Experimental study of the role of hypothalamopituitary system in control of pain

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The role of hypothalamopituitary system in control of pain was studied in rats by the hot-plate method, being with special reference to the effect of corticotrophin releasing factor(CRF) on the serum. ACTH level and on the pain threshold.1. CRF was first given intravenously in acute stage in 20 rats, and the effect of the pain threshold was compared with the serum level of ACTH, which is derived from the same precursor of beta-endorphine in the pituitary gland. Then CRF was chranically injected into the jugular vein of 10 rats, for 7 days and totally 170 mug/1.7 ml, by way of an osmotic mini-pump which was embedded subcutaneously. Results of acute and chronic intravenous injection of CRF didn't alter the level of threshold of pain. Moreover there was no relationship between the rain threshold and the serum. ACTH level, which was measured by RPA method.2. CPF was microinjected as much as 2 mug/lmul into the paraventricular nucleus of hypothalamus(PVN) of 10 rats with or without hypophysectomy, which didn't produce any change in pain threshold.3. Morphine was microinjected into the PVN of hypothalamus of 1.1 rats with or without hypophysectomy, which resulted in marked diminution of pain susceptibility. These findings suggested that CRF did not play the important role in mechanism of pain control of hypothalaipopituitary system. However, PVN appeared to be the important site in control of pain in hypothalamopituitary system.