L. Iela

Reproduction in the Mexican leaf frog, Pachymedusa dacnicolor: III. The female

The female of the Mexican leaf frog, Pachymedusa dacnicolor, displays a marked annual ovarian cycle. This consists of a long period of vitellogenic stasis, starting in early fall, soon after the breeding season, and ending in early spring. Oogonial proliferation continues throughout the year and new previtellogenic follicles are formed continuously. During the period of vitellogenesis, from spring to early summer, early, advanced, and postvitellogenic follicles are all found together, a situation that continues through the breeding season. This is correlated with the fact that a breeding female can lay three or more clutches per season. Breeding can begin as early as June and end as late as early September, with peak spawning activity taking place during July and August. An examination of the ovarian hormone secretion pattern in P. dacnicolor during the year revealed that plasma levels of testosterone and estradiol correlated with ovarian growth and attained highest levels in amplectant and ovulating females. Both hormones showed quite similar plasma levels and patterns of change during the annual reproductive cycle. Lowest plasma levels of testosterone and estradiol were found during fall and winter, in females possessing exclusively previtellogenic ovarian follicles. Plasma progesterone levels were maintained at a very low level throughout the year, except for the ovulatory surge, when amplectant and ovulating females may show a three- to sixfold increase. Plasma androstenedione showed a low peak during this phase of the reproductive cycle. Plasma levels of 5 alpha-dihydrotestosterone were 13 to 30 times lower than plasma testosterone levels. The potential roles of these gonadal steroids in controlling ovarian activity and reproduction are discussed briefly.

Immunoreactive luteinizing hormone-releasing hormone in the frog (Rana esculenta) brain: Distribution pattern in the adult, seasonal changes, castration effects, and developmental aspects

The present work describes the neuroanatomical distribution of the immunoreactive luteinizing hormone-releasing hormone (ir-LHRH) system in the brain of adult male and female, castrated male and developing Rana esculenta. No obvious sex differences in the distribution pattern of ir-LHRH were observed. Immunoreactive neuronal cell bodies are not contained within a single anatomically defined area of the brain. They are present as distinct groups in the olfactory bulbs, medial septal area, anterior preoptic area (APOA), retrochiasmatic area of the infundibulum, and interpeduncular nucleus-tegmentum area. Of the entire brain, the medial septal-APOA region exhibits the highest frequency of ir-LHRH cell bodies in both sexes. ir-LHRH fiber projections are present in the olfactory bulbs, medial septal area, APOA, floor of the diencephalon, subhabenular-periventricular area in the epithalamus, lateral suprachiasmatic area, ventrolateral infundibulum, median eminence, pars nervosa, optic tectum, interpeduncular nucleus-tegmentum area, and rhombencephalon grey. Castration seems to bear no effect on the pattern of ir-LHRH system in the frog brain. The influence of castration consisted in decreased intensity of the immunostaining and frequency of occurrence of the septal-APOA neuronal cell bodies. In median eminence, castration also induced a sensible decrease in the immunoreactivity, whereas in the pars nervosa of 50-day castrates ir-LHRH fibers totally disappeared. During ontogenesis, ir-LHRH elements first become evident in stage 31 tadpoles (beginning of metamorphic climax); LHRH immunoreaction is restricted to the cell bodies and fibers in the APOA and some fibers in the ventral hypothalamus and a few in median eminence. This condition remains unaltered until stage 33 when the tail is almost totally resorbed. The possible implications of the ir-LHRH-containing brain areas in the different aspects of reproduction in the frog are briefly discussed.

