Effects of intrathecal BAM22 on noxious stimulus-evoked c-fos expression in the rat spinal dorsal horn.
The effects of bovine adrenal medulla 22 (BAM22), a cleaved product of proenkephalin A, were investigated on the noxious stimulus-evoked expressions of spinal c-fos-like immunoreactivity (FLI). Heat (51 degrees C) applied to the tail evoked FLI predominantly in laminae I-II of the sacral spinal cord. Intrathecal (i.t.) BAM22 at a dose of 7 nmol decreased the expressions of the heat-evoked FLI by 68%, 64% and 56% in laminae I-II, III-IV and V-VI, respectively, and the decrease pattern was comparable to that induced by i.t. morphine (10 mug). Naloxone (1 mg/kg, i.p.) significantly enhanced the heat-evoked FLI in laminae III-VI, prevented the morphine-induced inhibition, and decreased the potencies of BAM22 in laminae I-II and V-VI by 23-40%. Higher dose of naloxone (10 mg/kg, i.p.) also partially reduced the BAM22-induced suppression. Following intraplantar injection of formalin (2.5%), FLI neurons were preferentially distributed not only in laminae I-II but also in laminae III-IV and V-VI of segments L4-L5. Pretreatment with BAM22 (7 nmol, i.t.) reduced the formalin-evoked FLI neurons by 72%, 61% and 58%, in laminae I-II, III-IV and V-VI, respectively. Naloxone (1 mg/kg. i.p.) enhanced the formalin-evoked expressions of FLI in laminae III-VI and decreased the potencies of BAM22 by 22-38% in laminae I-II and V-VI. The present study provided evidence at a cellular level showing that opioid and non-opioid effects of BAM22 on nociceptive processing in acute and persistent pain models were associated with modulation of noxious stimulus-evoked activity of the spinal dorsal horn neurons.
Zeng
Xueai
X
Department of Anatomy and Physiology, Bioengineering School, Fujian Normal University, Fuzhou, People's Republic of China.
Huang
Hao
H
Hong
Yanguo
Y
D000818:Animals; D002417:Cattle; D002452:Cell Count / Q000379:methods; D004347:Drug Interactions; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004745:Enkephalins / Q000008:administration & dosage; D005557:Formaldehyde; D005786:Gene Expression Regulation / Q000187:drug effects; D006358:Hot Temperature / Q000009:adverse effects; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D010146:Pain / Q000139:chemically induced / Q000378:metabolism*; D010147:Pain Measurement; D010812:Physical Stimulation / Q000009:adverse effects; D011498:Protein Precursors / Q000008:administration & dosage / Q000494:pharmacology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000166:cytology*
D004745:Enkephalins; D009292:Narcotic Antagonists; D009294:Narcotics; D011498:Protein Precursors; D016760:Proto-Oncogene Proteins c-fos; C029992:proenkephalin; D005557:Formaldehyde; D009270:Naloxone; D004744:Enkephalin, Methionine; C028837:BAM 22P; D009020:Morphine