Journal of Neurophysiology, Vol 60, Issue 6 2211-2222, Copyright © 1988 by APS
The development of transmission at an identified molluscan synapse. II. A quantal analysis of transmission
P. A. Pawson and R. Chase
Department of Biology, McGill University, Montreal, Quebec, Canada.
1. A quantal analysis of transmission at the identified molluscan synapse,
V2-RPr1, was performed during development. The study was intended to
determine the pre- and postsynaptic contributions to the marked changes in
transmitter release described in the previous report. 2. The success of the
quantal analysis was predicated on overcoming the problems associated with
extending the quantal analysis technique to central synapses. This involved
adopting the following strategies: 1) using a low-noise recording system
coupled with electrical filtering; 2) establishing objective criteria for
failures recognition; and 3) using three methods to determine the quantal
content: amplitude histograms, failures analysis, and the coefficient of
variation. 3. The correlation of the results obtained from an analysis of
amplitude histograms and from failures analysis were highly significant (P
less than 0.01) at all times studied. A similar significant correlation was
observed between the failures method and the coefficient of variation
methods. 4. The amplitude of the quantal unit declined progressively during
development (range: 131-25 microV), in parallel with the decrease in the
postsynaptic input resistance (range: 103-5 M omega). 5. At both
frequencies of stimulation (0.02 and 0.2 Hz), there is an approximately
20-fold increase in quantal content over the period of the study. Frequency
facilitation at the synapse is due to an increase in quantal content. 6.
Possible structural correlates for the developmental increase in quantal
content were discussed.
