Ultrastructural identification of axons supplying the M. retractor phalli cranialis in chickens

The chicken m. retractor phalli cranialis classified as a smooth muscle was examined by electron microscopy to study the innervation of this muscle using the dichromate/chromate fixation method for demonstration of biogenic amines (Tranzer and Richards, 1976). Approximately two axon complexes per 100 muscle cells were found in both sexes. The axon varicosities were divided into the following four types; varicosities with, 1) small clear vesicle and chromaffin-negative large granular vesicle (cholinergic), 2) chromaffin-positive, 6-hydroxydopamine (6-OHDA) susceptible small and large granular vesicle (adrenergic), 3) chromaffin-positive, 6-OHDA resistant pleomorphic and large granular vesicle (aminergic?), or 4) chromaffin-negative large opaque vesicle (peptidergic?). These results suggest that non-adrenergic, non-cholinergic nerve may also play an important role in the innervation of m. retractor phalli cranialis as well as of the smooth muscle in mammalian intestine.