Behavioural and neurobiological effects of colostrum ingestion in the newborn lamb associated with filial bonding
Résumé
In sheep, the onset of filial bonding relies on early intake of colostrum. The aim of our work was to describe in the newborn lamb housed with its mother the immediate post-ingestive effects of colostrum intake, in terms of behaviour and brain activity. In Experiment 1, lambs received five nasogastric infusions of colostrum, or saline, or sham intubations during the first 6 h after birth. Mother-young interactions were recorded before and after the first, third and fifth infusions. The activity of the dam and of the young, which diminished over time in all groups, was temporarily increased in both partners just after each intubation procedure. The number of high-pitched bleats was significantly lower in lambs that received colostrum than in the sham group, suggesting soothing or satiating properties of colostrum. In Experiment 2, newborn lambs received a single nasogastric infusion of colostrum or saline 4.5 h after birth, or were sham intubated. Neuronal activation was investigated 1.5 h later for maximum c-Fos activity. Infusion of colostrum and saline induced different patterns of c-Fos-like immunoreactivity in the paraventricular and supraoptic nuclei of the hypothalamus as compared with the sham group. A specific oxytocinergic/vasopressinergic (OT/VSP) cell population in the paraventricular nucleus was activated following colostrum and saline infusion, but not sham intubation. Only colostrum induced the activation of the cortical amygdala and insular cortex, two structures involved in learning, associative processes, reward and emotion. We hypothesize that filial bonding may be triggered through colostrum-rewarded learning/calming processes and that the OT/VSP system may play a role.