Circuit Motifs for Contrast-Adaptive Differentiation in Early Sensory Systems: The Role of Presynaptic Inhibition and Short-Term Plasticity

In natural signals, such as the luminance value across of a visual scene, abrupt changes in intensity value are often more relevant to an organism than intensity values at other positions and times. Thus to reduce redundancy, sensory systems are specialized to detect the times and amplitudes of informative abrupt changes in the input stream rather than coding the intensity values at all times. In theory, a system that responds transiently to fast changes is called a differentiator. In principle, several different neural circuit mechanisms exist that are capable of responding transiently to abrupt input changes. However, it is unclear which circuit would be best suited for early sensory systems, where the dynamic range of the natural input signals can be very wide. We here compare the properties of different simple neural circuit motifs for implementing signal differentiation. We found that a circuit motif based on presynaptic inhibition (PI) is unique in a sense that the vesicle resources in the presynaptic site can be stably maintained over a wide range of stimulus intensities, making PI a biophysically plausible mechanism to implement a differentiator with a very wide dynamical range. Moreover, by additionally considering short-term plasticity (STP), differentiation becomes contrast adaptive in the PI-circuit but not in other potential neural circuit motifs. Numerical simulations show that the behavior of the adaptive PI-circuit is consistent with experimental observations suggesting that adaptive presynaptic inhibition might be a good candidate neural mechanism to achieve differentiation in early sensory systems.     

Adipose tissue of Drosophila melanogaster: VII. Distribution of nuclear DNA amounts along the anterior-posterior axis in the larval fat body

The DNA content of fat body nuclei was measured cytophotometrically as a function of position along an anterior-posterior (A-P) axis of the tissue throughout larval development. There was a dramatic 55-fold increase in the average amount of DNA per nucleus during the first 3 days of this period, but there was no further increase during the final day. However, the rate of increase had regional specificity. The amount of DNA per nucleus correlated significantly with its position along the A-P axis of the tissue: nuclei in a posterior direction contain gradually increasing amounts of DNA. There was up to a seven-fold difference between the smallest anterior and largest posterior nucleus. In addition, for three of the ages studied there was a subgradient in the posterior region with a slope that was considerably steeper than that of the overall tissue gradient. The tissue has three characteristic morphological regions, anterior, medial, and posterior, which can be recognized early in development and which are maintained throughout the larval period. The distribution of nuclear DNA classes determined for cells in each region for the final 2 days of larval life became fixed before the final day of development. The significance of the DNA gradient in terms of a protein storage gradient is discussed.     

New equipment for the scaled up production of small spherical biocatalysts

Summary A new apparatus with a capacity up to 24 kg per hour for physical entrapment of cell fragments or whole cells in polymeric networks was constructed, based on a high speed rotating nozzle-ring. Immobilized biocatalysts are prepared at laboratory scale with bead size under 1 mm diameter, with a deviation of 10 % or less in size distribution.     

Statistical epistasis and functional brain imaging support a role of voltage-gated potassium channels in human memory

Despite the current progress in high-throughput, dense genome scans, a major portion of complex traits' heritability still remains unexplained, a phenomenon commonly termed "missing heritability." The negligence of analytical approaches accounting for gene-gene interaction effects, such as statistical epistasis, is probably central to this phenomenon. Here we performed a comprehensive two-way SNP interaction analysis of human episodic memory, which is a heritable complex trait, and focused on 120 genes known to show differential, memory-related expression patterns in rat hippocampus. Functional magnetic resonance imaging was also used to capture genotype-dependent differences in memory-related brain activity. A significant, episodic memory-related interaction between two markers located in potassium channel genes (KCNB2 and KCNH5) was observed (P(nominal combined)=0.000001). The epistatic interaction was robust, as it was significant in a screening (P(nominal)=0.0000012) and in a replication sample (P(nominal)=0.01). Finally, we found genotype-dependent activity differences in the parahippocampal gyrus (P(nominal)=0.001) supporting the behavioral genetics finding. Our results demonstrate the importance of analytical approaches that go beyond single marker statistics of complex traits.