Environment and Behavior: Neurochemical Effects of Different Diets in the Calf Brain

SIMPLE SUMMARY: Social stress is characterized by physiological changes in brain functions as well as changes in neuroendocrine system activities. Much evidence indicates that stress responses are mediated by three main stress-responsive cerebral regions: the prefrontal cortex, the paraventricular nucleus of the hypothalamus, and the nucleus of the solitary tract of the brainstem. This is the first study investigating the effects of different diets on the prefrontal cortex, the paraventricular nucleus, and the nucleus of the solitary tract in ruminants. The results obtained suggest that weaning not only reduces the stress and, consequently, alterations in the oxytocin neuronal population of the paraventricular nucleus but also stimulates myelination in the prefrontal cortex. These data support the importance of maintaining a healthy nutritional lifestyle, similar to that occurring in natural conditions. ABSTRACT: Calves reared for the production of white veal are subjected to stressful events due to the type of liquid diet they receive. Stress responses are mediated by three main stress-responsive cerebral regions: the prefrontal cortex, the paraventricular nucleus of the hypothalamus, and the nucleus of the solitary tract of the brainstem. In the present study, we have investigated the effects of different diets on these brain regions of ruminants using immunohistochemical methods. In this study, 15 calves were used and kept in group housing systems of five calves each. They were fed with three different diets: a control diet, a milk diet, and a weaned diet. Brain sections were immunostained to evaluate the distribution of neuronal nitric oxide synthase and myelin oligodendrocyte glycoprotein immunoreactivity in the prefrontal cortex; the expression of oxytocin in the paraventricular nucleus; and the presence of c-Fos in the A2 group of the nucleus of the solitary tract. The main results obtained indicate that in weaned diet group the oxytocin activity is lower than in control diet and milk diet groups. In addition, weaning appears to stimulate myelination in the prefrontal cortex. In summary, this study supports the importance of maintaining a nutritional lifestyle similar to that occurring in natural conditions.