High substance P-like immunoreactivity (SPLI) in the olfactory and electrosensory cells of gymnotid fish

Substance P has been proposed as a candidate neurotransmitter or neuromodulator in the nociceptive system. Using a light microscopial immunohistochemical peroxidase-anti-peroxidase technique we have detected high substance P-like immunoreactivity (SPLI) in several types of sensory organs of 4 species of gymnotiform teleost fish: olfactory epithelium, vestibular, lateral line and electrosensory organs. The olfactory nerve and its endings within the olfactory bulb and the telencephalon were also strongly labelled. At these sites no SPLI was revealed in other teleosts (Carassius auratus, Gnathonemus petersii). The findings suggest that substance P may be involved in neurotransmission or neuromodulation in these specific sensory systems of these species.