Advanced tracer techniques to monitor synaptic activity.

The two approaches presented here bypass postsynaptic receptors as indicators of quantal release, and thus they can provide information which is clearly distinct from that obtained with standard electrophysiological techniques. Indeed, the inherently variable responsiveness of the postsynaptic membrane makes it an unreliable indicator of presynaptic activity and this has fueled a lot of controversy, particularly in the area of synaptic plasticity. A major advantage of these two methods is their ability to detect changes at the single bouton level. This offers a lot of advantages including the possibility to study the functional role for exo-endocytosis but also plasticity against a background of great variability among a large number of synapses. The spatial resolving power of FM1-43 and anti-synaptotagmin antibodies may be valuable in future studies of spread of LTP between neighboring synapses and in the mapping the pattern of neuronal activity in complex networks of neurons.