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Abstracts from VI International Symposium on Avian EndocrinologyMarch 31 - April 5, 1996 Chateau Lake Louise, Alberta Continued The Role of Melatonin in the Circadian Systems of VertebratesM. Menaker, G. Tosini NSF Center for Biological Timing and Department of Biology,
Gilmer Hall, University of Virginia, Charlottesville, VA 22903,
USA It has been known for some time that melatonin is synthesized rhythmically under the control of circadian oscillators by isolated pineal glands of some fish, reptiles and birds and by the retina of Xenopus. Our recent results extend these findings to the parietal eye of the green iguana, to its retina and to the retinas of lampreys as well as several species of mammals, leading us to the working hypothesis that rhythmic melatonin synthesis is a property of all vertebrate photoreceptive structures. We know of no exceptions to this generalization, although in at least one case (the trout pineal) the oscillators driving the rhythm are not in the photoreceptive organ itself. Pineal melatonin always enters the blood, producing a rhythm of circulating melatonin that has been shown to drive the circadian rhythm of locomotor activity in several species of birds. In the iguana, circulating pineal melatonin drives a low amplitude circadian rhythm of body temperature as we have demonstrated by pinealectomy. Surprisingly, pinealectomy does not abolish the iguana's robust circadian rhythm of locomotor activity. These experiments make it clear that rhythmic circulating melatonin is not a "global" circadian signal; it can have specific effects on particular rhythms. It is likely that other instances of this kind of specificity will be uncovered as we learn more about melatonin's actions. Retinal melatonin is broken down within the retina itself by a different biochemical pathway than the one that breaks down circulating melatonin in the liver. Retinal melatonin usually does not enter the circulation (but there are clear exceptions to this in pigeons and quail). The fact that melatonin is universally produced in vertebrate retinas but rarely enters into the blood suggests strongly that it has an important local function associated with some aspect of photoreception. We propose that this (neuromodulatory?) function within photoreceptors was the original role of melatonin in vertebrates and that its action as a circulating hormone evolved secondarily. Plasticity of Melatonin Receptors in the Avian BrainD.N. Krause, M.L. Dubocovich1 Department of Pharmacology, University of California, Irvine,
CA 92717, USA; 1Department of Molecular Pharmacology and
Biological Chemistry, Northwestern University Medical School,
Chicago, IL 60611, USA In the avian brain, melatonin receptors are found primarily in the visual system, suggesting that this pineal hormone modulates central processing of visual information. Our recent studies in chick brain indicate that the level of visual input regulates the density of melatonin receptors in areas associated with the major route for visual input in birds, the tectofugal pathway (retina optic tectum n. rotundus ectostriatum periectostriatum). Chronic reductions in optic nerve activity by either unilateral optic nerve transection or intravitreal tetrodotoxin (TTX) injection resulted in decreases in melatonin receptor binding throughout the contralateral tectofugal pathway. Quantitative autoradiography of specific 2[125I]iodomelatonin binding to chick brain sections was used to measure melatonin receptor levels in discrete brain areas. Binding was significantly decreased in all tectofugal areas at one week, but not one day, after unilateral transection of the optic nerve. The effect was unilateral and corresponded to the projection path for the lesioned nerve. Similarly, binding density was decreased in the contralateral tectofugal pathway following a week of TTX injections into one eye (to suppress the electrical activity of retinal ganglion cells) and consequently the input of visual information to the brain. The effectiveness of TTX was verified by inhibition of the pupillary reflex. Following cessation of the TTX treatment, melatonin receptor binding in the tectofugal pathway recovered to control levels by 37 days, the same time course observed for recovery of the pupillary reflex. Production of melatonin is not affected by these experimental conditions. These studies reveal plasticity of melatonin receptors in avian brain and suggest that melatonin receptor expression can be functionally adjusted according to the overall level of neural activity in certain brain areas. Adjustments in the visual system may be relevant to chronic changes in light input, such as occurs seasonally. (Supported by MH42922) Effects of Melatonin in Synchronizing and Generating Avian Circadian RhythmsE. Gwinner, M. Hau, S. Heigl, T.J. Van't Hof, M. Zeman Max-Planck-Institut für Verhaltensphysiologie, D82346
