Wistar-Kyoto (WKY) rats as an endogenous depression model partially lack a response to classic selective serotonin reuptake inhibitors (SSRIs). Thus, this strain has the potential to be established as a model of treatment-resistant depression (TRD). However, the SSRI resistance in WKY rats is still not fully understood. In this study, WKY and control rats were subjected to a series of tests, namely, a forced swim test (FST), a sucrose preference test (SPT), and an open field test (OFT), and were scanned in a 7.0-T MRI scanner before and after three-week citalopram or saline administration. Behavioral results demonstrated that WKY rats had increased immobility in the FST and decreased sucrose preference in the SPT and central time spent in the OFT. However, citalopram did not improve immobility in the FST. The amplitude of low-frequency fluctuation (ALFF) analysis showed regional changes in the striatum and hippocampus of WKY rats. However, citalopram partially reversed the ALFF value in the dorsal part of the two regions. Functional connectivity (FC) analysis showed that FC strengths were decreased in WKY rats compared with controls. Nevertheless, citalopram partially increased FC strengths in WKY rats. Based on FC, global graph analysis demonstrated decreased network efficiency in WKY + saline group compared with control + saline group, but citalopram showed weak network efficiency improvement. In conclusion, resting-state fMRI results implied widely affected brain function at both regional and global levels in WKY rats. Citalopram had only partial effects on these functional changes, indicating a potential treatment resistance mechanism.

Significant technical challenges exist when measuring synaptic connections between neurons in living brain tissue. The patch clamping technique, when used to probe for synaptic connections, is manually laborious and time-consuming. To improve its efficiency, we pursued another approach: instead of retracting all patch clamping electrodes after each recording attempt, we cleaned just one of them and reused it to obtain another recording while maintaining the others. With one new patch clamp recording attempt, many new connections can be probed. By placing one pipette in front of the others in this way, one can 'walk' across the mouse brain slice, termed 'patch-walking.' We performed 136 patch clamp attempts for two pipettes, achieving 71 successful whole cell recordings (52.2%). Of these, we probed 29 pairs (i.e. 58 bidirectional probed connections) averaging 91 μm intersomatic distance, finding three connections. Patch-walking yields 80-92% more probed connections, for experiments with 10-100 cells than the traditional synaptic connection searching method.

Input comparison is thought to occur in many neuronal circuits, including the hippocampus, where functionally important interactions between the Schaffer collateral and perforant pathways have been hypothesized. We investigated this idea using multisite, whole-cell recordings and Ca2+ imaging and found that properly timed, repetitive stimulation of both pathways results in the generation of large plateau potentials in distal dendrites of CA1 pyramidal neurons. These dendritic plateau potentials produce widespread Ca2+ influx, large after-depolarizations, burst firing output, and long-term potentiation of perforant path synapses. Plateau duration is directly related to the strength and temporal overlap of pathway activation and involves back-propagating action potentials and both NMDA receptors and voltage-gated Ca2+ channels. Thus, the occurrence of highly correlated SC and PP input to CA1 is signaled by a dramatic change in output mode and an increase in input efficacy, all induced by a large plateau potential in the distal dendrites of CA1 pyramidal neurons.

Larval Drosophila offer a study case for behavioral neurogenetics that is simple enough to be experimentally tractable, yet complex enough to be worth the effort. We provide a detailed, hands-on manual for Pavlovian odor-reward learning in these animals. Given the versatility of Drosophila for genetic analyses, combined with the evolutionarily shared genetic heritage with humans, the paradigm has utility not only in behavioral neurogenetics and experimental psychology, but for translational biomedicine as well. Together with the upcoming total synaptic connectome of the Drosophila nervous system and the possibilities of single-cell-specific transgene expression, it offers enticing opportunities for research. Indeed, the paradigm has already been adopted by a number of labs and is robust enough to be used for teaching in classroom settings. This has given rise to a demand for a detailed, hands-on manual directed at newcomers and/or at laboratory novices, and this is what we here provide. The paradigm and the present manual have a unique set of features: • The paradigm is cheap, easy, and robust; • The manual is detailed enough for newcomers or laboratory novices; • It briefly covers the essential scientific context; • It includes sheets for scoring, data analysis, and display; • It is multilingual: in addition to an English version we provide German, French, Japanese, Spanish and Italian language versions as well. The present manual can thus foster science education at an earlier age and enable research by a broader community than has been the case to date.

