Aberrant Cortical Activity in Multiple GCaMP6-Expressing Transgenic Mouse Lines.
01 Sep 2017-Vol. 4, Iss: 5
TL;DR: Aberrant electrical activity, similar to interictal spikes, and accompanying fluorescence events in some genotypes of transgenic mice expressing GCaMP6 genetically encoded calcium sensors are reported, observed particularly in mice with Emx1-Cre and Ai93 transgenes across multiple laboratories.
Abstract: Transgenic mouse lines are invaluable tools for neuroscience but, as with any technique, care must be taken to ensure that the tool itself does not unduly affect the system under study. Here we report aberrant electrical activity, similar to interictal spikes, and accompanying fluorescence events in some genotypes of transgenic mice expressing GCaMP6 genetically encoded calcium sensors. These epileptiform events have been observed particularly, but not exclusively, in mice with Emx1-Cre and Ai93 transgenes, of either sex, across multiple laboratories. The events occur at >0.1 Hz, are very large in amplitude (>1.0 mV local field potentials, >10% df/f widefield imaging signals), and typically cover large regions of cortex. Many properties of neuronal responses and behavior seem normal despite these events, although rare subjects exhibit overt generalized seizures. The underlying mechanisms of this phenomenon remain unclear, but we speculate about possible causes on the basis of diverse observations. We encourage researchers to be aware of these activity patterns while interpreting neuronal recordings from affected mouse lines and when considering which lines to study.
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TL;DR: In this article, the authors observed that spontaneous activity reliably encoded a high-dimensional latent state, which was partially related to the mouse's ongoing behavior and was represented not just in visual cortex but also across the forebrain.
Abstract: Neuronal populations in sensory cortex produce variable responses to sensory stimuli and exhibit intricate spontaneous activity even without external sensory input. Cortical variability and spontaneous activity have been variously proposed to represent random noise, recall of prior experience, or encoding of ongoing behavioral and cognitive variables. Recording more than 10,000 neurons in mouse visual cortex, we observed that spontaneous activity reliably encoded a high-dimensional latent state, which was partially related to the mouse's ongoing behavior and was represented not just in visual cortex but also across the forebrain. Sensory inputs did not interrupt this ongoing signal but added onto it a representation of external stimuli in orthogonal dimensions. Thus, visual cortical population activity, despite its apparently noisy structure, reliably encodes an orthogonal fusion of sensory and multidimensional behavioral information.
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TL;DR: The ‘jGCaMP7’ sensors are four genetically encoded calcium indicators with better sensitivity than state-of-the-art GCaMP6 and specifically improved for applications such as neuropil or wide-field imaging.
Abstract: Calcium imaging with genetically encoded calcium indicators (GECIs) is routinely used to measure neural activity in intact nervous systems. GECIs are frequently used in one of two different modes: to track activity in large populations of neuronal cell bodies, or to follow dynamics in subcellular compartments such as axons, dendrites and individual synaptic compartments. Despite major advances, calcium imaging is still limited by the biophysical properties of existing GECIs, including affinity, signal-to-noise ratio, rise and decay kinetics and dynamic range. Using structure-guided mutagenesis and neuron-based screening, we optimized the green fluorescent protein-based GECI GCaMP6 for different modes of in vivo imaging. The resulting jGCaMP7 sensors provide improved detection of individual spikes (jGCaMP7s,f), imaging in neurites and neuropil (jGCaMP7b), and may allow tracking larger populations of neurons using two-photon (jGCaMP7s,f) or wide-field (jGCaMP7c) imaging.
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TL;DR: This paper found that neurons with similar trial-averaged activity often reflected different combinations of cognitive and movement variables, accounting for trial-by-trial fluctuations that are often considered 'noise'.
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TL;DR: A large set of driver and reporter transgenic mouse lines are reported, including 23 new driver lines targeting a variety of cortical and subcortical cell populations and 26 new reporter lines expressing an array of molecular tools.
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Cites background or result from "Aberrant Cortical Activity in Multi..."
...Events resembled those from the original report (Steinmetz et al., 2017) and our consistent observations in Emx1-IRES-Cre;Camk2a-tTA;Ai93 mice (five consecutive positive observations in each of five mice, one example shown in Figure 7D)....
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...We have recently reported the occurrence of aberrant cortical dynamics in some strains of GCaMP-expressing mice (Steinmetz et al., 2017)....
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TL;DR: Recordings from 30,000 neurons in 42 brain regions are used to delineate the spatial distribution of neuronal activity underlying vision, choice, action and behavioural engagement in mice and reveal organizing principles for the distribution of neurons encoding behaviourally relevant variables across the mouse brain.
