Membrane specialisations of the neuromuscular junction of the locust, Schistocerca gregaria

The ultrastructure of locust (Schistocerca gregaria) neuromuscular junctions as observed in freeze-fracture replicas is described and correlated with their appearance in thin sections of material prepared by various fixation regimes and by use of the sectioned replica technique. Two main specialisations are found at the junction. Postsynaptically there is a concentration of large intramembranous particles partitioning on fracturing with the E-face of the sarcolemma. These are associated with smaller, less defined subparticles thought to be proteinaceous projections seen in thin section. Presynaptically a raised row of particles is present on an elliptical plateau of the P-face of the nerve membrane, corresponding to a densely staining bar present in thin sections prepared using tannic acid and methylamine tungstate. These specialisations are found in both red and white fibres, indicating that the junctions are fast excitatory rather than inhibitory junctions. The bar-shaped particle array is not present 14 days after denervation. These specialisations are compared with those at synapses previously described and their possible function at a glutamatergic neuromuscular junction is discussed.