Circadian rhythm is an endogenous rhythm that persists in constant conditions with a period of nearly but not identical to 24 hr. Under natural conditions, the circadian clock is precisely entrained to the daily (24 hr) cycle, because environmental stimulus (especially light) induces a phase shift of the clock. In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus has been shown to be the primary pacemaker that drives daily rhythms of behavioral and physiological activity. Photic information is conveyed. from the retina to the SCN directly by the retinohypothalamic tract (RHT) and indirectly by the geniculohypothalamic tract (GHT). The transmitter of the RHT is glutamate, while the GHT is GABA and neuropeptide Y. Serotonergic innervation from the median raphe and melatonin from the pineal body are likely to provide non-photic information to the SCN. Single gene mutations that dramatically alter circadian phenotype were found in the hamster (tau) and mouse (clock). Moreover, the homologous genes of the Drosophila clock gene, per, were found in mammals and the homologue of the mammalian clock was found in Drosophila. These data suggest that the some constitutes of the biological clock may be conserved between Drosophila and mammals, and a transcription-translation feedback loop involving some clock gene products may be a oscillator itself.
A number of neurohumoral factors participate in the regulation of renal hemodynamics. Several methods have been developed to study directly the regulation of renal microcirculation. Here, we introduce an in vivo method to visualize renal microcirculation by using hydronephrotic rat kidney, a unique method originally developed by Steinhausen et al. More than 10 weeks after unilateral ureteral ligation in rats, the renal parenchyme becomes thinner and suitable for transillumination. After anesthesia, the hydronephrotic kidney was split at the greater curvature with a thermal cautery and then fixed in a water chamber containing Kreb's solution. The renal tissue was transilluminated and microscopically visualized using water immersion objectives. Renal microvessels including arcuate and interlobular arteries, afferent and efferent arterioles and glomerular capillaries could be easily observed on a display monitor at a final magnification of 2, 700 times. Topical application of angiotensin II elicited constriction of the interlobular artery and afferent and efferent arterioles dose-dependently. Thus, this preparation is a unique model allowing visualization of the whole renal vascular tree in vivo.