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Precise spike timing through the coordination and synchronization of neuronal assemblies is an efficient and flexible coding mechanism for sensory and cognitive processing (1-6). In cortical and subcortical areas, the [...]

Synchronization of spiking activity in neuronal networks is a fundamental process that enables the precise transmission of information to drive behavioural responses (1-3). In cortical areas, synchronization of principal-neuron spiking activity is an effective mechanism for information coding that is regulated by GABA (γ-aminobutyric acid)-ergic interneurons through the generation of neuronal oscillations (4,5). Although neuronal synchrony has been demonstrated to be crucial for sensory, motor and cognitive processing (6-8), it has not been investigated at the level of defined circuits involved in the control of emotional behaviour. Converging evidence indicates that fear behaviour is regulated by the dorsomedial prefrontal cortex (9-12) (dmPFC). This control over fear behaviour relies on the activation of specific prefrontal projections to the basolateral complex of the amygdala (BLA), a structure that encodes associative fear memories (13-15). However, it remains to be established how the precise temporal control of fear behaviour is achieved at the level of prefrontal circuits. Here we use single-unit recordings and optogenetic manipulations in behaving mice to show that fear expression is causally related to the phasic inhibition of prefrontal parvalbumin interneurons (PVINs). Inhibition of PVIN activity disinhibits prefrontal projection neurons and synchronizes their firing by resetting local theta oscillations, leading to fear expression. Our results identify two complementary neuronal mechanisms mediated by PVINs that precisely coordinate and enhance the neuronal activity of prefrontal projection neurons to drive fear expression., To identify the prefrontal circuitry involved in conditioned fear behaviour, mice were implanted with recording electrodes aimed at the dmPFC, and submitted to auditory fear conditioning, a robust learning paradigm [...]

Deletions leading to complete or partial removal of ParB were introduced into the Pseudomonas aeruginosa chromosome. Fluorescence microscopy of fixed cells showed that ParB mutants lacking the C-terminal domain or HTH motif formed multiple, less intense foci scattered irregularly, in contrast to the one to four ParB foci per cell symmetrically distributed in wild-type P. aeruginosa. All parB mutations affected both bacterial growth and swarming and swimming motilities, and increased the production of anucleate cells. Similar effects were observed after inactivation of parA of P. aeruginosa. As complete loss of ParA destabilized its partner ParB it was unclear deficiency of which protein is responsible for the mutant phenotypes. Analysis of four parB mutants showed that complete loss of ParB destabilized ParA whereas three mutants that retained the N-terminal 90 aa of ParB did not. As all four parB mutants demonstrate the same defects it can be concluded that either ParB, or ParA and ParB in combination, plays an important role in nucleoid distribution, growth and motility in P. aeruginosa.

Spectral density estimates are developed by smoothing of sharpened periodograms. Performances of sharpened estimators show improvement.

Likelihood-based methods are developed for estimating rules of cellular automata aimed at the regeneration of observed regular patterns. The likelihood formulation of the problem is congenial with the use of the minimum description length principle as a model selection tool, and the method is illustrated with a series of examples using binary images.

This article considers the problem of modeling a class of nonstationary time series using piecewise autoregressive (AR) processes. The number and locations of the piecewise AR segments, as well as the orders of the respective AR processes, are assumed unknown. The minimum description length principle is applied to compare various segmented AR fits to the data. The goal is to find the 'best' combination of the number of segments, the lengths of the segments, and the orders of the piecewise AR processes. Such a 'best' combination is implicitly defined as the optimizer of an objective function, and a genetic algorithm is implemented to solve this difficult optimization problem. Numerical results from simulation experiments and real data analyses show that the procedure has excellent empirical properties. The segmentation of multivariate time series is also considered. Assuming that the true underlying model is a segmented autoregression, this procedure is shown to be consistent for estimating the location of the breaks. KEY WORDS: Changepoint; Genetic algorithm; Minimum description length principle; Nonstationarity.

A widely used approach for completing-risk data with and without masking involves the specification of cause-specific hazard rates. The use of model selection method that are data-driven and automatic are discussed through numerical studies including a real dataset with masked failure causes.

