Effects of anaerobiosis on carbohydrate oxidation by roots of Pisum sativum

The aim of this work was to discover the effects of anaerobiosis on the breakdown of sugars by the apical 6 mm of the roots of 5-day-old seedlings of Pisum sativum. Estimates of the maximum catalytic activities of alcohol dehydrogenase, lactate dehydrogenase, phosphoenolpyruvate carboxylase and NADP-specific malic enzyme showed them to be comparable to that of phosphofructokinase. Metabolism of sucrose-[U-¹⁴C] by excised apices was restricted by anoxia mainly to conversion to ethanol, CO₂ alanine and glycolytic intermediates. Measurements of metabolites over a period of 240 min after transfer of excised apices to nitrogen showed a marked and continual accumulation of ethanol, a smaller continual accumulation of alanine, a small initial rise in lactate and no detectable accumulation of malate or pyruvate. The rates of CO₂ production, of accumulation of ethanol and alanine, and of the labelling of these compounds by sucrose-[¹⁴C] declined markedly during the first 240 min of anaerobiosis. The conclusion is that under anaerobic conditions carbohydrate metabolism in the pea root apex is largely restricted to alcoholic fermentation, and, to a lesser degree, to alanine production.     

The crystal structure of the bifunctional primase-helicase of bacteriophage T7

Within minutes after infecting Escherichia coli, bacteriophage T7 synthesizes many copies of its genomic DNA. The lynchpin of the T7 replication system is a bifunctional primase-helicase that unwinds duplex DNA at the replication fork while initiating the synthesis of Okazaki fragments on the lagging strand. We have determined a 3.45 A crystal structure of the T7 primase-helicase that shows an articulated arrangement of the primase and helicase sites. The crystallized primase-helicase is a heptamer with a crown-like shape, reflecting an intimate packing of helicase domains into a ring that is topped with loosely arrayed primase domains. This heptameric isoform can accommodate double-stranded DNA in its central channel, which nicely explains its recently described DNA remodeling activity. The double-jointed structure of the primase-helicase permits a free range of motion for the primase and helicase domains that suggests how the continuous unwinding of DNA at the replication fork can be periodically coupled to Okazaki fragment synthesis.     

The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism

Experimentation is at the heart of classical and modern behavioral ecology research. The manipulation of natural cues allows us to establish causation between aspects of the environment, both internal and external to organisms, and their effects on animals' behaviors. In recognition systems research, including the quest to understand the coevolution of sensory cues and decision rules underlying the rejection of foreign eggs by hosts of avian brood parasites, artificial stimuli have been used extensively, but not without controversy. In response to repeated criticism about the value of artificial stimuli, we describe four potential benefits of using them in egg recognition research, two each at the proximate and ultimate levels of analysis: (1) the standardization of stimuli for developmental studies and (2) the disassociation of correlated traits of egg phenotypes used for sensory discrimination, as well as (3) the estimation of the strength of selection on parasitic egg mimicry and (4) the establishment of the evolved limits of sensory and cognitive plasticity. We also highlight constraints of the artificial stimulus approach and provide a specific test of whether responses to artificial cues can accurately predict responses to natural cues. Artificial stimuli have a general value in ethological research beyond research in brood parasitism and may be especially critical in field studies involving the manipulation of a single parameter, where other, confounding variables are difficult or impossible to control experimentally or statistically.     

Temporal Constraints of Behavioral Inhibition: Relevance of Inter-stimulus Interval in a Go-Nogo Task

The capacity to inhibit prepotent and automatic responses is crucial for proper cognitive and social development, and inhibitory impairments have been considered to be key for some neuropsychiatric conditions. One of the most used paradigms to analyze inhibitory processes is the Go-Nogo task (GNG). This task has been widely used in psychophysical and cognitive EEG studies, and more recently in paradigms using fMRI. However, a technical limitation is that the time resolution of fMRI is poorer than that of the EEG technique. In order to compensate for these temporal constraints, it has become common practice in the fMRI field to use longer inter-stimulus intervals (ISI) than those used in EEG protocols. Despite the noticeable temporal differences between these two techniques, it is currently assumed that both approaches assess similar inhibitory processes. We performed an EEG study using a GNG task with both short ISI (fast-condition, FC, as in EEG protocols) and long ISI (slow-condition, SC, as in fMRI protocols). We found that in the FC there was a stronger Nogo-N2 effect than in the SC. Moreover, in the FC, but not in the SC, the number of preceding Go trials correlated positively with the Nogo-P3 amplitude and with the Go trial reaction time; and negatively with commission errors. In addition, we found significant topographical differences for the Go-P3 elicited in FC and SC, which is interpreted in terms of different neurotransmitter dynamics. Taken together, our results provide evidence that frequency of stimulus presentation in the GNG task strongly modulates the behavioral response and the evoked EEG activity. Therefore, it is likely that short-ISI EEG protocols and long-ISI fMRI protocols do not assess equivalent inhibitory processes.     

LIMaS: the JAVA-based application and database for microarray experiment tracking

Microarrays allow monitoring of gene expression for tens of thousands of genes in parallel and are being used routinely to generate huge amounts of valuable data. Handling and analysis of such data are becoming major bottlenecks in the utilization of the technology. To enable the researcher to interpret the results postanalysis, we have developed a laboratory information management system for microarrays (LIMaS) with an n-tier Java front-end and relational database to record and manage large-scale expression data preanalysis. This system enables the laboratory to replace the paper trail with an efficient and fully customizable interface giving it the ability to adapt to any working practice, e.g., handling many resources used to form many products (chaining of resources). The ability to define sets of activities, resources, and workflows makes LIMaS MIAME-supportive.LIMaS is available for download at (http://www.mgu.har.mrc.ac.uk/microarray.)     

An analysis of spontaneous behavior following acute MDMA treatment in male and female rats

3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a widely abused drug that impairs behavioral, emotional and cognitive functions in humans and animals. The aim of this study was to evaluate MDMA effects on the spontaneous behavioral repertoire of rats with a focus on the gender differences. MDMA was given subcutaneously in a single dose of 2.5, 5 and 10 mg/kg and the spontaneous behavior of male and female rats was studied using the open field test. Behavioral patterns (locomotion, rearing, floor-sniffing, air-sniffing, grooming, immobility and stereotypy) were registered in two sessions - 30 and 60 min following MDMA administration; each session lasting 5 min. We found that MDMA totally disrupted the structure and timing of spontaneous behavioral patterns in both genders; no evident differences were measured between either of the sessions. MDMA irrespective of the dosage produced hyperlocomotion, excessive floor-sniffing and almost absolute suppression of grooming and immobility. A biphasic effect of MDMA was found in rearing. Gender differences were present namely in rearing and sniffing stereotypy. This study also confirms that behavioral experiments should focus on more behavioral elements than only on e.g. locomotion and that the observer-based approach still gives the most reliable results.