Andechs, Germany In passerine birds, the periodic output of melatonin from the pineal organ is part of the basic circadian pacemaking system. Here, we first present evidence supporting this concept in house sparrows. Arrhythmic pinealectomized birds resumed thythmicity when treated with exogenous periodic melatonin. Several peculiarities of the entrainment pattern are consistent with the hypothesis that the periodic melatonin acts on another oscillator, presumably the SCN. Secondly, we show results indicating that the amplitude of the plasma melatonin rhythm is not constant but rather subject to modifications, eg., by latitude, season or a circannual oscillation. As a consequence of this, the properties, e.g., the strength of the pacemaker as a whole also shows seasonal and latitudinal changes. Preliminary data suggest that this may have important adaptive consequences for entrainment, for instance in migratory birds and in birds inhabiting arctic regions. Finally, we discuss data on the ontogeny of the melatonin rhythm indicating that a full amplitude plasma melatonin rhythm is already present around hatching or even earlier, not only in precocious but also in altricial birds. During these early stages of life, this rhythm is not yet self-sustained but rather depends on the periodic input of environmental factors, particularly light. One of the possible functions of this early melatonin rhythm is the synchronization of hatching. Melatonin Receptors in BirdsS.F. Pang, C.S. Pang, a.M.S. Poon, G.M. Brown Department of Physiology, University of Hong Kong, Hong Kong
and The Clarke Institute of Psychiatry, 250 College Street,
Toronto, ON, Canada Melatonin is a pineal hormone. It plays a role in the regulation of many organs and systems. Classically, the major sites of pineal melatonin action are considered to be the brain, retina and pituitary, with peripheral systems indirectly affected via the CNS. However, melatonin is a lipid soluble molecule and should be available to all tissues and organs. Direct peripheral actions of melatonin should be considered. In our laboratory, 2[125I]iodomelatonin (IMEL), a specific melatonin agonist, was used to investigate putative melatonin receptors in the neural and peripheral tissues of birds. To this end, putative melatonin receptors were demonstrated in the bird brain, retina, gut, spleen, thymus, bursa of Fabracious, adrenal gland, testis, ovary, kidney, lung and heart. The IMEL binding to bird tissues is rapid, stable, saturable, reversible and specific, and occurs with picomolar affinities and femtomolar densities. Autoradiographic studies indicated the IMEL binding in some tissues such as the brain, gut, adrenal gland, ovary and kidney is highly localized while in other tissues, such as the heart and lung, the binding is relatively diffused. Micromolar levels of guanine nucleotides inhibited the affinity and/or density of the IMEL binding in all tissues studied, suggesting that melatonin receptors in birds are Gprotein linked. The involvement of a pertussis toxinsensitive G protein in the inhibition of forskolin stimulated cAMP accumulation by melatonin in tissues such as the kidney and brain indicates that a Giprotein is involved in the melatonin signal transduction mechanism. Similar studies on melatonin receptor responses in other tissues, however, remain to be conducted. Detailed pharmacological and physiological comparisons of a few tissues have suggested the possibility of different melatonin receptor subtypes in the different tissues studied. A few melatonin receptor genes have been reported recently. Advances in melatonin receptor research in birds will provide important insights on the physiology of pineal melatonin and the photic environment in birds. (Supported by Neuroendocrinology Research Fund) Variability and Functional Aspects of Endogenous Circadian Rhythm in Japanese Quail Coturnix coturnix japonicaC. Guyomarc'h, S. Lumineau Laboratoire d'Ethologie, URA 373 ``Ethologie, Evolution,
Ecologie'', Campus de Rennes Beaulieu. 35042, Rennes Cedix France
A selection for rhythmic and arrhythmic Japanese quail in DD was conducted with fortytwo 3weekold Japanese quail. The absence or the presence of a free running rhythm of feeding activity in DD and the mean level of activity per 24 hours were noted.The freerunning period of the rhythm and the duration of the active phase were measured for rhythmic birds. Three pairs of the most rhythmic males and females, and 2 pairs of arrhythmic birds were selected. Young from these rhythmic and nonrhythmic pairs were born in the laboratory and were tested in DD under the same experimental and age conditions that were used for their parents. The number of rhythmic and of arrhythmic descendants of the different families differed significantly (Kruskall and Wallis Test, P = 0.0002 N=94). The total amount of activity per 