Giovanni Chieffi

Immunoreactive GnRH in Hypothalamic and Extrahypothalamic Areas

Publisher Summary This chapter reviews the presence and the physiological significance of gonadotropin-releasing hormone (GnRH) inside and outside the brain of vertebrates; surveys comparative aspects that reveal similarities and differences, discussed from the evolutionary and adaptive viewpoint. Immunoreactive GnRH perikarya are widespread in the brain even outside the hypothalamus. Immunoreactive GnRH fibers project in many directions alongwith the Median Eminence (ME). In Elasmobranchs, unique among vertebrates, their fibers project in various directions except ME. The discharge into the ventricular system and from there into the venous system is also a primitive mechanism of transport observed in the lamprey and stickleback. The possibility of alternative routes of communication with pituitary or other targets is hypothesized in Chondrichthyes. The detection of ir GnRH in the blood of Chondrichthyes is attractive in explaining a puzzling situation in these fish, as much as the brain may communicate with the pituitary. The involvement of messengers other than cyclic adenosine monophosphate (cAMP) is a general feature of the mechanism of action of GnRH at pituitary and gonadal levels.

Cell Biology of the Harderian Gland

The harderian gland is an orbital gland of the majority of land vertebrates. It is the only orbital gland in anuran amphibians since the lacrimal gland develops later during phylogenesis in some reptilian species. Perhaps because it is not found in man, little interest was paid to this gland until about four decades ago. In recent years, however, the scientific community has shown new interest in analyzing the ontogenetic and morphofunctional aspects of the harderian gland, particularly in rodents, which are the preferred experimental model for physiologists and pathologists. One of the main characteristics of the gland is the extreme variety not only in its morphology, but also in its biochemical properties. This most likely reflects the versatility of functions related to different adaptations of the species considered. The complexity of the harderian gland is further shown in its control by many exogenous and endogenous factors, which vary from species to species. The information gained so far points to the following functions for the gland: (1) lubrication of the eye and nictitating membrane, (2) a site of immune response, particularly in birds, (3) a source of pheromones, (4) a source of saliva in some chelonians, (5) osmoregulation in some reptiles, (6) photoreception in rodents, (7) thermoregulation in some rodents, and (8) a source of growth factors.

Stimulatory effect of a GnRH agonist (buserelin) in in vitro and in vivo testosterone production by the frog (Rana esculenta) testis

The summary testicular effects of an agonistic analogue of gonadotropin-releasing hormone (buserelin, GnRHa) have been studied in vitro and in vivo in the frog, Rana esculenta. During 3 h incubation GnRHa (8 X 10(-7) M) potentiated pituitary factors in stimulating testosterone production by minced testes in vitro. After 6 h of incubation 8 X 10(-7) M GnRHa stimulated maximal testosterone output. Testes of 10-day hypophysectomized animals did not show any GnRHa effect in vitro. In vivo, a direct effect of GnRHa on testicular testosterone production was demonstrated in hypophysectomized animals, although this effect was temperature-dependent, requiring the frog to be maintained at a high temperature (24 degrees C). No effect of GnRHa was detectable in frogs kept at a low temperature (4 degrees C).

Plasma and testicular estradiol and plasma androgen profile in the male frog Rana esculenta during the annual cycle.

Seasonal plasma and testicular estradiol levels were measured in the male frogs, Rana esculenta, by radioimmunoassay. In plasma samples a simultaneous measurement of androgens was carried out in order to investigate a possible relationship between androgens and estradiol-17 beta. Concomitantly with the estradiol-17 beta peak in plasma and testes during the April-May period, plasma androgens sharply decreased.

Molecular forms of immunoreactive gonadotropin-releasing hormone in hypothalamus and testis of the frog, Rana esculenta.

The hypothalamus and the testis of the frog, Rana esculenta, contain gonadotropin-releasing hormone (Gn-RH)-like peptides which are recognized by an antiserum raised against mammalian Gn-RH. Two molecular forms which coelute with synthetic chicken II and salmon Gn-RH from reverse-phase HPLC were distinguished in the hypothalamus. A single peak coeluting with synthetic chicken II Gn-RH was present in the testis.

