Molecular neuroendocrine events during stress in poultry.

Magnocellular neurons in the hypothalamic paraventricular nucleus containing arginine vasotocin (AVT) project to the posterior pituitary and release the peptide peripherally to target tissues. Parvocellular neurons contain either corticotropin-releasing hormone (CRH), AVT, or both neuropeptides and project to the median eminence. Corticotropin-releasing hormone and AVT are then transported to the anterior pituitary where they bind to CRH1 or vasotocin VT2 receptors, many found co-localized on the same pituitary cell type, the corticotrope. Central administration of CRH compared with AVT is more effective in releasing the stress hormone corticosterone, whereas peripheral administration of AVT is more efficacious. Simultaneous, peripheral administration of CRH and AVT also resulted in a synergistic release of corticosterone. Cell culture studies demonstrated a synergistic release of the second messenger, cyclic adenosine monophosphate, when both CRH and AVT were added to cells transfected with CRH and VT2 receptors, providing a possible explanation for the enhanced release of corticosterone following combined peripheral administration of the 2 peptides. A social stress model, mature male-male interaction, demonstrated activation of neurons in the paraventricular nucleus and suggested that the posterior pituitary as well as the anterior pituitary are involved in a social stress response.