Stephen Mark Smith, BMedSCi, MB BS PhD - US grants

DESCRIPTION (provided by applicant): Ion channel activity at the nerve terminal determines presynaptic action potential shape and Ca2+ entry and thus plays a pivotal role in the regulation of synaptic transmission. This is particularly important in the presynaptic terminals of the neocortex, due to this brain region's role in mediating higher neurological function under normal conditions and during disease states. We have recently developed a technique that permits electrophysiological recording from single, acutely isolated rat neocortical nerve terminals. The long-term objective of the laboratory is to answer questions about the physiological and pathophysiological regulation of synaptic transmission by directly studying neocortical, presynaptic ion channels with this technique. An increase in intracellular [Ca2+] ([Ca2+]i) is a critical signal at the synapse where it triggers exocytosis, plasticity and gene expression. Much more is known about signaling downstream of changes in intracellular Ca2+ than about the impact of changes in extracellular [Ca2+] ([Ca2+]o). Yet [Ca2+]o is likely to undergo significant changes as a result of electrical activity. The driving hypothesis for this proposal is that a decrease in synaptic cleft [Ca2+] is an important signal which regulates synaptic efficacy. We have recently discovered a novel, Ca2+-based signaling pathway in neocortical nerve terminals, comprised of a voltage sensitive non-specific cation (NSC) channel activated by decreases in [Ca2+]o. This interesting finding poses a number of questions: what is the mechanism by which changes in [Ca2+]o are detected and transduced to alterations in membrane conductance? Is the Ca2+ sensor-NSC channel signaling pathway modulated by other agents at the nerve terminal? What is the physiological impact of Ca2+ sensor-NSC channel signaling pathway on synaptic transmission? To answer these questions we plan to use a combination of electrophysiological, pharmacological and immunochemical techniques to: 1. Identify the constituents of the Ca2+ sensor-NSC channel signaling pathway. 2. Determine physiological modulators of Ca2+ sensor-NSC channel signaling pathway. 3. Determine the role of the Ca2+ sensor-NSC channel signaling pathway in synaptic transmission. The goals of this proposal are to understand the mechanism by which [Ca2+]o modulates ion channel activity in the synapses of the cortical nerve terminals and to determine how this Ca2+ sensor-NSC channel signaling pathway impacts synaptic transmission in the neocortex.

DESCRIPTION (provided by applicant): Cannabis is one of the most widely used psychotropic drugs and it has been linked with numerous serious adverse effects including dependence, psychiatric disorders, and cardio-respiratory disease. Detailed knowledge about the mechanisms by which this drug acts is crucial to understand its many effects, and may greatly assist the design of drugs to facilitate treatment of cannabis dependence and withdrawal. Identification of all the cannabinoid receptors is central to this problem. In addition to the two well-characterized classical cannabinoid receptors three other receptors have recently been identified. Based on its distribution and function in the brain it has also been suggested that the extracellular Ca-sensing receptor (CaSR) would be a suitable target for cannabinoids. In preliminary experiments we found that cannabinoids activate CaSR, a G-protein coupled receptor (GPCR), that is localized in the majority of nerve terminals in the brain, and decreases synaptic transmission when activated. These preliminary findings, coupled with the abundance of CaSR in the brain, may fundamentally change our understanding of the mechanism of action of cannabinoids. The objective of this proposal is to determine if CaSR is an important pathway in the action of cannabinoids and our hypothesis is that brain CaSR is activated directly by cannabinoids. We are ideally suited to perform this project because of our expertise in CaSR function in nerve terminals and expression systems. The sensitivity of CaSR to cannabinoids and the prevalence of CaSR in the brain will open up a new view of cannabinoid action, substantially changing thinking in the field. Successful completion of these specific aims will characterize the response of CaSR to cannabinoids, shedding light on the broader range of influence of CaSR. This work will define the tools necessary to dissect the relative contributions of CaSR and CB1 to cannabinoid modulation of synaptic transmission in the brain. Future proposals would combine pharmacological and genetic approaches to ascertain the impact of cannabinoids via CB1 and CaSR at central synapses. Our rationale is that the identification and characterization of a novel and prevalent cannabinoid receptor will facilitate our understanding of the behavioral actions of the commonly used drug cannabis. Moreover, distinguishing the various actions of cannabinoids may translate into the identification of a novel class of drugs that facilitate treatment of cannabis addiction and withdrawal. PUBLIC HEALTH RELEVANCE: Cannabis is a commonly used drug that is associated with drug dependence and serious psychiatric, cardiovascular and pulmonary diseases. New treatments are needed to help people stop using cannabis but this requires improved understanding of how cannabis works. We have discovered a new pathway in the brain that is activated by cannabis-like drugs. By studying this new pathway we will discover more about how cannabis works and so improve the chances of designing new treatments to help stop cannabis use.

