Cross-excitation in dorsal root ganglia does not depend on close cell-to-cell apposition

ABOUT 90% of neurons in dorsal root ganglia (DRGs) of rats 2-5 weeks of age are depolarized and excited by impulse activity in neighboring neurons tha t share the same DRG. Synaptic contacts are extremely rare in DRGs, but ins tances of close membrane apposition between pairs of neuronal somata are no t uncommon, especially in prenatal rats. Close membrane apposition could pe rmit electrotonic interactions among neighboring DRG neurons. We carried ou t an ultrastructural examination of DRGs taken from rats 2-5 weeks of age a nd found that by this age < 2% of cells remain in close apposition with nei ghbors. The remainder are separated by one or two layers of satellite glial cytoplasm. It is, therefore, unlikely that close apposition between adjace nt neurons contributes significantly to functional cross-excitation in the DRG. (C) 1998 Lippincott Williams & Wilkins.