RESUMEN
Previous studies have shown that the circadian system of Japanese quail is composed of multiple photic inputs and multiple oscillators. Among these are extraretinal photoreceptors that mediate both circadian and photoperiodic responses and circadian pacemakers in the eyes that, via neural and hormonal outputs, help to maintain rhythmicity of central circadian clocks (presumably located in the suprachiasmatic area of the hypothalamus). Furthermore, a component of the central circadian system is influenced by reproductive hormones. Under certain conditions, the circadian system of female quail can be induced to split into two circadian components: one driven by ocular pacemakers and one driven by feedback from reproductive hormones. Importantly, ovulation is either inhibited or permitted as these two oscillators (or sets of oscillators) constantly change internal phase relationships with each other, suggesting an "internal coincidence" mechanism in the control of ovulation. The oviposition patterns of quail in light-dark (LD) cycles also support an internal coincidence mechanism. The authors tested the hypothesis that the ocular pacemakers are an important component of an internal coincidence mechanism controlling ovulation by examinig the effects of blinding by complete eye removal (EX), and the effects of eye-patching, on the body temperature and oviposition patterns of quail exposed to 24-h LD cycles. They also examined the effects of EX on quail exposed to continuous light (LL) and to continuous darkness (DD). Neither EX nor eye-patching affected the oviposition patterns of birds in LD. Furthermore, robust body temperature and oviposition rhythms continued in EX birds in LL, but body temperature became arrhythmic in DD with the cessation of ovulation. The results do not show a role for ocular pacemakers in the control of ovulation, but they do support the hypotheses that (1) entrainment of the central oscillators by extraretinally perceived light is sufficient to preserve a normal ovulatory pattern in LD in the absence of the ocular pacemakers, and (2) in LL, feedback of reproductive hormones onto the central oscillators is sufficient to organize the circadian system even in the absence of the ocular pacemakers. Whether or not the ocular pacemakers are normally involved in the control of ovulation is still an open question.
Asunto(s)
Ritmo Circadiano/fisiología , Coturnix/fisiología , Fenómenos Fisiológicos Oculares , Ovulación/fisiología , Células Fotorreceptoras de Vertebrados/fisiología , Animales , Ceguera/fisiopatología , Temperatura Corporal , Femenino , Oviposición , Fotoperiodo , Privación Sensorial/fisiología , Visión Ocular/fisiologíaRESUMEN
A role for the circadian system in photoperiodic time measurement in Japanese quail is controversial. The authors undertook studies of the circadian and photoperiodic system of Japanese quail to try to identify a role for the circadian system in photoperiodic time measurement. The circadian studies showed that the circadian system acts like a low-amplitude oscillator: It is readily reset by light without significant transients, has a Type 0 phase response curve (PRC), and has a large range of entrainment. In fact, a cycle length that is often used in resonance protocols (LD 6:30) is within the range of entrainment. The authors employed T-cycle experiments; that is, LD cycles with 6- and 14-h photoperiods and period lengths ranging from 18 to 36 h to test for circadian involvement in photoperiodic time measurement. The results did not give evidence for circadian involvement in photoperiodic time measurement: T-cycles utilizing 6-h photoperiods were uniformly noninductive (that is, did not stimulate the reproductive system), whereas T-cycles utilizing 14-h photoperiods were inductive (stimulatory). A good match was observed between the phase-angles exhibited on the T-cycles employing 6-h photoperiods and the predicted phase-angles calculated from a PRC generated from 6-h light pulses.
Asunto(s)
Ritmo Circadiano/fisiología , Coturnix/fisiología , Fotoperiodo , Animales , Temperatura Corporal/fisiología , Femenino , Actividad Motora/fisiología , Oviposición/fisiología , Ovulación/fisiología , Factores de TiempoRESUMEN
The placenta is the central organ of fetomaternal exchange, which metabolically provides for the growth of the fetus and its membranes as a whole. The main structural components of the human placenta develop until the beginning of the second trimester of gestation, and continue to grow and differentiate. The dynamics of the histomorphological development of the placenta lasts until birth. The aim of this stereological investigation was to analyze and compare structural components of placental parenchyma during two periods of the 10th lunar month: from the 38th to 39th week, and in the 40th week of gestation. The results show that during the last four weeks of gestation the trophoblast of the chorionic villi changes the most. At the beginning of the 10th lunar month, alpha zones, bearers of transplacental gas transport, prevail. At the end of the 10th lunar month beta zones dominate (P < 0.005). These are metabolically active parts of trophoblast. These quantitative results of stereological analysis have to be assumed as structural evidence of the physiological maturity of human placenta.