Hippocampal synapses: do they talk to their neighbours?

Recent experimental findings show that fast synaptic transmission can exten d its actions beyond the immediate synaptic cleft. Whether this phenomenon results in significant crosstalk between typical neighbouring synapses rema ins unclear. This article considers two areas of the hippocampus, the CAI a nd dentate gyrus, where important neural processing occurs. The results dis cussed do not provide a simple answer to the question of whether synapses c an 'talk' to their neighbours, hut they do reveal crucial physiological con straints that determine the significance of synaptic crosstalk, thus adding considerably to our understanding of chemical synaptic transmission.