Topographic Distribution of the Melanocyte-Stimulating Hormone-Releasing Factor in Rat Hypothalamus. ∗

Summary

The topographic distribution of MSH-RF in the hypothalamus was studied in the rat. MSH-RF was determined by measuring the capacity of hypothalamic extracts to deplete pituitary MSH concentration in recipient animals. The activity of extracts prepared from sections of hypothalamus taken in 3 different planes showed the highest concentration of the releasing factor in the area of the paraventricular nucleus. The median eminence was the second most important active zone. Extracts from neural lobe of the hypophysis were also active though to a lesser degree than those from hypothalamus and their effect did not depend on either oxy-tocin or vasopressin. The possibility that MSH-RF could be produced by neurons having their soma in the paraventricular nucleus and axons ending in the median eminence and neural lobe of the hypophysis is discussed.