In the present study radioimmunoassay

fluorimetry and high performance liquid chromatography were used to determine neuropeptides and monoamine neurotransmitters in the rat brain after head irradiation with 10 Gy X-rays. The results showed that the immunoreactive (ir) L-Enk in the hypothalamus and irM-Enk in the pituitary decreased markedly

while the contents of NE

E and DA in the hypothalamus

5-HIAA in the diecephalon and the 5-HIAA to 5-HT ratio increased significantly. The monoamines in the other cerebral area showed no significant changes. These results suggest that the hypothalamus is comparatively radiosensitive and neurochemical changes in it may have profound influence on the functions of the nervous and endocrine system.