Trent Anderson, PhD - US grants

The steroid estrogen regulates many functions of the brain including behavior and cognition, while the prefrontal cortex (PFC) is a brain region that controls aspects of cognitive function and emotional behavior. Not surprisingly the PFC is estrogen sensitive, but there is currently little known about how it responds to estrogen. The goal of this research is therefore to determine how estrogen regulates the PFC. The research tests the prediction that of the two main types of estrogen receptors, alpha and beta, that the PFC is regulated by beta (ERb). Successful completion of these studies will provide novel information about an important but unexplored neuronal phenotype in the PFC. Innovative approaches are used to examine ERb neurons and the results of these studies can impact multiple research arenas. This research project will be used for the training of high school, undergraduate and graduate students, particularly underrepresented minorities, in neuroscience. Results will be disseminated through peer-reviewed publication and by student presentations at local and national meetings.

These studies explore the function of a select group of cells in the mouse PFC that express ERb. The PFC controls many behaviors including cognition, attention, and neuroendocrine stress responses. Estrogen can alter the development of this brain region, yet, little is known of the neurons in the PFC that express ERb, partly due to the absence validated reagents allowing the detection of ERb in brain. The proposed studies will examine this group of neurons in the PFC using a novel transgenic mouse that express a fluorescent protein in ERb neurons. Preliminary results show that the location of ERb expressing neurons changes across development of the PFC. Studies in this application will address the hypothesis that these changes reflect developmental alterations in estrogen sensitivity in different cortical layers across time. Using anatomical approaches, these studies will determine the identity of the cortical neurons that express ERb. Next, molecular approaches will be used to address the reason why estrogen receptor levels change in amount and location during cortical development and lastly, the function of identified ERb neurons in the PFC will be examined using electrophysiology

DESCRIPTION (provided by applicant): Migraine is one of the most common neurological disorders with over 29 million Americans suffering from the debilitating headaches and sensory disturbances that accompany a migraine attack. There is no cure for migraine and current treatment options are often ineffective or leave patients suffering from significant adverse side effects. While the underlying cause of migraine remains unknown many patients report an aura that is often perceived as a visual disturbance of flashing lights or blind spots. A neurological phenomenon known as cortical spreading depression (CSD) may cause migraine aura leading to the development of migraine pain. Migraine patients often identify specific migraine triggers including stress, alcohol, diet, the menstrual cycle and pregnancy. These triggers are also known to increase levels of neurosteroids in the brain. Neurosteroids can be synthesized directly in the brain or from peripherally produced sex steroids and can influence neuronal excitability through modulation of inhibitory GABAergic function. Increased neuronal excitability has been reported in migraine patients and can lower the threshold for developing CSD. While the effects of sex steroids in migraine have been extensively studied there is a critical gap in th understanding of how brain-derived neurosteroids may directly influence migraine. This proposal focuses on the actions and mechanism of neurosteroid induced changes to excitability and how they may impact CSD and migraine. We hypothesize that the effects of neurosteroids are cell type dependent and by selectively enhancing cortical inhibition paradoxically decrease the threshold for the development of CSD. Three specific aims test this hypothesis and the underlying mechanism utilizing cutting-edge advanced electrophysiological, imaging, optogenetic and LSPS circuit mapping techniques in an established animal model of CSD. First, how do neurosteroids differentially affect excitatory and inhibitory neurons? (Aim 1); second, what is the mechanism of neurosteroid mediated enhancement of CSD? (Aim 2); and third, do neurosteroids disinhibit the cortex and amplify synaptic circuits? (Aim 3). Our preliminary data demonstrate that neurosteroids decrease the threshold for CSD potentially through a select action on fast-spiking interneurons that reduces inhibitory drive onto excitatory pyramidal neurons. The data from the proposed experiments will provide insights into the pathophysiology of migraine as well as a mechanism through which neurosteroids may be a common mediator for several migraine triggers. Additionally, we will examine if specific neuronal populations can be targeted to prevent or inhibit CSD. These findings will allow us to identify mechanisms that may lead to enhanced excitability in migraine patients and potentially novel targets for therapeutic intervention to prevent or minimize migraine headache.

Post-traumatic headache (PTH) commonly occurs following mild traumatic brain injury (mTBI), also known as concussion. PTH is a secondary headache that often presents with a migraine-like phenotype and is subdivided as acute or persistent (PPTH) depending on whether it resolves within 3 months after injury. The pathophysiology of PTH and PPTH is not understood and no evidence-based treatments exist for these conditions. Critically, PPTH might differ from PTH, not only in the duration but also in underlying mechanisms and responsiveness to treatment. The reasons for emergence of PPTH in some patients remain unclear but may be related to risk factors including pre-existing migraine and the experience of a previous mTBI. We have developed an approach to investigate the mechanisms of PTH and PPTH as well as potential strategies for treatment. Using a weight drop method in male and female mice that recapitulates biomechanical properties and clinical features of mTBI, we have shown that a single mTBI is sufficient to induce clinically relevant PTH symptoms including an acute period of allodynia, elevated CGRP blood levels and lowered thresholds for induction of cortical spreading depression (CSD). Additionally, we have explored the concept that the transition from acute to chronic pain states may rely on a ?pain memory? that can be studied using the ?two-hit? model of hyperalgesic priming where a prior insult confers vulnerability to a subsequent provocative stimulus. Thus, following resolution of acute allodynia, mTBI mice transition into a long-lasting persistent phase (PPTH) where, remarkably, allodynia can be reinstated by physiologically relevant and common migraine triggers, including stress. CGRP is established in migraine pathogenesis and our data also suggest an important role in promoting PTH. Treatment with either a CGRP antibody or with onabotulinum toxin A (botox) prevents mTBI-related allodynia (PTH) as well as subsequent provoked allodynia representative of PPTH. However, blockade of CGRP after mTBI sensitization is established is ineffective in blocking provoked allodynia, while botox still maintains efficacy. We have hypothesized that mTBI results in CGRP release from meningeal afferents promoting PTH and central sensitization that underlies the development of PPTH, but that PPTH may be maintained in a CGRP-independent fashion. Additionally, we hypothesize that existing sensitization prior to a mTBI event will promote vulnerability to the development of CGRP-independent PPTH. We explore these hypotheses with two related but, independent, aims using behavioral, neurochemical, immunohistochemical and electrophysiolgical analyses. Aim 1 will determine whether, and when currently available therapies can block mTBI-related outcomes relevant to PTH and if these treatments can prevent the expression of PPTH. Aim 2 will determine if prior sensitization promotes more severe, long-lasting and CGRP-resistant PPTH. Our studies will fill in significant knowledge gaps about the role of CGRP in promoting PTH and the importance of pre-existing sensitization in establishing CGRP- independent PPTH. Such information will influence treatment as well as guide the discovery of new therapies.