A chronic compression of the dorsal root ganglion (CCD) upregulates expression of monocyte chemoattractant protein-1 (MCP-1) and mRNA for the C-C chemokine receptor, CCR2, in subpopulations of neurons in the compressed ganglion (White et al; Waters et al. SFN abstrs. 2004). Because CCD produces hyperalgesia and increased neuronal excitability, and certain chemokines can excite dorsal root ganglion (DRG) neurons in culture (Oh et al. J. Neurosci. 21:5027), we explored the effects of MCP-1 on the excitability of neurons in the intact DRG with prior CCD or without (control). Intracellular recordings were obtained, in vitro, from visualized somata of small, medium and large size. Neurons were also categorized, in response to electrical stimulation of the dorsal root, by axonal conduction velocity and by the absence or presence of a hump on the falling phase of the evoked action potential (the hump is typical for nociceptive neurons recorded in vivo). MCP-1 (100 nM, 1 min duration) was topically applied to the ...