Counting quanta: direct measurements of transmitter release at a central synapse.

Contradictory hypotheses regarding the nature of synaptic transmission in the CNS have arisen from indirect methods of quantal analysis. In this study, we directly count the quanta released following nerve stimulation to examine synaptic transmission at a fast glutamatergic synapse in the mammalian auditory brainstem. Our results demonstrate the relationship between spontaneous and nerve-evoked synaptic events, indicate that asynchronous transmitter release governs the time course of evoked transmission, and show that the stochastic quantal release process, as originally proposed at the neuromuscular junction, is highly conserved at this central synapse.