The regular distribution of mitochondrial DNA-containing nucleoids is essential for mitochondrial function and genome inheritance; however, the underlying mechanisms remain unknown. Our data reveal that mitochondria frequently undergo spontaneous and reversible pearling - a biophysical instability in which tubules undulate into regularly spaced beads. We discovered that pearling imposes a characteristic length scale, simultaneously mediating nucleoid disaggregation and establishing inter-nucleoid distancing with near-maximally achievable precision. Cristae invaginations play a dual role: lamellar cristae density determines pearling frequency and duration, and preserves the resulting nucleoid spacing after recovery. The distribution of mitochondrial genomes is thus fundamentally governed by the interplay between spontaneous pearling and cristae ultrastructure.

Proteins localized at the cellular interface mediate cell-cell communication and thus control many aspects of physiology in multicellular organisms. Cell-surface proteomics allows biologists to comprehensively identify proteins on the cell surface and survey their dynamics in physiological and pathological conditions. PEELing provides an integrated package and user-centric web service for analyzing cell-surface proteomics data. With a streamlined and automated workflow, PEELing evaluates data quality using curated references, performs cutoff analysis to remove contaminants, connects to databases for functional annotation, and generates data visualizations. Together with chemical and transgenic tools, PEELing completes a pipeline making cell-surface proteomics analysis handy for every lab.

Olfactory systems encode odours by which neurons respond and by when they respond. In mammals, every sniff evokes a precise, odour-specific sequence of activity across olfactory neurons. Likewise, in a variety of neural systems, ranging from sensory periphery to cognitive centres, neuronal activity is timed relative to sampling behaviour and/or internally generated oscillations. As in these neural systems, relative timing of activity may represent information in the olfactory system. However, there is no evidence that mammalian olfactory systems read such cues. To test whether mice perceive the timing of olfactory activation relative to the sniff cycle (’sniff phase’), we used optogenetics in gene-targeted mice to generate spatially constant, temporally controllable olfactory input. Here we show that mice can behaviourally report the sniff phase of optogenetically driven activation of olfactory sensory neurons. Furthermore, mice can discriminate between light-evoked inputs that are shifted in the sniff cycle by as little as 10 milliseconds, which is similar to the temporal precision of olfactory bulb odour responses. Electrophysiological recordings in the olfactory bulb of awake mice show that individual cells encode the timing of photoactivation in relation to the sniff in both the timing and the amplitude of their responses. Our work provides evidence that the mammalian olfactory system can read temporal patterns, and suggests that timing of activity relative to sampling behaviour is a potent cue that may enable accurate olfactory percepts to form quickly.

To interpret the sensory environment, the brain combines ambiguous sensory measurements with context-specific prior experience. But environmental contexts can change abruptly and unpredictably, resulting in uncertainty about the current context. Here we address two questions: how should context-specific prior knowledge optimally guide the interpretation of sensory stimuli in changing environments, and do human decision-making strategies resemble this optimum? We probe these questions with a task in which subjects report the orientation of ambiguous visual stimuli that were drawn from three dynamically switching distributions, representing different environmental contexts. We derive predictions for an ideal Bayesian observer that leverages the statistical structure of the task to maximize decision accuracy and show that its decisions are biased by task context. The magnitude of this decision bias is not a fixed property of the sensory measurement but depends on the observer's belief about the current context. The model therefore predicts that decision bias will grow with the reliability of the context cue, the stability of the environment, and with the number of trials since the last context switch. Analysis of human choice data validates all three predictions, providing evidence that the brain continuously updates probabilistic representations of the environment to best interpret an uncertain, ever-changing world.

Life scientists often desire to display the signal from two different molecular probes as a single colour image, so as to convey information about the probes' relative concentrations as well as their spatial corelationship. Traditionally, such colour images are created through a merge display, where each greyscale signal is assigned to different channels of an RGB colour image. However, human perception of colour and greyscale intensity is not equivalent. Thus, a merged image display conveys to the typical viewer only a subset of the absolute and relative intensity information present in and between two greyscale images. The Commission Internationale de l'Eclairage L*a*b* colour space (CIELAB) has been designed to specify colours according to the perceptually defined quantities of hue (perceived colour) and luminosity (perceived brightness). Here, we use the CIELAB colour space to encode two dimensions of information about two greyscale images within these two perceptual dimensions of a single colour image. We term our method a Perceptually Uniform Projection display and show using biological image examples how these displays convey more information about two greyscale signals than comparable RGB colour space-based techniques.