? A major goal in neuroscience is to understand the formation and development of synapses, the tiny membrane specializations that enable nerve cells to communicate with each other. The sequence of molecular signals leading to synapse formation (""""""""synaptogenesis"""""""") is qualitatively well known for the more accessible neuromuscular synapse. It is well established that, immediately after contacting the muscle cell, the nerve terminal secretes agrin to induce the clustering of acetylcholine (ACh) receptors at the postsynaptic site. After a cascade of events, the nerve is able to depolarize the muscle cell by releasing pulses of ACh. However, very little is known of the quantities (concentration, duration, onset, etc.) of the various neurochemical signals involved in synaptogenesis. Importantly, all except for one of the axons innervating a given myotube at birth retract after a period of a week or so according to a synaptic competition process that remains, for lack of quantitative methods, poorly understood. Such quantitative description is lacking because present experimental setups for the study of the neuromuscular junction do not allow for a precise control over the many variables involved in synaptogenesis. Therefore, we propose a quantitative approach based on substituting the presynaptic neuron by an artificial mimic, a nanofluidic device that will stimulate the muscle cell in a physiologically relevant way. We hypothesize that the focal delivery of synaptogenic factors will recruit the synaptic machinery to the stimulated area of the membrane. The device will consist of a set of microfluidic channels buried underneath the cell culture surface and that will """"""""communicate"""""""" with the cells through nanoholes. The cells will be sealed to the holes by applying suction to the microchannels. Unlike present experimental setups, our device will allow us to 1) confine the delivery of agrin/ACh to a submicron-diameter area of the cell membrane (as occurs in vivo); 2) interrogate the same area of the membrane with different factors sequentially; 3) stimulate several locations of the same cell simultaneously (with the same or dissimilar stimuli); and 4) experiment with high throughput (i.e. investigate large numbers of cells and stimulation conditions simultaneously). The proposed device has broad applicability to cell culture studies requiring nanometer-scale, focal exposure of the cells to a soluble factor. ? ?
