Dye coupling does not explain functional crosstalk within dorsal root ganglia

Most primary sensory neurons in rat dorsal root ganglia (DRGs) are depolarized during repetitive impulse activity in neighboring neurons that share the same ganglion. We wondered whether this functional crosstalk might be mediated by a network of cytoplasmic bridges (gap junctions) between neighboring neurons and their satellite glia. Neurobiotin was injected intracellularly in whole excised DRGs. Some of the animals were intact, and others underwent transection of the ipsilateral sciatic nerve 7 to 21 days prior to injection. A total of 44 directly injected neurons were recovered histologically. There was little or no evidence of dye spread to neighboring satellite cells or neurons that would have indicated the presence of cytoplasmic bridges, certainly not enough to account for the nearly universal functional coupling that occurs among these neurons. Functional crosstalk within DRGs must therefore employ a different mechanism.