BETA-APP GENE-EXPRESSION IS INCREASED IN THE RAT-BRAIN AFTER MOTOR-NEURON AXOTOMY

The response of the betaAPP gene to neuronal injury was studied in the facial and hypoglossal nerve nuclei of the rat after corresponding ne rve axotomy. Increased levels of betaAPP 695, 714, 751 and 770 mRNAs w ere observed after either facial or hypoglossal nerve axotomy in the p arent ipsilateral motor neurons. The increase was gradual, with maxima l values 7 days after axotomy. BetaAPP mRNA expression returned to nor mal values 60 days after the lesion. Increased betaAPP immunostaining was also detected in ipsilateral chromatolytic motor neurons. No chang e in betaAPP immunoreactivity was observed in oligodendrocytes, anothe r cell type expressing betaAPP under normal conditions. A rapid increa se in the expression of the GFAP gene was observed in reactive astrocy tes surrounding chromatolytic neurons in the ipsilateral facial or hyp oglossal nuclei. Thus, in contrast with other models of neuronal injur y, where only the Kunitz protease inhibitor-containing betaAPP mRNA is oforms are increased, all betaAPP mRNAs are increased in the axotomy m odel. Furthermore, although betaAPP expression has been shown to be in creased in reactive astrocytes following neuronal injury, in the prese nt study the increase was essentially found in the motor neurons react ing to axotomy.