The Mouse Primary Visual Cortex Is a Site of Production and Sensitivity to Estrogens

The classic female estrogen, 17β-estradiol (E2), has been repeatedly shown to affect the perceptual processing of visual cues. Although gonadal E2 has often been thought to influence these processes, the possibility that central visual processing may be modulated by brain-generated hormone has not been explored. Here we show that estrogen-associated circuits are highly prevalent in the mouse primary visual cortex (V1). Specifically, we cloned aromatase, a marker for estrogen-producing neurons, and the classic estrogen receptors (ERs) ERα and ERβ, as markers for estrogen-responsive neurons, and conducted a detailed expression analysis via in-situ hybridization. We found that both monocular and binocular V1 are highly enriched in aromatase- and ER-positive neurons, indicating that V1 is a site of production and sensitivity to estrogens. Using double-fluorescence in-situ hybridization, we reveal the neurochemical identity of estrogen-producing and -sensitive cells in V1, and demonstrate that they constitute a heterogeneous neuronal population. We further show that visual experience engages a large population of aromatase-positive neurons and, to a lesser extent, ER-expressing neurons, suggesting that E2 levels may be locally regulated by visual input in V1. Interestingly, acute episodes of visual experience do not affect the density or distribution of estrogen-associated circuits. Finally, we show that adult mice dark-reared from birth also exhibit normal distribution of aromatase and ERs throughout V1, suggesting that the implementation and maintenance of estrogen-associated circuits is independent of visual experience. Our findings demonstrate that the adult V1 is a site of production and sensitivity to estrogens, and suggest that locally-produced E2 may shape visual cortical processing

Optogenetic Delay of Status Epilepticus Onset in an In Vivo Rodent Epilepsy Model

Epilepsy is a devastating disease, currently treated with medications, surgery or electrical stimulation. None of these approaches is totally effective and our ability to control seizures remains limited and complicated by frequent side effects. The emerging revolutionary technique of optogenetics enables manipulation of the activity of specific neuronal populations in vivo with exquisite spatiotemporal resolution using light. We used optogenetic approaches to test the role of hippocampal excitatory neurons in the lithium-pilocarpine model of acute elicited seizures in awake behaving rats. Hippocampal pyramidal neurons were transduced in vivo with a virus carrying an enhanced halorhodopsin (eNpHR), a yellow light activated chloride pump, and acute seizure progression was then monitored behaviorally and electrophysiologically in the presence and absence of illumination delivered via an optical fiber. Inhibition of those neurons with illumination prior to seizure onset significantly delayed electrographic and behavioral initiation of status epilepticus, and altered the dynamics of ictal activity development. These results reveal an essential role of hippocampal excitatory neurons in this model of ictogenesis and illustrate the power of optogenetic approaches for elucidation of seizure mechanisms. This early success in controlling seizures also suggests future therapeutic avenues

Microglial Interactions with Synapses Are Modulated by Visual Experience

Microglia, the brain's immune cells, show unique interactions with nearby synaptic elements under non-pathological conditions that are sensitive to changes in sensory experience

Synaptic Mechanisms of Activity-Dependent Remodeling in Visual Cortex during Monocular Deprivation

It has long been appreciated that in the visual cortex, particularly within a postnatal critical period for experience-dependent plasticity, the closure of one eye results in a shift in the responsiveness of cortical cells toward the experienced eye. While the functional aspects of this ocular dominance shift have been studied for many decades, their cortical substrates and synaptic mechanisms remain elusive. Nonetheless, it is becoming increasingly clear that ocular dominance plasticity is a complex phenomenon that appears to have an early and a late component. Early during monocular deprivation, deprived eye cortical synapses depress, while later during the deprivation open eye synapses potentiate. Here we review current literature on the cortical mechanisms of activity-dependent plasticity in the visual system during the critical period. These studies shed light on the role of activity in shaping neuronal structure and function in general and can lead to insights regarding how learning is acquired and maintained at the neuronal level during normal and pathological brain development

The Role of Microglia and Fractalkine Signaling in Experience-dependent Synaptic Plasticity

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Neuroscience Graduate Program, 2016.The remodeling of circuitry is a fundamental aspect of brain function, contributing both to the initial wiring of the brain during development and to critical processes such as learning and memory in the adult. Changes to neural network function rely on structural and functional changes at synapses, and the mechanisms which modulate these synaptic changes critically contribute to cognitive function throughout the life span. Recently, microglia have come into the spotlight as regulators of synapses. These immune cells have been shown to display dynamic interactions with synapses in the non-pathological brain, although their contribution to synaptic plasticity is still poorly understood. My work has characterized microglial contributions to experience-dependent plasticity in the visual cortex in vivo. I show that manipulations of visual experience elicit a remarkably rapid behavioral response in microglia which is distinct from their inflammatory behavior. This response corresponds to the early phase of plasticity in this model when synapses are lost and when microglia increase their synaptic interactions, implicating microglia in the process of dynamic synapse removal. To determine the underlying mechanism behind this response, I examined the role of the chemokine fractalkine. Fractalkine signaling is a pathway well studied in neuroinflammation, where it allows for specificity of signaling between neurons and microglia and initiates chemotaxis of microglial cells. These functions could also be critical in the physiological process of synaptic rearrangement. I report that in the visual system, removal of fractalkine signaling does not alter microglial density, morphology, or process motility - key baseline microglial characteristics regulating their physiological functions. Removal of fractalkine signaling also fails to impact the dynamic microglia-neuron interactions thought to underlie their role in synapse remodeling. Additionally, unlike other systems where fractalkine signaling is necessary for circuit remodeling, it is not required for normal plasticity in either early or late forms of plasticity in the visual system. My findings suggest that microglia play an important role in synaptic plasticity, and use a subset of their pathological molecular repertoire in a time- and region-dependent manner to implement plastic changes in the non-pathological brain

The Role of P2Y12 in Non-Pathological Microglial Functions during Synaptic Plasticity

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Neurobiology and Neuroanatomy, 2016.Synaptic plasticity is critical for neurodevelopment and proper function of the adult nervous system. Studies show that microglia play critical roles in neurodevelopment, but mechanisms driving these roles are poorly understood. I explored purinergic signaling as a potential mediator between microglia and neurons during synaptic plasticity. Purinergic signaling has been implicated in microglial behavior, but studies focused on inflammatory roles. Non-inflamed microglia highly and selectively express the purinergic receptor, P2Y12, which functions in microglial chemotaxis. I posited that purinergic signaling contributes to the microglial motility underlying synapse surveillance and may be critical for microglial roles in synaptic refinement. My evidence suggests that P2Y12 disruption prevents ocular dominance shifts indicative of synaptic plasticity. P2Y12 disruption also decreases microglial process complexity, without affecting basal microglial process dynamics. In addition, microglial process dynamics appear to be regulated by arousal with increased surveillance during slow-wave sleep-like states. I find that noradrenergic signaling, contributing to arousal, is sufficient to suppress microglial process dynamics and inhibit microglial P2Y12-mediated roles in synaptic plasticity via microglial β2 adrenergic receptors. These data suggest microglia are active participants in cortical network remodeling in adolescent synaptic plasticity primarily during sleep states. These results not only describe novel neuro-immune interactions in the non-pathological brain, but provoke broader considerations of the importance of sleep in microglial roles during neurodevelopment and in neuropathology