Methionine enkephalinergic neuronal activity in cerebral nuclei of spontaneously hypertensive rats

The role of methionine enkephalin (ME) neurons in the development of genetic hypertension in SHR is the subject of this study. Methionine enkephalin-like immunoreactivity (MELI) and ME receptor binding (MERB) levels were assayed quantitatively by microdensitometry of fluorescence micrographs and autoradiographs of 85 cerebral nuclei and areas of both young and adult spontaneously hypertensive rats (SHR). Normotensive Wistar Kyoto rats (WKY) were used as controls. In young SHR, both MELI and MERB levels were markedly higher in the n. dorsalis nervi vagi, n. amygdaloideus medialis, and group of stria terminal nuclei than in those of young WKY, while both levels were lower in the n. reticularis lateralis, n. corporis mamillaris lateralis, and n. arcuatus. MELI levels in the tractus spinalis nervi trigemini and MERB in the n. tractus spinalis nervi trigemini and median eminence were also lower in young SHR, whereas MERB in the n. amygdaloideus centralis was higher. Alteration in these nuclei was no longer detectable in adult SHR. Whereas in adult SHR, both MELI and MERB levels in the n. reticularis medialis were higher than those of adult WKY, and MELI in the n. accumbens septi and MERB in the n. caudatus were also higher, while MELI in the area lateralis hypothalami was lower than that in adult WKY. The findings indicate that activation of ME neurons in the n. dorsalis nervi vagi and limbic area and also a decrease in ME neuronal activity in the area spinalis nervi trigemini, n. reticularis lateralis, and n. arcuatus may be casually related to the development of hypertension and hyperreactivity in SHR.