DESCRIPTION (provided by applicant): Cannabis is the most widely used illegal drug and it has been linked with numerous serious adverse effects. Cannabis has also been proposed as useful therapy for several neurological conditions including chronic pain, AIDS-related muscle wasting, and movement disorders. Detailed knowledge about the mechanisms by which this drug acts is crucial to understanding its many effects, and may greatly assist in the design of drugs to facilitate treatment of cannabis dependence and the above diseases. In addition to the two well-characterized classical cannabinoid receptors three other receptors have recently been identified. Based on the distribution and function in the brain of the extracellular Ca-sensing receptor (CaSR) it has been suggested that it a potential target for cannabinoids. In preliminary experiments we found that cannabinoids activate CaSR, a G-protein coupled receptor (GPCR), localized in the majority of nerve terminals in the brain, and activation of CaSR modulates synaptic transmission. These preliminary findings, coupled with the abundance of CaSR in the brain, may fundamentally change our understanding of the mechanisms of cannabinoid action. The objective of this proposal is to determine if CaSR is an important pathway in the action of cannabinoids and whether brain CaSR is activated directly by cannabinoids. We are ideally suited to perform this project because of our expertise in CaSR function in nerve terminals and expression systems. Successful completion of these specific aims will characterize the response of CaSR to cannabinoids, shedding light on the broader range of influence of CaSR and substantially change the thinking in this field. Our rationale is that the identification and characterization of a novel and prevalent cannabinoid receptor will facilitate our understanding of the behavioral actions of the commonly used drug cannabis. Moreover, distinguishing the various actions of cannabinoids may translate into the identification of a novel class of drugs that facilitate treatment of cannabis addiction and several neurological diseases.

? DESCRIPTION (provided by applicant): The major technological and analytical advances in human brain imaging achieved as part of the Human Connectome Projects (HCP) enable examination of structural and functional brain connectivity at unprecedented levels of spatial and temporal resolution. This information is proving crucial to our understanding of normative variation in adult brain connectivity. It is now timely to use the tools and analytical approaches developed by the HCP to understand how structural and functional wiring of the brain develops. Using state-of-the art HCP imaging approaches will allow investigators to push our currently limited understanding of normative brain development to new levels. This knowledge will critically inform prevention and intervention efforts targeting well known public health concerns (e.g., neurological and psychiatric disorders, poverty). The majority of developmental connectivity studies to date have used fairly coarse resolution, have not been multi-modal in nature, and few studies have used comparable methods to assess individuals across a sufficiently wide age range to truly capture developmental processes (e.g., early childhood through adolescence). Here we propose a consortium of five sites (Harvard, Oxford, UCLA, University of Minnesota, Washington University), with extensive complimentary expertise in brain imaging and neural development, including many of the investigators from the adult and pilot lifespan HCP efforts. Our synergistic integration of advances from the HARVARD-MGH and WU-MINN-OXFORD HCPs with cutting edge expertise in child and adolescent brain development will enable major advances in our understanding of the normative development of human brain connectivity. The resultant unique resource will provide rich, multimodal data on several biological and cognitive constructs that are of critical importance to health and well-being across this age range and allow a wide range of investigators in the community to gain new insights about brain development and connectivity. Aim 1 will be to optimize existing HCP Lifespan Pilot project protocols on the widely available Prisma platform to respect practical constraints in studying healthy children and adolescents over a wide age range and will also collect a matched set of data on the original Skyra and proposed Prisma HCP protocols to serve as a linchpin between the past and present efforts. Aim 2 will be to collect 1500 high quality neuroimaging and associated behavioral datasets on healthy children and adolescents in the age range of 5-21, using matched protocols across sites, enabling robust characterization of age-related changes in network properties including connectivity, network integrity, response properties during tasks, and behavior. Aim 3 will be to collect and analyze longitudinal subsamples, task, and phenotypic measures that constitute intensive sub-studies of inflection points of health-relevant behavioral changes within specific developmental phases. Aim 4 will capitalize on our success in sharing data in the HCP, and use established tools, platforms and procedures to make all data publically available through the Connectome Coordinating Facility (CCF).

? DESCRIPTION (provided by applicant): The major technological and analytical advances in human brain imaging achieved as part of the Human Connectome Projects (HCP) enable examination of structural and functional brain connectivity at unprecedented levels of spatial and temporal resolution. This information is proving invaluable for enhancing our understanding of normative variation in young adult brain connectivity. It is now timely to use the tools and analytical approaches developed by the HCP to understand how structural and functional wiring of the brain changes during the aging process. Using state-of-the art HCP imaging approaches will allow investigators to push our currently limited understanding of normative brain aging to new levels. We propose an effort involving a consortium of five sites (Massachusetts General Hospital, University of California at Los Angeles, University of Minnesota, Washington University in St. Louis, and Oxford University), with extensive complementary expertise in human brain imaging and aging and including many investigators associated with the original adult and pilot lifespan HCP efforts. This synergistic integration of advances from the MGH and WU-MINN-OXFORD HCPs with cutting-edge expertise in aging provides an unprecedented opportunity to advance our understanding of the normative changes in human brain connectivity with aging. Aim 1 will be to optimize existing HCP Lifespan Pilot project protocols to respect practical constraints in studying adults over a wide age range, including the very old (80+ years). Aim 2 will be to collect high quality neuroimaging, behavioral, and other datasets on 1200 individuals in the age range of 36 - 100+ years, using matched protocols across sites. This will enable robust cross-sectional analyses of age-related changes in network properties including metrics of connectivity, network integrity, response properties during tasks, and behavior. Aim 3 will be to collect and analyze longitudinal data on a subset of 300 individuals in three understudied and scientifically interesting groups: ages 36-44 (when late maturational and early aging processes may co-occur); ages 45-59 (perimenopausal, when rapid hormonal changes can affect cognition and the brain); and ages 80 - 100+ (the `very old', whose brains may reflect a `healthy survivor' state). The information gained relating to these important periods will enhance our understanding of how important phenomena such as hormonal changes affect the brain and will provide insights into factors that enable cognitively intact function into advanced aging. Aim 4 will capitalize on our success in sharing data in the Human Connectome Project (HCP), and will use these established tools, platforms, and procedures to make this data publicly available through the Connectome Coordination Facility.

