Distribution of monoamines within the median eminence in rats

The concentration of dopamine, norepinephrine, epinephrine and serotonin was determined in 6 rostrocaudal segments of the median eminence, 2 segments in the pituitary stalk, in the retrochiasmatic area and the pituitary lobes by radioenzymatic microassay in adult rats. The level of dopamine and norepinephrine was measured separately in the medial and lateral portions of the median eminence. All four amines measured were found unevenly distributed inside the median eminence: 1. the highest dopamine level was detected in the middle-caudal portions of the median eminence and in the rostral parts of the pituitary stalk; 2. high norepinephrine concentration was found in the retrochiasmatic area and this gradually diminished caudalwards; 3. relatively high epinephrine level was present in the rostral median eminence and retrochiasmatic area, but that in the caudal median eminence and pituitary stalk was low; 4. the level of serotonin increased caudalwards and showed a highest value in the caudal portion of the pituitary stalk. Relatively high dopamine and serotonin levels were also detectable in all three pituitary lobes where the concentration of norepinephrine was low and that of epinephrine was undetectable.