Effect of the serotonin agonist buspirone on behaviour and hypothalamic–pituitary–adrenal axis in confident and fearful mink

Abstract

Behavioural and hypothalamic–pituitary–adrenal (HPA) axis responses were investigated in farm mink ( Mustela vison) selected for either confident or fearful behaviour for nine generations. Two groups of 2-year-old confident ( n=12) and fearful ( n=12) female mink were given the serotonin (5-HT) 1A receptor agonist buspirone (1.25 mg/kg/day), whereas two other groups of 2-year-old confident ( n=12) and fearful ( n=12) female mink were given saline, continuously for 5 weeks via osmotic minipumps. Behavioural reactions towards a novel object and towards humans were tested after 19–25 days, and HPA axis reactivity [adrenocorticotropic hormone (ACTH), cortisol] was measured after 28–31 days of treatment. Confident mink were more exploratory than fearful mink towards humans and a novel object. Confident mink spent more time in contact with the object than did fearful mink during saline—but not during buspirone—treatment. buspirone increased approach–withdrawal conflict behaviour towards a object in fearful mink only. The chronic dose of buspirone did not reduce fear towards humans and did not affect latencies to reaction, number of contacts, number and duration of manipulations, and stereotypic behaviour in a Novel Object test. Different HPA axis responses have emerged between confident and fearful mink, together with a different degree of fear-related behaviour. Fearful mink have a higher cortisol combined with a lower ACTH secretion than confident mink in response to capture and blood sampling. The central serotonergic system may be involved, and even though the precise underlying mechanisms are presently unknown, treatment with a 5-HT 1A receptor agonist reduces the difference between confident and fearful mink in HPA axis reactivity.