Chimera monstrosa (rabbit fish) like other holocephalans is a rare, delicate deep sea fish. Owing to the difficulty of sampling individuals in good shape, there is a paucity of information available on the morphology and physiology of this species especially concerning reproduction. In holocephalans, a hypothalamus-pituitary-gonadal axis has been postulated and a GnRH molecule identical to cGnRH II has been identified. The aim of the present study was to correlate the presence of steroidogenic enzymes in the ovarian follicles with the presence of GnRH in the hypothalamus. Estrogens, the steroids that trigger the accumulation of yolk (vitellogenesis) in the oocytes are synthesized by the somatic cells of the follicle in the vitellogenic stages via a cascade of steroid dehydrogenases involving 3 beta-hydroxysteroid-dehydrogenase (3 beta-HSD; in the inner thecal layer) and aromatase cytochrome (P450; granulosa layer). Our results showed that 3 beta-HSD is present concomitant with the presence of cGnRH II in the preoptic area and in the ventral hypothalamus. Another form of immunoreactive GnRH, mGnRH is also present in the brain of C. monstrosa. It is localized in the ventral telencephalon and in the midbrain caudal diencephalon (boundary between ventral thalamus and tegmentum of the mesencephalon). This form of GnRH is probably correlated with sexual behaviour.
"Measurements of high levels of GnRH and a possible binding protein in the serum of H. colliei suggest that the main role of GnRH is to activate the synthesis and secretion of gonadotropins from the pituitary (Pierantoni et al., 1993; Sherwood and Lovejoy, 1993). Similarly, GnRH-II has been suggested to play a role in the release of gonadotropins, since this form was present in females during follicle maturation, absent in immature females; and 3b-hydroxys- teroiddehydrogenase (3b-HSD), one of the key enzymes together with P 450 aromatase involved in the synthesis of estrogens, was present concomitant with the presence of GnRH-II (Masini et al., 2008). In fact, the GnRH-II molecule in cartilaginous fishes was found to release gonadotropin from other vertebrate groups (teleosts , birds and mammals) (Sherwood and Lovejoy, 1993). "
[Show abstract][Hide abstract] ABSTRACT: The class Chondrichthyes, that includes Elasmobranchii and Holocephali, is a diverse group of fish occupying a key position at the base of vertebrate evolution. Their evolutionary success is greatly attributed to their wide range of reproductive strategies controlled by different endocrine mechanics. As in other vertebrates, hormonal control of reproduction in chondrichthyans is mediated by the neuropeptide gonadotropin-releasing hormone (GnRH) that regulates the brain control of gonadal activity via a hypothalamus-pituitary-gonadal (HPG) axis. Chondrichthyans lack of a direct vascular supply from the hypothalamus to the zone of the pituitary where the gonadotropic activity resides, thus transport between these two zones likely occurs via the general circulation. In the brain of elasmobranchs, two groups of GnRH, GnRH-I and GnRH-II were identified, and the presence of two immunoreactive gonadotropins similar to the luteinising (LH) and follicle stimulating (FSH) hormones was identified in the pituitary. In holocephalans, only GnRH-II has been confirmed, and while gonadotropin activity has been found in the buccal pituitary lobe, the presence of gonadotropin receptors in the gonads remains unknowns. The diversity of reproductive strategies display by chondrichthyans makes it difficult to generalise the control of gametogenesis and steroidogenesis; however, some general patterns emerge. In both sexes, androgens and estrogens are the main steroids during gonadal growth; while progestins have maturational activity. Androgens also form the precursors for estrogen steroid production. Estrogens stimulate the hepatic synthesis of yolk and stimulate the development of different part of the reproductive tract in females. The role of other gonadal steroids may play in chondrichthyan reproduction remains largely unknown. Future work should concentrate in filling the gaps into the currently knowledge of the HPG axis regulation, and the use of reproductive endocrinology as a non-lethal technique for management of chondrichthyan populations.
General and Comparative Endocrinology 06/2013; 192. DOI:10.1016/j.ygcen.2013.05.021 · 2.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The digital holographic interference microscope and the holographic interference contrast method were used for 3-D imaging of native blood erythrocytes of healthy people and patients with different pathologies. Three basic morphology kinds of blood erythrocytes were detected. A sphericity coefficient was used as quantitative characteristics of blood erythrocytes morphology. 3-D images of native blood specimens of healthy people and patients are presented. It is shown that 3-D erythrocytes morphology characterizes the state of a human organism. Investigation of 3-D erythrocytes morphology must be a part of general medical blood investigation and the digital holographic interference microscope is an effective device for such purposes.
Advanced Optoelectronics and Lasers, 2005. Proceedings of CAOL 2005. Second International Conference on; 10/2005
[Show abstract][Hide abstract] ABSTRACT: The gonadotropin-releasing hormone (GnRH) and corticotropin-releasing family (CRF) are two neuropeptides families that are strongly conserved throughout evolution. Recently, the genome of the holocephalan, Callorhinchus milii (elephant shark) has been sequenced. The phylogenetic position of C. milii, along with the relatively slow evolution of the cartilaginous fish suggests that neuropeptides in this species may resemble the earliest gnathostome forms. The genome of the elephant shark was screened, in silico, using the various conserved motifs of both the vertebrate CRF paralogs and the insect diuretic hormone sequences to identify the structure of the C. milii CRF/DH-like peptides. A similar approach was taken to identify the GnRH peptides using conserved motifs in both vertebrate and invertebrate forms. Two CRF peptides, a urotensin-1 peptide and a urocortin 3 peptide were found in the genome. There was only about 50% sequence identity between the two CRF peptides suggesting an early divergence. In addition, the urocortin 2 peptide seems to have been lost and was identified as a pseudogene in C. milii. In contrast to the number of CRF family peptides, only a GnRH-II preprohormone with the conserved mature decapeptide was found. This confirms early studies about the identity of GnRH in the Holocephali, and suggests that the Holocephali and Elasmobranchii differ with respect to GnRH structure and function.
General and Comparative Endocrinology 02/2011; 171(2):237-44. DOI:10.1016/j.ygcen.2011.02.001 · 2.47 Impact Factor
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