Preoptic area infusions of morphine disrupt-and naloxone restores parental-like behavior in juvenile rats

As in the adult lactating female, opioids disrupt (and naloxone restores), parental behavior in juvenile rats (~25 days of age). Because the preoptic area regulates the display of parental behavior in lactating females, we examined its parental behavior role in the juvenile rat. At 21 days of age, juvenile rats were implanted with bilateral cannulae aimed at the preoptic area using a modified Kopf stereotaxic and extrapolating from a developing-rat brain atlas [58], and divided into two groups: initiation and maintenance. On day 25, the initiation group received bilateral infusions of either morphine (0.50 μg), saline (0.25 μl), or morphine plus naloxone (0.25 μg). Thirty minutes later, they were exposed to three 1-6-day-old pups; the maintenance group was exposed to pups until they displayed 2 consecutive days of parental behavior, then infused. Morphine disrupted parental behavior in both the Initiation and Maintenance groups, and naloxone restored the behavior to control/saline levels. Parental behavior in the juvenile animal of both sexes, therefore, is under opioid regulation that parallels the adult female.