Changes in c-fos induction in dorsal horn neurons by hindpaw formalin stimulation following tibial neurotomy.
The hindpaw was partially denervated by the tibial nerve transection in adult rats. At post-transection intervals varying from 2 to 168 days, the hindpaw was stimulated bilaterally by subcutaneous injection of formalin. The excitability of dorsal horn neurons was expressed as the percentage ratio of the number of formalin-induced c-fos protein-like immunoreactive neurons (fos-neurons) on the neurotomized (experimental) side to that on the un-neurotomized (control) side. At 2 days post-injury, a marked reduction in the number of fos-neurons was noted in laminae I-VII of the lumbar spinal cord. Among these, reduction was greatest in the medial 3/8 of laminae I and II (terminal field of the tibial nerve, i.e. tibial territory), and smallest in the lateral 5/8 of the same laminae (the peroneal/hip territory). The low level of c-fos induction remained unchanged for 7 days. At 14 days, the excitability of neurons in all laminae showed a marked increase compared to the post-injury days 2 and 3 combined. Thereafter, the increased level of excitability in the tibial territory was maintained throughout the post-injury period examined in this study. On the other hand, a statistically significant increase in excitability in the peroneal/hip territory was only seen between 14 and 28 days and the excitability almost returned to the baseline (days 2 and 3 post-transection combined) level at 42 days. Although deeper laminae (III-VII) contained much less formalin-induced fos-neurons, they also exhibited post-injury excitability changes with a temporal pattern similar to that of the peroneal/hip territory of laminae I and II.(ABSTRACT TRUNCATED AT 250 WORDS)
Sugimoto
T
T
Second Department of Oral Anatomy, Okayama University School of Dentistry, Japan.
Ichikawa
H
H
Mitani
S
S
Hitsu
A
A
Nakago
T
T
D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D003714:Denervation; D005557:Formaldehyde / Q000494:pharmacology*; D006614:Hindlimb; D008161:Lumbosacral Region; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects*; D013977:Tibia / Q000294:innervation*
D016760:Proto-Oncogene Proteins c-fos; D005557:Formaldehyde