Unexplained peculiarities of the dorsal root ganglion

The cell soma of primary afferent neurons in the dorsal root ganglion (DRG) is assigned by classical neurophysiology the role of a metabolic depot, ch arged with supporting the peripheral sensory ending, the conducting axon, a nd the central synaptic terminals. However, certain peculiarities of DRG mo rphology and physiology do not sit well with this being its only role. For example, why are DRG cell somata electrically excitable, why are some able to fire repetitively on sustained depolarization, and why does the DRG lack a blood-nerve barrier? Consideration of these and related questions leads to several intriguing hypotheses: (1) Electrical excitability of the soma m ay be required to insure the reliable propagation of impulses past the DRG T-junction and into the spinal cord. (2) Invasion of the afferent spike int o the cell soma may provide an essential feedback signal necessary for the cell soma to regulate the excitability of the sensory ending. 3) The subpop ulation of DRG neurons that have repetitive firing capability may be respon sible for generating the background sensation that we feel as our body sche ma. Moreover, these neurons may be chemical sensors that provide essential information about our body's internal milieu. (C) 1999 International Associ ation for the Study of Pain. Published by Elsevier Science B.V.