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Specific binding sites for blood-borne insulin were determined to be selectively localized on axons and axon terminals in the external median eminence and the hypothalamic arcuate nucleus by means of quantitative fine structural radioautography. This localization suggests that discrete populations of hypothalamic nerve terminals are potential targets for the direct effects of insulin and that insulin may act through synaptic mechanisms to influence hypothalamic circuits regulating energy balance and hypophyseal function.

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The brain has generally been considered an insulin-independent organ, because insulin does not apparently exert a direct effect on brain glucose consumption. Recently, however, insulin receptors have been detected throughout the central nervous system (CNS) of several species. Since important insights into the functional significance of brain insulin receptors might be provided by identification of the cell type(s) possessing these receptors, we have attempted to localise them morphologically using light and electron microscope autoradiography. We report here results indicating that blood vessels throughout the CNS of the rat bind plasma insulin rapidly and with considerable specificity.

No abstract