Here, we describe a novel mechanism for the rapid regulation of surface levels of the neurotrophin receptor TrkB. Unlike nodose ganglion neurons, both retinal ganglion cells (RGCs) and spinal motor neurons (SMNs) in culture display only low levels of surface TrkB, though high levels are present intracellularly. Within minutes of depolarization or cAMP elevation, surface TrkB levels increase by nearly 4-fold, and this increase is not blocked by cycloheximide. These findings suggest that activity and cAMP elevation rapidly recruit TrkB to the plasma membrane by translocation from intracellular stores. We propose that a fundamental difference between peripheral nervous system (PNS) and central nervous system (CNS) neurons is the activity dependence of CNS neurons for responsiveness to their peptide trophic factors and that differences in membrane compartmentalization of the receptors underlie this difference.

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The addition of splenectomy to up-front cytoreductive surgery was feasible and safe. However, it appears to carry with it a shortened survival that is unrelated to postoperative morbidity. Our data raise the questions that splenectomy is needed for optimal cytoreduction in more biologically aggressive disease and that splenectomy may be an independent prognostic factor related to depressed immune function.