Abstract: Vision, choice, action and behavioural engagement arise from neuronal activity that may be distributed across brain regions. Here we delineate the spatial distribution of neurons underlying these processes. We used Neuropixels probes1,2 to record from approximately 30,000 neurons in 42 brain regions of mice performing a visual discrimination task3. Neurons in nearly all regions responded non-specifically when the mouse initiated an action. By contrast, neurons encoding visual stimuli and upcoming choices occupied restricted regions in the neocortex, basal ganglia and midbrain. Choice signals were rare and emerged with indistinguishable timing across regions. Midbrain neurons were activated before contralateral choices and were suppressed before ipsilateral choices, whereas forebrain neurons could prefer either side. Brain-wide pre-stimulus activity predicted engagement in individual trials and in the overall task, with enhanced subcortical but suppressed neocortical activity during engagement. These results reveal organizing principles for the distribution of neurons encoding behaviourally relevant variables across the mouse brain.
455 citations
References
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TL;DR: A family of ultrasensitive protein calcium sensors (GCaMP6) that outperformed other sensors in cultured neurons and in zebrafish, flies and mice in vivo are developed and provide new windows into the organization and dynamics of neural circuits over multiple spatial and temporal scales.
Abstract: Fluorescent calcium sensors are widely used to image neural activity. Using structure-based mutagenesis and neuron-based screening, we developed a family of ultrasensitive protein calcium sensors (GCaMP6) that outperformed other sensors in cultured neurons and in zebrafish, flies and mice in vivo. In layer 2/3 pyramidal neurons of the mouse visual cortex, GCaMP6 reliably detected single action potentials in neuronal somata and orientation-tuned synaptic calcium transients in individual dendritic spines. The orientation tuning of structurally persistent spines was largely stable over timescales of weeks. Orientation tuning averaged across spine populations predicted the tuning of their parent cell. Although the somata of GABAergic neurons showed little orientation tuning, their dendrites included highly tuned dendritic segments (5-40-µm long). GCaMP6 sensors thus provide new windows into the organization and dynamics of neural circuits over multiple spatial and temporal scales.
5,365 citations
TL;DR: This work introduces the most accurate predictive model of growth cone trajectories to date, and deepens the understanding of axon guidance events both in vitro and in vivo.
Abstract: Correct wiring is crucial for the proper functioning of the nervous system. Molecular gradients provide critical signals to guide growth cones, which are the motile tips of developing axons, to their targets. However, in vitro, growth cones trace highly stochastic trajectories, and exactly how molecular gradients bias their movement is unclear. Here, we introduce a mathematical model based on persistence, bias, and noise to describe this behaviour, constrained directly by measurements of the detailed statistics of growth cone movements in both attractive and repulsive gradients in a microfluidic device. This model provides a mathematical explanation for why average axon turning angles in gradients in vitro saturate very rapidly with time at relatively small values. This work introduces the most accurate predictive model of growth cone trajectories to date, and deepens our understanding of axon guidance events both in vitro and in vivo.
965 citations
TL;DR: These novel transgenic lines greatly expand the ability to monitor and manipulate neuronal activities with increased specificity, and develop driver and double reporter mouse lines and viral vectors using the Cre/Flp and Cre/Dre double recombinase systems.
929 citations
"Aberrant Cortical Activity in Multi..." refers background in this paper
...…be obscured in two-photon imaging, even when present in the field of view, either because the sampling rate is slow relative to their duration or because they may primarily appear in neuropil and many individual neurons may show little relationship to them (e.g., as shown in Muldoon et al., 2015)....
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TL;DR: It is demonstrated that Nkx2.2 functions as an integral component of a modular regulatory program to correctly specify pancreatic islet cell fates.
Abstract: Many pancreatic transcription factors that are essential for islet cell differentiation have been well characterized; however, because they are often expressed in several different cell populations, their functional hierarchy remains unclear. To parse out the spatiotemporal regulation of islet cell differentiation, we used a Neurog3-Cre allele to ablate Nkx2.2, one of the earliest and most broadly expressed islet transcription factors, specifically in the Neurog3+ endocrine progenitor lineage (Nkx2.2△endo). Remarkably, many essential components of the β cell transcriptional network that were down-regulated in the Nkx2.2KO mice, were maintained in the Nkx2.2△endo mice - yet the Nkx2.2△endo mice displayed defective β cell differentiation and recapitulated the Nkx2.2KO phenotype. This suggests that Nkx2.2 is not only required in the early pancreatic progenitors, but has additional essential activities within the endocrine progenitor population. Consistently, we demonstrate Nkx2.2 functions as an integral component of a modular regulatory program to correctly specify pancreatic islet cell fates.
921 citations
TL;DR: The results suggest serial information flow from sensory to motor areas during perceptual decision making, which is consistent with roles in motor planning and movement.
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"Aberrant Cortical Activity in Multi..." refers methods in this paper
...The clear skull cap implantation followed the method of Guo et al. (2014) but with some modifications....
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