Is substance P the neurotransmitter in the vestibular end organs?

The vestibular end organs of the rabbit were fixed intracardially with phosphate buffered 4% formaldehyde, sectioned for 15 micron cryostat sections and incubated with monoclonal substance P (SP) antibody. Specific SP-like immunoreactivity (SPLI) was observed within and below the sensory epithelia of both utricular and saccular maculae and ampullary cristae. Particularly strong SPLI was seen in the maculae which showed many SPLI-positive axons in the subepithelial space and a network of SPLI-positive structures in the basal zones of the sensory epithelium. The calyceal terminals of type I hair cells showed regularly SPLI. The possibility of a transmitter or modulator role for SP in the vestibular function is suggested.