There has been a revolution in optical methods that now make it possible to peer into the brain and monitor its function. However, optical methods for measuring the strength of individual synapses have been lacking. The availability of such a method would revolutionize our ability to monitor single synapses and make it possible, by optical methods, to detect and monitor the changes in synaptic strength that underlie learning and memory. We propose to adapt modern technologies to improve methods for imaging [Na+]i changes in small neuronal compartments like dendritic spines. These improvements will include using LED light sources and fast CCD cameras to improve the detection of small rapid fluorescence changes and the use of a new generation of more sensitive sodium indicator dyes. We will also use several techniques to separate spine signals from dendrite signals without the need for a 2- photon microscope system. These spine localized sodium fluorescence signals can be interpreted as reflecting synaptically activated Na+ currents. Measuring these currents will reveal information about the receptor types involved in synaptic signaling at individual synaptic sites. We will also measure how these signals change following stimulation protocols related to synaptic plasticity.
This project will improve techniques to image synaptically activated sodium concentration changes in dendrites. We will optimize the technique to observe signals in individual spines in pyramidal neurons from the rat hippocampus. These optical signals can be interpreted in terms of the strength of synaptic connections between neurons and the kinds of receptors in the spines. Information about synaptic strength is relevant for understanding plastic changes in brain circuits and therefore important for understanding the cellular mechanisms underlying learning and memory and several pathological conditions including Alzheimer's disease, schizophrenia and depression.