Intervention With the Mother–Infant Relationship Reduces Cell Proliferation in the Locus Coeruleus of Female Rat Pups
The Locus Coeruleus (LC) is a noradrenergic nucleus involved in several neuroendocrine and behavioral functions. During the neonatal period, the LC is critical for olfactory learning. Full development occurs during the early postnatal period. Environmental interventions after birth may affect neurogenesis. In rats, the neonatal handling procedure has been used as a model to analyze the effects of environmental intervention early in life. It has been related to several long-lasting behavioral and neuroendocrine changes. The present study analyzed the effects of handling on the number of neurons, cellular proliferation, and apoptosis in the LC of 11-day-old female rats. Wistar rat pups were submitted to brief maternal separation followed by handling (1 min per day from postnatal day [PND] 1 to 10). On PND 11, the LC was analyzed using immunohistochemistry for NeuN and BrdU, TUNEL staining, and electron microscopy. The intervention reduced the number of neurons in the LC but showed no significant change in the number of apoptotic cells, as measured by the TUNEL technique. However, the number of proliferating cells was significantly lower in the handled rat pups as compared with the nonhandled ones. This study demonstrates that the infant LC is sensitive to changes in maternal behavior. A seemingly mild environmental intervention during the neonatal period may reprogram the development of the LC, altering cell proliferation.