Leads to Sexually Dimorphic Dysregulation of miR-137 and Spatial Learning and Memory Deficits.

ATRX gene mutations have been identified in syndromic and non-syndromic intellectual disabilities in humans. ATRX is known to maintain genomic stability in neuroprogenitor cells, but its function in differentiated neurons and memory processes remains largely unresolved. Here, we show that the deletion of neuronal Atrx in mice leads to distinct hippocampal structural defects, fewer presynaptic vesicles, and an enlarged postsynaptic area at CA1 apical dendrite-axon junctions. We identify male-specific impairments in long-term contextual memory and in synaptic gene expression, linked to altered miR-137 levels. We show that ATRX directly binds to the miR-137 locus and that the enrichment of the suppressive histone mark H3K27me3 is significantly reduced upon the loss of ATRX. We conclude that the ablation of ATRX in excitatory forebrain neurons leads to sexually dimorphic effects on miR-137 expression and on spatial memory, identifying a potential therapeutic target for neurological defects caused by ATRX dysfunction

Behavioral Sex Differences Caused by Distinct Vasopressin Sources

Dysfunction in social communication is a prominent aspect of many psychopathologies and social disorders including autism, schizophrenia, and social anxiety. Consequently, development of clinical treatment for these disorders requires an understanding of neural circuitry underlying social communication. Sex differences are a persistent feature of social disorders, where autism is more prevalent in males, while social anxiety occurs more frequently in females. A critical gap in knowledge exists in understanding the role of sex-differences in the control of social behavior and communication. A reasonable hypothesis is that differences in neural circuitry underlie sex-differentiated dysfunctions in social behavior and communication. A well-studied circuit in this regard is the sexually dimorphic expression of the neuropeptide arginine vasopressin (AVP). AVP in the nervous system originates from several distinct sources which are, in turn, regulated by different inputs and regulatory factors. Using modern molecular approaches, we can begin to define the specific role of AVP cell populations in social behavior. We demonstrate a behavioral function for the sexually dimorphic AVP neurons in the bed nucleus of the stria terminalis (BNST) and in the paraventricular nucleus of the hypothalamus (PVN). Collectively, our results indicate that AVP cell groups appear to play opposite roles in social investigation by males and females, as BNST-AVP cell ablations and BNST AVP knockdown reduced male social approach, while PVN-AVP cell ablations increased female social approach. We next utilized circuit level tracing techniques to map the inputs and outputs of BNST and medial amygdala (MeA) AVP cells, which are the major source of sexually dimorphic AVP expression. Finally, we tested the function of several sexually dimorphic BNST-AVP projection areas, such as, the lateral septum (LS), lateral habenula (LHb), and dorsal raphe (DR). In male mice, but not female mice, optogenetic stimulation of the BNST AVP terminals in the LS increased their social investigation and anxiety-like behavior in the elevated-zero maze. Antagonism of V1aR in the LS blocked optogenetic-mediated increases in male social investigation and anxiety-like behavior. Therefore, activation of a distinct BNST-LS AVP circuit modulates sex-specific social approach and anxiety-like behavior, which is mediated by V1aR within the LS. This work suggests that sex differences in the neurochemical underpinnings of social behavior may contribute to sex differences in disorders of social behavior and communication

Investigating the neurobiological basis underlying the sex-specific production of courtship song in Drosophila: the roles of sex determination genes fruitless and doublesex