Voltage-gated sodium channels (VGSCs) are essential for action potential generation. Furthermore, drugs that directly target VGSCs are widely used to treat common diseases, such as pain, mood disorders, muscle spasms, seizures, and cardiac arrhythmias. However, side effects arise because of the widespread distribution of VGSCs and cross-sensitivity of the various VGSC subtypes to blockers. In addition, these drugs are not completely effective, underlining a substantial need for new drugs that target VGSCs. This has motivated us to identify and characterize new mechanisms by which VGSC function can be regulated. Regulation of voltage- gated ion channel function is an important pathway by which neuronal signaling and brain function is regulated, and G-protein coupled receptors (GPCRs) form a major element of the endogenous transduction mechanisms by which this occurs. However, unlike other ion channels, VGSCs have been assumed to be relatively insensitive to modulation by GPCR signaling. We have recently identified a pathway that is modulated by agents known to interact with the CaSR (calcium-sensing receptor). This pathway is widespread, present in the vast majority of neocortical neurons, and strong enough to completely and reversibly block VGSC currents when maximally stimulated. This novel, dynamic signaling pathway is positioned to substantially modulate neuronal excitability and brain function. Detailed knowledge about the underlying mechanisms is crucial to understand its many effects. The objectives of this proposal are to determine how CaSR modulators regulate VGSCs. Using a combination of electrophysiology and unbiased biochemical approaches we will identify the receptors mediating the inhibition of VGSC currents, measure the relative sensitivity to block of different VGSC isoforms, and determine if the pathway differentially regulates action potentials at nerve terminals and soma. These specific aims will test the hypothesis that CaSR modulators actions via VGSCs represent important new pathways for modulating neuronal excitability. We are ideally suited to perform this project because of our preliminary data and expertise. Our rationale is that the identification and characterization of a novel and prevalent receptor(s) and downstream pathway will facilitate our understanding of a prevalent and potentially powerful neurobiological signaling pathway. Successful completion of these specific aims will characterize new drug targets and eventually will lead to new therapeutics to improve control of pain, seizures, muscle spasm, and arrhythmias.

PROJECT SUMMARY Voltage-gated sodium channels (VGSCs) are essential for action potential generation. Furthermore, drugs that directly target VGSCs are widely used to treat common diseases, such as pain, mood disorders, muscle spasms, seizures, and cardiac arrhythmias. However, side effects arise because of the widespread distribution of VGSCs and cross-sensitivity of the various VGSC subtypes to blockers. In addition, these drugs are not completely effective, underlining a substantial need for new drugs that target VGSCs. This has motivated us to identify and characterize new mechanisms by which VGSC function can be regulated. Regulation of voltage- gated ion channel function is an important pathway by which neuronal signaling and brain function is regulated, and G-protein coupled receptors (GPCRs) form a major element of the endogenous transduction mechanisms by which this occurs. However, unlike other ion channels, VGSCs have been assumed to be relatively insensitive to modulation by GPCR signaling. We have recently identified a pathway that is modulated by agents known to interact with the CaSR (calcium-sensing receptor). This pathway is widespread, present in the vast majority of neocortical neurons, and strong enough to completely and reversibly block VGSC currents when maximally stimulated. This novel, dynamic signaling pathway is positioned to substantially modulate neuronal excitability and brain function. Detailed knowledge about the underlying mechanisms is crucial to understand its many effects. The objectives of this proposal are to determine how CaSR modulators regulate VGSCs. Using a combination of electrophysiology and unbiased biochemical approaches we will identify the receptors mediating the inhibition of VGSC currents, measure the relative sensitivity to block of different VGSC isoforms, and determine if the pathway differentially regulates action potentials at nerve terminals and soma. These specific aims will test the hypothesis that CaSR modulators actions via VGSCs represent important new pathways for modulating neuronal excitability. We are ideally suited to perform this project because of our preliminary data and expertise. Our rationale is that the identification and characterization of a novel and prevalent receptor(s) and downstream pathway will facilitate our understanding of a prevalent and potentially powerful neurobiological signaling pathway. Successful completion of these specific aims will characterize new drug targets and eventually will lead to new therapeutics to improve control of pain, seizures, muscle spasm, and arrhythmias.