Neuronal and non-neuronal Trk neurotrophin receptor-like proteins in Eisenia foetida (Annelida Oligochaeta).

The occurrence and distribution of Trk proteins, which are the high-affinity signal-transducing receptors for neurotrophins, have been investigated in earthworms (Eisenia foetida) using polyclonal antibodies which map within their catalytic domain. Western-blot analysis identified major protein bands whose estimated molecular masses were consistent with those of the full-length Trk proteins in vertebrates. Specific immunoreactivity for TrkA-, TrkB-, and TrkC-like was observed in neuronal populations of the dorsal cerebral, subpharyngeal and ventral cord ganglia. Furthermore, TrkA-like immunoreactivity was observed in subcutaneous neurons and nerve fibers between muscle layers in the peripheral nervous system. TrkB- and TrkC-like immunoreactivity was observed in the gut innervation. Non-neuronal expression of TrkB and TrkC proteins was found in epidermal cells, and TrkC-like immunoreactivity was detected in the gut epithelium.