The elaborate courtship ritual performed by Drosophila melanogaster males to interest females in copulation is used as a model to investigate the genetic and neurobiological basis for the specification of complex behaviours. One component of this courtship ritual is the ‘lovesong’, which both promotes mating and carries vital species-specific information. Sex mosaic studies have shown that specific regions of the central nervous system (CNS) must be male in order to produce this courtship song. Indeed, two genes in the sex determination hierarchy, fruitless (fru) and doublesex (dsx), which are responsible for sexual differentiation in both the CNS and soma, are required for wild-type song production. However, the critical differences underlying the sexually dimorphic production of courtship song are unknown; moreover, the relative contributions of fru and dsx to the generation of these differences are not known. The central aim of this thesis was to investigate the neurobiological basis for the sexually dimorphic production of courtship song; and in addition, to determine the individual and combined contributions of fru and dsx in creating these essential differences. The long-term goal of this study was to determine the mechanism by which genetic factors such as fru and dsx can create the potential for courtship song by specifying aspects of CNS development and function. As a first step towards this long-term goal, the work presented in this thesis has identified the individual and combined contributions of fru and dsx to the production of courtship song. Moreover, a requirement for both fru and dsx in the specification of a neural substrate underlying courtship song was shown. Using females constitutively expressing the male-specific fru isoforms, the individual contribution of fru to the production of courtship song was determined; and the amount and quality of song generated by these females was found to be highly aberrant. Thus fru alone does not specify courtship song production. In fact, wild-type courtship song was only achieved when females expressed the male-specific isoforms of both fru and dsx, demonstrating that both genes are required for the specification of courtship song. Next, the co-expression of fru and dsx was examined, where fru and dsx were found to be co-expressed in three distinct regions of the CNS. One of these regions, the mesothoracic ganglion (Msg), is strongly implicated in the production of courtship song, suggesting that fru and dsx may act in concert to specify courtship song production. A closer examination of this region revealed a male-specific population of fru-expressing neurons in the Msg. This population of neurons was not present in females constitutively expressing fru’s male-specific isoforms, demonstrating that fru alone does not specify the development of a sexually dimorphic Msg. Instead, a critical requirement for dsx, alongside fru, in the specification of this sexually dimorphic population of neurons was shown. Thus a critical requirement for both fru and dsx in the specification of courtship song, and in the creation of a sexually dimorphic population of neurons in the Msg has been revealed. Finally, to determine how this sexually dimorphic population of neurons is linked to courtship song production, this thesis described the generation of genetic tools to allow the visualization and manipulation of these sex-specific neurons. Using the UAS/GAL4 system of targeted gene expression, another sexually dimorphic population of neurons was identified in the posterior brain, which is, like the Msg, a region where fru and dsx are co-expressed. Together, these results suggest that fru and dsx act to generate sexually dimorphic populations of neurons in regions of co-expression, where these neurons may form part of the sex-specific neural circuits underlying the performance of sexually dimorphic behaviours

Specific Activation of Estrogen Receptor Alpha and Beta Enhances Male Sexual Behavior and Neuroplasticity in Male Japanese Quail

Two subtypes of estrogen receptors (ER), ERα and ERβ, have been identified in humans and numerous vertebrates, including the Japanese quail. We investigated in this species the specific role(s) of each receptor in the activation of male sexual behavior and the underlying estrogen-dependent neural plasticity. Castrated male Japanese quail received empty (CX) or testosterone-filled (T) implants or were daily injected with the ER general agonist diethylstilbestrol (DES), the ERα-specific agonist PPT, the ERβ-specific agonist DPN or the vehicle, propylene glycol. Three days after receiving the first treatment, subjects were alternatively tested for appetitive (rhythmic cloacal sphincter movements, RCSM) and consummatory aspects (copulatory behavior) of male sexual behavior. 24 hours after the last behavioral testing, brains were collected and analyzed for aromatase expression and vasotocinergic innervation in the medial preoptic nucleus. The expression of RCSM was activated by T and to a lesser extent by DES and PPT but not by the ERβagonist DPN. In parallel, T fully restored the complete sequence of copulation, DES was partially active and the specific activation of ERα or ERβ only resulted in a very low frequency of mount attempts in few subjects. T increased the volume of the medial preoptic nucleus as measured by the dense cluster of aromatase-immunoreactive cells and the density of the vasotocinergic innervation within this nucleus. DES had only a weak action on vasotocinergic fibers and the two specific ER agonists did not affect these neural responses. Simultaneous activation of both receptors or treatments with higher doses may be required to fully activate sexual behavior and the associated neurochemical events

Investigation of Novel Circuits Involved in Virgin Female Receptivity of Drosophila melanogaster

Courtship is a behavior that allows the display of fitness of one sex to the other and gates possible subsequent mating. This behavior is crucial for reproduction and has strong innate components in all animals. Courtship in Drosophila melanogaster consists of a series of highly stereotyped actions that the male performs towards the female. He sings with vibrations of the wings, touches and licks her abdomen, while she evaluates the information presented to her.(...