24h differed between families (P=0.0001; N=90). A relationship between rhythmicity and total activity was found: rhythmic birds were significantly more active than arrhythmic birds (Mann Whitney; P=0.001). A pilot experiment with F2 birds revealed a relationship between presence of circadian rhythmicity in DD and ultradian rhythmicity in general expression of behaviour in chicks, a better synchronization between rhythmic birds and also a more rapid synchronization to a daynight cycle. In LD, rhythmic chicks were more active per 24h than non rhythmic chicks and, when sexually mature, they displayed more frequently. Moreover, rhythmic birds seemed to be smaller than arrhythmic birds. Development of Post-Hatching Melatonin Rhythm in Zebra Finches (Poephila guttata)T.J. Van't Hof, E. Gwinner Max-Planck Institute für Verhaltensphysiologie, D-82346,
Andechs, Germany We examined levels of melatonin in the pineal, eyes and plasma over a 24h period during development in the altricial zebra finch. Beginning as early as 2 days after hatching there was a distinct 24rhythm in melatonin in the pineal and plasma. Beginning at day 7 after hatching there was also a 24h rhythm present in the eyes. In the pineal and eyes the amplitude of the 24h rhythm increased with age. In contrast, the amplitude of the plasma melatonin rhythm at age 2 days was already within the range of the adults and did not increase with age. These results confirm and expand earlier findings in the European starling and parallel those from precocial birds indicating that the circadian system is already competent at or shortly after hatching even in altricial birds. Circannual Rhythms in StarlingsA. Dawson. Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton,
Huntingdon, Cambs. PE17 2LS UK If intact male starlings are chronically held on 12h daylengths, most undergo repeated cycles of testicular growth, regression, photorefractoriness, moult and renewed photosensitivity. However, if castrated starlings are so treated they become refractory, as judged by decreasing LH, and a proportion moult, but thereafter they show little evidence of cyclicity. The aim of this study was to examine physiological changes in such cycles in detail and to ascertain whether testosterone plays a role in cyclicity. The majority of intact males held on 12h days for 15 months underwent a gonadal cycle, moult and renewed testicular growth. Changes in LH loosely followed testicular changes but prolactin showed no consistent patterns. In females, only 5 of 9 birds cycles; 2 remained photosensitive and 2 remained refractory. Changes in both LH and prolactin were erratic. None of 9 castrates showed clear evidence of cyclicity in LH, only 6 moulted and prolactin was again erratic. In 6 castrates which had testosterone implants for 6 months, removal of the implants was immediately followed by moult in all birds. There was no immediate increase in LH but in 3 birds, there was an increase 2-3 months later, roughly coincident with the end of moult, which could signify transition from refractoriness to photosensitivity. The same was true of castrates with implants for 12 months. Controls on 8L showed an immediate increase in LH but no moult on removal of implants. This suggests that the circannual rhythms seen in intact birds may result from a sequence of mutually exclusive physiological stages rather than being driven by a central clock. Endocrine and Developmental Effects of Environmental Contaminants in BirdsJ.B. French Jr., P.F.P. Henry, M.a. Ottinger, B.a. Rattner Patuxent Environmental Science Center, National Biological
Service, Laurel, MD 20708-4041, USA Evidence from diverse field and experimental studies have converged recently to suggest that abnormal sexual and reproductive development in wildlife might be caused by the endocrine-like activity of pollutants acting on embryos. For example, hormonal and gonadal anomalies in alligators from Lake Apopka in Florida are associated with high levels of DDT and dicofol, experimental work on laboratory rodents has identified estrogenic and androgenic properties of several common pollutants, including polychlorinated biphenyls, and, injection of gull eggs with metabolites of DDT produces greater numbers of intersex gonads in the male hatchlings. Frequent female pairs and low reproductive success in colonies of seabirds located near polluted areas may be explained by this hypothesis. Our breeding and egg-injection studies are investigating the potential of Aroclor 1242 and hydroxylated PCB congener 30, both with known estrogenic activity, to alter the course of embryonic development of reproductive structures and to affect subsequent reproductive function in American kestrels. Preliminary findings indicate that gonadal morphology of hatchling and fledglings appeared consistent with the genetic sex of exposed birds, and histological preparations showed only very little intersexuality of male testes. Analyses in progress include plasma estradiol and testosterone, LHRH and catecholamine levels in the brain and cytochrome P450 levels in the liver. These and other contemporary findings will be discussed to provide a perspective on the hypothesis that contaminants are affecting endocrine and reproductive functions in wild birds. Hormonal Induction of Ovulation and Oviposition in QuailS. Wakabayashi, H. Sakai, M. Kikuchi, S. Ishii Department of Biology, Nihon University School of Dentistry,
