Prenatal stress puzzle, the oxytocin piece: Prenatal stress alters the behaviour and autonomic regulation in piglets, insights from oxytocin

Developmental changes in response to prenatal stressors (PNS) can result in anxiety and abnormal social development in the offspring. Oxytocin (OT) reduces anxiety, whereas OT deficiencies are associated with social behaviour deficits. Hence, we hypothesized that OT could reverse some of the PNS effects. Female offspring from three socially stressed (PNS 35–56 days of gestation) and three control sows were tested at 18 days of age. In each litter, two piglets received 24 IU of OT intranasally and two piglets received saline as a control treatment. After 45 min, each piglet was isolated for 15 min in a separate room. The PNS piglets displayed fewer alert behaviours during social isolation than control piglets (saline-control: 93.6 ± 0.2, OT-control: 82.5 ± 0.2, saline-PNS: 52.0 ± 0.2, and OT-PNS piglets: 67.8 ± 0.2). All other behavioural differences were the result of the administration of OT to PNS piglets, which reestablished a few behavioural changes such as the time spent standing in PNS piglets, with OT-PNS piglets standing more than saline-PNS piglets (77.8 ± 6.7 s vs. 57.1 ± 6.7 s respectively), and as much as saline- and OT-controls (76.7 ± 6.7 s and 70.0 ± 6.7 s respectively). Furthermore, saline-PNS piglets spent more time sitting than control piglets, and OT reversed this effect in OT-PNS piglets, with OT-PNS piglets sitting no more than controls. Prenatal stress and the administration of OT interacted in their effect on the heart rate, with OT-control and PNS piglets (saline or OT) having lower mean heart rate than saline-control piglets (saline-control: 168 ± 4, OT-control: 159 ± 4, saline-PNS: 146 ± 5, and OT-PNS piglets: 149 ± 5). Neither PNS nor OT administration influenced the RMSSD of the heart rate. In conclusion, these preliminary results suggest that social stress in mid-gestation results in some behavioural differences and alters the development of the autonomic nervous system in the sow's offspring, in this case female offspring. Exogenous OT administration reversed some behavioural changes, suggesting a common physiological basis.