The Role of the Vasotocin Four Receptor (VT4R) in the Stress Response of Broilers

Previous studies in our laboratory have shown that the vasotocin two receptor (VT2R) is located predominantly on corticotropes suggesting a function in the release of the hormone ACTH.  Current work shows that a second vasotocin receptor , the VT4R, likewise participates in the avian stress response.  Utilizing acute and repetitive immobilization as stressors, Fos protein was quantified in brain structures while cfos mRNA was determined in the pituitary.  An antibody to the VT4R was used to ascertain the distribution of the receptor in brain and pituitary sections.  Real time RT-PCR was completed to determine gene expression in pituitary.  Results showed that following acute or repetitive stress, corticosterone plasma levels were significantly elevated.  With both acute and repetitive stress, significantly higher Fos protein was detected in neurons of the paraventricular nucleus and the lateral septum.  VT4R were found in the paraventricular nucleus, the supraoptic nucleus and in tanycytes within and about the median eminence.   In the pituitary, VT4R were colocalized in corticotropes located in the cephalic lobe.  Basal relative gene expression levels of four vasotocin receptors and two corticotropin releasing hormone receptors in pituitary tissue were also determined.  It was shown that the VT2R and VT4R were abundant in pituitary while corticotropin releasing hormone type one receptor (CRHR1) was the most abundant pituitary CRH receptor. In contrast to brain, following repetitive stress, pituitary cfos mRNA was significantly reduced suggesting that stress induced cAMP/protein kinase A (PKA) signaling pathway might inhibit protein kinase C (PKC)/c-fos signaling pathway in the chicken anterior pituitary.