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.