Photoperiod-independent hypothalamic regulation of luteinizing hormone secretion in a free-living Sonoran desert bird, the Rufous-winged Sparrow (Aimophila carpalis).

We investigated the regulation of luteinizing hormone (LH) in the male Rufous-winged Sparrow,Aimophila carpalis, a resident of the Sonoran desert that breeds after irregular summer rains. Although the testes develop in March due to increasing photoperiod and regress in September due to decreasing photoperiod, LH does not consistently increase in the spring as in other photoperiodic birds. However, throughout the year increased plasma LH is correlated with rainfall. To investigate this rainfall-associated regulation of LH secretion, we quantified immunocytochemical labeling for gonadotropin-releasing hormone I (GnRH-I), proGnRH (the GnRH precursor), and gonadotropin-inhibitory hormone (GnIH) in the hypothalamus of free-living adult males caught before (low LH), and during (high LH) the monsoon rainy season. Compared to pre-monsoon birds, birds caught during the monsoon season had larger immunoreactive GnRH-I (GnRH-I-ir) and proGnRH-ir cell bodies, as well as fewer, less densely labeled proGnRH-ir cell bodies. Birds caught during the monsoon had fewer, less densely labeled GnIH-ir cell bodies than birds caught before the monsoon. Further, there was no GnIH-ir labeling in the median eminence on either capture dates, suggesting that GnIH is not released to the pituitary gland via the portal vein at this time of year, but there were fewer GnIH-ir fibers in the preoptic area of birds caught during the monsoon season. Our data support the hypothesis that environmental factors associated with increased rainfall during the monsoon season stimulate GnRH synthesis and release to increase LH secretion. These data also suggest that GnIH could inhibit GnRH neuronal activity prior to the monsoon season.

Effects of early embryonic exposure to genistein on male copulatory behavior and vasotocin system of Japanese quail.

Genistein is a phytoestrogen, particularly abundant in soybeans that can bind estrogen receptors and sex hormone binding proteins, exerting both estrogenic and antiestrogenic activity. In this study we used the Japanese quail embryo as a test end-point to investigate the effects of early embryonic exposure to genistein on male copulatory behavior and on vasotocin parvocellular system. Both differentiate by the organizational effects of estradiol during development and may therefore represent an optimal model to study the effects of xenoestrogens. We injected two doses of genistein (100 and 1000 microg) into the yolk of 3-day-old Japanese quail eggs. Other eggs were treated with either 25 microg of estradiol benzoate or sesame oil as positive and negative controls. At the age of 6 weeks, behavioral tests revealed a significant decrease of all aspects of copulatory behavior (in comparison to the control group) in estradiol-treated birds. In contrast, genistein-treated animals demonstrated various degrees of decrease in the mean frequencies of some aspects of the sexual behavior. The computerized analysis of vasotocin innervation in medial preoptic, stria terminalis and lateral septum nuclei revealed a statistically significant decreased immunoreactivity in treated animals compared to control ones. These results demonstrate that genistein, similarly to estradiol, has an organizational effect on quail parvocellular vasotocin system and on copulatory behavior. In conclusion, present results confirm, in this avian model, that embryonic exposure to phytoestrogens may have life-long effects on sexual differentiation of brain structures and behaviors.

Early embryonic administration of xenoestrogens alters vasotocin system and male sexual behavior of the Japanese quail.

The copulatory behavior and the parvocellular vasotocin (VT) system of the nucleus of the stria terminalis (BST) are sexually dimorphic in the Japanese quail. Embryonic administration of estradiol benzoate (EB) induces an organizational effect determining the disappearance of such a dimorphism (male shows behavior and cerebral phenotype of the female). The VT parvocellular system can therefore be considered an accurate marker of the sexual differentiation of brain circuits and a very sensitive indicator of the activity of estrogen-like substances on neural circuits. To test this hypothesis we administered diethylstilbestrol (DES), a powerful synthetic xenoestrogen, genistein (GEN), a phytoestrogen produced by soy, and bisphenol A (BPA). After 3 days of incubation, quail eggs were injected with vehicle, EB, DES, GEN or BPA. Administration of BPA caused an early blockage of development and no further analyses were done on the BPA groups. At puberty, the copulatory behavior of EB- or DES-treated male quail was totally abolished, whereas only the highest doses of GEN determined a significant decrease of the behavior. After the tests, the animals were sacrificed and perfused. The fractional area (FA) covered by VT immunoreactivity was analyzed in BST, medial preoptic nucleus, and lateral septum by computerized image analysis. The FA was significantly reduced after treatment with EB, DES and GEN at high doses. These results confirm that the sexually dimorphic VT system of the Japanese quail is a sensible indicator of the effects of xenoestrogens at the level of the central nervous system.