Motor nerve terminals on abdominal muscles in larval flesh flies,Sarcophaga bullata: Comparisons withDrosophila

Abstract

Motor nerve terminals on abdominal body-wall muscles 6A and 7A in larval flesh flies were investigated to establish their general structural features with confocal microscopy, transmission electron microscopy, and freeze-fracture procedures. As in Drosophila and other dipterans, two motor axons supply these muscles, and two morphologically different terminals were discerned with confocal microscopy: thin terminals with relatively small varicosities (Type Is), and thicker terminals with larger varicosities (Type Ib). In serial electron micrographs, Type Ib terminals were distinguished from Type Is terminals by their larger cross-sectional area, more extensive subsynaptic reticulum, more mitochondrial profiles, and more clear synaptic vesicles. Type Ib terminals possessed larger synapses and more synaptic contact area per unit terminal length. Although presynaptic dense bars of active zones were similar in mean length for the two terminal types, there were almost twice as many dense bars per synapse for Type Ib terminals. Freeze-fractures through the presynaptic membrane showed particle-free areas indicative of synapses on the P-face, within which were localized aggregations of large intramembranous particles indicative of active zones. These particles were similar in number to those found at active zones of several other arthropod neuromuscular junctions. In general, synaptic structural parameters strongly paralleled those of the anatomically homologous muscles in Drosophila melanogaster. In live preparations, simultaneous focal recording from identified varicosities and intracellular recording indicated that the two terminals produced excitatory junction potentials of similar amplitude in a physiological solution similar to that used for Drosophila.

Modification of a Hydrophobic Layer by a Point Mutation in Syntaxin 1A Regulates the Rate of Synaptic Vesicle Fusion

“…Because the average mini amplitude was not significantly different between the mutant and the wild type ( p > 0.1), this increase in EPSP amplitude most likely reflected an enhancement in presynaptic release. Factoring in the respective average mini amplitude in these flies and after correction of EPSP amplitudes for nonlinear summation [45,46], there was a 2-fold increase in quantal content from 40.0 ( n = 8) in the wild type to 79.9 ( n = 11) in the mutant (Figure 7F; p < 0.001). As with the mini measurement, there was no difference in resting potentials of the muscle fiber between the wild type and the mutant.…”

“…In this case, minis were analyzed following an EPSP after the membrane potential had returned to pre-stimulation levels. Quantal content was determined as the ratio of the average EPSP amplitude and the average mini amplitude after correction of EPSP amplitude for nonlinear summation following the methods described by Stevens (1976) [45] and Feeney et al (1998) [46]. Corrected EPSP amplitude = E{Ln[E/(E − recorded EPSP)]}, where E = difference between reversal potential and resting potential.…”

“…Corrected EPSP amplitude = E{Ln[E/(E − recorded EPSP)]}, where E = difference between reversal potential and resting potential. The reversal potential used in this correction was 0 mV [46]. For simplicity, the average amplitude of EPSPs presented in Figures 9F, 10B, and 10D was not corrected for nonlinear summation.…”

Syncrip/hnRNP Q influences synaptic transmission and regulates BMP signaling at the Drosophila neuromuscular synapse

“…Spontaneous release was analyzed using the Mini Analysis Program (Synaptosoft Inc., Decatur, GA). Evoked EJP amplitude was corrected by using nonlinear summation (McLachlan and Martin, 1981; Feeney et al, 1998). The quantal content of evoked release was calculated from individual muscle by ratio of the averaged EJP and averaged mEJP amplitude.…”

Active zone assembly and synaptic release

“…The active zones of Drosophila synapses often display electron-dense T-shaped bodies (T-bars), which have been proposed to participate in the tethering of vesicles [16] to direct them to sites of exocytosis at the base of the T-bar [7]. It was recently demonstrated that a protein called Bruchpilot is an integral component of Drosophila active zones [17,18].…”