Motoneurone numbers in rat neonatal lateral motor columns: use of antibody to choline acetyltransferase to identify motoneurones.

The number of motoneurones in the rat lumbosacral and brachial motor columns were determined during the neonatal period, following identification of the motoneurones with antibodies to the enzyme choline acetyltransferase. Motoneurone numbers declined by less than 15% between 21 days embryonic and 4 days postnatal. These observations suggest that there is little change in the population of motoneurones during the period of extensive loss of polyneuronal innervation of muscle.