Distribution of FMRFamide-like Immunoreactivity in the Amphibian Brain: Comparative Analysis

FMRFamide is a small neuropeptide present in particular neurons of the basal forebrain and midbrain of the vertebrate groups studied, especially fishes and mammals. In order to assess interspecies variation, the distribution of FMRFamide‐like immunoreactivity was studied in the brains of 13 species of amphibian. Although FMRFamide‐immunoreactive (IR) terminals occurred throughout much of the brain, IR cell groups were noted in circumscribed regions of the CNS. In the eight anuran species studied, two major populations of labeled perikarya were observed: one in the septopreoptic area and another one in the caudal portion of the diencephalon. The rostrocaudal extent of both and the number of labeled somata in each neuronal group displayed species‐specific differences. In urodeles and gymnophiones, labeled perikarya were located in the diencephalon, but there were remarkable species differences in the number of such cells. It is discussed whether sex or season of collection may account for some of the differences observed. The distribution of FMRFamide‐IR perikarya, fibers, and pathways in the brain of anurans, urodeles, and gymnophiones was compared. The existence of FMRFamide perikarya in the anterior preoptic neuropil and medial septum appeared to be a feature common to all anurans; labeled neurons in the dorsal thalamus, however, may be present only in the (viviparous) gymnophione Typhlonectes compressicauda. Cerebrospinal fluid contacting FMRFamide neuronal cell bodies and fibers were observed in each of the three taxonomic orders. The data are compared with those previously obtained for other groups of vertebrates. J. Comp. Neurol. 414:275–305, 1999.

The function of fat bodies in relation to the hypothalamo-hypophyseal-gonadal axis in the frog, Rana esculenta.

SummaryIn this study the authors have tried to furnish experimental support for the importance of fat bodies in the normal functioning of the hypothalamo-hypophyseal-gonadal system of the male frog, Rana esculenta. These experiments have shown a hypothalamohypophyseal control of the mobilization of fat body contents, directly involved in the control of testicular activity. Furthermore it is proposed that the fat body contents are released into the testis through direct vascular contacts between the two organs. We suggest that the A1 cells (lactotrophs) and/or B2 cells (FSH-gonadotrops) of the pars distalis contain a factor responsible for the mobilization of fat body contents, and that the pars distalis gonadotropins are incapable of stimulating the testis in the absence of fat bodies. In the light of these results a scheme has been put forward showing the position of fat bodies in the hypothalamohypophyseal-gonadal axis of the frog.

GnRH in the invertebrates: an overview.

Publisher Summary This chapter provides an overview of GnRH in the invertebrates. The gonadotropin-releasing hormone (GnRH), which was previously called luteinizing hormone-releasing hormone (LHRH), represents a pivotal peptide in animal reproduction. GnRH is a decapeptide originally isolated from the porcine and ovine hypothalamus and is characterized for its ability to enhance the release of pituitary gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). All known forms of GnRH peptides have in common a pyroglutamyl residue at the amino terminus and an amidated glycine at the carboxy terminus. Except for the octoGnRH, all other known forms are decapeptides and differ by one or more amino acids; amino acids 4 and 9 are conserved in all forms known to date. Studies involving an evolutionary approach to GnRH have adopted one particular strategy; attention is on understudied invertebrate taxonomic groups. Invertebrate species that vary in their phylogenetic relationships are likely to reveal differences, as well as similarities, in GnRH form and function. Studies on invertebrate species are beginning to provide further insights on the structural and functional similarities and differences. The perspective that evolution has acted to shape the GnRH molecule effectively leads to investigations in a comparative approach.

Effect of temperature and light on the production of androgens in the maleRana esculenta

The present data show that experimentally-controlled environmental variables (light and temperature) can alter circulating androgen levels in the male green frog,Rana esculenta, treated in different phases of the testicular cycle.

