Altered methionine enkephalin immunoreactivity in cerebral nuclei of spontaneously hypertensive rats.

In young SHR, methionine enkephalin-like immunoreactivity (ME) levels were lower than WKY in the tractus spinalis n. trigemini, n. reticularis lateralis, n. arcuatus and n. corporis mamillaris lateralis, whereas higher in the n. dorsalis n. vagi, n. amygdaloideus medialis and n. striae terminalis. In adult SHR, the alteration in these nuclei disappeared. ME levels were higher than those of WKY in the n. reticularis medialis and n. accumbens septi, while lower in the area lateralis hypothalami. The alteration was not due to hypertension, since acute hypertension induced with angiotensin II produced no change in these nuclei. The decrease in ME neuronal activity in bulbar sensory and somatosensory afferents, and n. arcuatus, and ME neuronal activation in the limbic depressor neurons may be involved in the development of hypertension and hyper-reactivity in SHR.