Persistence of somatic and dendritic growth associated processes and induction of dendritic sprouting in motoneurones after neonatal axotomy in the rat.

The effect of neonatal axotomy on the maturation of motoneurone somadendritic morphology was studied in identified motoneurones innervating the ankle dorsiflexor muscles tibialis anterior (TA) and extensor digitorum longus (EDL) of the rat by intracellular injection of Lucifer Yellow and confocal microscopy. At birth, the entire somatodendritic surface is covered with fine filopodial growth-associated processes. These are eliminated from the soma and proximal dendrites during the first postnatal week as part of a somatofugal process of dendritic maturation. Following neonatal axotomy, the postnatal elimination of growth associated processes was halted and new, axonal-like processes were seen to sprout from the soma and proximal dendrites in some of the axotomized motoneurones. These results indicate that synaptic interaction with the target muscle during the early postnatal period is essential for the maturation of the somatodendritic receptive surface of the motoneurone.