Circuit Dynamics of Adult Visual Cortex

Learning and other forms of plasticity result from changes in transmission at existing synapses or the construction or elimination of synapses. Synapses occur at the juxtaposition of boutons, with their postsynaptic partners, dendrites and cell bodies. It has been assumed that connections in the primary visual cortex (V1) become static after the critical period. Recent studies show, however, that dendritic spines appear and disappear during adulthood in the normal brain. Our first objective was then to determine whether axonal branches and boutons also undergo morphological changes. To do so, we performed longitudinal studies of virally labeled neurons and their processes. An adeno-associated virus bearing the gene for enhanced green fluorescent protein (AAV.EGFP) provided long-term labeling of axons and their boutons in adult Macaque V1. To image the neurons in vivo, a custom-designed two-photon microscope and viewing chamber provided repeated imaging of selected locations. We examined the same EGFP-labeled axonal arbors at several time points over periods of weeks in the adult normal cortex. We found that axons are dynamic entities, in which a subset of boutons appeared and disappeared overtime, and that though axonal length and branching was largely stable, a small subset of terminals underwent elongation, retraction or appeared de novo. These results suggest an ongoing process of synaptogenesis and synapse elimination in adult V1. To further investigate structural plasticity in the adult V1, we studied the cortical reorganization that accompanies retinal lesions. Removal of visual input cause axonal sprouting of long-range horizontal connections from pyramidal cells in layer 2/3. Our in vivo approach allowed us to determine the dynamics of the process of sprouting. Immediately following retinal lesions, there was a remarkable rise in axonal density. In the following weeks, the massive increase in axon collaterals was accompanied by a comparable rate of axonal elimination. Also, boutons increased their rate of appearance and elimination beyond the rates seen in normal cortex. These data indicate that the initial sprouting of axons followed by the subsequent refinement, may account for the dynamics of receptive field changes observed during the course of topographic reorganization of visual cortex

Monitoring the 5'UTR landscape reveals isoform switches to drive translational efficiencies in cancer

Transcriptional and translational control are key determinants of gene expression, however, to what extent these two processes can be collectively coordinated is still poorly understood. Here, we use Nanopore long-read sequencing and cap analysis of gene expression (CAGE-seq) to document the landscape of 5' and 3' untranslated region (UTR) isoforms and transcription start sites of epidermal stem cells, wild-type keratinocytes and squamous cell carcinomas. Focusing on squamous cell carcinomas, we show that a small cohort of genes with alternative 5'UTR isoforms exhibit overall increased translational efficiencies and are enriched in ribosomal proteins and splicing factors. By combining polysome fractionations and CAGE-seq, we further characterize two of these UTR isoform genes with identical coding sequences and demonstrate that the underlying transcription start site heterogeneity frequently results in 5' terminal oligopyrimidine (TOP) and pyrimidine-rich translational element (PRTE) motif switches to drive mTORC1-dependent translation of the mRNA. Genome-wide, we show that highly translated squamous cell carcinoma transcripts switch towards increased use of 5'TOP and PRTE motifs, have generally shorter 5'UTRs and expose decreased RNA secondary structures. Notably, we found that the two 5'TOP motif-containing, but not the TOP-less, RPL21 transcript isoforms strongly correlated with overall survival in human head and neck squamous cell carcinoma patients. Our findings warrant isoform-specific analyses in human cancer datasets and suggest that switching between 5'UTR isoforms is an elegant and simple way to alter protein synthesis rates, set their sensitivity to the mTORC1-dependent nutrient-sensing pathway and direct the translational potential of an mRNA by the precise 5'UTR sequence

Undirected singing rate as a non-invasive tool for welfare monitoring in isolated male zebra finches

