. Effects of adult or perinatal hormonal environment on ultradian rhythms in locomotor activity of laboratory LEWIZtm rats. PHYSIOL BEHA V 38(2) [229][230][231][232][233][234][235][236][237][238][239][240] 1986.-Four experiments were performed with male and female rats of the inbred strain LEW/Ztm maintained under a light-dark schedule of 12: 12 hours. The animals were subject to castration CGOX) or ovariectomy (OVX), estradiol 17J3-implantation (E2-capsules), and perinatal hormonal treatments with testosterone propionate (TP) aod an androgen antagonist (cyproterone acetate, CA). Results indicated a difference in the locomotor activity pattern between the two sexes as a result of the endogenous estradiol levels of the adult animals. The activity pall ern of male LEW rats was characterized by ultradian rhythms of 4 and 4.8 hr periods. The female LEW rats, on the other hand, generally exhibited a clear circadian activity pattern and no uttradian activity rhythms. Following ovariectomy, each of the females showed distinct ultradian rhythms. These disappeared after E2-implantation. Castration of adult males had no effect on the ultradian activity pattern. Implantation of E2-capsules resulted in a marked decrease of the ultradian activity components. Perinatal treatment of the males with an androgen antagonist (CA) did not appear to effect ultradian rhythms during adulthood. Females treated perinatally with testosterone showed a significant increase in the ultradian activity components. This effect is assumed to be due to low estrogen levels in these animals during adulthood. Our study supports the assumption that ultradian rhythms are a result of changes in I he phase relationships between several circadian oscillators. The synchrony of these oscillations seems to be facilitated by estradiol.
Ultradian rhythmsLocomotor activity Gonadectomy Brain differentiation Laboratory rat SEVERAL weU-known phenomena of circadian rhythms in mammals can be explained by the model of the circadian system as a composite of multiple, highly ordered oscillators [40][41][42]46]located in or close to the suprachiasmatic nuclei in the hypothalamus [47]. The origin of similar temporal variations on a smaUer time scale, caUed ultradian or short-term rhythms, remains unclear [11]. Ultradian rhythms in locomotor activity are known to exist in laboratory rats [8, 9, 2~30, 49], however, attracting much less attention than circadian rhythms.A recent study of LEW/Ztm rats has shown that ultradian rhythms of 4 and 4.8 hr periods are geneticaUy fixed in this Estradiol Testosterone inbred strain (9]. The persistence of these ultradian rhythms foUowing the disruption of circadian organization under continuous light supported the assumption that the activity rhythms of this strain are caused by an independent ultradian oscillator [9]. Alternatively, the persistence of ultradian rhythms can be explained by changes in the phase relationships between several circadian oscillators [46). The ultradian rhythms of the inbred strain LEW/Ztm are sex-specific, ...
