Analysis of synaptic quantal depolarizations in smooth muscle using the wavelet transform

The time-frequency characteristics of synaptic potentials contain valuable information about the process of neurotransmission between nerves and their target organs. For example, at the synapse between autonomic nerves and sm ooth muscle, two central issues of neurophysiology, i,e., I) the probabilit y of ntiurotransmitter release and 2) the quantal behavior of transmission can be deduced from analysis of the rising phases of evoked excitatory junc tion potentials (eEJP's) recorded from smooth muscle. eEJP rising phases ar e marked by prominent inflexions, which reflect these Features of neuronal activity. Since these inflexions contain time-varying frequency information , we have applied recent techniques of time-frequency analysis based upon w avelet transforms to eEJP's recorded from the guinea-pig vas deferens ill v itro. We find that these techniques allow accurate and convenient character ization of neuronal release sites, and that their probability of release fa lls between 0.001-0,004, We have also analyzed eEJP's recorded in the prese nce of the chemical 1-heptanol, which reveals quantal depolarizations. Thes e results have helped clarify the nature of the quantal depolarizations tha t underly eEJP's. The present method offers significant advantages over tho se previously employed for these tasks, and holds promise as a novel approa ch to the analysis of synaptic potentials.