Behavioural differences in sheep that have either High or Low Cortisol Responses to Adrenocorticotropin

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 72-87-HPA Axis
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-84
Kevin Tao-kwang Lee*1, Caroline Lee2, Iain J Clarke3 and Belinda A Henry3
1Monash University, Victoria, Australia, 2CSIRO, 3Monash University, Australia
Physiological functions, such as behavior and metabolism, are influenced by the stress state of individuals.  In female sheep, we have identified subgroups of an outbred population with high or low cortisol responses to Synacthen (adrenororticotropin). The high responders (HR) have greater predisposition to obesity than low responders (LR)1. The aim of the present study was to quantify behavioural traits in HR and LR.  The mean (±SEM) response to adrenocorticotropin (Synacthen; 0.2µg/kg) (area under curve of plasma cortisol x minutes) was 405±22 units ng/ml x min in HR and 169±18 ng/ml x min in LR (n=10/group; P<0.001).

Behaviour was analysed in the following paradigms:-

-       isolation in an enclosure (5 x 3m)(test 1)

-       response to human intruder between subject and a conspecific (test 2)

-       competition for food (test 3)

Indices of behavior were formulated to measure locomotion, vocalization, defecation, urination, contact with periphery of an enclosure and time to feed, depending upon the test. In test 1, LR showed increased tendency to escape the enclosure, bleated more often and had more locomotor activity than HR (Total Activity Score for LR was 6.5 ± 1.4 vs HR 2.9 ± 1.5, p<0.05).  In test 2, LR animals spent more (P<0.05) time (109 ± 25sec) facing the human at a close distance than HR (63 ± 25sec). HR ignored the human intruder.  This fearlessness in LR was also seen in test 3. Here, either HR or LR sheep competed with a control animal by exiting a gate and moving down a 13m long corridor to a food trough.  LR were more likely to commence feeding prior to the controls (mean 8.8 ± 3.7sec before the controls) compared with HR which did not compete as strongly with the controls (mean time to feeding, 2.5 ± 4.4sec after controls)(P<0.05). 

These differences in behaviour possibly relate to innate strategies, such that LR sheep have a more passive-aggressive coping style. This is generally consistent with previously reported behavior of LR mice2.  The greater level of activity in LR may contribute to their reduced tendency to become obese on a high energy diet. The central pathways underlying these different patterns of behavior are yet to be defined.

1 Henry BA & Clarke IJ (2012) Characterizing the cellular mechanisms of post-prandial thermogenesis in skeletal muscle. Joint Annual Meeting: ASN-ADSA-ASAS Joint Symposium, Phoenix Arizona. Abstract 8. 2Touma et al (2008) Psychoneuroendocrinology 33:839.

Nothing to Disclose: KTKL, CL, IJC, BAH

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