[Expression of preprodynorphin mRNA in the spinal cord after inflammatory abdominal stimulation in rats]

Abstract

Dynorphin, an opioid peptide, is thought to play an important role in the modulation of nociceptive neural networks at the level of the spinal cord. Fos protein is involved in the transcriptional regulation of the dynorphin gene. Although several studies have been carried out on dynorphin gene expression by noxious somatic stimuli, few have evaluated the effect of noxious visceral stimuli on the expression of dynorphin gene. In the present studies we analysed the expression of the dynorphin gene mediated by a noxious visceral stimulus in a rat model by exposure of abdominal tissue to carrageenan. Expression of preprodynorphin and c-fos mRNAs in the spinal cord neuron was examined using ribonuclease protection assays. After inflammation, a rapid increase in the levels of c-fos mRNA in the thoracic spinal cord was observed. c-fos mRNA levels rose within 30 minutes after injection, and remained elevated for 1 hour, subsequently falling to control levels. In contrast, preprodynorphin mRNA began to increase from 30 minutes after injection and remained elevated for at least 2 days. In situ hybridization with alpha 35S-labeled cRNA probe demonstrated that in the lower thoracic spinal cord preprodynorphin mRNA was expressed in dorsal horn neurons. In celiac ganglia, both preprodynorphin and c-fos mRNAs were not detected. In the peripancreatic abdominal tissue, there was acute severe inflammation consisting of necrosis and marked polymorphonuclear leucocytic infiltration. These data demonstrate that after abdominal tissue inflammation, activation of dynorphin biosynthesis occurred in thoracic spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)