Biology subjects

Davidson, A. M.

Publications and source records attributed to Davidson, A. M..

3 recordsLinked to original sources

bioRxiv2022

Lateral Axonal Modulation is Required for Stimulus-Specific Olfactory Conditioning in Drosophila

Effective and stimulus-specific learning is essential for animals survival. Two major mechanisms are known to aid stimulus-specificity of associative learning. One is accurate stimulus-specific representations in neurons. The second is limited effective temporal window for the reinforcing signals to induce neuromodulation only after sensory stimuli. However, these mechanisms are often imperfect in preventing unspecific associations; different sensory stimuli can be represented by overlapping populations of neurons, and more importantly the reinforcing signals alone can induce neuromodulation even without coincident sensory-evoked neuronal activity. Here, we report a crucial neuromodulatory mechanism that counteracts both limitations and is thereby essential for stimulus specificity of learning. In Drosophila, olfactory signals are sparsely represented by cholinergic Kenyon cells (KCs), which receive dopaminergic reinforcing input. We find that KCs have numerous axo-axonic connections mediated by the muscarinic type-B receptor (mAChR-B). By using functional imaging and optogenetic approaches, we show that these axo-axonic connections suppress both odor-evoked calcium responses and dopamine-evoked cAMP signals in neighboring KCs. Strikingly, behavior experiments demonstrate that mAChR-B knockdown in KCs impairs olfactory learning by inducing undesired changes to the valence of an odor that was not associated with the reinforcer. Thus, this local neuromodulation acts in concert with sparse sensory representations and global dopaminergic modulation to achieve effective and accurate memory formation. HighlightsO_LILateral KC axo-axonic connections are mediated by muscarinic type-B receptor C_LIO_LIKC connections suppress odor-evoked calcium responses and dopamine-evoked cAMP C_LIO_LIknockdown of the muscarinic type-B receptor impairs olfactory learning C_LIO_LIImpaired learning is due to changes to the valence of the unconditioned odor C_LI

neuroscience↗

bioRxiv2020

Free-living marine nematodes diversity at Ponta Delgada-Sao Miguel (Azores archipelago, North-East Atlantic Ocean): first results from shallow soft-bottom habitats

Contrasting (sand, algae, rocky-dominated, mixed) benthic habitats were sampled to characterize marine nematode diversity inhabiting surface sediments in Sao Miguel (Azores, North-East Atlantic Ocean) in July 2019. Nematodes were extracted from the surface layer of sediments and morphologically identified using light microscopy. Nematode taxonomy was based on living/fresh specimens) to ensure a suitable recognition of morphological traits. Our results provide a preliminary checklist of free-living marine nematode genera from 21 intertidal and sublittoral sandy beach sites along the coast of Sao Miguel island, Azores archipelago, Portugal. The nematode fauna was represented by 4 orders, 21 families, and 43 genera. Cyatholaimus, Desmodora and Daptonema had two morphospecies each. Enoplida was represented by 8 families and 13 genera, while Chromadorida by 7 families and 18 genera, the latter corresponding to the most diverse nematode group. Monhysterida had 5 families and 10 genera and Araeolaimida was represented by a single 1 family and 2 genera. The most common genera (i.e., accounting for 75% of all organisms) included Adoncholaimus (most abundant genus, 32 specimens), Axonolaimus (18), Cyatholaimus (17), Enoploides (13), Rhabdocoma, and Acanthopharynx (11). Viscosia and Enoplolaimus were represented by 7 specimens, whilst Halalaimus, Desmoscolex, Monophostia, Daptonema, and Theristus obtained only 6 each. The dominant nematode taxa of Sao Miguel island have been commonly previously reported in other coastal habitats including sandy beaches. They can be considered typical meiofaunal components of intertidal sandy beaches. Many of the nematode morphotypes found in Sao Miguel island could represent new species to science. As far as we know, this is the first report on free-living nematodes for Sao Miguel Island and for marine shallow water in the Azores. Our findings will serve as an import baseline for future research aiming to improve our understating of nematode communities in volcanic islands such as Sao Miguel in the Azores archipelago.

ecology↗

bioRxiv2016

Experimental and Computational Investigation of the Structure of Peptide Monolayers on Gold Nanoparticles

The self-assembly and self-organization of small molecules at the surface of nanoparticles constitute a potential route towards the preparation of advanced protein-like nanosystems. However, their structural characterization, critical to the design of bio-nanomaterials with well-defined biophysical and biochemical properties, remains highly challenging. Here, a computational model for peptide-capped gold nanoparticles is developed using experimentally characterized CALNN-and CFGAILSS-capped gold nanoparticles as a benchmark. The structure of CALNN and CFGAILSS monolayers is investigated by both structural biology techniques and molecular dynamics simulations. The calculations reproduce the experimentally observed dependence of the monolayer secondary structure on peptide capping density and on nanoparticle size, thus giving us confidence in the model. Furthermore, the computational results reveal a number of new features of peptide-capped monolayers, including the importance of sulfur movement for the formation of secondary structure motifs, the presence of water close to the gold surface even in tightly packed peptide monolayers, and the existence of extended 2D parallel {beta}-sheet domains in CFGAILSS monolayers. The model developed here provides a predictive tool that may assist in the design of further bio-nanomaterials.

biochemistry↗