Effects of ovarian maturation and insemination on the length of intermoult in Thermobia domestica

ABSTRACT. A study of the individual variability in the length of intermoult periods allows correlations to be established between reproductive and moulting cycles in adult females of Thermobia domestica (Packard) (Thysanura, Lepismatidae). By keeping the females without or with males and by changing the day of insemination, it is shown that the intermoult periods vary with the rate of ovarian maturation from the beginning of each stadium. Females with slow oocyte growth are never inseminated, even in the presence of males; they have short intermoults. Females with rapid oocyte growth can be inseminated and the timing of insemination regulates the length of the intermoults. It appears that the variability in duration of the intermoult only concerns the first part of the stadium (postecdysial period of the reproductive cycle=period of intense vitellogenesis), whereas the second part of the stadium (pre-ecdysial period=previtellogenesis) has an almost constant length. The endocrine mechanisms involved are considered, taking into account the cyclic changes in hormonal levels already described in other papers.     

Macronutrient Self-Selection Pattern in Rats under Different Lighting Conditions

The effect of constant darkness (DD) and constant light (LL) on the circadian pattern of macronutrient self-selection, daily food intake and body weight was analysed in rats using an automated computer system. No significant differences in energy intake were observed between groups as regards energy intake or macronutrient preferences. Fat and CHO intakes showed a negative correlation (p < 0.005 in LL and p < 0.0005 in DD and LD), while protein intake remained constant, which suggests the existence of separate regulation mechanisms governing the intake of protein and energy. Energetic requirements can be preponderantly covered by CHO or fat, depending on the preferences of the animal. Body weight measurements reflected no significant variations between groups at the end of the experiment. However, the circadian pattern of wheel-running activity and the intake of the three macronutrients measured in both constant lighting conditions varied with respect to that observed in LD. This was particularly true in the case of LL, when constant illumination exerted a decoupling effect on the rhythms. The results indicate that lighting conditions modulate the circadian pattern of wheel-running activity and macronutrient intake. However, changes in temporal organisation of food intake did not affect macronutrient preferences, daily energy intake, number of meals, feeding duration or body weight, suggesting the existence of a double, circadian and homeostatic, control of such variables.     

On the existence of limit cycles for the enzyme-catalyzed hydrolysis reaction in a zero-dimensional representation of a membrane

This article is a continuation of the work done by N. J. Zabusky and R. H. Hardin [2] on an enzyme-catalyzed unbuffered hydrolysis reaction in a one-dimensional membrane. We consider the zero-dimensional approximation to a membrane. The system is then governed by a pair of ordinary differential equations. We give a sufficient condition on the parameters of the system for the existence of a limit cycle and present numerical solutions for realistic parameter ranges. Furthermore, we also give a sketched proof of the existence of a pH front for the stationary solutions of the full system of partial differential equations.     

20-Hydroxyecdysone and ovarian maturation in the firebrat Thermobia domestica (Thysanura: Lepismatidae)

The effects of 20-hydroxyecdysone on ovary maturation in the firebrat Thermobia domestica were investigated by in vivo injections of different doses of the hormone on various days of the reproductive cycle. Several females were neck-ligated or treated with precocene II before injection. Experiments were also performed on ovarioles incubated in vitro. It was demonstrated that 20-hydroxyecdysone has direct and dose-dependent effects on the ovary, inducing growth of all the previtellogenic follicles whatever the day of the reproductive cycle, except at times when the ovaries contain follicles undergoing choriogenesis. The major effect of the hormone is the stimulation of young-follicle formation in the anterior part of the previtellarium and the accelerated growth of a set of basal previtellogenic follicles, which reach the critical size required for yolk deposition. However, 20-hydroxyecdysone did not induce cellular differentiation, in particular, the enlargement of the perioocyte space and the development of oocyte microvilli, which normally occur before yolk precursor incorporation. The present results give a better understanding of the temporal relationships between molting and reproductive cycles and also explain the periodicity of ovarian maturation.     

Boom, bust, and the human body: Further evidence on the relationship between height and business cycles

Historical time series for average human height exhibit short- and medium-term cycles that can be associated with business cycles in the 19th and 20th century. Using spectral analysis, we calculate the proportion of cyclical fluctuations in height series attributable to economic cycles. We also analyze the extent to which these cyclical phenomena change over time. In the U.S., the association between height cycles and business cycles was weaker among richer segments of the society, and weaker among men than among women. Additionally, the relationship diminished over time, probably with the rich preceding the population at large.     

On the analysis of substrate cycles in large metabolic systems

The simultaneous operation of paired, opposing reactions (substrate cycles) or parallel reactions (dual pathways) with seeming wastage of ATP is widespread in cellular metabolism. Analysis of such “futile” pathways has hitherto been limited to loci with only two or three interconnecting fluxes. We introduce here a method that allows straightforward analysis of more complex systems. The method involves the linear superposition of “fundamental” modes, one or more of which may be energetically wasteful. Decomposition of a flux pattern into such modes allows computation of the amount of free energy “wasted” at any locus. Appropriate normalizations of energy wastage yield a number of indices useful for assessing the energetic impact of futile pathways on the cell and for comparing the degree of regulation of substrate cycles or dual pathways under different metabolic conditions. This approach is applied to steady-state flux data obtained in the protozoanTetrahymena pyriformis and in isolated rat hepatocytes under a variety of conditions.     

Change in Hair Cycle and Hair Length in Nude Mice by Administration of Deuterium Oxide

D₂O increased hair length in Balb/c nu/nu (nude) mice in our previous study although it has an antimitotic effect in cells. To investigate the mechanism of the effect on the hair length, we examined the change by the administration of D₂O in the duration of the hair cycle and the proliferating activity of the hair matrix in relation with hair length in nude mice. The results showed that 20 or 30% D₂O administration did not change the gross structure of the hairs, the proliferative activity and keratinization of the hair matrix cells, but elongated the hair cycle. The duration of the hair cycle increased by the administration of D₂O in a dose-dependent manner over the examined range and these effects were reversible by discontinuation of D₂O. The change in the hair length correlated with the change in the hair-existing phase particularly. We also showed that the mast cell density in the skin, which is related to the hair cycle, increased in the deuterated mice at anagen VI stage which nearly corresponds to the hair-existing phase. The increase in the mast cell density may be related to the increase in the hair cycle duration. These findings indicate that the increase in hair length may be due to the increase in the duration of the hair cycle, in particular, an increase in the hair-existing phase. This study thus suggests that D₂O slows not only short-term cycles such as circadian clock or ultradian clock, but also the hair cycle which is a long-term cycle.