Uptake and degradation of blood-borne insulin by the olfactory bulb

Insulin found within the brain is derived from the blood and can affect var ious central nervous system (CNS) functions. The olfactory bulb contains on e of the highest concentrations of insulin and insulin receptors within the CNS. To determine the mechanism underlying this high concentration of insu lin, we used radioactively iodinated insulin to compare the blood to tissue transport rates and tissue degradation rates for the olfactory bulb, whole brain and spinal cord. We found that the olfactory bulb had both the highe st transport rate across the blood-brain barrier (BBB) and the highest rate of degradation. Because a higher degradation rate would decrease, not incr ease, tissue concentrations of insulin, BBB transport may he the primary me chanism by which high concentrations of insulin are maintained within the o lfactory bulb. This illustrates an adaptive aspect of the BBB in its regula tion of the exchange of information molecules between the blood and the CNS . Published by Elsevier Science Inc.