Neonatal Tactile Stimulation Reverses Alterations In Novel Object Recognition, Sociability And Neuroendocrine Levels Induced By Neonatal Isolation In Male Adult Mandarin Voles (Microtus Mandarinus)

In rodent studies, early life social stress is known to produce long-lasting negative effects in the brain and behavior. Some of these changes are supposed to be reversed by tactile stimulation. For instance, experimental studies have found that neonatal tactile stimulation (NTS) could reverse or prevent the effects of neonatal isolation (NI) on the adulthood behavioral and emotional responses to environmental stimuli and shows the sexual difference on the NTS effect. However, it remains unclear whether NTS affects nonspatial learning and memory, sociability or expression of neuroendocrine sunstances.Mandarin voles (Microtus mandarinus) are ideal animal models to investigate these factors because they are highly social rodents and display biparental care. In current study, we compared anxiety, learning and memory, sociality and levels of central oxytocin (OT), arginine vasopressin (AVP) between NI and NTS to explore whether NTS could prevent or reverse these effects of NI on the adult male voles. In addition, we also measured the body weights before weaning and examined the levels of serum corticosterone. The main results include the following points:1. From postnatal day1(PND1) to PND21, neonatal isolated males subjected to NTS were significantly heavier than NI males, but there has no significant differences between controls and NTS males.2. In the open-field test, compared with NI males, neonatal isolated males subjected to NTS showed significantly lower anxiety-like behavior, but there has no significant differences between controls and NTS males.3. The preference index of novel object recognition test was not statistically different between NI males and NTS males, but we found a significantly decrease in NI males compared with controls. However, there has no significant differences between controls and NTS males.4. Compared with controls, NI males displayed decreased levels of affiliation and aggressive to male stimulus vole. However, NTS males displayed increased levels of affiliation and aggression to male stimulus vole compared with NI males.5. No significant differences of OT levels in paraventricular nucleus (PVN) were found between NTS males and controls, but OT levels had a significantly decreased in NI group.6. There were significant differences in AVP expression in PVN among three groups. Compared with controls, AVP expression in PVN significantly decreased in NI males and significantly elevated in NTS males.7. A significantly higher levels of serum corticosterone were found in NI males, but there has no significant differences between controls and NTS males.These results indicated that adequate tactile stimulation in early life plays an important role in the prevention of behavioral disturbances. It perhaps promotes the sociability and the nonspatial learning and memory of adult males possibly through the alteration of central OT, AVP and the serum corticosterone.