Surugadai 1813, Chiyodaku, Tokyo 101; Department of Biology,
Waseda University, NishiWaseda, Tokyo 16950, Japan Captive breeding has been successful for some endangered avian species but unsuccessful for others. In the course of our captive breeding of the Japanese crested ibis, Nipponia nippon, we examined the possibility that ovulation could be induced by the administration of gonadotropins. A survey of the literature indicates that exogenous hormone administration has never previously been shown to induce ovulation in chicken or quail hens with a completely regressed ovary. In our study we used a glycoprotein fraction prepared from acetonedried chicken pituitary glands. As the route of administration, we combined two methods, a chronic administration by implantation of an osmotic pump and daily injections simulating the LH surge. Three out of seven treated birds laid eggs. One of the three hens laid five eggs and each of the other 4 hens laid only one egg. Among the 7 eggs, two hatched and both were male. One of them was revealed to be fertile by mating. Instead of the chicken pituitary glycoprotein we then used pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) for the chronic treatment and the injections, respectively. Substitution of the chicken pituitary glycoprotein fraction with PMSG and hCG gave a worse result, in that only one bird laid. It was concluded that hormone administration is useful method to induce ovulation, but improvement of the method is necessary. Neuroendocrine Basis of Reproductive FlexibilityT.P. Hahn, G.F. Ball Department of Psychology, Johns Hopkins University, Baltimore,
MD 21218, USA Birds with flexible or opportunistic reproductive schedules are often presumed to be able to initiate breeding at any time of year. In contrast, "typical" seasonal species are prevented from breeding for part of the year by a period of absolute refractoriness, when they show no reproductive response to either photoperiodic or extraphotoperiodic cues. Absolute refractoriness is correlated in a number of species with dramatically reduced hypothalamic content of gonadotropin releasing hormone (GnRH). Thus, insensitivity to reproductive stimuli during absolute photorefractoriness may result in part from a temporary inability of the hypothalamus to transduce perceived stimuli into a neuroendocrine signal (i.e., GnRH secretion). The temporal flexibility displayed by reproductive opportunists implies that no period of absolute refractoriness (either to photoperiod or to extraphotoperiodic cues) is present. Recent evidence from crossbills (Loxia sp.), northtemperate opportunistic breeders, reveals seasonal cycles in reproductive physiology, that suggest some form of "relative refractoriness", similar to that observed in quail (Coturnix sp.), may be present. Little is known of the neuroendocrine basis of relative refractoriness, however relatively refractory quail apparently do not show reduced hypothalamic content of GnRH. Maintenance of hypothalamic GnRH content would facilitate continuous responsiveness to environmental cues, and help explain how relatively refractory quail can resume reproductive development if exposed to sufficiently long days. It also could explain how opportunistic breeders might initiate or maintain reproductive development yearround, while displaying fundamentally seasonal reproductive cycles. We propose that opportunistic breeders will at most become relatively refractory, that they will therefore retain the capacity to respond to both photoperiodic and extraphotoperiodic cues throughout the year, and that this capacity will reflect seasonally constant hypothalamic GnRH content. We present preliminary evidence consistent with this idea for whitewinged crossbills (Loxia leucoptera), which appear to undergo seasonal cycles of luteinizing hormone secretion and gonadal development without any obvious changes in hypothalamic GnRH content. Differences of Dependency on Photoperiods and Temperature in Termination of Reproductive Activity in Three Galliform SpeciesM. Wada Department of Biology, College of Arts and Sciences, Tokyo
Medical and Dental University, 2-8-30 Kohnodai, Ishikawa-shi,
