Abstract
The experiments were performed to investigate the effect of anterior pituitary hormones and sex hormones on the feature of circadian variations in concentrations of norepinephrine (NE) and serotonin (5-HT) in the whole brain, the hippocampus and the hypothalamus of male rats. The effect on spontaneous movement was also examined. Wistar male rats weighing about 180g were housed in a room with constant ambient temperature of 22 ± 1°C under artificial light (light on from 05 : 00 to 19 : 00h).The hypophysectomized rat or the hypophysectomized and castrated rat was administrated subcutaneously with anteropituitary extract (AP extract) every day at 11 : 00h for 5 consecutive days from the day of hypophysectomy. Castration was performed before the day of hypophysectomy. On the day of experiment, these rats were decapitated with a guillotine at 14 : 00, 17 : 00, 20 : 00, 23 : 00, 02 : 00, 05 : 00, 08 : 00, 11 : 00 or 14 : 00h. Concentrations of NE and 5-HT were determined by fluorimetric method. NE was isolated from the whole brain or the hippocampus using Dowx50 cation exchange resin column and from the hypothalamus by alumina batch operation.
The results are as follows :
1) NE concentration in the whole brain revealed a circadian variation, which had its peak at 05 : 00h and was low in the day time, whereas 5-HT concentration showed a fluctuation which had its peak at 14 : 00h in the intact rat. NE and 5-HT contents in the whole brain in the hypophysectomized rat did not show a clear circadian variation. Definite circadian variations of NE and 5-HT contents as observed in the intact rat reappeared in the hypophysectomized rat following the administration of AP extract. Circadian variations of NE and 5-HT contents were not observed in the whole brain of the hypophysectomized and castrated rat, but were restored by the administration of AP extract. However, there was observed a phase shift in these animals.
2) 5-HT content in the hippocampus showed a circadian variation with its peak in the night, at 02 : 00h. This rhythm was not observed in the hypophysectomized rat, but was restored by the administration of AP extract. NE content in the hippocampus of the intact rat showed a circadian variation with a nadir at 05.00h and a peak at 11 : 00h, and this was maintained in the hypophysectomized rat. This pattern was disturbed by the administration of AP extract and the content increased remarkably. NE content in the hippocampus of the hypophysectomized and castrated rat increased also remarkably by the administration of AP extract.
3) NE content in the hypothalamus showed a clean circadian variation with a peak at 20.00h in the intact rat. During the day time the level was relatively low. Similar pattern of circadian variation was still observed in either the hypophysectomized rat or the castrated rat, but there was observed a phase shift of its peak by +180°. Administration of AP extract into the hypophysectomized rat, which had a phase shift by +180°, further advanced the appearance of peak, resulting a phase shift by +270° compared with the time of peak in the intact rat.
4) The spontaneous movement in the hypophysectomized rat, in the castrated rat or the hypophysectomized and castrated rat was remarkably decreased compared with that in the intact rat, but the rhythm similar to that in the intact rat was maintained. The spontaneous movement was-increased following the administration of AP extract.
It is concluded from the present results that the anterior pituitary hormones exert considerable influences on the feature of circadian variations in the brain monoamines levels by themselves and also through the hormones from its target glands. This is supported by the result from the experiment on spontaneous movement.