Research on the songbird zebra finch (Taeniopygia guttata) has advanced our behavioral, hormonal, neuronal, and genetic understanding of vocal learning. However, little is known about the impact of typical experimental manipulations on the welfare of these birds. Here we explore whether the undirected singing rate can be used as an indicator of welfare. We tested this idea by performing a post hoc analysis of singing behavior in isolated male zebra finches subjected to interactive white noise, to surgery, or to tethering. We find that the latter two experimental manipulations transiently but reliably decreased singing rates. By contraposition, we infer that a high-sustained singing rate is suggestive of successful coping or improved welfare in these experiments. Our analysis across more than 300 days of song data suggests that a singing rate above a threshold of several hundred song motifs per day implies an absence of an acute stressor or a successful coping with stress. Because singing rate can be measured in a completely automatic fashion, its observation can help to reduce experimenter bias in welfare monitoring. Because singing rate measurements are non-invasive, we expect this study to contribute to the refinement of the current welfare monitoring tools in zebra finches.Fil: Yamahachi, Homare. Universitat Zurich; SuizaFil: Zai, Anja T.. Universitat Zurich; SuizaFil: Tachibana, Ryosuke O.. Universitat Zurich; SuizaFil: Stepien, Anna E.. Universitat Zurich; SuizaFil: Rodrigues, Diana I.. Universitat Zurich; SuizaFil: Cavé Lopez, Sophie. Universitat Zurich; SuizaFil: Lorenz, Corinna. Universite Paris Saclay; Francia. Universitat Zurich; SuizaFil: Arneodo, Ezequiel Matías. Universitat Zurich; Suiza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Giret, Nicolas. Universite Paris Saclay; FranciaFil: Hahnloser, Richard H. R.. Universitat Zurich; Suiz

Axonal Dynamics of Excitatory and Inhibitory Neurons in Somatosensory Cortex

Electrophysiology-delivery of fluorescent viral vectors-and two-photon microscopy were used to demonstrate the rapidity of axonal restructuring of both excitatory and inhibitory neurons in rodent cortical layer II/III following alterations in sensory experience

A Bluetooth-Low-Energy Sensor Node for Acoustic Monitoring of Small Birds

ISSN:1530-437XISSN:1558-174

Hippocampal Remapping after Partial Inactivation of the Medial Entorhinal Cortex

Hippocampal place cells undergo remapping when the environment is changed. The mechanism of hippocampal remapping remains elusive but spatially modulated cells in the medial entorhinal cortex (MEC) have been identified as a possible contributor. Using pharmacogenetic and optogenetic approaches, we tested the role of MEC cells by examining in mice whether partial inactivation in MEC shifts hippocampal activity to a different subset of place cells with different receptive fields. The pharmacologically selective designer Gi-protein-coupled muscarinic receptor hM4D or the light-responsive microbial proton pump archaerhodopsin (ArchT) was expressed in MEC, and place cells were recorded after application of the inert ligand clozapine-N-oxide (CNO) or light at appropriate wavelengths. CNO or light caused partial inactivation of the MEC. The inactivation was followed by substantial remapping in the hippocampus, without disruption of the spatial firing properties of individual neurons. The results point to MEC input as an element of the mechanism for remapping in place cells

Change in axonal density plotted as a function of days of deprivation.

<p>Expressed as a ratio of axonal length at the indicated duration of deprivation to that measured before deprivation. The green line depicts axons of inhibitory interneurons whose somata are located in deprived barrel columns and are projecting into the non-deprived barrel columns. The yellow line depicts axons of excitatory neurons in the non-deprived barrel columns that are projecting into the deprived barrel columns.</p

Axons of inhibitory interneurons located in the non-deprived rows following whisker plucking.

<p>(A) Top, the whisker barrel map. Rectangular box depicts the region of axonal reconstructions shown on the right. Middle, axons located within non-deprived rows before whisker plucking. Right, same area after 2 d of plucking. In the reconstruction, the axons that persisted over both sessions are shown in blue, axons retracted from the first to second imaging session in red, and new axons in yellow. Scale bar  = 50 µm. (B–D) Changes in axonal length for 2 (B), 14 (C), and 30 (D) d of whisker plucking. Left, the distribution of axonal length that was lost between each baseline and post-plucking time point. Right, the distribution of axonal length that was gained between the baseline and post-plucking time points. The data for each pair of time points were obtained by averaging over several mice. Here, the magnitude of the axonal changes for each data pair is normalized with respect to the maximum length of axon that was retracted within any bin. The maximum length of retracted axon in each data pair is therefore 1.0 (in arbitrary units of length), and the length of added axon is measured with respect to that value. The dimensions of the bins are 50 µm×50 µm. The average locations of barrel columns for animals in each condition are marked on each map, with deprived barrel columns indicated in white and non-deprived barrel columns indicated in green.</p