Immunohistochemical demonstration of the presence and localization of diverse molecular forms of gonadotropin-releasing hormone in the lizard (Podarcis s. sicula) brain

The immunohistochemical presence and the distribution pattern of four different molecular forms of gonadotropin-releasing hormone (GnRH) were investigated in the brain of both sexes of the lizard, Podarcis s. sicula. Animals used in this study were collected in November and April, representing two different periods of the reproductive cycle. The antisera used were those raised against synthetic mammalian GnRH, chicken GnRH-I and II, and salmon GnRH. Strong immunoreaction was obtained for salmon, chicken-I, and chicken-II GnRHs, whereas a very weak reaction was seen for the mammalian form of GnRH. The distribution of immunoreactive-GnRH perikarya and fibers did not vary with the sex, the reproductive condition of the animals, or the antiserum used. Also, the intensity of immunoreaction with any one antiserum was quite similar in both periods of the year and in all brains examined. The immunoreactive perikarya was seen as two distinct groups, one in the mesencephalon and the other in the infundibulum. Immunoreactive fiber endings were seen in the telencephalon, the optic tectum, the anterior preoptic area, the median eminence, the central grey matter, the rhombencephalon, and the cerebellum. No immunoreactive perikarya were seen in the telencephalon or the anterior preoptic area.

Circannual testicular rhythm in the green frog, Rana esculenta

Abstract We followed testis weight, seminiferous tubule diameter, spermatogenetic activity, pituitary gonadotropin secretory activity and spermiation response in Rana esculenta, under day length 12:12. On this lighting schedule, groups of frogs were studied at 4°C, 15°C and 24°C. A group of frogs reared in the laboratory under natural temperature and lighting conditions served as captive controls, whereas freshly captured frogs were used as wild controls. In frogs exposed to 24°C the testicular growth was greatly speeded up compared to other groups, but long-term exposure to this temperature apparently caused regression of pituitary gonadotropic activity and testicular growth. Circannual testicular rhythm was evident in frogs reared at constant 15°C. In the 4°C group the testicular cycle proceeded for 120 days and then apparently “stopped” at a specific phase associated with winter stasis. The rhythm, in fact, was reinitiated by an appropriate environmental input (15°C). In summary, it was demonstrated th...

Development and distribution of FMRFamide-like immunoreactivity in the toad (Bufo bufo) brain

By using immunohistochemistry, we studied the development and distribution of the FMRFamide-like immunoreactive (ir) neuronal system in the toad brain during the ontogeny. In addition to this, experimental evidence was provided to show that the rostral forebrain-located FMRFamide neurons originate in the olfactory placode and then migrate into the brain along the olfactory pathway. During early development, within the brain, FMRFamide-ir perikarya first appeared in the periventricular hypothalamus. Later in development, FMRFamide-ir cells were visualized in the rostralmost forebrain simultaneously with similar ir cells in the developing olfactory mucosa. Selective ablation of the olfactory placode(s), prior to the appearance of the first FMRFamide-ir cells in the brain, resulted in the total absence of ir cells in the telencephalon (medial septum and mediobasal telencephalon) of the operated sides(s). The preoptic-suprachiasmatic-infundibular hypothalamus-located FMRFamide-ir neurons were not affected by olfactory placodectomy, arguing that they do not originate in the placode. This result points to the placode as the sole source of such neurons in the rostral forebrain.

The possible significance of testosterone in the female green frog Rana esculenta

Abstract The high level of testosterone in the plasma of the female Rana esculenta has raised a number of questions about the possible role of this hormone in reproductive physiology. To provide an explanation of this problem, in vivo and in vitro metabolism studies were carried out and the effect of testosterone on central and peripheral target organs was studied. Testosterone (T), 5α-dihydrotestosterone (DHT), estrone (E1), 17β-estradiol (E2) and 17α-OH-pregnenolone were found in ovarian tissue. The in vitro experiments showed that the ovary could metabolize testosterone into 5α-dihydrotestosterone, 11-ketotestosterone (11K-T) and 17β-estradiol, while the oviduct transformed it into 5α-dihydrotestosterone and 11-ketotestosterone. Testosterone administration to intact females provoked a slight increase in the plasma estrogen levels and to castrates it effected a partial restoration of the pituitary gonadotropic cells. On the oviduct only 5α-dihydrotestosterone seemed to have some effect but slight. The d...