EXPRESSION OF PREPRODYNORPHIN mRNA IN THE RAT NUCLEUS CAUDALIS

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The expression of preproenkephalin mRNA was examined using techniques for quantitative analysis of in situ hybridization in nucleus caudalis neurons following electrical stimulation of trigeminal primary afferents at the low and high intensities. Stimulation at both intensities principally enhanced the expression of this mRNA in laminae I and II neurons of the nucleus caudalis. The enhancement of the expression was found at one and two hours after the stimulation of high and low intensities, respectively, and was continued until 24 hour at the end of stimulations. Quantitative analysis of in situ hybridization revealed that the increment in the expression of this gene appears to be mainly due to an increase in the intensity of expression of this mRNA.Compared with our previous reports in which the expression of preproenkephalin mRNA was enhanced in a bimodial temporal pattern after stimulation at the low intensity of the primary afferents and this enhancement were mainly due to increase in the number of the positive neurons, the present result for the expression of preprodynorphin mRNA indicate that the expression of this mRNA in nucleus caudalis neurons are increaced in different manner from that of preproenkephalin mRNA following stimulation of trigeminal primary afferents, suggesting that in the nucleus caudalis the expression of two opioid peptide genes, preprodynorphin and preproenkephalin, are differentially regulated by primary afferents.