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

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.

Genetic Analysis of SolubleN-Ethylmaleimide-Sensitive Factor Attachment Protein Function inDrosophilaReveals Positive and Negative Secretory Roles

“…Average EJP amplitude was calculated from a minimum of 10 EJPs evoked at 0.1 Hz from each cell. EJPs were corrected for nonlinear summation using the procedure of McLachlan and Martin (1981), as adapted by Feeney et al (1998). Average miniature EJP (mEJP amplitude) was calculated from a minimum of 40 mEJPs from each cell.…”

Transmission, Development, and Plasticity of Synapses

“…The CAZ of Drosophila synapses is readily identifiable by EM as a T-bar structure ( Figure 1A) (Feeney et al 1998). EM tomography provides a detailed picture of CAZ ultrastructure.…”

“…Each varicosity (termed a synaptic bouton) contains spatially segregated active zones (AZs) that reside opposite a distinct cluster of glutamate receptors (GluRs) on the postsynaptic muscle surface ( Figure 1A). AZs are readily identifiable by electron microscopy (EM) as electron-dense T-bar structures (Feeney et al 1998) (Figure 1A). The precise matching of AZ to GluR cluster has allowed optical imaging of synaptic vesicle (SV) release at individual release sites at the fly NMJ (Peled and Isacoff 2011;Melom et al 2013), yielding an experimental system that offers unprecedented tools for analyzing how synaptic transmission is organized and regulated at individual AZs.…”

Characterization of development, behavior and neuromuscular physiology in the phorid fly, Megaselia scalaris

“…The terminals of the Ib and Is motor neurons are well known in structure and function in D. melanogaster and for a species of flesh fly, Sarcophaga bullata (Feeney et al, 1998), so we chose to investigate these two motor nerves on muscle six within the 4th abdominal segment in M. scalaris for comparative physiological purposes. The Ib axon produces smaller EPSPs than the Is axon in both M. scalaris and D. melanogaster.…”