Vincenty's (1975) formulas for the direct and inverse geodetic problems (i.e., in relation to the geodesic) have been verified by comparing them with a new formula developed by adapting a fourth-order Runge-Kutta scheme for the numerical solution of ordinary differential equations, advancing the work presented by Kivioja in 1971. A total of 3,801 lines of varying distances (10 to 18,000 km) and azimuths (0 to 90[degrees], because of symmetry) were used to compare these two very different techniques for computing geodesics. In every case, the geodesic distances agreed to within 0.115 mm, and the forward and reverse azimuths agreed to within 5 x [10.sup.-6] seconds of arc, thus verifying Vincenty's formula. If one wishes to plot the trajectory of the geodesic, however, the fourth-order Runge-Kutta extension of Kivioja's formula is recommended as a numerically efficient and convenient approach. CE Database subject headings: Geodetic surveys; Distance measurement; Azimuth.

The complete 64 508 bp nucleotide sequence of the IncP-1[beta] antibiotic-resistance plasmid pB10, which was isolated from a waste-water treatment plant in Germany and mediates resistance against the antimicrobial agents amoxicillin, streptomycin, sulfonamides and tetracycline and against mercury ions, was determined and analysed. A typical class 1 integron with completely conserved 5' and 3' segments is inserted between the tra and trb regions. The two mobile gene cassettes of this integron encode a [beta]-Iactamase of the oxacillin-hydrolysing type (Oxa-2) and a gene product of unknown function (OrfE-like), respectively. The pB10-specific gene load present between the replication module (trfA1) and the origin of vegetative replication (oriV) is composed of four class II (Tn3 family) transposable elements: (i) a Tn501-like mercury-resistance (mer) transposon downstream of the trfA1 gene, (ii) a truncated derivative of the widespread streptomycin-resistance transposon Tn5393c, (iii) the insertion sequence element IS1071 and (iv) a Tn 1721-like transposon that contains the tetracycline-resistance genes tetA and tetR. A very similar Tn501-like mer transposon is present in the same target site of the IncP-1[beta] degradative plasmid pJP4 and the IncP-1[beta] resistance plasmid R906, suggesting that pB10, R906 and pJP4 are derivatives of a common ancestor. Interestingly, large parts of the predicted pB10 restriction map, except for the tetracycline-resistance determinant, are identical to that of R906. It thus appears that plasmid pB10 acquired as many as five resistance genes via three transposons and one integron, which it may rapidly spread among bacterial populations given its high promiscuity. Comparison of the pB10 backbone DNA sequences with those of other sequenced IncP-1[beta] plasmids reveals a mosaic structure. While the conjugative transfer modules (trb and tra regions) and the replication module are very closely related to the corresponding segments of the IncP-1[beta] resistance plasmid R751 and even more similar to the IncP-1[beta] degradative plasmids pTSA and pADP-1, the stable inheritance operons klcAB-korC and kleAEF are most similar to those of the IncP-1[beta] resistance plasmid pB4, and clearly less similar to the other IncP-1[beta] plasmids. This suggests that IncP-1[beta] plasmids can undergo recombination in the environment, which may enhance plasmid diversity and bacterial adaptability.

Liquid cultures of Mucor circinelloides were studied to examine lipid metabolism. Major labelled lipids in cultures incubated with (super14C)acetate were triacylgylcerol (TAG), phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Phosphatidic acid metabolism to diacylglycerol and TAG was achieved by an increase in the pH to 8.0. GPATT exhibited an obvious selectivity for palmitoyl-CoA and the LPAAT for oleoyl- and linoleoyl-CoA.

Image segmentation is fundamental to many image analysis problems. It aims to partition a digital image into a set of nonoverlapping homogeneous regions. The main contribution of this paper is the development of a new segmentation procedure which is designed to segment images corrupted by correlated noise. This new segmentation procedure is based on Rissanen's minimum description length (MDL) principle and consists of two components: i) an MDL-based criterion in which the "best" segmentation is defined as its minimizer and ii) a merging algorithm which attempts to locate this minimizer. The performance of this procedure is illustrated via a simulation study, with promising results. Index Terms - Correlated noise, image segmentation, merging algorithm, minimum description length.