Electrophysiological recordings were made in vitro from primary afferent ne
urons with unmyelinated axone (C-neurons) in excised rat dorsal root gangli
a. Spike activity triggered in neurons with myelinated axons (A-neurons) by
stimulation of the peripheral nerve or the dorsal root produced a transien
t depolarization in passive neighboring C-neurons that share the same gangl
ion. About 90% of neurons sampled responded with this "cross-depolarization
". Cross-depolarization was associated with functional excitation as indica
ted by an increase in firing probability in response to previously subthres
hold intracellular test pulses. Furthermore, it yielded a net increase of t
he input resistance of the affected C-neurons.
We suggest that functional coupling among DRG neurons could serve a metabol
ic role, providing a functionally relevant feedback signal useful for contr
olling the excitability of nociceptive sensory endings. In addition, the re
sults provide a novel mechanism whereby afferent nociceptors could be stimu
lated by activity in low-threshold mechanoreceptors, particularly in the ev
ent of nerve injury. Hence, the coupling between afferent A- and C-neurons
in dorsal root ganglia provides a novel candidate mechanism for neuropathic
pain. (C) 1999 IBRO. Published by Elsevier Science Ltd.