Assessing Cellular Stress and Inflammation in Discrete Oxytocin-secreting Brain Nuclei in the Neonatal Rat Before and After First Colostrum Feeding

The goal of this protocol is to isolate oxytocin-receptor rich brain nuclei in the neonatal brain before and after first colostrum feeding. The expression of proteins known to respond to metabolic stress was measured in brain-nuclei isolates using Western blotting. This was done to assess whether metabolic stress-induced nutrient insufficiency in the body triggered neuronal stress. We have previously demonstrated that nutrient insufficiency in neonates elicits metabolic stress in the gut. Furthermore, colostrum oxytocin modulates cellular stress response, inflammation, and autophagy markers in newborn rat gut villi prior to and after first feed. Signaling protein markers associated with the endoplasmic reticulum stress [ER chaperone binding immunoglobulin protein (BiP), eukaryotic translation initiation factor 2A (eIF2a), and eIF2a kinase protein kinase R (p-PKR)], as well as two inflammation-signaling proteins [nuclear factor-κB (NF-kB) and inhibitor κB (IkB)], were measured in newborn brain nuclei [nucleus of the solitary tract (NTS), paraventricular nucleus (PVN), supra-optic nucleus (SON), cortex (CX), striatum nuclei (STR), and medial preoptic nucleus (MPO)] before the first feed (unprimed by colostrum) and after the start of nursing (primed by colostrum). Expression of BiP/GRP78 and p-eIF2a were upregulated in unprimed and downregulated in primed NTS tissue. NF-kB was retained (high) in the CX, STR, and MPO cytoplasm, whereas NF-kB was lower and unchanged in NTS, PVN, and SON in both conditions. The collective BiP and p-eIF2 findings are consistent with a stress response. eIf2a was phosphorylated by dsRNA dependent kinase (p-PKR) in the SON, CX, STR, and MPO. However, in the NTS (and to a lesser extent in PVN), eIf2a was phosphorylated by another kinase, general control nonderepressible-2 kinase (GCN2). The stress-modulating mechanisms previously observed in newborn gut enterocytes appear to be mirrored in some OTR-rich brain regions. The NTS and PVN may utilize a different phosphorylation mechanism (under nutrient deficiency) from other regions and be refractory to the impact of nutrient insufficiency. Collectively, this data suggests that brain responses to nutrient insufficiency stress are offset by signaling from colostrum-primed enterocytes.