Effects of Neonatal Tactile Stimulation and Maternal Separation on the Anxiety and the Emotional Memory in Adult Female Rats
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Abstract
We investigated the long-lasting effects of early postnatal tactile stimulation (TS) and maternal separation (MS) on the emotional behaviors of adult female rats. A split-litter design was introduced to remove confusing factors such as maternal disturbance. Pups of the non-tactile stimulation (NTS) group did not receive any handling. Pups subjected to the TS treatment were handled and marked for approximately 30 s daily from postnatal days (PND) 2-9 or from PND 10-17. Pups subjected to the MS treatment were handled and marked in the same way as the TS pups and then individually placed in a cup with familiar nest bedding for 1 h daily. At the age of 3 months, female rats with different neonatal experiences were employed in the light/dark box test and the one-trial passive avoidance response. Both PND 2-9 TS and PND 10-17 TS groups exhibited more time spent in the illuminated chamber of the light/dark box, and longer step-through latencies in the passive avoidance response when compared to the NTS group, indicating that early life TS treatment reduced novelty-induced anxious emotion and facilitated the retention of emotional memory in adult female rats. No significant effects were found on any behavioral measures between the MS groups and the TS groups, suggesting that neonatal short-time MS treatment was not intensive enough to alter the emotional behaviors, at least in female rats. Infantile age was not an effective factor for these measures. This result supports the hypothesis that neonatal tactile stimulation and maternal separation lead to different effects on the neural development of postnatal pups.
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