Chiba 272 Japan In Japanese quail (Coturnix japonica), termination of reproductive activity is dependent not only on photoperiodic change (from long days to short days) but also on temperature change (a lowering of temperature). This process is very different from that found in white-crowned sparrows. To investigate what factors are responsible for this difference, other galliform species, Northern bobwhite (Collinus virginianus) and Asian blue quail (Coturnix chinensis) were subjected to the same experimental protocol, in which birds were transferred from long days with mild temperature (LD) to long days with cold temperature (LDcold), short days with mild temperature (SD), and short days with cold temperature (SDcold). In Northern bobwhites, circulating LH decreased and the testes regressed in SD and SDcold groups; the results were similar to those in white-crowned sparrows. On the other hand, in Asian blue quail, circulating LH did not decrease nor the testes regress in SD group. The birds did not fully respond to SDcold conditions compared to Japanese quail. The overall results indicate that the termination of reproductive activity depends on the habitat the species lives in. HORMONES, EGG YOLK, AND DEVELOPMENT.H. Schwabl. The Rockefeller University Field Research Center for
Ecology and Ethology, Tyrrel Road, Millbrook, NY 12545, USA. Vertebrate eggs contain maternal hormones, growth factors and their mRNAs, which modify developmental processes and influence the fitness of the offspring. In this presentation evidence will be presented that 1) that avian egg yolk contains maternal sex steroid hormones; 2) that these hormones influence offspring development and 3) discuss possible mechanisms by which these maternal hormones are transferred into the yolk. The yolk of canary (Serinus canaria) eggs contains maternal testosterone and that the amount of yolk testosterone increases in each subsequently laid egg of a clutch. Experimental manipulations of the testosterone contents of freshly laid eggs suggest 1) that the variable doses of maternal testosterone can result in the differential growth of the nestlings in a clutch, possibly by modifying their ability to beg for food after hatching; and 2) that maternal testosterone may permanently alter the levels of the aggressive behavior of the offspring regardless of their genetic sex. Changes in testosterone levels in egglaying females may also explain the occurence of differential amounts of testosterone in their eggs. These results suggest that ovarian sex steroid hormones serve as a link between the mother and her offspring. This may allow females to optimize reproduction by hormonally influencing developmental processes and the phenotype of the offspring. PHOTOPERIODISM IN AMERICAN TREE SPARROWS: ROLE OF THE THYROID GLAND.F.E. Wilson. Division of Biology, Kansas State University, Ackert Hall,
Manhattan, KS 66506-4901, USA. When exposed to seasonal-like daylengths, obligately photoperiodic American tree sparrows (Spizella arborea) oscillate between photosensitive and photorefractory states. Although the etiology of these states is unknown, a simulated annual reproductive cycle, complete with testicular growth, photorefractoriness, and the recovery of photosensitivity, can be generated in the absence of the eyes and/or the pineal. However, such a cycle cannot be generated in the absence of the thyroid. The effects of radiothyroidectomy before, at, and after the onset of photostimulation demonstrate the thyroid dependence of seasonal reproduction and postnuptial molt and suggest that these events are programmed early during photostimulation. Photoinduced gonadal growth has both thyroid-independent and -dependent components, and once programming has occurred, thyroid hormones (THs) are not required either for full-blown testicular growth or for photorefractoriness or molt. Because later expression of programmed seasonal events is not temporally tied to TH availability, and because exogenous thyroxine injected on the first day of photostimulation (but not one week earlier) can program thyroidectomized males for seasonal reproduction and molt, THs (or TH-dependent ligands) likely effect seasonality be exerting organizational-like actions on photo-activated control circuits. The effects of radiothyroidectomy suggest also that thyroid-dependent testicular growth is programmed already by Week 1 on long days, and photorefractoriness and molt, between Weeks 1 and 3, and, therefore, that photostimulation opens a window, during which time euthyroid birds are programmed for seasonality. The demonstration that photorefractoriness can be dissociated from photoinduced gonadal growth argues that separate control circuits mediate these annually periodic events. Evidence, Past and Present, of Endocrine Disruption in Fish-Eating Birds in the Great LakesG.a. Fox, K.a. Grasman1 Canadian Wildlife Service, National Wildlife Research Centre,
Hull, PQ K1A 0H3 Canada; 1Department of Biological Sciences,
