Structural characterization of peripheral nerve cells and nerve-muscle junctions of the oviduct of stable fly (Diptera: Muscidae)

Fine structure of both peripheral nerve cells and neuromuscular junctions associated with the oviduct of stable fly, Stomoxys calcitrans (L.), was described. Twelve or more multipolar peripheral neurons were found along major branch nerves that enter the ovipositor. Several were suspended in the haemacoel and others were in close proximity to the surface of tile oviduct. Some peripheral neurons contained an abundance of neurosecretory granules that ranged in size from 32 to 180 nm in diameter. No glial elements enveloped the perikarya of such cells. Neurosecretory axons were usually found in the boundary region of large nerves just beneath the stroma. Peripheral nerve cells in close apposition to oviduct muscles were generally non-neurosecretory and were ensheathed in a glial perineurium. Peripheral neurons were surrounded occasionally by an extensive network of extracellular spaces in the glial perineurium. Other smaller neurons were found within large nerve trunks. Nerve-muscle junctions contained large clusters of synaptic vesicles and occasionally included small groups of neurosecretory granules. Many nerve terminals on the surface of the oviduct contained a complex postsynaptic folding of sarcolemma. Active transmission sites were indicated by increased densities along the neurolemma. Some neurohemal release sites were also evident.