Dynamic clamp with StdpC software

Abstract

Dynamic clamp is a powerful method that allows the introduction of artificial electrical components into target cells to simulate ionic conductances and synaptic inputs. This method is based on a fast cycle of measuring the membrane potential of a cell, calculating the current of a desired simulated component using an appropriate model and injecting this current into the cell. Here we present a dynamic clamp protocol using free, fully integrated, open-source software (StdpC, for spike timing-dependent plasticity clamp). Use of this protocol does not require specialist hardware, costly commercial software, experience in real-time operating systems or a strong programming background. The software enables the configuration and operation of a wide range of complex and fully automated dynamic clamp experiments through an intuitive and powerful interface with a minimal initial lead time of a few hours. After initial configuration, experimental results can be generated within minutes of establishing cell recording.

Figure 1. The general dynamic clamp setup using StdpC

The dynamic clamp system forms a closed observation-stimulus loop in which the measured and amplified membrane potential (Vout) is input to the StdpC software (StdpC workstation), which calculates a corresponding trans-membrane current according to a model specified by the user. The software then issues an appropriate current command, which is converted into a physical current injection by the amplifier. A second, independent, analog to digital converter and PC with standard electrophysiology recording software monitors and saves all aspects of the experiment (Electrophysiology workstation). The measurement-injection loop is repeated at 10-20 kHz making the interaction essentially instantaneous for the target neuron.

Figure 2. The main window of the StdpC graphical interface

The main control elements are marked by 8 markers:

1. General menus for file control (loading/saving protocols and scripts) and configuration.

2. Start and Stop button to control execution of the dynamic clamp

3. Dropdown choice of the used hardware driver

4. Message window displaying status information and a log of user actions

5. Panel for configuring of up to 6 different simulated synapses

6. Panel for configuring up to 6 ionic conductances

7. Spike generator module for configuring computer generated neuronal activity.

8. Data displays for debugging the dynamic clamp configuration.

Many of the configuration buttons open separate dialog windows like the one illustrated in Box 1.

Figure 3. Anticipated results

Example results of dynamic clamp. A) Results of a simulated chemical synapse between a tonically spiking cell (top) and a silent post-synaptic cell (bottom). The middle sub-panel shows the injected dynamic clamp current for timescales of 10 ms (blue) and 40 ms (cyan). The injected current resulted in the EPSPs shown in red and magenta respectively (bottom). Note how the current through the simulated channels reverts during a post-synaptic spike (arrow). B) A simulated voltage-activated potassium current was introduced into a cultured hippocampal neuron. Action potentials were generated by applying 100 pA current steps of 50 ms duration. The effect of the simulated current can be observed as a reduction in amplitude and duration of the action potentials (top) as the conductance, and therefore the injected current (bottom), increased. The action potentials were aligned at the maximum slope of the rising phase as indicated by the dashed line. C) Results of a pattern clamp experiment. The target cell spikes tonically when the pattern clamp is off (top). When the gap junction coupling in pattern clamp is not strong enough, the target neuron will only be clamped partially (middle) but sufficient conductance leads to a complete clamp (bottom). Pattern clamp is switched on at the arrowheads. Panels D and E are detailed views of the episodes shaded in grey in panel C. The red trace was recorded from the target neuron, the black trace shows the desired pattern. Currents injected are shown in blue in the bottom panels. With 300 nS conductance, the pattern clamp is not able to prevent intrinsic spiking (C, arrowhead). This is readily achieved at 2 μS maximal conductance even though the currents injected for this > 6 times larger conductance are only 2-3 times larger owing to the better match achieved. Animal care and use protocols complied with Home Office (UK) guidelines. The compositions of the saline and internal solutions used in these experiments are described in the Supplementary Methods.