Mutants have smaller neuromuscular junctions than normal.

The neuromuscular junctions of Nlg1^H324/Nlg1^I960 larvae are smaller than normal. The average bouton number per muscle area and average number of boutons normalized to synaptic branch length are significantly reduced, and the average diameter of the largest bouton at a given neuromuscular junction is slightly but significantly increased in the mutants.

Ultrastructurally, presynaptic active zones are still formed in Nlg1^H324/Nlg1^I960 mutant boutons. The mutant active zones contain T-bars and clustered synaptic vesicles. The synaptic vesicles are present at approximately normal size and density, with large vesicle diameters in slightly higher numbers than normal. A subset of the mutant boutons show a reduction in thickness of the subsynaptic reticulum (SSR). The relative SSR area is significantly reduced in the mutant boutons compared to controls, and in extreme cases, boutons appear to be in "direct contact" with the contractile muscle filaments without being surrounded by SSR. Active zones are still present at locations lacking SSR and maintain the tight apposition of presynaptic and postsynaptic membranes. The number of membrane ruffles in active zones is strongly increased in the mutants, while the distance of these ruffles to the centre of the T-bar is unchanged.

The mean amplitude of the evoked excitatory junctional current (EJC) from neuromuscular junctions of Nlg1^H324/Nlg1^I960 third instar larvae is significantly reduced compared to controls at both 0.5mM and 1mM extracellular Ca[2+]. The mean amplitude of spontaneous miniature EJCs at the mutant neuromuscular junction is unchanged relative to wild type.