The identification of neurotransmitter receptors and voltage-sensitive ion channels on astrocytes (reviewed by Barres, 1991) has renewed interest in how these cells respond to neuronal activity. To investigate the physiology of neuron astrocyte signaling, we have employed primary cortical cultures that contain both neuronal and glial cells. As the neurons in these cultures exhibit synchronous spontaneous synaptic activity, we have used both calcium imaging and whole-cell recording techniques to identify physiological activity in astrocytes related to neuronal activity. Whole-cell voltage-clamp records from astrocytes revealed rapid inward currents that coincide with bursts of electrical activity in neighboring neurons. Calcium imaging studies demonstrate that these currents in astrocytes are not always associated with slowly propagating calcium waves. Inclusion of the dye Lucifer yellow within patch pipettes confirmed that astrocytes are extensively coupled to each other but not to adjacent neurons, indicating that the currents observed are not due to gap junction connections between these cell types. These currents do not reflect widespread diffusion of glutamate or potassium released during neuronal activity since a population of small, round, multipolar presumed glial cells that are not dye coupled to adjacent cells did not display electrical currents coincident with neuronal firing, even though they respond to locally applied glutamate and potassium. These findings indicate that, in addition to the relatively slow signaling conveyed by calcium waves, astrocytes also display rapid electrical responses to neuronal activity.

Markerless and accurate tracking of mouse movement is of interest to many biomedical, pharmaceutical, and behavioral science applications. The additional capability of tracking body parts in real-time with minimal latency opens up the possibility of manipulating motor feedback, allowing detailed explorations of the neural basis for behavioral control. Here we describe a system capable of tracking specific movements in mice at a frame rate of 30.3 Hz. To achieve these results, we adapt DeepLabCut – a robust movement-tracking deep neural network framework – for real-time tracking of body movements in mice. We estimate paw movements of mice in real time and demonstrate the concept of movement-triggered optogenetic stimulation by flashing a USB-CGPIO controlled LED that is triggered when real time analysis of movement exceeds a pre-set threshold. The mean time delay between movement initiation and LED flash was 93.44 ms, a latency sufficient for applying behaviorally-triggered feedback. This manuscript presents the rationale and details of the algorithms employed and shows implementation of the system using behaving mice. This system lays the groundwork for a behavior-triggered ‘closed loop’ brain-machine interface with optogenetic stimulation of specific brain regions for feedback.

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