During extinction learning (EL), an individual learns that a previously learned behavior no longer fulfills its original purpose, or is no longer relevant. Recent studies have contradicted earlier theories that EL comprises forgetting, or the inhibition of the previously learned behavior, and indicate that EL comprises new associative learning. This suggests that the hippocampus is involved in this process. Empirical evidence is lacking however. Here, we used fluorescence in situ hybridization of somatic immediate early gene (IEG) expression to scrutinize if the hippocampus processes EL. Rodents engaged in context-dependent EL and were also tested for renewal of (the original behavioral response to) a spatial appetitive task in a T-maze. Whereas distal and proximal CA1 subfields processed both EL and renewal, effects in the proximal CA1 were more robust consistent with a role of this subfield in processing context. The lower blade of the dentate gyrus (DG) and the proximal CA3 subfields were particularly involved in renewal. Responses in the distal and proximal CA3 subfields suggest that this hippocampal subregion may also contribute to the evaluation of the reward outcome. Taken together, our findings provide novel and direct evidence for the involvement of distinct hippocampal subfields in context-dependent EL and renewal.
The development of electrodes for efficient CO2 reduction
while forming valuable compounds is critical. The use of enzymes as
catalysts provides the advantage of high catalytic activity in combination
with highly selective transformations. We describe the electrical
wiring of a carbon monoxide dehydrogenase II from Carboxydothermus
hydrogenoformans (ChCODH II) using
a cobaltocene-based low-potential redox polymer for the selective
reduction of CO2 to CO over gas diffusion electrodes. High
catalytic current densities of up to −5.5 mA cm–2 are achieved, exceeding the performance of previously reported bioelectrodes
for CO2 reduction based on either carbon monoxide dehydrogenases
or formate dehydrogenases. The proposed bioelectrode reveals considerable
stability with a half-life of more than 20 h of continuous operation.
Product quantification using gas chromatography confirmed the selective
transformation of CO2 into CO without any parasitic co-reactions
at the applied potentials.
Using viologen-based redox polymers to wire a variety of different hydrogenases to electrodes and gas diffusion electrodes is the basis to mitigate high potential deactivation of the enzyme, deactivation by molecular O 2 , as well as for highcurrent density H 2 oxidation bioanodes. To overcome electron transfer limitations by electron hopping within the viologen-modified polymer film, a new redox polymer was designed with the highest possible viologen content together with monomers bearing crosslinking units. In combination with an immobilization sequence consisting of oxidative grafting of amino functions, covalent attachment of polymer units to these functionalities, and crosslinking of the polymer layers, an unprecedently fast electron transfer became possible. This enabled a very high current density normalized by the amount of the [NiFe] hydrogenase embedded within a viologen polymer on gas diffusion electrodes.
An enzymatic biofuel cell is integrated on a screen-printed electrode as a basis for a self-powered biosensor. A glucose/O 2 biofuel cell consisting of a pyrroloquinoline quinone-dependent glucose dehydrogenase embedded within an Os-complex modified redox polymer bioanode to oxidize glucose and a non-limiting bilirubin oxidase-based gas diffusion biocathode in the direct-electron transfer regime for the reduction of O 2 showed a glucose-dependent current and power output. For full integration on a single screen-printed electrode, a miniaturized agar salt bridge was introduced between the two bioelectrodes to ensure operation of the assembly in a two-compartment configuration with each electrode operating at optimal conditions.
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