ON THE ORIGIN OF SKEWED DISTRIBUTIONS OF SPONTANEOUS SYNAPTIC POTENTIALS IN AUTONOMIC GANGLIA

The histograms of spontaneous synaptic potentials at synapses in auton omic ganglia are described by distributions consisting of mixtures of Gaussians, rather than by single Gaussian distributions. The possible origin of these mixed distributions is investigated, using Monte-Carlo simulations of the action of spontaneously released units of transmit ter. A single unit of acetylcholine of fixed size, released from an ac tive zone with receptor patches both beneath and adjacent to the zone, does not give rise to the observed histograms. But if the unit is of variable size, consisting of integer multiples of smaller units, and r elease is from an active zone onto either the receptor patch beneath, or in addition onto adjacent patches, then the histogram is well descr ibed by a mixture of Gaussians. However, this explanation is unlikely to be correct as present evidence suggests that in most cases the rele ased unit of transmitter saturates the postsynaptic receptor patch ben eath the active zone. The final case considered is where a unit of tra nsmitter is spontaneously released from an active zone, simultaneously with a unit in an adjacent zone less than one micron away. The histog ram of potentials then conforms to those observed even when there are differences in the sizes of the receptor patches. It is suggested that this kind of release could provide an explanation for distributions o f spontaneous potentials that are mixtures of Gaussians.