Social challenge increases cortisol and hypothalamic monoamine levels in matrinxã (Brycon amazonicus)

Abstract

The neural circuitry for social behavior and aggression appears to be evolutionarily conserved across the vertebrate subphylum and involves a complex neural network that includes the hypothalamus as a key structure. In the present study, we evaluated the changes in monoamine levels in the hypothalamus and on serum cortisol and plasma glucose of resident matrinxã (Brycon amazonicus) submitted to a social challenge (introduction of an intruder in their territory). The fight promoted a significant increase in hypothalamic 5-HT, NA and DA levels and on the metabolites 5-HIAA and DOPAC, and decreased 5-HIAA/5-HT and DOPAC/DA ratios in resident fish. Furthermore, an increase in serum cortisol and plasma glucose was also observed after the fight. Resident fish presented a high aggressiveness even with increased 5-HT levels in the hypothalamus. The alteration in hypothalamic monoaminergic activity of matrinxã suggests that this diencephalic region is involved in aggression and stress modulation in fish; however, it does not exclude the participation of other brain areas not tested here.

Effect of the early social environment on behavioural and genomic responses to a social challenge in a cooperatively breeding vertebrate

“…In the hypothalamus, egr-1 was only influenced by the rearing treatments. The hypothalamus is a key area regulating many different social behaviours, including aggression, parental care, sexual behaviour and social cognition, and the activity of the HPA axis Wolkers et al 2015). Because of the broad effect of egr-1 on many different pathways, the higher egr-1 hypothalamus expression in +F fish compared to ÀF fish might indicate that +F fish are able to show a greater extent of plasticity than ÀF fish in a wide array of social behaviours and social contexts.…”

Monoaminergic levels at the forebrain and diencephalon signal for the occurrence of mutualistic and conspecific engagement in client reef fish

“…bites) in fish introduced to a real opponent situation 53 . Higher serotonergic activity in the diencephalon has also been reported in fish following the loss of a fight 53 , while the event of winning a fight seems to contribute to a reduction of 5-HIAA/5-HT ratio in resident fish 54 , 55 . Considering that the 5-HIAA/5-HT ratio is mostly an indicator of neurotransmitter use, representing its release and metabolism 56 – 61 , this would mean that in an interspecific context, clients would have a higher serotonergic activity in the diencephalon, similar to what occurs with fish after the loss of a contest.…”

“…For instance, DA levels have also been reported to show a negative correlation in the zebrafish’s diencephalon in response to aggressive behaviour 53 . Furthermore, matrinxã ( Brycon amazonicus ) subjected to a social challenge (introduction of an intruder to their territory) showed lower hypothalamic DOPAC/DA ratios during fights 54 .…”

The presence of a conspecific induces risk‐taking behaviour and enlargement of somata size of dopaminergic neurons in the brain of male medaka fish

“…Recent research shows that the brain dopamine level in teleosts increased after being stressed by chasing, handling and air exposure (Gesto et al, 2013;Weber et al, 2015). Furthermore, Wolkers et al (2015) demonstrated that territorial resident matrinxã fish (Brycon amazonicus) have a high dopamine level in the hypothalamus of the brain after being subjected to a social challenge stress by introducing an intruder into their territory. Nonetheless, little information is known about which brain regions with dopaminergic neurons are activated in stressed and/or risk-taking medaka fish.…”