ORNITHINE DECARBOXYLASE-LIKE IMMUNOREACTIVITY IN RAT SPINAL MOTONEURONS AND MOTORIC NERVES

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in the forma tion of the polyamines putrescine, spermidine and spermine. In the pre sent study ornithine decarboxylase-like immunoreactivity (ODC-LI) was localized immunocytochemically in rat spinal motoneurons, motoric nerv es and myoneural junctions in several muscles. In the spinal cord ODC- LI was expressed in most of the large multipolar neurons located in th e ventral horn at cervical and lumbar levels. ODC-LI was localized in the cytoplasm, dendrites and axons of the labelled neurons. The nuclei of motoneurons were unlabelled; however, the nuclear membranes and th e surrounding cytoplasm were strongly stained. ODC-immunoreactive (IR) axons could be traced through the white matter entering the ventral r oots. The myelinated axons in the ventral roots and in the nerve bundl es among the muscles were intensely stained with ODC antiserum. The my oneural junctions apposing individual muscle fibers showed ODC-LI with slightly less intensity. Some ODC-IR nerve fibers were seen in the mu scle spindles. The present results show that motoneurons in adult rat spinal cord express ODC-LI and that ODC-LI is transported to motoric n erves and myoneural junctions. This suggests that polyamines can be sy nthesized both in the motoneuron somata and in their peripheral projec tions. Polyamines may thus regulate cellular functions in all parts of motoneurons. In addition, polyamines may be secreted from their dista l projections and have trophic effects on Schwann cells and/or muscula r tissue.