Effects of light-dark cycles on the circadian conidiation rhythm inNeurospora crassa

The effects of 24 hr light-dark cycles on the circadian conidiation rhythm inNeurospora crassa were compared among will-typefrq ⁺ and clock mutantsfrq ⁺,frq ³,frq ⁷,frq ⁹ andfrq ¹¹. The minimum length of the light period necessary for complete entrainment to the light-dark cycles was almost 2 hr infrq ⁺,frq ³ andfrq ⁷ strains. The minimum duration of the dark period necessary for the appearance of circadian conidiation was almost 4 hr in all of the strains except thefrq ¹¹ strain. The phase of the conidiation rhythm was dependent on the light to dark transition in thefrq ¹ strain in all light-dark cycles examined and in thefrq ⁺ andfrq ³ strains when the light period was shorter than 16 hr. In contrast, the phase of thefrq ⁷ strain was dependent on the light to dark transition when the light period was shorter than 10 hr.     

How Does the Crayfish Swimmeret System Work? Insights from Nearest-Neighbor Coupled Oscillator Models

Rhythmic movements of crayfish swimmerets are coordinated by a neural circuit that links their four abdominal ganglia. Each swimmeret is driven by its own small local circuit, or pattern-generating module. We modeled this networkas a chain of four oscillators, bidirectionally coupled to their nearest neighbors, and tested the models ability to reproduce experimentally observed changes in intersegmental phases and in period caused by differential excitation of selected abdominal ganglia. The choices needed to match the experimental data lead to the followingpredictions: coupling between ganglia is asymmetric; the ascending and descending coupling have approximately equal strengths; intersegmental coupling does not significantly affect the frequency of the system; and excitation affects the intrinsic frequencies of the oscillators and might also change properties ofintersegmental coupling.     

Resting Energy Expenditure in Obese African American and Caucasian Women

The prevalence of obesity among African American women approaches 50% and greatly exceeds rates for Caucasian women. In addition, black women lose less weight than white during obesity treatment and gain more weight when untreated. This study assessed resting energy expenditure (REE) and body composition in obese white (n=122) and black (n=44) women to explore the relationship between biological variables and these observed differences. REE and body composition were assessed by indirect calorimetry and densitometry, respectively, before weight loss. REE was significantly lower in black subjects (1637.6 ± 236.9 kcal/d) than in white (1731.4 ± 262.0) (p=0.04). REE remained significantly lower in blacks than whites after adjusting for body weight (p=0.02). REE, adjusted for fat-free mass, was also significantly lower in blacks than whites (p<0.0001), although the overestimation of fat-free mass by densitometry in blacks may have contributed to this finding. There were no differences between the groups in respiratory quotient. These results suggest that a decreased REE may exist in obese black women, and it may be related to the observed differences between black and white women in the prevalence of obesity and in the response to weight loss treatment. These crosssectional findings await confirmation in longitudinal studies.     

Variable thermal sensitivity as output of a circadian clock controlling the bimodal rhythm of temperature choice in the ant Camponotus mus

Along a thermal gradient and under a LD 1212 h cycle, nurse workers of the ant Camponotus mus select for the brood two different temperatures daily: 30.8°C at the middle of the light period (circadian phase = 90°), and 27.5°C 8 h later, during the dark period (CP = 210°). Brood-carrying activity proved to be self-sustained, running its two daily bursts free with a similar period of 23.5 h, under both LL and DD. The LD alternation acted as a strong Zeitgeber. A phase-delay of the LD 1212 h cycle reset the overt rhythm at once, being both daily events locked-on to the delayed light: dark transition. However, changes in expression, non-occurrence, or even splitting of the two daily brood-carrying events during resetting depended on the phase of the delayed DL transition. By comparing the occurrence of activity with predictions based on a threshold curve of thermal sensitivity, results indicated that an immediate resetting of the involved pacemaker actually takes place. Nurse workers do not directly control the total time spent by the brood at the selected temperature. Instead, the endogenously-driven thermal sensitivity triggers their thermal-searching behavior at two critical times of the day, when environmental temperature is expected to reach its maximum and minimum.     

