Expression of Nrg^180ΔC in a Nrg^l4 mutant background results in a significant increase in synaptic retraction in third instar larvae compared to controls. NMJ length is increased compared to controls. NMJ length and bouton number are increased compared to controls. The bouton area is significantly reduced compared to controls.

Flies expressing Nrg^180ΔC in a Nrg^l4 mutant background are unable to establish a normal function of the Giant Fibre (GF)-Trochanteral Muscle (TTMn) circuit; there are significant increases in average response latencies and a decrease in following frequencies after a train of stimulations at 100 Hz when compared to wild type. Morphological defects are seen at GF terminals. The GFs are present at the synaptic target area, however large areas of the synaptic terminals are either thinner or swollen and often contain large vacuole-like structures. Synaptic gap junctions are still present in animals that do not show any functional response.