Synapses are specialized sites of cell-cell contact that mediate communication between neurons in the nervous system. It is now widely believed that aberrant development or function of either excitatory or inhibitory synapses contributes to neurological impairments such as mental retardation, autism spectrum disorders and epilepsy. To understand how synapse dysfunction underlies these neurological disorders, it is paramount that we discover how synapses form and function in the non-perturbed state. The NIH-sponsored research of the five investigators in the user group is specifically focused on this research goal: understanding how synaptic connections are formed, modified, and maintained in the nervous system of a variety of experimental organisms. Projects include: mechanisms of synapse formation in the central and peripheral nervous system, neuromodulation, and the regulation of intrinsic excitability. Array tomography is a novel imaging modality that represents a new approach to high resolution imaging of synaptic structure in intact nervous systems. The Zeiss Axio Imager Z2 fluorescence imaging system that we propose to purchase will allow this user group to study synaptic structure and function at an unprecedented resolution using an innovative sectioning and reconstruction strategy devised by Dr. Stephen Smith and colleagues at Stanford University. Traditional immunohistochemsitry using antibodies against synaptic markers on brain tissue sections yields poor resolution of synaptic puncta due to antibody penetration problems in relatively thick tissue sections (e.g. 255m) and limited resolution along the Z axis during imaging, even when employing confocal microscopy. Array tomography circumvents these issues by antibody staining of ultrathin cryosections (e.g. 70nm) of nervous system tissue. There are numerous additional benefits to utilizing array tomography over traditional immunohistochemistry including the possibility of obtaining ultrastructural information from the tissue using scanning electron microscopy after immunofluorescence imaging and, perhaps most importantly for our purposes, the ability to perform multiple rounds of antibody staining of the same tissue section. As the position of the tissue is fixed on the slide, repeated staining with different antibodies against synaptic proteins will allow cataloging of which synaptic components are present or absent at all of the synapses in a single neuron. All five investigators in the user group have reached the limit of what can be achieved in assaying synapse morphology and function with traditional immunofluorescence methods. Thus, it is critical to furthering the research mission of these groups that the array tomography imaging technology be available on the Brandeis campus. PUBLIC HEALTH RELEVANCE: Numerous studies now point to defects in synapse formation as a possible cause for neurological disorders such as autism, mental retardation, and epilepsy. One approach to understanding how aberrant synapse formation contributes to these widespread neurological impairments is to first investigate how synapses are formed, maintained, and function in the non-pathological state using light microscopy. Acquisition of the Zeiss Axioimager Z2 System for Array Tomography will allow for unprecedented high-resolution imaging of synapses from the nervous system of a variety of experimental organisms.