Quantitative Autoradiographic Evidence for Insulin Receptors in the Choroid Plexus of the Rat Brain

Author:

Baskin Denis G123,Brewitt Barbara2,Davidson David A2,Corp Eric4,Paquette Thomas1,Figlewicz Dianne P14,Lewellen Thomas K5,Graham Michael K5,Woods Stephen G,Dorsa Daniel M163

Affiliation:

1. Departments of Medicine, University of Washington Seattle, Washington

2. Biological Structure, University of Washington Seattle, Washington

3. VA Medical Center Seattle, Washington

4. Psychology, University of Washington Seattle, Washington

5. Radiology, University of Washington Seattle, Washington

6. Pharmacology, University of Washington Seattle, Washington

Abstract

Techniques of in vitro receptor autoradiography were used to visualize binding of 125I-insulin on slices of frozen rat brain. Slide-mounted sections of frozen rat brain were incubated in 0.05 nM porcine 125I-monoio-doinsulin, alone or mixed with 1 μM unlabeled porcine insulin, ribonuclease, or glucagon, for 2 h at 22°C. The labeled brain slices were apposed to LKB Ultrofilm to generate autoradiograms. The method permitted equal access of labeled insulin to both sides of the blood-brain barrier and localization of insulin binding sites in small anatomic regions. Quantitative estimates of specific iodoinsulin binding were made by computer digital image densitometry of the autoradiographic film images. High concentrations of specific binding sites for iodoinsulin were present in the choroid plexus of the lateral (26.9 ± 2.0 × 103 fmol/mm2), fourth (18.3 ± 3.0 × 10-3 fmol/mm2), and third (13.2 ± 1.5 × 103fmol/mm2) ventricles (insulin binding is expressed per unit area of autoradiographic image). Binding to the third ventricular choroid plexus was similar to the concentrations observed for liver slices and the external plexiform layer of the olfactory bulb. Specific binding of iodoinsulin in the cingulate cortex and other surrounding regions was less than in choroid plexus. Ribonuclease or glucagon had no measurable effect on binding when mixed with labeled insulin. The results support the hypothesis that the choroid plexus has a high density of receptors for insulin, and suggests that the choroid plexus may be a target of CSF insulin action and/or a site of insulin transport into the CSF.

Publisher

American Diabetes Association

Subject

Endocrinology, Diabetes and Metabolism,Internal Medicine

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