Localization of Insulin to Neuronal Cells
Insulin has been identified in the brain of various animal species1, including the human2. Although various biologic effects for insulin have been described in the central nervous system3,4,5, the exact origin of the peptide remains unclear. A local (i.e. central nervous system) origin for the peptide has been suggested by some groups of investigators5,6, while others contend that insulin enters the brain from the blood vascular system 7. For example, Frank et al, using 125I-insulin, demonstrated the hormone’s ability to cross the neonatal rabbit blood-brain barrier. In subsequent studies, the mechanism by which insulin traverses the vascular endothelium was not clear as there was an absence of externalization (as a part of transcytosis) of the hormone at the brain capillary antiluminal membrane8. Baskin et al observed the uptake of insulin by the adult rat hypothalamus to be from cerebro-spinal fluid9. The cerebrospinal fluid insulin levels in turn have been found to correlate closely with plasma insulin concentrations10,11. On the other hand, insulin mRNA has been demonstrated in the brain5,12, providing the essential biochemical basis for the local synthesis of hormone.
KeywordsNorepinephrine Stein Hematoxylin Collagenase Zucker
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