Maternal stimulation affects the number of motor neurons in a sexually dimorphic nucleus of the lumbar spinal cord.

The role of maternal stimulation in the development of a lumbar motor nucleus (spinal nucleus of the bulboca vernosus, SNB) was investigated. The perineum, which has afferents to the lumbar region, is stimulated throughout early development by maternal licking, a behavior that is elicited by chemosignals secreted by the pups. In the present study, half of the dams were treated with intranasal zinc sulfate throughout the postpartum period, which led to a specific reduction in maternal stimulation of pup perineum by interfering with the reception of eliciting signals. Adult offspring of both sexes from anosmic dams had 11% fewer SNB motor neurons than normally stimulated controls, an effect which was most apparent in the rostral portion of the nucleus. There was no effect of treatment on neuron size. It was concluded that afferent input provided by species-typical maternal behavior contributes to the number of neurons that survive the neonatal period of normal cell death.