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  • 1
    Electronic Resource
    Electronic Resource
    Reproductive Endocrinology of Birds (1980)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 42 (1980), S. 457-472 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.42.030180.002325
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  • 2
    Electronic Resource
    Electronic Resource
    Reproduction and Resistance to Stress: When and How (2003)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 15 (2003), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Environmental and social stresses have deleterious effects on reproductive function in vertebrates. Global climate change, human disturbance and endocrine disruption from pollutants are increasingly likely to pose additional stresses that could have a major impact on human society. Nonetheless, some populations of vertebrates (from fish to mammals) are able to temporarily resist environmental and social stresses, and breed successfully. A classical trade-off of reproductive success for potential survival is involved. We define five examples. (i) Aged individuals with minimal future reproductive success that should attempt to breed despite potential acute stressors. (ii) Seasonal breeders when time for actual breeding is so short that acute stress should be resisted in favour of reproductive success. (iii) If both members of a breeding pair provide parental care, then loss of a mate should be compensated for by the remaining individual. (iv) Semelparous species in which there is only one breeding period followed by programmed death. (v) Species where, because of the transience of dominance status in a social group, individuals may only have a short window of opportunity for mating. We suggest four mechanisms underlying resistance of the gonadal axis to stress. (i) Blockade at the central nervous system level, i.e. an individual no longer perceives the perturbation as stressful. (ii) Blockade at the level of the hypothalamic-pituitary-adrenal axis (i.e. failure to increase secretion of glucocorticosteroids). (iii) Blockade at the level of the hypothalamic-pituitary-gonad axis (i.e. resistance of the reproductive system to the actions of glucocorticosteroids). (iv) Compensatory stimulation of the gonadal axis to counteract inhibitory glucocorticosteroid actions. Although these mechanisms are likely genetically determined, their expression may depend upon a complex interaction with environmental factors. Future research will provide valuable information on the biology of stress and how organisms cope. Such mechanisms would be particularly insightful as the spectre of global change continues to unfold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2003.01033.x
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  • 3
    Electronic Resource
    Electronic Resource
    Gonadotropin-Inhibitory Peptide in Song Sparrows (Melospiza melodia) in Different Reproductive Conditions, and in House Sparrows (Passer domesticus) Relative to Chicken-Gonadotropin-Releasing Hormone (2003)
    Oxford, UK : Blackwell Science, Ltd
    Journal of neuroendocrinology 15 (2003), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Gonadotropin-releasing hormone (GnRH) regulates reproduction in all vertebrates. Until recently, an antagonistic neuropeptide for gonadotropin was unknown. The discovery of an RFamide peptide in quail that inhibits gonadotropin release in vitro raised the possibility of direct hypothalamic inhibition of gonadotropin release. This peptide has now been named gonadotropin-inhibitory hormone (GnIH). We investigated GnIH presence in the hypothalamus of two seasonally breeding songbird species, house sparrows (Passer domesticus) and song sparrows (Melospiza melodia). Using immunocytochemistry (ICC), GnIH-containing neurones were localized in both species in the paraventricular nucleus, with GnIH-containing fibres visible in multiple brain locations, including the median eminence and brainstem. Double-label ICC with light microscopy and fluorescent ICC with confocal microscopy indicate a high probability of colocalization of GnIH with GnRH neurones and fibres within the avian brain. It is plausible that GnIH could be acting at the level of the hypothalamus to regulate gonadotropin release as well as at the pituitary gland. In a photoperiod manipulation experiment, GnIH-containing neurones were larger in birds at the termination of the breeding season than at other times, consistent with a role for this neuropeptide in the regulation of seasonal breeding. We have yet to elucidate the dynamics of GnIH synthesis and release at different times of year, but the data imply temporal regulation of this peptide. In summary, GnIH has the potential to regulate gonadotropin release at more than one level, and its distribution is suggestive of multiple regulatory functions in the central nervous system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2003.01062.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of Acute Treatment with 8-OH-DPAT and Fluoxetine on Aggressive Behaviour in Male Song Sparrows (Melospiza melodia morphna) (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of neuroendocrinology 15 (2003), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The role of serotonin in modulating male aggressive behaviour was investigated in male song sparrows, Melospiza melodia morphna, using two different serotonergic drugs, fluoxetine and 8-OH-DPAT. Fluoxetine is a selective serotonin reuptake inhibitor of the neuronal reuptake pump increasing synaptic concentrations of serotonin, and 8-OH-DPAT is a specific serotonin (5-HT1A) receptor agonist. The serotonergic control of aggression in passerines has not been previously investigated. We examined these behaviours within a controlled setting using a laboratory simulated territorial intrusion, with a hierarchical scale to quantify male–male aggressive behaviour. Utilizing this scale, we quantified the extent of male aggressive behaviour in two experiments. In experiment 1, song sparrows were given 100 µl, s.c. injections of either fluoxetine (10 mg/kg) or 8-OH-DPAT (1 mg/kg). Experiment 2 was a dose–response study using three doses of 8-OH-DPAT (0.1, 1 and 10 mg/kg). In both studies, aggressive behaviour was measured 1 h after injection for 10 min in response to the presence of a novel male decoy combined with playback of conspecific song. Both drugs significantly reduced male aggressive behaviour, and 8-OH-DPAT did so in a dose-dependent manner. The effect of the two drugs upon general activity was also measured using infra-red perch hop detectors. Activity levels were not effected by either fluoxetine or 8-OH-DPAT at all of the respective doses, indicating that the reduction in aggressive behaviour was specific. These results demonstrate that, in a passerine species, the serotonergic system negatively regulates male–male aggressive behaviour. These results further demonstrate that aggression can be effectively studied in a laboratory setting and natural aggressive responses can be elicited using this method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.2003.00968.x
