MAST-CELLS IN THE BRAIN - EVIDENCE AND FUNCTIONAL-SIGNIFICANCE

For the past two decades the brain has been considered to be an immune -privileged site that excludes circulating cells from the parenchyma, New evidence indicates that some hematocytes reside in the brain, whil e others traffic through it. Mast cells belong to both of these functi onal types. Moreover the appearance of mast cells in the CNS can be tr iggered behaviorally. After a brief period of courtship, for example, there is a marked increase in mast cells in the medial habenula of sex ually active doves compared with controls, Exposure to gonadal steroid s that occur endogenously or that are administered exogenously increas es both the number of mast cells and their state of activation in the brain, These results show that hematopoietic cells can provide targete d delivery of neuromodulators to specific regions of the brain, thereb y influencing neural-endocrine interactions.