Wright State University, Dayton, OH 45435, USA The contamination of food-chains with persistent bioaccumulative chlorinated pollutants has been associated with a variety of injuries in fish-eating birds in the Great Lakes. Wildlife biologists have documented decreased parental care, reproductive failures, developmental abnormalities (feminization of testicular tissue and gross malformations), thyroid disfunction (goitre and hypothyroxinemia) and immune suppression (thymic atrophy and reduced T cell-mediated response to phytohemagglutinin) in one or more species in the past 25 years. These observations are consistent with those reported for laboratory studies of DDE- and PCB-exposed birds and mammals, and with those of ring doves fed two levels of an organochlorine mixture calculated to produce residues in their eggs of 15% and 30% of those observed in Lake Ontario herring gull eggs in 1976. Corticosterone, Gonadal Development and Energetic Condition in Neotropical Migrants: Comparisons between Spring and Fall Migration and Implications for ConservationR.L. Holberton, F.R. Moore1 Department of Biology, University of Mississippi, USA;
1Department of Biological Sciences, University of Southern
Mississippi, USA We are examining the corticosterone (B) stress response and its relationship to energetic condition and gonadal state in Neotropical migrants during spring and fall migration. We are testing the hypothesis that patterns of B release in response to capture stress differ between spring and fall and that these difference reflect seasonal changes in gonadal activity as well as in energy demand. Fall migrants (e.g., warblers, thrushes), sampled at stopover sites in New England and along the Northern Gulf of Mexico, exhibited elevated plasma levels of B at the time of capture but showed no further increase in B in response to handling stress when sampled several times up to an hour after capture. This pattern differs significantly from that reported for non-lipogenic, non-hyperphagic birds similarly sampled during the nonmigratory period when low B levels rise rapidly in response to stress. This apparent modulation of the stress response in fall is believed to facilitate migratory hyperphagia and lipogenesis. Although, in general, migrants sampled in spring showed a pattern of B expression similar to that found in fall, they exhibited greater variation in hormone level that appears to be related to gonadal development and energetic condition. In spring, male birds with greater cloacal protuberances (CP - used as an indirect measure of gonadal development), showed patterns of B release similar to that seen during the breeding season while others in poorer energetic condition and with less developed CPs showed higher levels of B. We are currently investigating the exact nature of the relationships between B, energy reserves, gonadal development, habitat quality and migratory success as these factors may have implications for conservation concerns in this declining group of birds. Variation in Plasma Corticosterone Levels in the Chicken (Gallus domesticus), Grey Duck (Anas Superciliosa) and Mallard (Anas platyrhynchos)J.F. Cockrem, M. Forman, K.E. Littin, R.M. Osborne Department of Physiology and Anatomy, Massey University,
Palmerston North, New Zealand Variations in corticosterone levels within individual birds have not been widely studied, so we examined the repeatability of basal and stressinduced rises in corticosterone in several species. Chickens (n=10) were sampled on four occasions at 0, 15 and 40 min from being picked up, with repeated handling for the first 15 min. Mean plasma corticosterone levels were initially low (1.27 + 0.10 ng/ml), increased at 15 min (4.18 + 0.43 ng/ml) and declined at 40 min (2.00 + 0.21 ng/ml). Some chickens had virtually no corticosterone response to handling. The response in some birds was identical over the four sampling occasions whilst in other birds it varied markedly. Native grey ducks (n=10) were sampled in the same way as the chickens. Their corticosterone responses were greater and the return to basal levels slower than the chickens (mean levels 6.26 + 0.57 , 21.68 + 1.25 and 16.78 + 1.80 ng/ml). Again, some birds were consistent in their responses whereas others varied. Marked differences between individuals in their corticosterone responses were also found in grey ducks sampled monthly for eight months. In another study corticosterone levels were high in wild mallard ducks caught in a trap (58.13 + 6.24 ng/ml), and decreased as the amount of contact with people increased (43.36 + 6.81 ng/ml after 6 weeks in captivity; 17.14 + 0.87 ng/ml after 5 months in captivity; 2.26 + 0.41 ng/ml in birds reared indoors for 3 months). The results indicate that corticosterone levels are a function both of the recent history of a bird and of inherent differences between birds. The elucidation of the physiological basis of consistent differences between birds in their corticosterone levels provides a challenge for future research. |