Induction of nitric oxide synthase activity and motoneuronal cell damage

Experimental findings obtained in our laboratory on the induction of nitric oxide synthase (NOS), the synthetic enzyme of the free radical nitric oxide, in motoneurons of the rat after different paradigms of injury are summarized. NOS was found to be induced in the mature axotomized facial motoneurons. However, no induction of NADPH-diaphorase histochemical staining, which is a marker of NOS activity, was detected in facial motoneurons after axotomy at birth, when evidence of apoptosis was obtained in the facial nucleus on the side of the lesion. On the other hand, NOS activity was found to be indu-ced in mature facial motoneurons in the absence of degenerative changes, concomitantly with facial muscle paralysis caused by botulin toxin A. Together, our data indicate that the death of motoneurons, at least of the immature ones, can occur in the absence of NOS induction; that NOS induction in mature motoneurons is not necessa-rily related to their death, and that NOS can be induced in motoneurons by different paradigms of structural and functional injury.