Protein kinase C in preovulatory follicles from the hen ovary

Auxiliary effects of camphor on reproductive function of Japanese quail

In recent decades, reproductive problems were raised alongside the continuous genetic selection for performance purposes in poultry. As such, a negative correlation was observed between reproductive and production performance, which may possibly imply that the high growth rate in poultry causes physiological disorders such as decreased libido and frequency of mating. A study was conducted to establish the efficacy of feeding graded levels of camphor on reproductive function of Japanese quail as a bird model. Two-hundred-and-eighty one-day-old quail chicks were randomly assigned to individual cages in 7 treatments (zero [control], 250, 500, 750, 1,000, 5,000, or 10,000 ppm of camphor). The results demonstrated that testosterone concentration displayed an uncertain attitude, as the lower dosages of camphor used (250, 500, and 750 ppm) had the highest values. Thyroxine (T₄) linearly increased with increasing camphor levels in male birds (P < 0.05). Triiodothyronine (T₃) also was increased in the groups receiving a camphor-containing diet in comparison with the control (P < 0.05). The male birds' libido behavior was linearly increased with the increase of camphor concentration (P < 0.05). Dietary camphor in 500 and 10,000 ppm caused the highest percentage of fertility (P < 0.0001) and hatchability (P = 0.0117), respectively. As well, the groups with 5,000 and 10,000 ppm of camphor accounted for the highest percentage of hatched-fertile eggs (P = 0.0055). The highest rate of sperm penetration in the yolk inner perivitelline layer (IPVL) was demonstrated by the group allotted with 10,000 ppm camphor (P < 0.05). This group also had the highest hole persistency in IPVL. Conclusively, the result indicated that camphor can be added in poultry diet for the improvement of reproductive functions.

Vasoactive intestinal peptide promotes differentiation and clock gene expression in granulosa cells from prehierarchal follicles

Vasoactive intestinal peptide (VIP) signaling via cyclic adenosine monophosphate (cAMP) is reported to stimulate steroidogenesis in ovarian granulosa cells from a variety of vertebrate species, including the domestic hen. Prior to follicle selection in the hen ovary (i.e., cyclic recruitment) follicle-stimulating-hormone (FSH)-induced cAMP signaling is absent within the granulosa layer until immediately following follicle selection. As a consequence, granulosa cells remain in an undifferentiated state and are unable to initiate FSH-induced steroidogenesis. VIP receptors (VPAC1 and VPAC2), like the FSH receptor, are G protein-coupled receptors, so we predicted that VIP signaling in granulosa cells is also absent in follicles that have not yet been selected into the preovulatory hierarchy. Initial studies established that mRNA encoding VPAC1 and VPAC2 are expressed within the granulosa cells throughout follicle development. Nevertheless, undifferentiated granulosa cells from prehierarchal (6-8 mm) follicles do not accumulate cAMP in response to a 4-hr incubation with chicken VIP; the capacity for such receptor signaling is attained only following selection within actively differentiating granulosa cells. VIP treatment did, however, increase expression of mRNA encoding the Gallus circadian clock protein, BMAL1-but only in granulosa cells collected from selected follicles. These findings provide evidence that, at follicle selection, the acquisition of VIP-induced cAMP cell signaling helps initiate and promote the differentiation of of granulosa cells. Furthermore, we propose that VIP signaling may regulate BMAL1 expression and, thus, a daily rhythmicity within granulosa cells of preovulatory follicles. Mol. Reprod. Dev. 83: 455-463, 2016. © 2016 Wiley Periodicals, Inc.

