Mutants show a 35% reduction in the number of type Ib boutons/muscle surface area at the neuromuscular junction (NMJ) compared to controls. There is also an increased frequency of extra large and irregularly shaped boutons at the mutant NMJs compared to controls. Ultrastructurally, synaptic contacts at mutant boutons appear largely normal with respect to electron density and the presence of presynaptic T-bars. The length of individual electron dense zones observed on single sections of mutant boutons is mostly within the range seen in controls. However, tightly juxtaposed electron dense zones are frequently observed on sections of mutant boutons. The mean surface area of receptor fields is considerably increase in homozygous and hemizygous mutants compared to controls.

The frequency and amplitude of spontaneous miniature excitatory junctional currents at the mutant neuromuscular junction is not significantly different from that of controls. The amplitude of excitatory junctional currents evoked by low-frequency stimulation of motoneurons is not significantly different from that of controls.