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Early spring sex differences in luteinizing hormone response to gonadotropin releasing hormone in co-occurring resident and migrant dark-eyed juncos ( Junco hyemalis )

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ABSTRACT

In early spring female juncos vary in LH following repeated stimulation with GnRH.

Resident and migrant males do not vary in LH.

Suggests the pituitary as a critical point of control for reproductive timing.

Sex difference suggests selection shaped responsiveness at critical time points.

Sex difference suggests selection shaped responsiveness at critical time points.

No MeSH data available.


Schematic outline of sampling procedure: Briefly, immediately after capture a blood sample was collected for baseline levels of LH. Individuals then received the first injection (i.m.) with GnRH followed five minutes later with another small blood sample to measure LH. Exactly thirty minutes after the first GnRH injection, individuals received a second injection with GnRH, followed by a third thirty minutes later (60 min after the first injection). A final blood sample was collected five minutes after the third GnRH injection (65 min after the first GnRH injection).
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f0005: Schematic outline of sampling procedure: Briefly, immediately after capture a blood sample was collected for baseline levels of LH. Individuals then received the first injection (i.m.) with GnRH followed five minutes later with another small blood sample to measure LH. Exactly thirty minutes after the first GnRH injection, individuals received a second injection with GnRH, followed by a third thirty minutes later (60 min after the first injection). A final blood sample was collected five minutes after the third GnRH injection (65 min after the first GnRH injection).

Mentions: Immediately after capture, a small ∼50 μl blood sample was obtained from the alar wing vein for baseline measures of LH. The birds then received an intramuscular injection into the pectoralis muscle of a dose of 62.5 μg chicken GnRH per kilogram body mass (American Peptide, Sunnyvale, CA) in PBS vehicle (∼50 μl injection volume); this dose is capable of fully activating the HPG axis in this species (Jawor et al., 2006). Five minutes following the first injection a second blood sample was taken from the wing vein for post-GnRH measures of LH. Previous work in this species and another songbird indicate LH levels peak 5 min following injection and significantly decline by 20 min and return to baseline 30 min post-injection (Bergeon Burns, 2012, Bergeon Burns et al., 2014, Wingfield et al., 1979). The birds then received a 2nd injection of GnRH 30 min after the 1st injection, followed by a 3rd injection 30 min following the 2nd injection. A final blood sample was collected 5 min following the 3rd injection of GnRH (for visual summary of sampling protocol see Fig. 1). All birds were held in an opaque bag between injections. Blood samples were stored on ice until later processing in the laboratory. Samples were centrifuged to separate red blood cells from plasma. Plasma was aspirated with a Hamilton syringe and placed into a microcentrifuge tube. Plasma was stored at −20 °C until shipped to The Roslin Institute, The University of Edinburgh for LH quantification.


Early spring sex differences in luteinizing hormone response to gonadotropin releasing hormone in co-occurring resident and migrant dark-eyed juncos ( Junco hyemalis )
Schematic outline of sampling procedure: Briefly, immediately after capture a blood sample was collected for baseline levels of LH. Individuals then received the first injection (i.m.) with GnRH followed five minutes later with another small blood sample to measure LH. Exactly thirty minutes after the first GnRH injection, individuals received a second injection with GnRH, followed by a third thirty minutes later (60 min after the first injection). A final blood sample was collected five minutes after the third GnRH injection (65 min after the first GnRH injection).
© Copyright Policy - CC BY
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036536&req=5

f0005: Schematic outline of sampling procedure: Briefly, immediately after capture a blood sample was collected for baseline levels of LH. Individuals then received the first injection (i.m.) with GnRH followed five minutes later with another small blood sample to measure LH. Exactly thirty minutes after the first GnRH injection, individuals received a second injection with GnRH, followed by a third thirty minutes later (60 min after the first injection). A final blood sample was collected five minutes after the third GnRH injection (65 min after the first GnRH injection).
Mentions: Immediately after capture, a small ∼50 μl blood sample was obtained from the alar wing vein for baseline measures of LH. The birds then received an intramuscular injection into the pectoralis muscle of a dose of 62.5 μg chicken GnRH per kilogram body mass (American Peptide, Sunnyvale, CA) in PBS vehicle (∼50 μl injection volume); this dose is capable of fully activating the HPG axis in this species (Jawor et al., 2006). Five minutes following the first injection a second blood sample was taken from the wing vein for post-GnRH measures of LH. Previous work in this species and another songbird indicate LH levels peak 5 min following injection and significantly decline by 20 min and return to baseline 30 min post-injection (Bergeon Burns, 2012, Bergeon Burns et al., 2014, Wingfield et al., 1979). The birds then received a 2nd injection of GnRH 30 min after the 1st injection, followed by a 3rd injection 30 min following the 2nd injection. A final blood sample was collected 5 min following the 3rd injection of GnRH (for visual summary of sampling protocol see Fig. 1). All birds were held in an opaque bag between injections. Blood samples were stored on ice until later processing in the laboratory. Samples were centrifuged to separate red blood cells from plasma. Plasma was aspirated with a Hamilton syringe and placed into a microcentrifuge tube. Plasma was stored at −20 °C until shipped to The Roslin Institute, The University of Edinburgh for LH quantification.

View Article: PubMed Central - PubMed

ABSTRACT

In early spring female juncos vary in LH following repeated stimulation with GnRH.

Resident and migrant males do not vary in LH.

Suggests the pituitary as a critical point of control for reproductive timing.

Sex difference suggests selection shaped responsiveness at critical time points.

Sex difference suggests selection shaped responsiveness at critical time points.

No MeSH data available.