A short red light pulse during dark phase of LD-cycle perturbs the hamster's circadian clock

In this study we investigated the influence of red light, which naturally occurs during dawn and dusk, on locomotor activity and body temperature rhythms of Djungarian hamsters (Phodopus sungarus). A single weak red light pulse given 2 h before regular lights on had acute as well as long-term effects persisting for several days following exposure. The hamsters immediately stopped their locomotor activity, accompanied by a drop in body temperature. In the following undisturbed nights (LD 168) the nocturnal activity stopped earlier than usual. This lasting effect of the light pulse was more pronounced than the acute effect. The activity phase compressed gradually during 3 to 5 days after the light pulse was administered while time of activity onset was almost unaffected. It took 6 to 11 days for complete recovery of the original activity phase. The maximal activity compression and the recovery period depended on the duration of the single red light pulse and its intensity. Red light pulses of 15 min duration were about twice effective as 1 min pulses; and the effect of a red light pulse of 130 mW/m² was about 1.5 times stronger than a 30 mW/m² red light pulse. The maximal value of activity phase compression reached in this experiment was 2.5+0.2 h with a recovery period of 11.1±0.3 days following a given red light pulse of 90 mW/m² and 15 min. The morning oscillator seems to be persistently affected. This indicates a very high photosensitivity of the Djungarian hamster's circadian system to red light.Abbreviations T _b body temperature - DD constant darkness - LD light:dark cycle - LL constant light - duration of activity phase - CT circadian time - PRC phase response curve - SCN suprachiasmatic nuclei     

Termination of leech swimming activity by a previously identified swim trigger neuron

Cell Tr2 is a neuron in the subesophageal ganglion of the leech that can trigger swim episodes. In this report, we describe the ability of Tr2 to terminate ongoing swim episodes as well as to trigger swimming. Stimulation of Tr2 terminated ongoing swim episodes in nearly every preparation tested, while Tr2 stimulation triggered swim episodes in only a minority of the preparations. We suggest that the primary role of Tr2 is in the termination rather than the initiation of swimming activity.The swim trigger neuron Tr3 and a swim-gating neuron, cell 21, hyperpolarized during Tr2-induced swim termination. Another swim-gating neuron, cell 204 was sometimes slightly excited, but more often, hyperpolarized during Tr2-induced swim termination. In contrast to these cells, Tr2 stimulation excited another swim-gating neuron, cell 61. The responses of the swimgating cells were variable in amplitude and sometimes not evident during Tr2-induced swim termination. Hence, the effects of Tr2 stimulation on swim-gating neurons seem unlikely to be the direct cause of swim termination.Oscillator cells examined during Tr2-induced swim termination include: 27, 28, 33, 60, 115, and 208. The largest effect seen in an oscillator neuron was in cell 208, which was repolarized by up to 10 mV during Tr2 stimulation. Tr2 stimulation did not produce any obvious synaptic effects in motor neurons DI-1, VI-1, and DE-3. Our findings indicate that other, yet undiscovered, connections are likely to be important in Tr2-induced swim termination. Therefore, we propose that cell Tr2 is probably a member of a distributed neural network involved in swim termination.Abbreviations DP dorsal posterior nerve - Mx midbody ganglion x - Rx neuromere x of the subsesophageal (rostral) ganglion - DE dorsal excitatory motor neuron - DI dorsal inhibitory motor neuron - VI ventral inhibitory motor neuron     

Separation of intact and damaged hepatocytes in sucrose following non-enzymatic liver perfusion

