Rapid Effects of an Aggressive Interaction on Dehydroepiandrosterone, Testosterone and Oestradiol Levels in the Male Song Sparrow Brain: a Seasonal Comparison

Abstract

Across vertebrates, aggression is robustly expressed during the breeding season when circulating testosterone is elevated, and testosterone activates aggression either directly or after aromatisation into 17β-oestradiol (E2 ) in the brain. In some species, such as the song sparrow, aggressive behaviour is also expressed at high levels during the nonbreeding season, when circulating testosterone is non-detectable. At this time, the androgen precursor dehydroepiandrosterone (DHEA) is metabolised within the brain into testosterone and/or E2 to promote aggression. In the present study, we used captive male song sparrows to test the hypothesis that an acute agonistic interaction during the nonbreeding season, but not during the breeding season, would alter steroid levels in the brain. Nonbreeding and breeding subjects were exposed to either a laboratory simulated territorial intrusion (L-STI) or an empty cage for only 5 min. Immediately afterwards, the brain was rapidly collected and flash frozen. The Palkovits punch technique was used to microdissect specific brain regions implicated in aggressive behaviour. Solid phase extraction followed by radioimmunoassay was used to quantify DHEA, testosterone and E2 in punches. Overall, levels of DHEA, testosterone and E2 were higher in brain tissue than in plasma. Local testosterone and E2 levels in the preoptic area, anterior hypothalamus and nucleus taeniae of the amygdala were significantly higher in the breeding season than the nonbreeding season and were not affected by the L-STI. Unexpectedly, subjects that were dominant in the L-STI had lower levels of DHEA in the anterior hypothalamus and medial striatum in both seasons and lower levels of DHEA in the nucleus taeniae of the amygdala in the breeding season only. Taken together, these data suggest that local levels of DHEA in the brain are very rapidly modulated by social interactions in a context and region-specific pattern.

Inhibition of local estrogen synthesis in the hippocampus impairs hippocampal memory consolidation in ovariectomized female mice

“…2). DH E 2 levels were similar in absolute quantity to those reported in other studies of hippocampal and brain DH E 2 content in mice (Overk et al, 2013) and songbirds (Fokidis et al, 2015; Heimovics et al, 2016), although most studies, including the current study, focus on relative quantity of brain E 2 content between regions or time periods. These data suggest that letrozole suppresses an increase in DH E 2 levels 30 min after infusion at a dose shown to impair OR and OP memory consolidation in vivo .…”

Neural Androgen Synthesis and Aggression: Insights From a Seasonally Breeding Rodent

“…Furthermore, sparrows exhibit increased aromatase activity, an enzyme that converts T to E 2 , and increased ERα and ERβ mRNA expression in brain nuclei that regulate aggression ( 73 , 74 ). A more recent study confirmed that neural levels of DHEA, T, and E 2 are higher in brain tissue than in circulation and that a single STI event alone can induce localized changes in neural DHEA levels ( 75 ). Taken together, these data suggest that circulating DHEA is an important source of neurally-derived steroids and that DHEA metabolism in the brain stimulates territorial aggression during the non-breeding season of birds.…”

Neurosteroids in Adult Hippocampus of Male and Female Rodents: Biosynthesis and Actions of Sex Steroids

“…Extensive evidence has been accumulated that the systems of local steroid synthesis exist in the organs other than gonads and adrenal since 1980s ( 1 , 2 ). Local production of steroids in the brain has been investigated in various vertebrates, including teleost fish ( 3 , 4 ), amphibia ( 5 – 7 ), birds ( 8 , 9 ), rodents ( 10 – 14 ), non-human primates, and humans ( 15 – 17 ).…”