Stimulus level effects on neural excitation and eCAP amplitude.

The common assumption that the electrically evoked compound action potential (eCAP) has a linear relationship with the number of excited nerve fibres is derived from the acoustical unitary response concept. This study tests the validity of this hypothesis for electrical stimulation. Five guinea pigs were implanted with the tip of a human HiFocus electrode. eCAPs were measured with the forward masking paradigm, using anodic- and cathodic-leading biphasic current pulses and the inter-pulse interval was varied. Masker and probe amplitudes were varied either individually or simultaneously. Surprisingly, at high levels decreasing eCAP amplitudes were measured with increasing stimulus current. In search for an explanation, the experimental conditions were implemented in our 3D computational model of the implanted guinea pig cochlea to perform a functional comparison. In the final experiment, with fixed inter-pulse interval (IPI) and anodic-leading pulses, increasing stimulus currents showed growing numbers of excited nerve fibres and decreasing eCAP amplitudes at high levels, again. While simulating the relative contribution of single fibres to the overall eCAP, an explanation for this could be found in a waveform change in the modelled single fibre action potentials at high levels. We conclude that highly stimulated nerve fibres have another contribution to the eCAP response than lower stimulated fibres, which leads to a reduction of the eCAP amplitude at high levels.

Autosomal SNP typing of forensic samples with the GenPlex™ HID System: results of a collaborative study.

The GenPlex™ HID System (Applied Biosystems - AB) offers typing of 48 of the 52 SNPforID SNPs and amelogenin. Previous studies have shown a high reproducibility of the GenPlex™ HID System using 250-500pg DNA of good quality. An international exercise was performed by 14 laboratories (9 in Europe and 5 in the US) in order to test the robustness and reliability of the GenPlex™ HID System on forensic samples. Three samples with partly degraded DNA and 10 samples with low amounts of DNA were analyzed in duplicates using various amounts of DNA. In order to compare the performance of the GenPlex™ HID System with the most commonly used STR kits, 500pg of partly degraded DNA from three samples was typed by the laboratories using one or more STR kits. The median SNP typing success rate was 92.3% with 500pg of partly degraded DNA. Three of the fourteen laboratories counted for more than two thirds of the locus dropouts. The median percentage of discrepant results was 0.2% with 500pg degraded DNA. An increasing percentage of locus dropouts and discrepant results were observed when lower amounts of DNA were used. Different success rates were observed for the various SNPs. The rs763869 SNP was the least successful. With the exception of the MiniFiler™ kit (AB), GenPlex™ HID performed better than five other tested STR kits. When partly degraded DNA was analyzed, GenPlex™ HID showed a very low mean mach probability, while all STR kits except MiniFiler™ had very limited discriminatory power.