The physiology and morphology of two types of electrosensory neurons in the weakly electric fishApteronotus leptorhynchus

Summary Previous anatomical and physiological studies of the gymnotoid electrosensory lateral line lobe (ELLL) suggest that the anatomically identified basilar and non-basilar pyramidal cells correspond to the physiologically defined E and I cells. Intracellular injection of horseradish peroxidase (HRP) into physiologically identified E and I cells confirms this hypothesis. The morphologies and physiological responses of the basilar and non-basilar pyramidal cells were compared. Both types of pyramidal cells have extensive apical dendritic trees that interact with a parallel fiber network in the ELLL. The apical dendritic trees of the non-basilar pyramidal cells have a wider spread along the rostrocaudal axis of the ELLL than those of the basilar pyramidal cells. This difference is discussed in reference to the interaction of these cell types with the parallel fibers of the ELLL. The density of apical dendritic branches was measured and related to the distance of these branches from the cell body. No obvious differences were seen between the dendritic density patterns of basilar and non-basilar pyramidal cells. An interesting correlation, however, exists between the atypical physiological characteristics of two basilar pyramidal cells and their dendritic density patterns. Two cells of the medial (ampullary) segment of the ELLL were analyzed. Like the pyramidal cells of the three lateral (tuberous) regions of the ELLL, the physiology of these cells appears to be related to the presence of an extended basilar process. The ampullary cells, however, have apical dendritic trees that are oriented orthogonally to the dendritic trees of the pyramidal cells.Abbreviations AM amplitude modulation - DML dorsal molecular layer - ELLL electrosensory lateral line lobe - EOD electric organ discharge - HRP horseradish peroxidase - LC lobus caudalis - Npd nucleus praeeminentialis dorsalis - PSTH post stimulus time histogram     

23Na and flame photometric studies of the NMR visibility of sodium in rat muscle.

23Na nuclear magnetic resonance spectroscopy (NMR) is increasingly being used to study Na+ gradients and fluxes in biological tissues. However, the quantitative aspects of 23Na NMR applied to living systems remain controversial. This paper compares sodium concentrations determined by 23Na NMR in intact rat hindlimb (n = 8) and excised rat gastrocnemius muscle (n = 4) with those obtained by flame photometric methods. In both types of samples, 90% of the sodium measured by flame photometry was found to be NMR-visible. This is much higher than previously reported values. The NMR measurements for intact hindlimb correlated linearly with the flame photometric measurements, implying that one pool of sodium, predominantly extracellular, is 100% visible. From measurements on excised muscle, in which extracellular space is more clearly defined, the NMR visibility of intracellular Na+ was calculated to be 70%, assuming an extracellular space of 12% of the total tissue water volume and an extracellular NMR visibility of 100%. 23Na transverse relaxation measurements were carried out using a Hahn spin echo on both intact hindlimb (n = 1) and excised muscle (n = 2) samples. These showed relaxation curves that could each be described adequately using two relaxation times. The rapidly relaxing component showed a T2 value of 3-4 ms and the slowly relaxing component a T2 of 21-37 ms. A spin lattice relaxation (T1) measurement on intact hindlimb yielded a value of 51 ms. These relatively long relaxation times show that the quadrupolar relaxation effect of Na+ complexing to large macromolecules or being otherwise motionally restricted is relatively weak. This is consistent with the high NMR visibilities reported here.     

Complete genome sequence of Methanoculleus marisnigri Romesser et al. 1981 type strain JR1

Methanoculleus marisnigri Romesser et al. 1981 is a methanogen belonging to the order Methanomicrobiales within the archaeal phylum Euryarchaeota. The type strain, JR1, was isolated from anoxic sediments of the Black Sea. M. marisnigri is of phylogenetic interest because at the time the sequencing project began only one genome had previously been sequenced from the order Methanomicrobiales. We report here the complete genome sequence of M. marisnigri type strain JR1 and its annotation. This is part of a Joint Genome Institute 2006 Community Sequencing Program to sequence genomes of diverse Archaea.     

