Diffusional barrier around the hypothalamic arcuate nucleus in the rat.

The contour lines of horseradish peroxidase injection sites in the ventrobasal hypothalamus were distorted by the border between arcuate and ventromedial nuclei as well as between arcuate nucleus and median eminence. The dense array of tanycyte processes is assumed to isolate the arcuate nucleus from the neighboring territories by establishing a diffusional barrier surface.