EXPRESSION OF NEUROPEPTIDES AND NEUROPEPTIDE MESSENGER-RNAS IN SPINAL-CORD AFTER AXOTOMY IN THE RAT, WITH SPECIAL REFERENCE TO MOTONEURONS AND GALANIN

The extent to which the plasticity in peptide expression observed in d eveloping spinal motoneurons occurs following proximal peripheral axot omy in the adult rat was examined using in situ hybridization and immu nohistochemical techniques to visualize the changes. Transient upregul ation of galanin, vasoactive intestinal polypeptide (VIP) and substanc e P messenger ribonucleic acids (mRNAs) was observed within subpopulat ions of motoneurons ipsilateral to lesion for periods lasting 2-3 week s after injury. In contrast, the axotomy-induced heterogenous increase s in somatostatin and neuropeptide tyrosine mRNA expression in ipsilat eral motoneurons remained elevated, or, in the case of somatostatin, c ontinued to increase for the time period studied (1 month). Immunohist ochemical analysis agreed with the in situ hybridization results, show ing some motoneurons within the injured ventral horn to contain galani n-, VIP- or somatostatin-like immunoreactivity. In some instances, gal anin-immunoreactive motoneurons colocalized with calcitonin gene-relat ed peptide immunoreactivity. Most of the neurons expressing the injury -induced peptides appeared large, presumably alpha-motoneurons, but th ere were also many small neurons expressing galanin in the ventral hor n ipsilateral to lesion. This may represent evidence for peptide synth esis in gamma-motoneurons. The only peptide mRNA studied to be down-re gulated in response to axotomy was enkephalin. The results show that p eptide expression in injured motoneurons is dramatically altered, the significance of which remains to be determined.