Effects of AVP V1a and CRH receptor antagonist on psychological stress responses to frustrating condition in sheep

Abstract

Arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are released in the brain to regulate behavioral and physiological stress responses. To elucidate the respective roles of these peptides under certain stressors, we examined the effects of intracerebroventricular infusions of either AVP V1a receptor antagonist, [Pmp1, Tyr (Me)2]- Arg8-Vasopressin (Pmp, Tyr-AVP) or CRH receptor antagonist, alpha-helical CRF 9-41 (αhCRF) on stress responses induced by frustrating condition in sheep. Four ovariectomized Corriedale ewes were assigned to the experiment. In a "frustrating" condition (FC), food was withheld for 60 minutes from only the experimental ewe while this ewe was in the presence of the other ewes that were given food. As "non-frustrating" control condition (C), food was withheld for 60 minutes from all ewes, thereby controlling for the nonspecific effects of lack of food. FC induced a significant rise in the plasma cortisol concentration (p < 0.05) and increased the pawing number and rectal temperature compared with that in C (p < 0.1). The effects of either Pmp, Tyr-AVP or αhCRF on these stress responses were analyzed. The rise in cortisol restored nearly to the control level by infusion of Pmp, Tyr-AVP or αhCRF. The pawing number restored nearly to the control level by αhCRF. The hyperthermia restored nearly to the control level by Pmp, Tyr-AVP. These data suggest that both endogenous CRH and AVP might be concerned with inducing physiological and behavioral stress responses to frustrating condition in sheep.