Protein kinase C is partly involved in c-fos protein expression of nocuously-activated neurons but may not in concomitant modulatory action through opioid receptors at the spinal level in rats.
The present study was aimed to examine if protein kinase C (PKC) activation is necessarily involved in both the c-fos protein expression in the nocuously-activated c-fos protein-like immunoreactive (Fos-LI) neurons and the concomitant opioid receptor-mediated modulation in the dorsal horn circuitry of the spinal cord. Formalin was injected into a hindpaw of rats 5 min after the rats were pretreated with intrathecal (i.t.) administration of chelerythrine (Chel), an inhibitor of PKC, naloxone (Nal), combined administration of these two (Chel + Nal), or vehicle (n=5 in each group),respectively. By using immunocytochemical techniques, the formalin-induced Fos-LI neurons in the lumbar dorsal horn were calculated 1 h after formalin injection. The results showed that: (1) i.t. Chel significantly reduced the number of Fos-LI neurons in the dorsal horn of the spinal cord on the side ipsilateral to the formalin injection, showing a decrease by 60.3% (P<0.001) as compared to that observed in the i.t.vehicle group; (2) i.t. Nal significantly increased the number of Fos-LI neurons in the ipsilateral dorsal horn, with an increase of 46.0% (P<0.01) as compared to that in the i.t.vehicle group, the highest percentage increase being found in the deeper laminae of the dorsal horn; and (3) i.t. Chel + Nal also exhibited a significant decrease in Fos-LI neurons in the ipsilateral dorsal horn as compared to i.t. Nal group, showing a reduction of 53.2%, a value similar to that in the i.t. Chel group. These results suggest that: (1) PKC plays a role in the c-fos protein expression only in nearly one half of the Fos-LI neurons in the dorsal horn; and (2) PKC is possibly not involved in the concomitant modulation on the nociception mediated by micro- (and also partly delta-) opioid receptors in the spinal cord.
Nie
Hong
H
Department of Neurobiology, Shanxi Medical University, Taiyuan, Shanxi 030001, China.
Wang
Hang
H
Zhang
Rui-Xin
RX
Gao
Wang-Cai
WC
Qiao
Jian-Tian
JT
D000818:Animals; D005557:Formaldehyde / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000378:metabolism / Q000503:physiopathology*; D020671:Posterior Horn Cells / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis* / Q000502:physiology; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000819:agonists; D013116:Spinal Cord / Q000502:physiology*
D009292:Narcotic Antagonists; D016760:Proto-Oncogene Proteins c-fos; D017465:Receptors, Opioid, delta; D005557:Formaldehyde; D009270:Naloxone; D011493:Protein Kinase C