Bennett M R, Farnell L, Gibson W G
Department of Physiology, University of Sydney, New South Wales, Australia.
Proc Biol Sci. 1998 Feb 22;265(1393):271-7. doi: 10.1098/rspb.1998.0292.
The histograms of spontaneous synaptic potentials at synapses in autonomic 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 transmitter. A single unit of acetylcholine of fixed size, released from an active 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 release is from an active zone onto either the receptor patch beneath, or in addition onto adjacent patches, then the histogram is well described by a mixture of Gaussians. However, this explanation is unlikely to be correct as present evidence suggests that in most cases the released unit of transmitter saturates the postsynaptic receptor patch beneath the active zone. The final case considered is where a unit of transmitter is spontaneously released from an active zone, simultaneously with a unit in an adjacent zone less than one micron away. The histogram 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 of spontaneous potentials that are mixtures of Gaussians.
自主神经节中突触处自发突触电位的直方图是由高斯混合分布描述的，而不是单一的高斯分布。利用递质自发释放单元作用的蒙特卡罗模拟，研究了这些混合分布的可能起源。从一个有源区释放出的固定大小的单个乙酰胆碱单元，其下方和相邻位置都有受体斑块，并不会产生观察到的直方图。但是，如果该单元大小可变，由较小单元的整数倍组成，并且从有源区释放到下方的受体斑块上，或者还释放到相邻斑块上，那么直方图就可以用高斯混合分布很好地描述。然而，这种解释不太可能正确，因为目前的证据表明，在大多数情况下，释放出的递质单元会使有源区下方的突触后受体斑块饱和。最后考虑的情况是，一个递质单元从一个有源区自发释放，同时一个相邻区域（距离小于一微米）的单元也自发释放。即使受体斑块大小存在差异，此时的电位直方图也与观察到的直方图相符。有人提出，这种释放方式可以解释自发电位的高斯混合分布。
