scramb1Δ38/scramb2Δ57 double mutant larval neuromuscular junctions exhibit a significant increase in the number of synaptic vesicles and more vesicles docked at the active zone. The single mutants, on the other hand, do not show significant changes in the ultrastructure of neuromuscular junctions, except that there are more than one docked vesicle at the active zone of most of the type 1b boutons examined.
The rate of reserve pool recruitment of synaptic vesicles is markedly enhanced in scramb1Δ38/scramb2Δ57 double mutant boutons, as indicated by a significantly faster rate of fluorescence brightness decline. The extent of fluorescence decline induced by a 5-min stimulation of the nerve at 0.5Hz in the double mutant is also significantly enhanced relative to control. These results reveal that reserve pool recruitment in double-mutant synapse is abnormally enhanced.
Reserve pool recruitment of synaptic vesicles in scramb1Δ38/scramb2Δ57 double mutant larvae is rescued to control levels through the expression of scramb1Scer\UAS.cAa under the control of Scer\GAL4Act.