Localization of substance P in middle ear mucosa and peripheral auditory pathways in guinea pigs]

The distribution and intracellular localization of substance P (SP) in middle ear mucosa (MEM), cochlea and spiral ganglion (SG) were studied by immunohistochemical technique and immunoelectron microscopy. There was a widespread distribution of SP positive nerve fibers (NF) along the median and small vessels of MEM. SP-immunoreactivity (SP-IR) positive cells could be seen in the MEM near the promontorium tympani. In the Corti's organ, SP-IR positive products were located at the base of inner hair cells. The majority of positive NF emerged like strings of beads and were radially distributed from osseous spiral laminal to the Corti's organ. About 50% of the SG cells were SP-IR positive. Two types of SP-IR positive NF were found in the VIII cranial nerve by light microscopy. Small clear vesicles with a diameter of 50-70nm were localized in the cytoplasm of the type-I SG cells by immunoelectron microscopy. In the outer membrane and inside the mitochondria, SP-IR positive substances could be distinguished as an electron dense matter. The possibility of SP as an afferent neurotransmitter or modulator in cochlea and the significance of its presence in the MEM were discussed.