Expression of Nrg^180YF in a Nrg^l4 mutant background does not result in a significant increase in synaptic retraction in third instar larvae compared to controls. NMJ length and bouton number are slightly increased compared to controls. The bouton area is not significantly different from controls.

Flies expressing Nrg^180YF 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.