Graduate Thesis Or Dissertation
 

Characterization and localization of arginine vasotocin receptors in the brain and kidney of an amphibian

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1j92g9998

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  • Because arginine vasotocin (AVT) activates male sexual behaviors in the rough-skinned newt (Taricha granulosa), quantitative autoradiography with radiolabelled arginine vasopressin (³H-AVP) was used to localize and characterize putative AVT receptors in the brain of this amphibian. Binding of ³H-AVP to sites within the medial pallium was saturable, specific, reversible, of high affinity (K[subscript d]=1 nM) and low capacity (57 fmol/mg protein). These binding sites appear to represent authentic central nervous system receptors for AVT. Furthermore, ligand specificity for the binding sites in this amphibian differs from that reported for AVP binding sites in rat brains. Dense concentrations of specific binding sites were located in the olfactory nerve as it entered the olfactory bulb, within the medial (hippocampal) pallium, dorsal pallium, and amygdala pars lateralis of the telencephalon, and in the tegmental region of the medulla. Concentrations of binding sites differed significantly among various brain regions. A comparison of male and female newts collected during the breeding season revealed no sexual dimorphism. These areas may represent site(s) of action where AVT elicits sexual behaviors in male T. granulosa. Gonadectomy of male and female newts (30 days) resulted in significantly reduced concentrations of AVT receptors in the amygdala pars lateralis, compared to concentrations in sham-operated controls. This effect was specific to the amygdala; other brain areas were not affected. These findings support the hypothesis that, in vertebrates in general, one action of gonadal steroid hormones on neural substrates is to maintain receptors to behaviorally active neuropeptides. Specific binding sites for ³H-AVP were localized over the kidney glomeruli. Scatchard analysis showed a single class of receptors with a dissociation constant of 0.77 nM and a binding site concentration of 35 fmol/mg protein. Localization of AVT receptors over kidney glomeruli and ligand specificity of these sites supports the hypothesis that AVT causes antidiuresis in urodele amphibians via a vasoconstricting (pressor) action rather than a tubular antidiuretic response.
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