The effects of cortisol administration on social status and brain monoaminergic activity in rainbow troutOncorhynchus mykiss

Abstract

SUMMARY The hypothesis that circulating cortisol levels influence the outcome of social interactions in rainbow trout was tested. Juvenile rainbow trout Oncorhynchus mykiss were given a single intraperitoneal (i.p.)implant containing either cortisol (110 mg kg–1 fish), or cortisol plus the glucocorticoid receptor antagonist RU486 (mifepristone; 1100 mg kg–1 fish), and sampled after 5 days of social interactions with either a similar sized (<1.5% difference in fork length)or smaller conspecific (>5% difference). Within size-matched pairs of fish,cortisol treatment significantly increased the probability that the treated fish within each pair became subordinate, an effect that was abolished by simultaneous administration of RU486. Cortisol treatment also reduced the usual success of the larger fish within a pair to preferentially become dominant from 86% to 40% of pairs. To investigate one potential mechanism underlying the apparent effect of cortisol in predisposing trout to low social status, fish were treated with cortisol or cortisol+RU486 for 5 days, after which brain monoamines [5-hydroxytryptamine (5-HT); dopamine (DA)] and their major metabolites [5-hydroxyindolacetic acid (5-HIAA);3,4-dihydroxy-phenylacetic acid (DOPAC)] were measured. Significant increases of serotonergic activity ([5-HIAA]/[5-HT] ratio) were detected in the telencephalon with cortisol treatment, an effect that was eliminated by simultaneous administration of RU486. Also, cortisol treatment significantly decreased dopaminergic activity in the telencephalon. Somewhat surprisingly,the effects of cortisol treatment on monoaminergic activity in the hypothalamus were opposite to those in the telencephalon. Moreover, in no case did administration of RU486 abolish these effects. These results suggest that the effects of cortisol on social status in rainbow trout may be mediated via the modulation of central signaling systems and subsequent changes in behaviour and/or competitive ability, although the exact site of action in the brain remains uncertain.

Behavioral plasticity in rainbow trout (Oncorhynchus mykiss) with divergent coping styles: When doves become hawks

“…It was later shown that rapid resumption of feeding following transfer to a novel environment also predicts social dominance and level of aggression towards territorial intruders in non-selected aquaculture strains of rainbow trout (Øverli et al, 2004;Schjolden et al, 2005a). Most of the behavioural characteristics of the HR line are consistent with previously reported effects of the steroid hormone cortisol in non-mammalian vertebrates (Gregory and Wood, 1999;Øverli et al, 2002b;DiBattista et al, 2005). However, it seems unlikely that cortisol alone is responsible for controlling all behavioural aspects of stress coping style (Koolhaas et al, 2007;Øverli et al, 2007).…”

The response of brain serotonergic and dopaminergic systems to an acute stressor in rainbow trout: a time-course study

“…For instance, it has been shown in mammals that 5HT stimulates CRF release by the hypothalamus (Boisvert et al, 2011;Calogero et al, 1989) and also ACTH release by the pituitary (Calogero et al, 1993). Additionally, serotonergic activity is affected by other elements of the stress response such as cortisol, CRF or AVT (DiBattista et al, 2005;Dinan, 1996;Price and Lucki, 2001;Sangiao-Alvarellos et al, 2004;Summers et al, 2005). Therefore, we consider that studying the temporal pattern of activation of serotonergic signaling after exposure to a stressor is of vital importance to understanding the participation of the brain serotonergic system in the integrated stress response.…”

Agonistic encounters and cellular angst: social interactions induce heat shock proteins in juvenile salmonid fish

“…The scoring scheme was similar to that used previously for assigning social status to pairs of rainbow trout (e.g. DiBattista et al 2005DiBattista et al , 2006 and assigns higher scores to more dominant behaviours. A single behaviour score was calculated from all observations with a principal components analysis, and the fish with the higher overall behaviour score within each pair was assigned dominant social status.…”