Network Adaptation Improves Temporal Representation of Naturalistic Stimuli in Drosophila Eye: II Mechanisms

Retinal networks must adapt constantly to best present the ever changing visual world to the brain. Here we test the hypothesis that adaptation is a result of different mechanisms at several synaptic connections within the network. In a companion paper (Part I), we showed that adaptation in the photoreceptors (R1–R6) and large monopolar cells (LMC) of the Drosophila eye improves sensitivity to under-represented signals in seconds by enhancing both the amplitude and frequency distribution of LMCs'' voltage responses to repeated naturalistic contrast series. In this paper, we show that such adaptation needs both the light-mediated conductance and feedback-mediated synaptic conductance. A faulty feedforward pathway in histamine receptor mutant flies speeds up the LMC output, mimicking extreme light adaptation. A faulty feedback pathway from L2 LMCs to photoreceptors slows down the LMC output, mimicking dark adaptation. These results underline the importance of network adaptation for efficient coding, and as a mechanism for selectively regulating the size and speed of signals in neurons. We suggest that concert action of many different mechanisms and neural connections are responsible for adaptation to visual stimuli. Further, our results demonstrate the need for detailed circuit reconstructions like that of the Drosophila lamina, to understand how networks process information.     

Network Adaptation Improves Temporal Representation of Naturalistic Stimuli in Drosophila Eye: I Dynamics

Because of the limited processing capacity of eyes, retinal networks must adapt constantly to best present the ever changing visual world to the brain. However, we still know little about how adaptation in retinal networks shapes neural encoding of changing information. To study this question, we recorded voltage responses from photoreceptors (R1–R6) and their output neurons (LMCs) in the Drosophila eye to repeated patterns of contrast values, collected from natural scenes. By analyzing the continuous photoreceptor-to-LMC transformations of these graded-potential neurons, we show that the efficiency of coding is dynamically improved by adaptation. In particular, adaptation enhances both the frequency and amplitude distribution of LMC output by improving sensitivity to under-represented signals within seconds. Moreover, the signal-to-noise ratio of LMC output increases in the same time scale. We suggest that these coding properties can be used to study network adaptation using the genetic tools in Drosophila, as shown in a companion paper (Part II).     

<Emphasis Type="Italic">SNCA</Emphasis> alleles rs356219 and rs356165 are associated with Parkinson’s disease and increased α-synuclein gene expression in CD45<Superscript>+</Superscript> blood cells

Impaired metabolism of α-synuclein (SNCA) and its aggregation are key molecular events underlying Parkinson’s disease (PD). Emerging data show that there is a connection between PD and the gene locus containing the SNCA gene. Meta-analyses have demonstrated a highly significant PD connection with single nucleotide polymorphisms (SNPs) rs356165 (A/G) and rs356219 (A/G) in the SNCA gene. We conducted SNP genotyping in 260 PD patients (n = 260) and 262 healthy people (n = 262) from northwestern regions of Russia. Linkage disequilibrium was registered between rs356219 and rs356165 alleles (D' = 0.926). It was confirmed that G alleles (rs356165 and rs356219) are associated with increased risk of PD development. For the first time, we have evaluated the relationship between rs356165 and rs356219 and levels of SNCA mRNA and α-synuclein protein in CD45⁺ peripheral blood cells in drug-naïve PD patients (n = 43) and controls (n = 39). Both the level of mRNA SNCA gene and that of α-synuclein protein were increased in carriers of rs356219 and rs356165 compared to carriers with AA genotype in control group (in the group of healthy people) (p = 0.046 and p = 0.039, respectively). Linkage disequilibrium was shown between associated marker alleles. Our data suggest that rs356165 and rs356219 allele variants may affect the PD development by up-regulation of SNCA expression.     

Identification of sequence-specific DNA-binding factors by label transfer: application to the adenovirus-2 major late promoter.

A method of affinity labelling proteins specifically associated with DNA target sequences is proposed. The method utilizes covalent UV-crosslinking of proteins to highly labelled DNA (e.g. in crude cell or nuclear extracts) followed by degradation of the DNA to short oligonucleotides. Proteins selectively labelled by attached residual oligonucleotides are readily amenable to molecular mass determination. Using this approach, we have characterized a HeLa polypeptide specifically bound to a short segment of the adenovirus-2 major late promoter (Ad2 MLP). A molecular mass value (approximately 51 kD) and precise location of the crosslinking site(s) of the protein within the MLP (-55 with respect to the cap site) were determined.     

Cleavage by ribonuclease III of the complex of 30 S pre-ribosomal RNA and ribosomal proteins of Escherichia coli

In lysates of Escherichia coli strain AB301-105, newly-formed 30 S pre-ribosomal RNA moved in a complex with protein, at 53 S. A 53 S particle also formed from the purified RNA and 30 S and 50 S ribosomal proteins, and could be cleaved by RNAase III to yield 30 S and 48 S particles.