Adriana Galvan - US grants

Summary ? Core B The Anatomy and non-human primate behavior Core (Core B) will be an essential part of the Udall Center at Emory University. One of the major functions of this Core will be to prepare and process brain tissue from experimental animals generated by the Center projects. This service will be done with standardized histologic techniques, and will provide information that will be indispensable for the interpretation of the functional experiments under projects 1 and 2, and will facilitate sharing and comparisons of results among all three projects. Specifically, the Core will provide the following services: (1) Use of immunohistochemical and microscopy approaches to evaluate the degree of dopaminergic depletion in animals treated with 6- hydroxydopamine (6-OHDA, used in mice in project 1) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, used in monkeys in projects 2 and 3); (2) use of histological markers to delineate nuclei in the motor thalamus in rodents (projects 1) and monkeys (projects 2 and 3); (3) histological reconstructions of recording electrode trajectories (projects 1 and 2); (4) analysis of the degree and pattern of expression of opsins after viral transfection (projects 1 and 2); (5) detection and digital reconstruction of biocytin-filled neurons (project 1); and (6), the cataloguing and storing of brain tissue of MPTP-treated monkeys. A second major service of Core B will be to systemically treat Rhesus monkeys from projects 2 and 3 with the neurotoxin MPTP and evaluate parkinsonism resulting from this treatment with standardized methods. This will allow us to generate animals with similar levels of parkinsonism across both projects, and will facilitate comparisons of data generated by them. By providing these services, the Core will help to free up time and resources from the research projects. In addition, the use of standardized anatomical and behavioral assessment techniques will help us to maintain a consistently high level of quality of Center research.

PROJECT SUMMARY Patients with Parkinson?s disease (PD) experience progressive motor impairments that lead to severe disability. The motor impairments of PD are associated with abnormal neuronal activity in the basal ganglia, a group of brain structures involved in movement planning and execution. The long-term goal of our research is to elucidate how the abnormal activity of the basal ganglia relates to the motor deficits in PD, with the goal of developing novel therapies to treat parkinsonism with improved specificity and fewer unwanted side effects. The proposed studies are focused on the external segment of the globus pallidus (GPe), a key structure in the basal ganglia circuitry. Traditionally, the GPe was thought to be composed of a single neuron type; it is now established that this nucleus contains different types of neurons that can be classified based on their projection targets (?upstream? to the striatum, or ?downstream? to the subthalamic nucleus or internal pallidum). In rodent models of PD, there is evidence that PD-related abnormalities occur selectively in specific types of GPe neurons, raising the possibility that different GPe neuron populations might make distinct contributions to the normal and pathological roles of the GPe. However, the translational relevance of these findings is limited by functional and anatomical differences between the rodent and primate GPe. Our experiments will define functional differences between classes of GPe neurons in normal rhesus monkeys and in monkeys rendered parkinsonian by treatment with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Monkeys are an excellent animal model for studying PD-related changes in brain activity, because their basal ganglia and connected brain structures closely resemble those in humans, and because MPTP-treated monkeys show the majority of the motor impairments seen in PD patients. We will use electrophysiological in vivo recordings to evaluate differences in the firing rates and patterns of GPe-upstream and GPe-downstream neurons. The projections of individual GPe neurons will be identified by their antidromic responses to electrical stimulation of the target structures (aim 1). To determine how GPe neurons modulate the activity in the striatum, subthalamic nucleus or internal pallidum, we will selectively silence GPe axonal terminals in each of these nuclei, using optogenetic methods. We will also determine whether selective silencing of GPe terminals alters PD-motor impairments in monkeys (aim 2). Finally, we will use histologic techniques to identify proteins whose expression reveals specific GPe neuron projection patterns (aim 3). Our studies will begin to determine how the activities of primate GPe neuron subtypes differ, how they regulate the activity in other basal ganglia neurons in the normal and parkinsonian states, and whether they are involved in the pathophysiology of parkinsonism. The knowledge gained from these studies is significant, as it may enable us to develop new treatments for PD that harness functional and anatomical differences of GPe neuron types.

PROJECT SUMMARY Abnormal activity patterns in specific neuron networks may underlie dysfunction in many brain diseases. It is therefore a goal of translational research to manipulate the activity of specific brain pathways in an effort to restore normal function. Current clinical neuromodulation methods (such as deep brain stimulation) are relatively non-specific, and can lead to significant side effects. Novel genetically based neuromodulation techniques have made it possible to more precisely target specific neuron populations. Among these, chemogenetic techniques have gained attention because of their high translational potential. These methods involve the use of engineered receptors that are introduced into specific neuron types using genetic manipulations. The receptors will not be activated by endogenous neurotransmitters, but only by exogenously applied compounds. Thus, a systemically administered drug can elicit specific actions in genetically targeted neuron populations. While widely used in rodents, chemogenetic methods in primates remains in its infancy. We are interested in the use of chemogenetic tools to control ligand-gated ion channels (LGICs) in primates. These channels can directly influence the electrical properties of neurons and increase or decrease the neuronal activity depending on the ion channel. A recently developed subtype of LGICs, termed ?pharmacologically selective actuator molecules? (PSAMs), is based on nicotinic receptors which are engineered to not recognize their endogenous activator, acetylcholine, but to be selectively activated by very small doses of the clinically approved drug varenicline. The fact that the PSAM approach re-purposes a clinically used drug makes it highly attractive for translation into therapy for human diseases. However, PSAMs have not yet been used in primates (human or non-human). It is therefore essential to examine the expression and function of these receptors in monkeys. In this project, we plan to study whether PSAMs can be used in monkeys to manipulate neuron activities and behavior. It is our long-term goal to test the potential of PSAMs as an antiparkinsonian treatment. In the proposed experiments, we will express PSAMs in the internal pallidum (GPi) of monkeys using viral vectors. We have chosen GPi as a target because GPi activity is abnormal in various movement disorders, including Parkinson?s disease (PD), and manipulation of GPi activity (such as pallidotomy procedures) has antiparkinsonian properties. Once the (inhibitory) PSAMs are expressed in GPi, we will systemically administer varenicline, expecting to induce a reduction of the activity of GPi neurons and slow movement. The expression of PSAMs will be verified by in vivo PET imaging, as well as post-mortem histology. Data generated by this project will be used for a subsequent R01 proposal in which we will examine the effects of PSAM-mediated inactivation of GPi in MPTP-treated parkinsonian monkeys. If we find that this technique has antiparkinsonian properties without inducing adverse effects, it could be developed into a new therapy for treating PD symptoms with fewer side effects than the currently available methods.