Neuronal glucose transporter isoform 3 deficient mice demonstrate features of autism spectrum disorders.

Neuronal glucose transporter (GLUT) isoform 3 deficiency in null heterozygous mice led to abnormal spatial learning and working memory but normal acquisition and retrieval during contextual conditioning, abnormal cognitive flexibility with intact gross motor ability, electroencephalographic seizures, perturbed social behavior with reduced vocalization and stereotypies at low frequency. This phenotypic expression is unique as it combines the neurobehavioral with the epileptiform characteristics of autism spectrum disorders. This clinical presentation occurred despite metabolic adaptations consisting of an increase in microvascular/glial GLUT1, neuronal GLUT8 and monocarboxylate transporter isoform 2 concentrations, with minimal to no change in brain glucose uptake but an increase in lactate uptake. Neuron-specific glucose deficiency has a negative impact on neurodevelopment interfering with functional competence. This is the first description of GLUT3 deficiency that forms a possible novel genetic mechanism for pervasive developmental disorders, such as the neuropsychiatric autism spectrum disorders, requiring further investigation in humans

Acute alcohol exposure during neurulation: Behavioral and brain structural consequences in adolescent C57BL/6J mice

Prenatal alcohol exposure (PAE) can induce physical malformations and behavioral abnormalities that depend in part on the developmental timing of alcohol exposure. The current studies employed a mouse FASD model to characterize the long-term behavioral and brain structural consequences of a binge-like alcohol exposure during neurulation; a first-trimester stage when women are typically unaware that they are pregnant. Time-mated C57BL/6J female mice were administered two alcohol doses (2.8 g/kg, four hours apart) or vehicle starting at gestational day 8.0. Male and female adolescent offspring (postnatal day28–45) were then examined for motor activity (open field and elevated plus maze), coordination (rotarod), spatial learning and memory (Morris water maze), sensory motor gating (acoustic startle and prepulse inhibition), sociability (three-chambered social test), and nociceptive responses (hot plate). Regional brain volumes and shapes were determined using magnetic resonance imaging. In males, PAE increased activity on the elevated plus maze and reduced social novelty preference, while in females PAE increased exploratory behavior in the open field and transiently impaired rotarod performance. In both males and females, PAE modestly impaired Morris water maze performance and decreased the latency to respond on the hot plate. There were no brain volume differences; however, significant shape differences were found in the cerebellum, hypothalamus, striatum, and corpus callosum. These results demonstrate that alcohol exposure during neurulation can have functional consequences into adolescence, even in the absence of significant brain regional volumetric changes. However, PAE-induced regional shape changes provide evidence for persistent brain alterations and suggest alternative clinical diagnostic markers

Age-Related Deficits in Spatial Memory and Hippocampal Spines in Virgin, Female Fischer 344 Rats

Effects of aging on memory and brain morphology were examined in aged, 21-month-old, and young, 4-month-old, Fischer 344 female rats. Spatial memory was assessed using the object placement task, and dendritic spine density was determined on pyramidal neurons in the hippocampus following Golgi impregnation. Consistent with previous studies, aged females showed poorer object placement performance than young subjects. Young subjects significantly discriminated the location of objects with a 1.5-hour intertrial delay while aged subjects did not. Spine density of basal dendrites on CA1 pyramidal cells was 16% lower in the aged subjects as compared to the young subjects. No differences in spine density were found between young and aged subjects in basal dendrites of CA1 or in either dendritic field of CA3 pyramidal neurons. Thus, decreased hippocampal CA1 dendritic spine density in aged rats may contribute to poorer spatial memory as compared to young rats. The possibility that the neuroplastic changes observed in this study may pertain only to female subjects having had a specific set of life experiences is discussed. Different factors, such as reproductive status, diet, and handling may contribute to neuroplasticity of the brain during aging; however, this view requires further examination