Susan B Powell - US grants

DESCRIPTION: The current training proposal is part of a larger project investigating the development and neurobiological basis of spontaneous stereotyped behaviors in deer mice. This work represents an animal model of Stereotypic Movement Disorder and thus will be a close complement to our studies of stereotypy and related repetitive behavior disorders in individuals with developmental disabilities. Stress has been assumed to play an important role in the pathogenesis and expression of abnormal repetitive behaviors in various clinical populations as well as animals reared or housed in adverse environmental circumstances. Unfortunately, few data are available to test such an assumption. Thus, the present project will test directly the role of stress in the pathogenesis and expression of stereotyped behavior. The first approach to this problem will be to assess the effect of increased stress responsiveness on the development of spontaneous stereotypy in deer mice. This involves increasing the stress responsiveness of deer mice through extended maternal separation and assessing the development of stereotyped behavior. The second aim is to assess indices of stress responsiveness in stereotypic and non-stereotypic deer mice. This aim involves assessing stress-induced alterations in HPA axis and dopamine function in both stereotypic and non-stereotypic mice. In order to understand more fully the role that glucocorticoid and dopamine function play in the pathophysiology of stereotypy, glucocorticoid receptor mRNA expression in hippocampus and dopamine transporter densities in dopamine terminal fields will also be compared in stereotypic and non-stereotypic deer mice

DESCRIPTION (provided by applicant): Clinical evidence suggests that a prolonged period of untreated psychosis may be associated with increased severity of symptoms and decreased overall quality of life. Taken together with the extremely debilitating nature of schizophrenia, there is a renewed interest in the early identification and treatment of psychotic disorders, including prodromal symptoms. While the efficacy, safety, and ethics of early intervention are being examined in the clinical arena, preclinical studies on the therapeutic potential and long-term consequences of prophylactic treatments in animals are warranted in order to inform this debate. Because some forms of schizophrenia appear to be attributable to early developmental perturbations, many animal studies have examined the influences of specific developmental manipulations on behaviors and neural circuitry relevant to schizophrenia. Two developmental rat models, isolation rearing and neonatal ventral hippocampal lesions, result in both sensorimotor gating deficits and locomotor hyperactivity. The use of these two complementary developmental manipulations is important because they differ in their timing and mode of insult, but result in similar behavioral and neuronal abnormalities. These models will allow the examination of the therapeutic potential of prophylactic treatment and the potential side effects of chronic treatment during ontogeny. Isolation rearing is a non-pharmacological, environmental perturbation that deprives the rats of social contact from weaning through adulthood. Neonatal ventral hippocampal lesions involve a discrete, neuroanatomical insult that has temporal and regional specificity. Studies in this application will test whether long-term early administration of antipsychotic medications will prevent the development of isolation rearing or neonatal hippocampal lesion-induced deficits in sensorimotor gating and locomotor habituation. Considering the potential sensitivity of the models to repeated handling, antipsychotic drugs will be administered through the drinking water for an 8 week period initially and then at different time points to determine the critical developmental window of antipsychotic treatment. The specific aims are: 1: To determine the optimal parameters and functional effects of early developmental antipsychotic administration in rats. 2. To assess the effects of prophylactic antipsychotic treatment on isolation rearing induced behavioral deficits. 3. To assess the effects of prophylactic antipsychotic treatment on neonatal ventral hippocampal lesion induced behavioral deficits.