This study deals with isolation of rat hepatocytes by a non-enzymatic method and the separation of intact and damaged cells in sucrose medium. Low speed centrifugation in isotonic sucrose medium of a hepatocyte suspension obtained by mechanical desaggregation of liver pre-perfused with EDTA solution results in the formation of a cell pellet which contains two different layers. A darker layer contains hepatocytes with intact plasma membranes. Their respiratory activity and xenobiotic metabolism are close to those of the cells isolated by collagenase perfusion. The study of distribution of lipophilic cation tetraphenylphosphonium (TPP⁺) indicates a predominantly mitochondrial localization of TPP⁺ in the intact cells following non-enzymatic and collagenase isolation. Hepatocytes in the upper layer have damaged plasma membranes. As a result they lose the potential to accumulate TPP⁺, and have low rates of endogenous respiration and biotransformation activity. Addition of exogenous NADPH restores the capability to metabolize xenobiotics. Washing and incubation of these hepaticytes in an intracellular type medium results in restoration of uncoupler-stimulated oxygen consumption and generation of membrane potential in the presence of a succinate substrate. These properties are close to those of hepatocytes permeabilized by digitonin treatment. Thus, the procedure allows the simultaneous isolation of both intact and permeabilized hepatocytes with functionally active intracellular structures without the use of relatively expensive chemicals such as collagenase and Percoll.Abbreviations 4-OHBP 4-hydroxybiphenyl - BP biphenyl - BSA bovine serum albumin - DNP 2,4-dinitrophenol - EDTA ethylendiamintetraacetate - NADPH nicotinamide adenine dinucleotide phosphate reduced - p-NA p-nitroanisole - p-NPh p-nitrophenol - TPP⁺ tetraphenylphosphonium     

Modeling the leech heartbeat elemental oscillator I. Interactions of intrinsic and synaptic currents

We have developed a biophysical model of a pair of reciprocally inhibitory interneurons comprising an elemental heartbeat oscillator of the leech. We incorporate various intrinsic and synaptic ionic currents based on voltage-clamp data. Synaptic transmission between the interneurons consists of both a graded and a spike-mediated component. By using maximal conductances as parameters, we have constructed a canonical model whose activity appears close to the real neurons. Oscillations in the model arise from interactions between synaptic and intrinsic currents. The inhibitory synaptic currents hyperpolarize the cell, resulting in activation of a hyperpolarization-activated inward currentI _h and the removal of inactivation from regenerative inward currents. These inward currents depolarize the cell to produce spiking and inhibit the opposite cell. Spike-mediated IPSPs in the inhibited neuron cause inactivation of low-threshold Ca⁺⁺ currents that are responsible for generating the graded synaptic inhibition in the opposite cell. Thus, although the model cells can potentially generate large graded IPSPs, synaptic inhibition during canonical oscillations is dominated by the spike-mediated component.     

苯并噻唑醌类化合物对呼吸链酶系的抑制作用

合成了2-氯-5-正十二硫烷基-6-甲基-4,7-苯并噻唑醌(2-Cl-DMMDBT)和2-氯-5-正丁烷氨基-6-甲基-4,7-苯并噻唑醌(2-Cl-BAMDBT)两种化合物,研究了它们对线粒体呼吸链酶系的抑制作用.结果表明:2-Cl-DMMDBT和2-C1-BAMDBT对琥珀酸氧化酶及泛醌氧化酶的电子传递活性均表现一定的抑制作用,而对细胞色素氧化酶无作用,说明二者的抑制作用发生在泛醌反应区.二者对NADH氧化酶的抑制行为略有不同,2-Cl-DMMDBT是一个逐渐加强的过程,最终可致酶活性完全抑制,而2-Cl-BAMDBT则表现为瞬间抑制.比较了2-Cl-DMMDBT和2-Cl-BAMDBT对琥珀酸氧化酶的抑制能力,长侧链的2-Cl-DMMDBT比短侧链的2-Cl-BAMDBT抑制能力强很多.     

Fluctuation of free IAA under inductive and non-inductive photoperiods in Chenopodium rubrum

Fluctuation in levels of endogenous free IAA has been followed in the SD plant Chenopodium rubrum under photoperiodic conditions inductive or not inductive of flowering. Endogenous IAA was measured fluorimetrically as -pyrone. The level of IAA shows little fluctuation under continuous illumination. An endogenous rhythm of IAA fluctuation was found in plants transferred from light to continuous darkness, with a natural period of 30 hrs. The troughs of minimum IAA level within the endogenous rhythm coincided with the peaks in the endogenous rhythm of flowering response, which possessed the same period length. The concentration of IAA in the shoot always decreased at the end of cycles of dark period that induce flowering. The results are discussed in relation to the role of IAA in flowering of SD plants.