Electrophysiologic characteristics of large neurons in dorsal root ganglia during development and after hind paw incision in the rat.
BACKGROUND
Withdrawal thresholds in the paw are lower in younger animals, and incision further reduces these thresholds. The authors hypothesized that these differences result in part from changes in intrinsic electrophysiologic properties of large neurons.


METHODS
Using isolated whole dorsal root ganglion, current clamping was performed to determine the electrophysiologic properties of large neurons before and after incision in animals aged 1 and 4 weeks. Mechanical withdrawal thresholds were used to follow paw sensitivity.


RESULTS
After paw incision, withdrawal thresholds decreased to a similar degree at both ages, but returned to control threshold at 72 h only in the 1-week-old animals. The resting membrane potential was less negative and the rheobase and the resistance of the membrane were lower at baseline in the 1-week-old animals (P < 0.05). After incision, the membrane potential became more depolarized and the rheobase was less in both ages. These changes remained 72 h after the incision in both ages.


CONCLUSIONS
These findings suggest that lower mechanical thresholds in the younger animals may be partially attributed to the intrinsic electrophysiologic properties of the larger-diameter afferent neurons. The lack of resolution of the electrophysiologic changes in the young despite the resolution of the withdrawal response suggests that continued input from large fibers into the central nervous system may occur at this age despite the apparent resolution of behavioral changes. Further studies are needed to determine the etiology of these differences, their impact in the central nervous system, and whether theses changes can be prevented.
Ririe
Douglas G
DG
Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1009, USA. dririe@wfubmc.edu
Liu
Baogang
B
Clayton
Bridgette
B
Tong
Chuanyao
C
Eisenach
James C
JC
D000200:Action Potentials / Q000502:physiology; D000367:Age Factors; D000818:Animals; D004594:Electrophysiology; D005727:Ganglia, Spinal / Q000254:growth & development* / Q000601:surgery; D006614:Hindlimb / Q000254:growth & development* / Q000294:innervation* / Q000601:surgery; D008297:Male; D009474:Neurons / Q000502:physiology*; D017288:Pain Threshold / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley