Short Term Memory May Be the Depletion of the Readily Releasable Pool of Presynaptic Neurotransmitter Vesicles

Table 1. Time constants used to fit the RRP endocytosis curves of the various articles.

The correct functional form of the endocytosis curve can presumably be derived from the
findings of (22). They found that single vesicle endocytosis occurs with a decaying exponential
with the time constant of 56 ms (in young rat calyx of Held). When three or more vesicle were
fused per active zone (with roughly 600 active zones in the calyx) then each vesicle added about
1900 ms to the time constant (22) fitted 1700 ms). If each active zone releases the same number
of vesicles then the ensuing endocytosis is a sum of two exponentials - the fast 56 ms for the first
two vesicles and then a slow 1900*(number of vesicles) ms time constant for the subsequent
vesicles. In Figure 13 I show the experimental data from (18) and compare it with the predicted
data from a normal distribution causing an average of two vesicles to release per active zone with
a standard deviation of 1 vesicle per active zone. The overlap is excellent. I inquired into what
change in parameters would cause the calyx curve to coincide with the memory decay curve from
Figure 9. One possibility is to increase the 1.9 second multiplicative time constant to 100
seconds*(number of vesicles), another one is to increase the number of vesicles per active zone
or increasing the average number of vesicles released after an action potential train.

13

<<   10   11   12   13   14   15   16   >>

More intriguing information