The Neuroendocrine Regulation of Stress in Birds Involves a New Structure Called the Nucleus of the Hippocampal Commissure

The major hypothalamic nucleus regulating the stress response in mammals and birds is the paraventricular nucleus. It contains corticotropin releasing hormone (CRH) and vasopressin (in mammals) or arginine vasotocin (in birds) neurons. Both neuronal types project to the median eminence and release adrenocorticotropic hormone (ACTH) from the pituitary. The cardiovascular system in turn transports ACTH to the adrenal gland for the release of stress hormones. Our recent data show that a structure dorsal to the paraventricular nucleus (PVN), located in the septum, contains a significant population of CRH neurons. The structure is called the nucleus of the hippocampal commissure (NHpC). Food was removed from broiler chicks over a 24h period. Blood and brain samples were collected at 2h, 4h, 8h, 12h and 24h. Plasma was analyzed for corticosterone utilizing a radioimmunoassay procedure. Frozen brain samples were dissected, RNA extracted and gene expression was determined by quantitative RT-PCR. Results showed that the first significant increase in CRH mRNA was shown to occur in the NHpC. A second significant increase in CRH mRNA occurred in the PVN. The third significant increase occurred in the PVN displaying an elevation of AVT mRNA. Importantly, the first significant elevation of the stress hormone corticosterone occurred concurrently with the rise in CRH mRNA in the NHpC and plateaued following the significant increase in CRH and AVT mRNA in the PVN. Results suggest the involvement of the NHpC in the traditional avian HPA axis. Supported in part by grants from NSF (#0842937) and the Arkansas Biosciences Institute.