Involvement of protein kinase C and arachidonic acid pathways in the gonadotropin-releasing hormone regulation of oocyte meiosis and follicular steroidogenesis in the goldfish ovary

The involvement of protein kinase C (PKC) and arachidonic acid (AA) pathways were investigated in the GnRH regulation of oocyte meiosis and follicular testosterone production in the goldfish ovary. The results clearly demonstrate differences in the postreceptor mechanisms involving the stimulatory and inhibitory actions of GnRH peptides on basal and gonadotropin (GtH)-induced reinitiation of oocyte meiosis and steroidogenesis. In isolated goldfish follicles in vitro, the observed stimulatory effects of both salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II) on germinal vesicle breakdown were completely blocked by addition of PKC inhibitors, suggesting the involvement of PKC, presumably through activation of phospholipase C/diacylglycerol pathways in the GnRH-induced reinitiation of oocyte meiosis. Administration of an AA metabolism inhibitor, however, only blocked the stimulatory effect of sGnRH without affecting cGnRH-II-induced meiosis. As observed previously, in the presence of GtH, sGnRH was found to inhibit GtH-induced resumption of meiosis and testosterone production, whereas cGnRH-II was without effect. The inhibitory effect of sGnRH on GtH-induced meiosis and steroidogenesis was completely reversed by addition an AA metabolism inhibitor, whereas PKC inhibitors had no effect. These findings provide functional evidence in support of the novel hypothesis that goldfish ovarian follicles contain GnRH-receptor subtypes with different ligand selectivity mediating stimulatory and inhibitory actions of sGnRH and cGnRH in the goldfish ovary.

Expression and function of brain-derived neurotrophin factor and its receptor, TrkB, in ovarian follicles from the domestic hen (Gallus gallus domesticus)

This report summarizes patterns of mRNA expression for the brain-derived neurotrophic factor (BDNF) together with its high-affinity neurotrophin receptor trkB within the hen ovary during follicle development, describes hormonal mechanisms for the regulation of trkB gene expression and provides preliminary evidence for a novel function for BDNF-mediated TrkB signaling within the granulosa layer. Levels of BDNF mRNA in the thecal layer and of trkB mRNA within the granulosa cell layer increase coincident with entrance of the follicle into the preovulatory hierarchy. Localization of the BDNF mRNA transcript correlates with expression of BDNF protein within the theca interna of preovulatory follicles, while localization of trkB mRNA and protein occurs extensively within the granulosa cell layer of preovulatory follicles. This pattern of expression suggests a paracrine relationship between theca and granulosa cells for BDNF signaling via TrkB. Vasoactive intestinal peptide and gonadotropin treatments stimulate increases in levels of trkB mRNA within cultured granulosa cells derived from both prehierarchal and preovulatory follicles, and this response is increased by co-treatment with 3-isobutyl-1-methylxanthine. Finally, BDNF treatment of cultured granulosa cells from preovulatory follicles results in a modest, but significant, reduction in basal progesterone production, whereas this effect was reversed by k252a, an inhibitor of Trk kinase activity. These results support the proposals that BDNF functions as a paracrine signal in hen granulosa cells and that its physiological functions may include the modulation of steroidogenesis.

Effects of oestradiol-17beta and testosterone on progesterone production in the cultured granulosa cells of Japanese quail

In order to study the effects of steroid hormones on steroidogenesis in the avian ovary, quail granulosa cells were cultured with follicle stimulating hormone (FSH), oestradiol-17beta or testosterone. The progesterone content of the medium during the culture period of 66 h and the following 3 h of incubation with luteinising hormone (LH), was measured by radioimmunoassay. When FSH, oestradiol-17beta or testosterone were added during the 66 h culture, subsequent progesterone production by the cells during 3 h of incubation with LH was significantly increased. However, testosterone also stimulated progesterone production in the medium during the 66 h culture period, whereas FSH oroestradiol-17beta did not. Addition of staurosporine during culture inhibited both LH-stimulated progesterone production and testosterone-stimulated progesterone production. These results indicate that the processes during which granulosa cells acquired responsiveness to LH, and testosterone stimulates progesterone production might both be mediated by a staurosporine-sensitive protein kinase C-dependent pathway in quail granulosa cells.