Dehydroepiandrosterone Heightens Aggression and Increases Androgen Receptor and Aromatase mRNA Expression in the Brain of a Male Songbird.

Dehydroepiandrosterone (DHEA) is a testosterone/oestrogen precursor and known modulator of vertebrate aggression. Male song sparrows (Melospiza melodia morphna) show high aggression during breeding and nonbreeding life-history stages when circulating DHEA levels are high, and low aggression during molt when DHEA levels are low. We previously showed that androgen receptor and aromatase mRNA expression are higher during breeding and/or nonbreeding in brain regions associated with reproductive and aggressive behaviour, although the potential role of DHEA in mediating these seasonal changes remained unclear. In the present study, nonbreeding male song sparrows were captured and held in the laboratory under short days (8 : 16 h light/dark cycle) and implanted with s.c. DHEA-filled or empty (control) implants for 14 days. DHEA implants increased aggression in a laboratory-based simulated territorial intrusion. Brains of DHEA-implanted birds showed higher aromatase mRNA expression in the preoptic area (POA) and higher androgen receptor mRNA expression in the periventricular nucleus of the medial striatum (pvMSt) and ventromedial nucleus of the hypothalamus. The DHEA-induced increases in aromatase expression in the POA and androgen receptor expression in the pvMSt are consistent with previously reported seasonal increases in these markers associated with naturally elevated DHEA levels. This suggests that DHEA facilitates seasonal increases in aggression in nonbreeding male song sparrows by up-regulating steroid signalling/synthesis machinery in a brain region-specific fashion

Male territorial aggression and androgen modulation in high latitude populations of the Sooty, Passerella iliaca sinuosa, and Red Fox Sparrow, Passerella iliaca zaboria

The Fox Sparrows, Passerella iliaca, include multiple groups and subspecies distributed at several latitudes from the Alaskan arctic to the southwestern United States. As such, this species represents a potential model for investigating latitudinal variation in androgen secretion and aggressive territoriality in male passerines. Breeding male Fox Sparrows from two subspecies within two groups, the Sooty Fox Sparrow, P. i. sinuosa, and the Red Fox Sparrow, P. i. zaboria, were assessed for aggressive territoriality and androgen responsiveness at multiple latitudes in arctic and subarctic Alaska. Subarctic Sooty Fox Sparrows had higher circulating androgen levels in the early (8.54 ng/ml) versus mid–late breeding season (2.44 ng/ml). Males in the mid–late breeding season did not up-regulate androgen secretion in response to social challenge, but were aggressive and spent more time within 5 m of a decoy during a simulated territorial intrusion (STI) than early breeding males. Male subarctic Red Fox Sparrows had slightly higher circulating androgen levels (2.29 ng/ml) than arctic males (1.10 ng/ml) in the mid–late breeding season. However, androgen levels were not correlated with blood collection time after a social challenge in either group, suggesting that neither arctic nor subarctic males up-regulate androgen secretion during the mid–late breeding period. Arctic males spent more time within 5 m of a decoy and sang less than subarctic males during an STI in the mid–late breeding season. These findings demonstrate that the Fox Sparrow is a tractable model for investigating the latitudinal regulation of aggressive territoriality and androgen responsiveness in passerines

Oxytocin Effects on Chemosensory Function in a Clinical Setting—a Preliminary Study

Background: Despite the large body of literature on the effects of oxytocin via the exchange of social chemo-signals, no previous study tested the effects of oxytocin stimulation during parturition on the mother’s chemical senses. Therefore, in the present study, we investigated the effects of oxytocin, administered via intramyometrial and intravenous injection, on general odor processing andgustatory functioning in women shortly after giving birth via Caesarean section. Methods: General olfactory and gustatory sensitivity, and subjectively perceived taste intensities and hedonic ratings, next to self-reported mood and nausea were assessed 1 day before the Caesarean section in 21 women and again a few hours after the oxytocin stimulations. Results: We found no changes in general olfactory sensitivity, self-reported mood, or nausea between test sessions. However, following oxytocin, women rated the quality of sweet taste as significantly more positive and tended to exhibit higher gustatory sensitivity. Conclusions: Although this study was performed in a highly controlled clinical environment, we cannot rule out potential confounders related to parturition, and our interpretation on the specific effects of oxytocin therefore is limited. However, our findings agree with the literature reporting oxytocin effects on chemo-sensory functions. We speculate that an increased preference for sweet taste might be particularly relevant during the early post-partum and breastfeeding period, facilitating thenecessary nutrient supply to the newborn via the intake of calorie-rich carbohydrate food