Assessment of Synaptic Function During Short-Term Facilitation in Motor Nerve Terminals in the Crayfish

Abstract

An enhanced buildup of [Ca 2+ ] i occurs during short-term facilitation (STF) at the crayfish neuromuscular junction (NMJ). As a model system, this NMJ allows discrete postsynaptic quantal events to be counted and characterized in relation to STF. Providing 10 pulses, at 20 and 40Hz, we monitored postsynaptic quantal events over a discrete region of a nerve terminal with a focal macropatch electrode. Characteristics of quantal events were clustered into groups by peak amplitude and time to the peak amplitude. Since the synapses at this NMJ have varied spacing of active zones, number of active zones and synaptic size, the graded nature of synaptic recruitment is likely one means of titrating synaptic efficacy for the graded depolarization on the non-spiking muscle fiber. Synapses in this preparation would appear to have a "quantal signature" that can be used for quantifying their activity which is useful in estimating the overall number of active sites. We use mixture modeling to estimate n (number of active sites) and p (probability of vesicle fusion) from the quantal characteristics. In a preparation that was stimulated at 40Hz, synapses were recruited (increase in n) and the number active synapses increased in p. In a different preparation, p increased as the stimulation was changed from 20 to 40Hz, but n did not show a substantial increase; however, during the STF train, p increases slightly. This study provides a novel approach in determining subsets of the single evoked quanta to better estimate n and p which describe synaptic function. © Desai-Shah et al.; Licensee Bentham Open.This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

Effect of temperature change on synaptic transmission at crayfish neuromuscular junctions

“…This may suggest that lower temperature disrupts the calcium influx in the presynaptic terminal. Therefore, with longer trains of stimulation, more calcium could accumulate in the presynaptic terminals to result in more vesicle fusion events (Cooper et al, 1995; Desai-Shah et al, 2008). We had assumed that the nerve may have failed in being evoked at colder temperature, as occurs in squid axons (Prosser and Nelson, 1981; Weight and Erulkar, 1976), but upon a higher stimulation frequency or with the addition of 5-HT or OA, the EPSPs would increase to measurable levels.…”

Different mechanisms of Ca2+ regulation that influence synaptic transmission: Comparison between crayfish and Drosophila neuromuscular junctions

“…Some of the experimental protocols for the crayfish NMJ are reported in Desai-Shah et al, (2008). All experiments were performed using the first and second walking legs of freshly obtained crayfish, Procambarus clarkii, measuring 6-10 cm in body length (Atchafalaya Biological Supply Co., Raceland, LA).…”

“…Currently, we are investigating the regulation of STF by NCX, PMCA and SERCA in the crayfish NMJ during STF . Using quantal analysis, we have already shown a role of STF on synaptic efficacy in crayfish NMJ (Desai-Shah et al, 2008). In this report herein, our goal was to compare and contrast the Drosophila NMJ using similar experimental paradigms and pharmacological approaches, but in addition, using a mutational strain to compromise SERCA to compare pharmacological approaches.…”