Expression of preprodynorphin and preproenkephalin mRNA in nucleus tractus solitarii of rats subjected to endotoxin (and effect of naltrexone on the expression)
Previous studies have shown that opioid peptides in the central nervous system are involved in the pathogenesis of endotoxic shock in the rat. In the present study in situ hybridization technique was used to examine the expression of mRNA coding for preprodynorphin and preproenkephalin within the nucleus tractus solitarii (NTS) of rats challenged with endotoxin as well as the effect of opioid antagonist naltrexone on the opioid gene expression. Thirteen Wistar male rats were divided into four groups: saline control; single endotoxin; naltrexone + endotoxin and single naltrexone. Animals were killed 60 min after the drug or saline injection and the brain stems were removed quickly and frozen, sectioned for in situ hybridization, using 35S-labeled oligonucleotide probe. The expressions of both dynorphin- and enkephalin-mRNA in NTS showed a significant increase in endotoxic shocked rats. These effects were partially and significantly blocked by the pretreatment with naltrexone. Saline and naltrexone per se produced no significant effect. The results suggest that endotoxin may activate the expression of genes coding for preprodynorphin and preproenkephalin in NTS, with opioid receptors being involved in the whole chain of reaction.