Molecular Ecological Analysis of Methanogens and Methanotrophs in Blanket Bog Peat

Abstract Methane production and methane oxidation potential were measured in a 30 cm peat core from the Moorhouse Nature Reserve, UK. The distribution of known groups of methanogens and methane oxidizing bacteria throughout this peat core was assessed. Using 16S rRNA gene retrieval and functional gene probing with genes encoding key proteins in methane oxidation and methanogenesis, several major groups of microorganisms were detected. Methane production and oxidation was detected in all depths of the peat core. PCR amplification and oligonucleotide probing experiments using DNA isolated from all sections of the peat core detected methanotrophs from the groups Methylosinus and Methylococcus and methanogens from the groups Methanosarcinaceae, Methanococcaceae, and Methanobacteriaceae. 16S rDNA sequences amplified with the Methylosinus-specific primer were shown to have a high degree of identity with 16S rDNA sequences previously detected in acidic environments. However, no methanogen sequences were detected by the probes available in this study in the sections of the peat core (above 7 cm) where the majority of methanogenesis occurred, either because of low methanogen numbers or because of the presence of novel methanogen sequences. Received: 9 March 1999; Accepted: 21 June 1999     

Partially formed native tertiary interactions in the A-state of cytochrome c.

Considerable insight into protein structure, stability, and folding has been obtained from studies of non-native states. We have studied the extent of native tertiary contacts in one such molecule, the A-state of yeast iso-1-ferricytochrome c. Previously, we showed that the interface between the N and C-terminal helices is completely formed in the A-state. Here, we focus on interactions essential for forming the heme pocket of eukaryotic cytochromes c. To determine the extent of these interactions, we used saturation mutagenesis at the evolutionarily invariant residue leucine 68, and measured the free energy of denaturation for the native states and the A-states of functional variants. We show that, unlike the interaction between the terminal helices, the native interactions between the 60s helix and the rest of the protein are not completely formed in the A-state.     

Genetics in the study of mosquito susceptibility to Plasmodium

Within the past several years, a number of powerful genetic and genomic tools have been developed for use in research on the African malaria vector Anopheles gambiae. While these tools have been developed with a broad range of potential applications in mind, they have been particularly useful in advancing the effort to clone a set of An. gambiae genes that enable a refractory strain of this mosquito to encapsulate and kill a wide variety of different malaria parasites to which this mosquito is normally fully susceptible. This paper describes the latest progress in this map-based cloning research, which involves the collaborative contributions of a number of different laboratories in Europe and the United States.     

The circadian basis of ovarian diapause regulation in Drosophila melanogaster: is the period gene causally involved in photoperiodic time measurement?

Females of a wild-type strain of Drosophila melanogaster (Canton-S), and of several clock mutants (period), were able to discriminate between diapause-inducing short days and diapause-averting long days with a well-defined critical daylength. The critical daylengths of a short-period mutant (pers) and a long-period mutant (perL2) were almost identical, both to each other and to that of Canton-S. The critical daylength of an arrhythmic mutant (perol), however, was about 3 hr shorter than that of Canton-S, and that of per- was about 5 hr shorter. Exposure of Canton-S females to Nanda-Hamner experiments, consisting of a 10-hr photophase coupled to a dark phase varying between 4 and 74 hr, showed (1) that the photoperiodic clock in D. melanogaster measures nightlength rather than daylength, and (2) that photoperiodic time measurement is somehow based on (or affected by) constituent oscillators in the circadian system. Nanda-Hamner results for the period mutants all showed similar profiles regardless of genotype, or the presence or absence of per locus DNA. These results suggest that photoperiodic induction and locomotor activity do not share a common pacemaker in D. melanogaster, and that the per gene is not causally involved in nightlength measurement by the photoperiodic clock, although flies in which the per locus is missing (per-) or defective (perol) show an altered critical value.