The facial nucleus (FN) of the rat is composed of multipolar neurons generated between gestational days G12 and G15. This nucleus is involved in the mechanisms underlying muscle contraction during the sucking reflex. After birth, the neuronal substrate of this reflex is gradually organized to allow the performance of other functions such as gnawing, chewing, swallowing and drinking. Undernourishment is known to produce different degrees of delayed brain development, the greatest of which are similar to the characteristics of the premature syndrome. Neuronal morphological alterations are associated with sucking-reflex deficiencies, which interfere with feeding by the newborn. The current study shows that perinatal undernourishment leads to dendritic arbor hypoplasia and small alterations of soma size in Golgi--Cox impregnated FN neurons of rats. The data suggest that these morphological alterations of FN neurons, may be associated with shifts in the input and integration of signals, and may finally modify the elaboration of motoneuron discharges partly modulating bucolabial muscle contraction during sucking movements and facial expression. Additionally, neonatal nutritional rehabilitation modifies the effects on FN neuronal development, ameliorating the influence of early adverse nutritional conditions.