Esyt2¹/Esyt2^MB02922 third instar larvae do not display any significant differences in the number of synaptic boutons, nor the number or density of active zones at neuromuscular junction relative to controls. No differences in the frequency or amplitude of miniature excitatory postsynaptic currents (mEPSCs) in abdominal muscles of the mutant larvae are observed in either low (0.4 mM) or high (3 mM) extracellular Ca[2+] concentrations, but the amplitude of the excitatory postsynaptic currents is about halved (with a concomitant decrease in quantal content) compared to wild-type at both low and high Ca[2+]. The mutants also exhibit defects in short-term synaptic plasticity: at 0.4 mM Ca[2+] they show enhanced facilitation and at 3 mM Ca[2+] reduced depression relative to controls. However, Esyt2¹/Esyt2^MB02922 larvae show similar rate of vesicle pool depletion during high frequency (10Hz) stimulation as controls as well as comparable pool recovery rate. No significant change in the density or distribution of synaptic vesicles within NMJ boutons is observed in these larvae and active zone length as well as T-bar morphology is also normal.