Peripheral Administration of a Corticotropin-Releasing Factor Antagonist Increases the Vocalizing and Locomotor Activity of Isolated Guinea Pig Pups

Guinea pig pups vocalized more and were more active during a 60-min period of isolation in a novel environment when injected SC with 50 μg of the corticotropin-releasing factor (CRF) antagonist, [d-Phe]CRF ₁₂₋₄₁ , than when injected with saline vehicle only. More pups exhibited eye closing and extensive piloerection when injected with saline than when injected with the antagonist. Plasma levels of cortisol following testing were not affected by the injections. These results support the hypothesis that endogenous CRF contributes to the normal decline in vocalizing and locomotor activity that guinea pig pups show with continued isolation. The results also suggest that endogenous CRF plays a role in the eye closing and piloerection of isolated pups. The finding that the dose of the antagonist used altered behavior, yet was not sufficient to lower plasma cortisol levels, supports earlier evidence that the observed effects of CRF are not due to the actions of ACTH or glucocorticoids.