Changes in properties of substantia gelatinosa neurons after surgical incision in the rat: in vivo patch-clamp analysis.
BACKGROUND
Noxious information through A delta and C afferent fibers is transmitted to substantia gelatinosa, a process that plays an important role in plastic changes of nociceptive processing in pathophysiological conditions. In this study, changes in properties of substantia gelatinosa neurons and their sensitivity to systemic administration of lidocaine after surgical incision were investigated using the in vivo patch-clamp technique.


METHODS
Under urethane anesthesia, in the current clamp mode, spontaneous activities and responses of substantia gelatinosa neurons to nonnoxious air-puff stimuli and noxious pinch stimuli were recorded before and after 1-cm-long incisions had been made in hairy skin of the hindquarters of rats. Systemic administration of lidocaine (2 mg/kg) was applied at 30 min after the incision.


RESULTS
Stable recordings for 30 min or more after the incision were obtained from 18 substantia gelatinosa neurons that were classified as multireceptive (n = 8), nociceptive (n = 5), and subthreshold (n = 5) neurons. Action potential firing disappeared immediately after completion of the wound closure in most multireceptive and nociceptive neurons, and sustained spontaneous action potential firing was observed in 23% of these substantia gelatinosa neurons. Responsiveness of these substantia gelatinosa neurons, but not that of subthreshold neurons, increased after the incision. Systemic administration of lidocaine suppressed spontaneous firings of action potentials of the substantia gelatinosa neurons and reversed the increased responsiveness of the neurons.


CONCLUSIONS
The results suggest that (1) changes in properties of substantia gelatinosa neurons after incision vary depending on the classification of substantia gelatinosa neurons and (2) systemic administration of lidocaine can reverse increased responsiveness of substantia gelatinosa neurons after incision injury.
Kawamata
Mikito
M
Department of Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Japan. mikitok@sapmed.ac.jp
Furue
Hidemasa
H
Kozuka
Yuji
Y
Narimatsu
Eichi
E
Yoshimura
Megumu
M
Namiki
Akiyoshi
A
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D005071:Evoked Potentials; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D010149:Postoperative Pain / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013376:Substantia Gelatinosa / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission
D008012:Lidocaine