DESCRIPTION (provided by applicant): A significant body of research supports the idea that deficits in cortical fast-spiking inhibitory systems may underlie the psychotic features and cognitive deficits associated with schizophrenia-related disorders. Recent data from neurodevelopmental animal models indicate that the loss of function of the parvalbumin-(PV) positive fast-spiking inhibitory neurons may occur early during postnatal development, specifically during the critical period of their maturation. These results strongly suggest that the period of active maturation of this fundamental inhibitory system may constitute a sensitive period during which the confluence of genetic and environmental factors may set the stage for the development of schizophrenia-like symptoms in late adolescence/early adulthood. Thus, studies directed to determine factors that affect the maturational process of this inhibitory system may shed light into the origins of schizophrenia. This project will test two primary hypotheses: (1) that the period of maturation of PV-interneuronal circuits constitutes a sensitive period in which increased oxidative stress in brain, due to the activation of the IL-6/Nox2 pathway, leads to schizophrenia-like behavior in early adulthood; and (2) that this sensitive period also constitutes a window of intervention for pharmacological treatment strategies aimed at prevention of psychosis. These hypotheses will be tested in mice subjected to two developmental manipulations known to lead to disruptions in the PV- interneuronal circuitry and schizophrenia-related behaviors in early adulthood: i.e. perinatal exposure to the NMDA receptor antagonist ketamine (pNM model), and social isolation rearing (SI model). Three specific aims will be developed: Aim 1 will test the hypothesis that there is a sensitive period of brain redox dysregulation in the pNM and SI models that leads to schizophrenia-like neurochemical and behavioral disruptions in late adolescence/early adulthood. Aim 2 will determine whether increased brain and circulating IL-6 correlate with active oxidative stress in brain in the two developmental models, assess whether circulating IL-6 constitutes a peripheral biomarker predictive of brain dysfunction, and test whether the neurochemical and behavioral effects of SI and pNM are absent in IL-6 KO mice. And finally, Aim 3 will assess whether early or late interventions leading to attenuation of brain oxidative stress, by use of a Nox2 inhibitor (apocynin), an IL-6 blocker, or by increasing antioxidant defenses with N-acetyl cysteine, protects the PV-interneuronal system and prevents development of schizophrenia-like behaviors in late adolescence/early adulthood. Public Health Impact: This project studies a specific set of inhibitory neurons which are critical for normal cognitive function, and known to be dysfunctional in schizophrenia. The proposed studies may suggest novel anti-inflammatory and/or anti-oxidant treatments during early life to protect this fundamental GABAergic system and thus prevent the development of schizophrenia and other psychotic conditions. PUBLIC HEALTH RELEVANCE: Schizophrenia affects millions of Americans when they reach early adulthood, but to date, there is scarce knowledge of the underlying disease processes occurring before symptoms appear. Using two neurodevelopmental mouse models of schizophrenia, this project will determine whether the period of maturation of inhibitory circuits, during early postnatal development, constitutes a sensitive period when the brain is most vulnerable to oxidative stress processes that lead to the dysfunction of specific inhibitory circuits and the appearance of schizophrenia-like symptoms in early adulthood. These studies will delineate the mechanisms inducing the increased oxidative stress in two models and the periods when they occur, and assess whether strategies that prevent oxidative stress ameliorate the neurochemical and behavioral disruptions.

? DESCRIPTION (provided by applicant): Autism spectrum disorder (ASD) is a highly heritable, but genetically complex, neurodevelopmental disorder. Increasing evidence points to an interaction between genetic vulnerability and environmental risk factors in the generation of ASD. Human genetics and animal models suggest that alterations in synapse formation and maintenance may be fundamental to the etiology of ASD, and recent human exome-profiling studies suggest transcription and chromatin remodeling functions may be affected. Epigenetic regulation of gene transcription, including through developmentally dynamic and cell type-specific patterns, is a plausible mechanism mediating long-term environmental contributions to ASD. Environmental impacts on the overall configuration of DNA methylation (methylome) may lead to aberrant silencing or activation of genes involved brain circuitry maturation, with subsequent functional and behavioral consequences. Recently, the first analysis of whole- genome single-base resolution methylome maps of developing frontal cortex in mice and humans revealed extensive methylome reconfiguration during development from fetal to young adult. Importantly, a specific form of cytosine methylation, in non-CG sites, accumulated preferentially in neurons, coinciding with the period of synaptogenesis in both species. These results point to a potential role of the neuronal methylome in healthy development of neural circuits that could be particularly vulnerable to pathological disruption. Leveraging on these data, as well as on preliminary data showing dynamic changes in CG methylation patters during the transition between embryonic and early life in mouse brain, this proposal will test the hypothesis that alteration of specific forms of DNA methylation are involved in the origins of ASD. To test this hypothesis, Aim 1 will produce single-base resolution methylome maps in the two major neuronal populations in frontal cortex i.e. excitatory and inhibitory neurons, in a well-established model of ASD, the maternal immune activation (MIA) model. Additionally, to test for additive effects of environmental exposures in a compromised gestation, Aim 2 will expose the MIA animals to the environmental toxin PBDE. Finally, Aim 3 will analyze the methylome changes produced by MIA in animals that are deficient for the autism risk gene Shank3 to test for gene x environment interactions. The transcriptional consequences of methylome changes will be assessed by RNA- Seq for each neuronal population at each time-point during development, and long term behavioral consequences will be assessed through a battery of behavioral tests relevant to ASD. New, sophisticated computational analysis procedures will be used to integrate diverse and large-scale empirical data sets to provide a powerful and stringent test of our hypotheses.

Autism spectrum disorder (ASD) is characterized by social and communication deficits as well as restricted, repetitive behaviors (RRBs). RRBs include ?lower order? motor stereotypies such as body rocking and hand waving as well as more elaborate, compulsive behaviors or ?higher order? RRBs such as checking and hoarding and insistence on sameness. Although RRBs, along with social and communicative deficits, constitute the triad of symptoms essential to the diagnosis of autism, RRBs have been surprisingly understudied. The extant question in the field is: what neural circuits mediate RRBs and how might these circuits be altered in ASD and thus targeted for treatment? Insistence on sameness behavior can be measured in tasks of cognitive flexibility using reversal learning paradigms. Individuals with ASD have specific deficits in reversal learning paradigms that use a probabilistic reinforcement schedule, which can be tested in mice using similar cross-species paradigms to probe neural circuitry and treatments. Because prenatal inflammation is a risk factor for autism and other neurodevelopmental disorders, we and others have conducted studies of maternal immune activation (MIA) in model organisms. In addition to social deficits, MIA mice have deficits in probabilistic reversal learning similar to that observed in ASD. Disruptions in frontal cortex function, particularly orbito-frontal cortex (OFC) and striatum lead to deficits in cognitive flexibility. Preliminary data from our lab show that OFC->dorsal medial striatum (DMS) circuit activation disrupts probabilistic reversal learning in a manner consistent with ASD. Intriguingly, structural and functional abnormalities of the OFC are evident in ASD, which may contribute to RRBs. Thus, we hypothesize that probabilistic reversal learning deficits in MIA mice are due to overactivation of OFC-DMS circuit and that inhibiting this circuit will ameliorate the deficits. Aim 1 studies will test whether optogenetic activation of OFC->DMS glutamate projections will exacerbate RRBs in MIA mice and/or replicate RRBs in control mice. Channelrhodopsin (ChR2, a blue light-gated cation channel) will be expressed via the CamKII promoter selectively in glutamate neurons in the OFC. Fiber optic probes will be implanted in the DMS to stimulate terminals from the OFC during the reversal phase of the task. Aim 2 studies test whether OFC-DMS circuit inhibition ameliorates cognitive flexibility deficits in MIA mice. Specifically, a CamKII promoter-driven halorhodopsin (eNpHR3.0, a green light-gated chloride ion pump) will be infused into the OFC, and stimulation of fiber optic probes in the DMS will test whether optogenetic inhibition of OFC->DMS neurons attenuates cognitive flexibility deficits in MIA mice. Because both ASD and MIA are associated with decreased GABA function in frontal cortex, Aim 3 studies test whether enhancing OFC GABA transmission ameliorates cognitive flexibility deficits in MIA mice. These experiments will provide evidence for a specific circuit involved in RRBs in MIA and a possible remediation through inhibition of the circuit and potential treatment approaches for RRBs in ASD.