Adrenocortical and heterophil/lymphocyte responses to challenge in hens showing short or long tonic immobility reactions

Abstract

1. Adult White Leghorn hens showing short or long tonic immobility reactions were classified as low-fear (LF) or high-fear (HF) responders, respectively. Following cannulation, their adrenocortical responsiveness to ACTH administration and the effects of chronic frustration induced by thwarting of feeding on plasma corticosterone concentrations and heterophil/lymphocyte (H/L) ratios were measured at regular intervals. 2. ACTH injection elicited significant and similar mean increases in circulating corticosterone concentrations in both the LF and HF groups. 3. Absolute H/L ratios were higher in HF than in LF hens after cannulation, although both groups showed similar proportional increases from pre-operation ratios. 4. Plasma corticosterone concentrations and H/L ratios were significantly increased at 20 h and 44 h respectively after the frustration of feeding regime began. Thus, adrenocortical activation preceded increases in H/L ratios but, whereas the elevated plasma corticosterone concentrations found after 20 h remained virtually constant thereafter, H/L ratios rose progressively throughout the 68 h frustration period. 5. There were no significant differences between groups in their plasma corticosterone and H/L responses to frustration. However, a consistent trend towards greater adrenocortical activation was observed in the HF than in the LF hens.