TRKC-LIKE IMMUNOREACTIVITY IN THE PRIMATE DESCENDING SEROTONINERGIC SYSTEM

In the search for substances with a potential role in plastic responses of spinal motoneurons we have studied the distribution of trkC-like immunoreactivity in the spinal cord of adult monkeys (Macaca fascicularis). The presence of trkC, which is a signal-transducing receptor for neurotrophin-3, was detected by the use of indirect immunofluorescence with a rabbit polyclonal antibody raised against a synthetic peptide corresponding to the carboxy-terminal domain of the mouse trkC-encoded protein, thus detecting only full-length signal-transducing receptors. trkC-immunoreactive fibres/varicosities could be found at all spinal cord levels and the densest innervation was found in the autonomic intermediolateral and Onuf's nuclei, but somatic motoneuron pools also received a significant contribution of trkC-immunoreactive fibres. Terminals immunoreactive for trkC were also seen in the dorsal horn. Double-labelling experiments revealed a high degree of coexistence between trkC- and 5-hydroxytryptamine (serotonin)-like immunoreactivity in all areas except in the dorsal horn, The results of the present study suggest that neurotrophic signalling with an influence on serotoninergic as well as nonserotoninergic inputs to the adult monkey spinal cord is at hand.