Functional connectivity and dynamics in Huntington’s disease striatal cultures…

Sara Fernández-García, Mercè Masana, Javier G. Orlandi, Gerardo García-Díaz Barriga, Jordi Soriano and Jordi Alberch

SFN Meeting, 2017

[WEB]

Striatum, the main hub of the basal ganglia circuitry, is the most affected region in Huntington’s disease (HD). In HD, mutant-huntingtin (mHtt) causes an excitatory-inhibitory imbalance of the basal ganglia output pathways and induces motor symptoms. Although alterations of striatal Medium-sized Spiny Neurons (MSN) occur at early stages of the disease, little is known about how this translates into functional changes in the network dynamics. Using high-speed, high-resolution calcium imaging, we have recorded simultaneously hundreds of cells from striatal primary cultures in WT and the R6/1 mouse model of HD and characterized the spontaneous activity patterns of every cell as well as their collective activity. Although most of the striatum is composed by inhibitory neurons, we showed that isolated striatal cultures are functionally active, without the need of excitatory inputs. The percentage of active population is ~10% whilst in cortex ~50% of the population showed spontaneous active in basal conditions. At the single cell level, we identified three populations based on their fluorescence activity traces in both WT and R6/1. Type 1 (fast increase/exponential decay) characteristic of neurons; Type 2 (slow calcium transients) characteristic of astrocytic calcium waves; and Type 3 (non-detectable fluorescence changes). Heterogeneity in cell populations was confirmed by immunocytochemistry against neuronal and glial (MAP2/GFAP) markers. At the population level, both WT and R6/1 include a subset of neurons that display highly coherent activity, indicating the presence of a functional network. Bursting properties of this group are similar between genotypes. Blockade of GABA_A receptors by bicuculline increased number of active neurons while decreased astrocytic signal. Also, the previously reported silent population became active, showing a characteristic neuronal activity profile. The large silent population was inhibited in basal conditions, but the underlying network is revealed through system-wide disinhibition. Indeed, bicuculline boosts coherent activity throughout the culture and increases burst duration and amplitude, but not frequency, in both genotypes. These results indicate that striatal network dysfunction in HD may not arise from local disinhibition but probably from aberrant afferent activity. Therefore, further analysis is required to characterize the contribution of different neurotransmitter systems to the striatal network dynamics in healthy and HD cultures. Understanding functional network alterations mediated by mHtt is fundamental to decipher initial key mechanisms to finally target early symptoms in HD.

NETCAL: An interactive platform for large-scale, NETwork and population…

Javier G. Orlandi, Sara Fernández-García, Andrea Comella-Bolla, Mercè Masana, Gerardo García-Díaz Barriga, Mohammad Yaghoubi, Josep M. Canals, Michael A. Colicos, Jörn Davidsen, Jordi Alberch and Jordi Soriano

SFN Meeting, 2017

[WEB]

Calcium imaging has become the preferred technique in neuroscience to simultaneously record the activity of thousands of cells. Yet most tools to analyze the recordings are rather rudimentary or require extensive knowledge of other disciplines, from machine learning to big data and network theory. Moreover, there is often a disconnection between the experiments and their analysis and outcome, usually taking place days apart and/or being done by different people.
We present NETCAL, a MATLAB-built, dedicated software platform to record, manage and analyze high-speed high-resolution calcium imaging experiments. Its ease of use, interactive graphical interface and exhaustive documentation is aimed to wet-lab researchers, but it will also meet the needs of any experienced data scientist through its plugin and scripting system. We have developed a large set of tools and incorporated state-of-the-art algorithms and toolboxes for large-scale analysis of network and population dynamics. Analyses include: automated cell detection (both static and dynamic); trace and population sorting through machine learning, clustering and pattern recognition; bursting dynamics; spike detection; network inference (from functional networks to causal relations); and many more. Several of these tools are also available in real-time, e.g. cells and spikes can be monitored during the actual recording, giving the researcher extensive feedback on the progress of the experiment.
We have tested and used the software in several different experimental preparations and laboratory equipment. For instance, NETCAL has been used to test the viability and performance of differentiation protocols from human induced pluripotent stem cells (hISPCs); to characterize the individual and collective behavior of dissociated cortical and striatal cultures from Huntington’s disease (HD) mouse models; to reveal the communication between neurons and astrocytes in rat hippocampal cultures; and to detect propagating activity patterns in cortical cultures. Although NETCAL has been developed for calcium recordings in cultures, we have successfully tested and used it in other preparations, e.g., in-vivo calcium imaging and multi-electrode arrays.
Our platform has been developed by scientists for scientists, to promote and foster the development of tools for the replication and validation of experimental results. The software is highly modular, and its implementation provides easy extendability to adapt it to the specific requirements of any research group.