Erin M. Schuman - US grants

Understanding the cellular basis of learning and memory formation in the brain will lead to drug interventions that can ameliorate the memory loss associated with many modern diseases. Long-term potentiation (LTP) in the hippocampus, a brain structure known to be important for human memory formation, involves long-lasting increases in synaptic efficacy which are thought to form the basis of memory storage in the brain. The cellular events that initiate LTP occur in the postsynaptic neuron. In contrast, the longer lasting phases of LTP appear to involve alterations in presynaptic neurotransmitter release, leading to the requirement for a retrograde signal which travels from postsynaptic to presynaptic cells during the initiation of LTP. The main objective of this proposal is to further our understanding of how 3 different putative retrograde molecules function in synaptic transmission and plasticity in the hippocampus. One goal of this study is to characterize the mechanisms by which the recently identified neural messenger nitric oxide (NO), and 2 other diffusible signals, carbon monoxide and arachidonic acid, regulate synaptic transmission and plasticity in the hippocampus. Another aim is to determine whether LTP induction results in the activity of a putative NO target, an ADP-ribosyltransferase. Studies are proposed to characterize NO-stimulated ADP-ribosylated proteins in the hippocampus and to assess their contributions to synaptic transmission and long-term potentiation. Finally, the existence of diffusible signals in the hippocampus predicts that many synapses near the site of signal generation may be influenced. Following from this idea, studies are proposed to characterize the spreading of synaptic potentiation that has been observed between synapses into neighboring CA1 pyramidal neurons.

DESCRIPTION (provided by applicant): The Gordon Research Conference on Neural Plasticity has been held in alternate years since 1977. We are requesting partial support for the Neural Plasticity Conference planned for July 15 to 20, 2001 at the Salve Regina University in Newport, RI. The Gordon Research Conferences were established to stimulate scientific interchange in an informal setting. Interchange is promoted by the informal nature of the conference, by the large amount of time committed to question and answer periods in the scientific sessions, and by the many opportunities for discussion in other settings, such as meals, poster sessions and structured and unstructured social activities. The Gordon Research Conference rule prohibiting publication or citation of the meetings and presentations promotes open discussion of the latest results and current ideas. This format has been particularly useful for the Conference on Neural Plasticity, a highly interdisciplinary meeting in which the subject of modifiability of the nervous system is explored at molecular, cellular, systems, and computational levels. The 2001 Conference will have 9 scientific sessions and a keynote talk by Dr. Richard Morris, a scientist at the forefront of learning and memory. The scientific sessions will cover a range of topics of current interest in Neural Plasticity, from protein trafficking during plasticity to brain circuits modified by reward systems. The speakers and session chairs are all world leaders in their fields. Full participation by conference attendees is encouraged in several ways. Afternoon poster sessions provide an opportunity for all interested participants to present and discuss their work. Each scientific session will include, in addition to the scheduled speakers, one or 2 short talks by junior participants, selected from the submitted abstracts. This is something that worked very well, and was highly rated by conference participants in 1999. Question and answer periods are generously scheduled. Social events permit new participants to meet speakers and chairs informally. The beautiful environment provided by the Salve Regina campus is an attractant for speakers and participants to linger long after the end of each session. Past participants have found these informal interactions to be the distinct advantage of the Gordon Conference, giving rise to a stimulating and productive meeting.

[unreadable] DESCRIPTION (provided by applicant): The pre-and post-synaptic elements of synaptic junctions are linked together by cell adhesion molecules: proteins that play crucial roles in stabilizing, signaling and adjusting the strength of the synapse. The cadherins, 1 type of adhesion molecule, link together 2 adjacent cell membranes by forming homodimers in 1 membrane that interact across the junction (synaptic cleft) with homodimers formed in the opposing cell membrane. In the last decade, much effort has been devoted to understanding the structure and molecular associations of the classic cadherins. Crystallographic and biophysical studies have yielded somewhat conflicting results and, as yet an unclear, picture of the interactions of the cadherin extracellular domain during dimerization. To better understand the dynamics of cadherin interactions we are developing Fluorescence Resonance Energy Transfer (FRET) based sensors to monitor cadherin associations across cellular junctions. FRET is unique in its ability to provide signals that are sensitive to changes in intra-or intermolecular distances in the 1-10 nm range, well below the inherent diffraction limit of conventional fluorescence microscopy. Cadherins will be fluorescently tagged in their extracellular domains; FRET-donor and FRET-acceptors will be expressed in pre-and postjunctional cells and the strength of adhesion will be monitored. It has long been known that and the structural integrity of cadherins is dependent on the local Ca2+ concentration. In the absence of Ca2+, cadherins undergo a reversible loss of their rod-like structure and collapse. Experimental data as well as simulations predict that Ca2+ is dynamically regulated in the synaptic cleft. We predict that alterations in cleft Ca2+ have important ramifications for cadherin-cadherin adhesion and signaling. We will use FRET to monitor dynamically, in living cells, cadherin interactions and conformational changes induced by changes in extracellular calcium and synaptic activity. By virtue of their localization at synaptic cleft and their interactions with cytoplasmic proteins, like beta-catenin, the cadherins occupy a pivotal position that can contribute to the synaptic dysfunction associated with disease. For example, in the absence of presenilin 1, a protein mutated in some forms of Alzheimer's disease, cadherins become destabilized at adherent junctions and fail to localize properly. This mislocalization presumably leads to profound alterations in synaptic structure and function. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): The pre-and post-synaptic elements of synaptic junctions are linked together by cell adhesion molecules: proteins that play crucial roles in stabilizing, signaling and adjusting the strength of the synapse. The cadherins, 1 type of adhesion molecule, link together 2 adjacent cell membranes by forming homodimers in 1 membrane that interact across the junction (synaptic cleft) with homodimers formed in the opposing cell membrane. In the last decade, much effort has been devoted to understanding the structure and molecular associations of the classic cadherins. Crystallographic and biophysical studies have yielded somewhat conflicting results and, as yet an unclear, picture of the interactions of the cadherin extracellular domain during dimerization. To better understand the dynamics of cadherin interactions we are developing Fluorescence Resonance Energy Transfer (FRET) based sensors to monitor cadherin associations across cellular junctions. FRET is unique in its ability to provide signals that are sensitive to changes in intra-or intermolecular distances in the 1-10 nm range, well below the inherent diffraction limit of conventional fluorescence microscopy. Cadherins will be fluorescently tagged in their extracellular domains; FRET-donor and FRET-acceptors will be expressed in pre-and postjunctional cells and the strength of adhesion will be monitored. It has long been known that and the structural integrity of cadherins is dependent on the local Ca2+ concentration. In the absence of Ca2+, cadherins undergo a reversible loss of their rod-like structure and collapse. Experimental data as well as simulations predict that Ca2+ is dynamically regulated in the synaptic cleft. We predict that alterations in cleft Ca2+ have important ramifications for cadherin-cadherin adhesion and signaling. We will use FRET to monitor dynamically, in living cells, cadherin interactions and conformational changes induced by changes in extracellular calcium and synaptic activity. By virtue of their localization at synaptic cleft and their interactions with cytoplasmic proteins, like beta-catenin, the cadherins occupy a pivotal position that can contribute to the synaptic dysfunction associated with disease. For example, in the absence of presenilin 1, a protein mutated in some forms of Alzheimer's disease, cadherins become destabilized at adherent junctions and fail to localize properly. This mislocalization presumably leads to profound alterations in synaptic structure and function. [unreadable] [unreadable]