OT Analysis

All participants arrived at the laboratory between 10 a.m. and 3 p.m. Parents were asked to refrain from food intake and nursing, 30 min before arriving. Infants were separated from their parents at least 15 min before sample collection. Saliva samples were collected using a Salivette Saliva Collection Device (Sarstedt, Rommelsdorft, Germany). Parents were asked to chew a roll of cotton until it was saturated. Salivettes were kept ice-chilled before being centrifuged at 4°C at 1,500 × g for 15 min and the liquid samples stored at −80°C. To concentrate the samples by threefold or fourfold, the liquid samples were lyophilized overnight and kept at −20°C until assayed. The dry samples were reconstructed in the assay buffer immediately before analysis using an OT EIA commercial kit (Assay-Design, Ann Arbor, MI, USA), consistent with previous research (22).