Maternal attenuation of hypothalamic paraventricular nucleus norepinephrine switches avoidance learning to preference learning in preweanling rat pups

Infant rats learn to prefer stimuli paired with pain, presumably due to the importance of teaming to prefer the caregiver to receive protection and food. With maturity, a more 'adult-like' teaming system emerges that includes the amygdala and avoidance/fear teaming. The attachment and 'adult-like' systems appear to co-exist in older pups with maternal presence engaging the attachment system by lowering corticosterone (CORT). Specifically, odor-shock conditioning (11 odor-0.5 mA shock trials) in 12-day-old pups results in an odor aversion, although an odor preference is learned if the mother is present during conditioning. Here, we propose a mechanism to explain pups ability to 'switch' between the dual teaming systems by exploring the effect of maternal presence on hypothalamic paraventricular nucleus (PVN) neural activity, norepinephrine (NE) levels and teaming. Maternal presence attenuates both PVN neural activity and PVN NE levels during odor-shock conditioning. Intra-PVN NE receptor antagonist infusion blocked the odor aversion teaming with maternal absence, while intra-PVN NE receptor agonist infusion permitted odor aversion teaming with maternal presence. These data suggest maternal control over pup teaming acts through attenuation of PVN NE to reduce the CORT required for pup odor aversion teaming. Moreover, these data also represent pups' continued maternal dependence for nursing, while enabling aversion teaming outside the nest to prepare for pups future independent living. (C) 2007 Elsevier Inc. All rights reserved.