Identification of sex hormones in the ovarian extracts of Torpedo marmorata and Bufo Vulgaris.

An analysis based on chromatography, derivatives formation, and ultraviolet spectrography, has been made of steroid hormones isolated from the ovaries of Torpedo marmorata and Bufo vulgaris. Estradiol-17β, estriol, and progesterone have been identified in the ovarian extracts of Torpedo marmorata; and estradiol-17β estrone, estriol, and progesterone in those of Bufo vulgaris. Quantitative data are presented and discussed in relation to current hypotheses on the biosynthesis of steroid hormones, and on the significance of the occurrence of progesterone in the ovaries of lower vertebrates.

Regulation of Ovarian Steroidogenesis

The surge of interest in comparative endocrinology over the last thirty years has advanced our knowledge of gonadal steroidogenesis in nonmammalian vertebrates. In particular, the last decade has seen major advances thanks to the isolation and characterization of various compounds and the advent of more sensitive methods for hormone measurement.

Hypothalamus-hypophysis and testicular GnRH control of gonadal activity in the frog, Rana esculenta: Seasonal GnRH profiles and annual variations of in vitro androgen output by pituitary-stimulated testes ☆

The binding of a gonadotrophin-releasing hormone (GnRH) long acting analog (GnRHA), D-Ser (But)6,Pro9-NEt GnRH (HOE 766), to pituitary and testicular extracts and the presence of GnRH-like material in testes and hypothalamuses were measured in the frog, Rana esculenta. Also, the cellular localization of immunoreactive GnRH was investigated in testes by immunohistochemical staining. Furthermore, lyophilized preparations of pituitary crude homogenates from animals caught monthly were tested in vitro for their ability to stimulate androgen production by December testes. Satisfactory results on specific 125I-GnRH binding were difficult to obtain in view of its low binding capacity. Moreover, binding in testicular homogenates was of the same order of magnitude (about 2%) as that found in pituitaries. In a cospecific radioimmunoassay for GnRH nonapeptide, both hypothalamic and testicular extracts gave displacement parallel to the standard curve. Immunoreactive GnRH did not significantly fluctuate in hypothalamuses, while it peaked in testes during December and July. Immunoreactive GnRH was evidenced in June and September testes employing immunohistochemical staining. In particular, the interstitial cells and the Sertoli cells were faintly stained. Testes of December animals stimulated by February pituitaries produced larger quantities of androgens as compared with testes stimulated with hypophyseal preparations from the remaining periods of the year. In conclusion, the present results are consistent with the idea that seasonal changes of the hypothalamus-hypophyseal activity play an important role in regulating the hormonal response in vertebrate testes. Moreover, we report that, in addition to rats, GnRH-like material is present in frog testes and for the first time it has been shown that such putative intratesticular material undergoes seasonal fluctuations in a vertebrate.

Receptors for sex hormones in the skin of the amphibia

Abstract The retention of [ 3 H]-testosterone and the occurrence of specific receptors for sex hormones in the skin of males of Rana esculenta and Triturus cristatus were studied. In R. esculenta a selective uptake of testosterone and a receptor for androgens were observed, whereas in T. cristatus only a receptor for estrogens was found. These findings suggest that the body skin may be a secondary sex character in R. esculenta .

Morphology of the Harderian gland of the Gecko, Tarentola mauritanica.

ABSTRACT The Harderian gland of the gecko, Tarentola mauritanica, was studied at the histological, histochemical, and ultrastructural levels. It is a nonlobate compound acinar gland surrounded by a thin capsule of connective tissue. Numerous connective tissue‐type mast cells, ultrastructurally similar to those described in other higher vertebrates, were identified in the interstitial tissue between the acini. Pyramidal or columnar‐shaped secretory glandular cells were observed in the acini. In the glandular cells, two types of structures could be distinguished on the basis of their high or low electron density. Lipid droplets were found in the cytoplasm of the Harderian gland of both sexes. Histochemical tests showed that the Harderian gland of the gecko is a seromucous gland. The secretion is essentially merocrine, although an apocrine type of secretion is sometimes observed. J. Morphol. 244:137–142, 2000.