Distribution of substance P-like immunoreactivity in the pedal ganglion of Mytilus galloprovincialis.

Nerve cell bodies and fibers displaying Substance P-like (SP-li) immunoreactivity have been identified in the pedal ganglia (PG) of Mytilus galloprovincialis. Most reactive neurons are small-sized, unipolar and are located in the ganglionic cortex. Positive fibers form a dense network in the neuropile and run parallel in the commissure and in the nerves and connective tracts. The positivity of the labelled elements to a monoclonal antibody indicates that SP-li substance of Mytilus contains a portion immunologically similar to the C-terminal pentapeptide responsible for the pharmacological activity of vertebrate SP.