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  • 5
    Electronic Resource
    Electronic Resource
    Energy metabolism, testosterone and corticosterone in white-crowned sparrows (1999)
    Springer
    Journal of comparative physiology 185 (1999), S. 463-470 
    Details
    ISSN: 1432-1351
    Keywords: Key words Metabolism ; White-crowned sparrows ; Testosterone ; Corticosterone ; Activity ; AbbreviationsBMR basal metabolic rate ; D duration of subjective night ; L duration of subjective day ; RMR resting metabolic rate ; T testosterone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The influence of the steroid hormones testosterone and corticosterone on energy metabolism and activity of birds is largely enigmatic. We measured resting metabolic rate during night and day in 12 long-term castrated and 12 intact male white-crowned sparrows (Zonotrichia leucophrys gambelii) under short-day (8:16 SD), long-day (20:4 LD), LD+testosterone implant and LD−testosterone implant conditions. Each male was sequentially measured under all four conditions. Photostimulation increased testosterone, resting metabolic rate, food intake, hopping activity and body mass in castrates and intact males. Surprisingly, testosterone levels and metabolic rates did not differ between intact and castrated males. Testosterone implantation increased activity and food intake, but decreased body mass and resting metabolic rate in both groups. Removing testosterone implants reversed the effects on resting metabolic rate, activity and food intake. Corticosterone levels, measured immediately at the end of metabolism measurements, showed birds were not stressed. Corticosterone had no apparent relationship with resting metabolic rate and there was no interaction between corticosterone and testosterone. Overall, positive changes in testosterone levels resulted in a decrease of resting metabolic rate. We speculate that testosterone increases activity, and birds compensate for increased activity metabolism by reducing resting metabolic rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003590050407
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  • 6
    Electronic Resource
    Electronic Resource
    Androgen in high concentrations in the blood of female western gulls,Larus occidentalis (1980)
    Springer
    Naturwissenschaften 67 (1980), S. 514-515 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01047637
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  • 7
    Electronic Resource
    Electronic Resource
    Changes in pituitary and adrenal sensitivities allow the snow bunting (Plectrophenax nivalis), an Arctic-breeding song bird, to modulate corticosterone release seasonally (1998)
    Springer
    Journal of comparative physiology 168 (1998), S. 353-358 
    Details
    ISSN: 1432-136X
    Keywords: Key words Corticotropin-releasing factor ; ACTH ; Vasotocin ; Mesotocin ; Diazapam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Several free-living avian species have recently been shown to seasonally modulate corticosterone release in response to capture and restraint. We examined possible mechanisms underlying seasonal adrenocortical modulation in snow buntings (Plectrophenax nivalis), a species that breeds and molts (the energetically costly replacement of feathers) in the Alaskan Arctic. Snow buntings dramatically reduced baseline and maximal corticosterone titers during molt compared to the breeding season. This effect is not explained by changes in either corticosterone binding protein capacity or the overall condition of the bird (assessed by weight and fat storage). Although the adrenal's capacity to secrete corticosterone is reduced during molt, adrenal insensitivity does not fully explain reduced maximal output since exogenous adrenocorticotropic-hormone enhanced corticosterone release during both seasons. In contrast, no exogenous adrenocorticotropic hormone releasing factor (corticotrophin-releasing factor, arginine vasotocin or mesotocin) enhanced corticosterone secretion during molt. This suggests that the pituitary's endogenous adrenocorticotropic secretion was maximal in response to capture and handling, making the pituitary an important site regulating corticosterone levels. Taken together, these results indicate that seasonal modulation of corticosterone release in this species is controlled at both the adrenal and pituitary glands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050154
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  • 8
    Electronic Resource
    Electronic Resource
    The adrenocortical stress-response of Black-legged Kittiwake chicks in relation to dietary restrictions (1999)
    Springer
    Journal of comparative physiology 169 (1999), S. 303-310 
    Details
    ISSN: 1432-136X
    Keywords: Key words Corticosterone ; Testosterone ; Food-stress ; Nest-bound chicks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In this study we examined hormonal responses of Black-legged Kittiwake (Rissatridactyla) chicks to experimental variations in energy content and nutritional quality (low or high lipid to protein ratio, LPR) of their food. Starting at the age of 10 days, chicks were fed either high or low LPR fish at 30, 50, 70 and 100% of ad libitum energy intake. After 20 days of treatment, chicks were exposed to a standardized acute handling and restraint stress protocol, where a baseline sample was taken immediately after taking a chick from the nest, and three additional blood samples were taken at intervals up to 50 min. Testosterone and corticosterone titres in plasma were measured via radioimmunoassay. We found that baseline testosterone levels were not significantly affected by the experimental treatments. Food-restricted chicks had elevated baseline and acute stress-induced levels of corticosterone compared to chicks fed ad libitum. An elevation of circulating levels of corticosterone in energetically stressed individuals was further magnified by low nutritional quality of food. Baseline and acute stress-induced corticosterone levels of chicks were negatively correlated with their fat reserves. We conclude that the physiological condition of Black-legged Kittiwake chicks can be assessed reliably by measuring circulating levels of corticosterone. We discuss short- and long-term effects of elevated corticosterone secretion in food-stressed nest-bound chicks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050225
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