ISSN:
1432-0878
Keywords:
Alpha2 receptors
;
Hypothalamus
;
Circumventricular organs
;
Clonidine
;
G-protein
;
Domestic mallard
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary In the present study, we have employed the monoradioiodinated α2-agonist clonidine ([125I]-CLO) to characterize duck hypothalamic α2-adrenoceptors and to localize α2-specific binding sites in the duck brain. To validate the α2-specificity of [125I]-CLO using an enriched duck hypothalamic membrane fraction, a radioreceptor assay was established by altering the membrane protein concentration, time, temperature and ionic milieu of incubation, and in the presence or absence of protease inhibitors. Competitive displacement studies revealed the following sequence of potency to displace [125I]-CLO: yohimbine〉(-)-epinephrine〉clonidine〉 (-)-norepinephrine〉phentolamine〉(-)-phenylephrine〉(-)-isoproterenol〉prazosin. The non-hydrolyzable guanosine 5′-triphosphate analog guanylylimidodiphosphate markedly inhibited [125I]-CLO binding suggestive of G-protein involvement. With regard to the histological distribution, diencephalic structures, such as the habenula and the nucleus reticularis of the thalamus, were densely labeled by [125I]-CLO. In the hypothalamus, α2-adrenoceptors were detected in the antidiuretic hormone-synthesizing nucleus paraventricularis, the nucleus praeopticus medialis, the nucleus anterior medialis hypothalami, the nucleus magnocellularis praeopticus, the nucleus commissurae pallii, the nucleus inferior hypothalami and the regio lateralis hypothalami. Circumventricular organs, such as the plexus choroidei, organum subfornicale, organum paraventriculare and the corpus pineale, were endowed with α2-specific binding sites, as were the cell layers of the tectum opticum. In addition, telencephalic structures revealed high receptor densities. The presence of well characterized α2-specific adrenoceptors in hypothalamic structures of the duck brain including associated telencephalic regions supports physiological investigations with regard to functional α2-adrenergic modulation of antidiuretic hormone release in the duck.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00338058
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