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First published online November 24, 2003
Journal of Experimental Biology 207, 143-154 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00734
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The low-affinity glucocorticoid receptor regulates feeding and lipid breakdown in the migratory Gambel's white-crowned sparrow Zonotrichia leucophrys gambelii

Meta M. Landys1,*, Marilyn Ramenofsky1, Christopher G. Guglielmo2 and John C. Wingfield1

1 Department of Biology, University of Washington, Box 351800, Seattle, WA 98195, USA
2 Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA



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  		Fig. 1. Pictorial representation of the experimental design used to evaluate effects of RU486 treatment in the Gambel's white-crowned sparrow. Spring migrants and wintering birds were held on 16 h:8 h L:D and 8 h:16 h L:D, respectively. (A) Experimental protocol designed to investigate the behavioral responses of birds to RU486 treatment under ad libitum food conditions. Treatment effects were tested by comparing birds one day before and one day after RU486 injections. Controls received vehicle injections. Birds were monitored for differences in locomotor activity (as determined by motion detectors in registration cages) and daily food intake. (B) Experimental protocol designed to investigate the behavioral and metabolic responses of birds to RU486 treatment during a food manipulation trial. On the morning following the second RU486 injection, food in chambers was removed for four hours. Birds in a second chamber continued to experience ad libitum food conditions. Locomotor activity and plasma metabolites were monitored during the trial. After food was replaced, locomotor activity and food intake were measured to determine how RU486 affects recovery. Controls continued to receive vehicle injections.

 


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  		Fig. 2. Validation of RU486 as a corticosterone antagonist in the Gambel's white-crowned sparrow. Changes in fat score and plasma corticosterone (ng ml-1) were compared among three treatment groups: (1) birds with empty implants and vehicle injections (controls), (2) birds with implants of corticosterone and vehicle injections (B group) and (3) birds with implants of corticosterone and injections of 50 mg kg-1 RU486 (B+RU486 group). Corticosterone concentrations were determined from blood samples collected in under 3 min of disturbance. Corticosterone implants were effective in elevating plasma corticosterone levels, and caused an increase in fat score. RU486 treatment inhibited corticosterone-induced fat deposition. Nine animals were included in each treatment group. Error bars represent S.E.M. Different letters above bars indicate significant differences among groups.

 


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  		Fig. 3. Effects of RU486 treatment on daily food intake (g day-1) of spring migrants and wintering birds. Administration of RU486 significantly decreased food intake only in spring migrants. Daily food intake is shown before and after RU486 injections. Black bars, controls; white bars, RU486-treated birds. Sample size is indicated. Asterisks indicate significant differences between treatment groups. Error bars represent S.E.M.

 


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  		Fig. 4. Effects of RU486 treatment on locomotor activity (hops min-1) in spring migrants and in wintering birds. Locomotor activity was determined with motion detectors in registration cages and was investigated during three periods of the day: early-day, late-day and night. In response to treatment, locomotor activity changed similarly in controls and in RU486-treated birds during all examined periods. Locomotor activity is shown before and after RU486 injections. Sample size is indicated. Error bars represent S.E.M.

 


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  		Fig. 5. Effects of RU486 treatment on plasma corticosterone (ng ml-1) in spring migrants and wintering birds. Corticosterone concentrations were determined from blood samples collected in under 3 min of disturbance. Administration of RU486 caused a decrease in plasma corticosterone during both life-history stages. Black bars, controls; white bars, RU486-treated birds. Sample sizes are shown. Asterisks indicate significant differences between treatment groups. Error bars indicate S.E.M.

 


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  		Fig. 6. Daytime locomotor activity (hops min-1), plasma free fatty acids (mmol l-1) and plasma corticosterone (ng ml-1) during the food manipulation trial, both in spring migrants and in wintering birds. White-crowned sparrows were treated with RU486 or with vehicle and were either in a fasting state or were provided with ad libitum food. Locomotor activity was higher in fasting birds than in birds held on ad libitum food. Plasma free fatty acids and plasma corticosterone also increased with fasting, and RU486 suppressed the fasting-associated increase in fatty acids. Corticosterone concentrations were determined from blood samples collected in under 3 min of disturbance. Sample size is indicated. Asterisks indicate significant differences between groups. Error bars represent S.E.M.

 


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  		Fig. 7. Daytime food intake (g day-1) and night-time locomotor activity (hops min-1) during the recovery period following the food manipulation trial, both in spring migrants and in wintering birds. Birds with a history of fasting were compared with birds that had been maintained on ad libitum food. Fasted birds showed an increase in food intake during the recovery period in winter but not in spring. In spring migrants, RU486 decreased food intake both in fasted birds and in birds that had been maintained on ad libitum food. By contrast, during winter, RU486 decreased food intake only in fasted birds. Night-time locomotor activity was unaffected by RU486 treatment or by history of feeding conditions. Sample size is indicated. Asterisks indicate significant differences between groups. Error bars represent S.E.M.

 

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© The Company of Biologists Ltd 2004