A system for precise temperature control of isolated nervous tissue under optical access: application to multi-electrode recordings.

Background: Since temperature severely affects all physiological processes, exact temperature control during electrophysiological measurements is indispensable. However, none of the tempering system approaches previously described is fully satisfactory for extracellular recordings with sharp multi-electrode arrays (MEAs).

New Method: We developed a set-up offering a homogeneously tempered and at the same time light-transparent stage for an ex vivo preparation. The Peltier element based tempering unit of our system is physically separated from the preparation stage avoiding electrical disturbances of extracellular recordings. We implemented a digital feedback controller on a microcontroller to minimise the deviation between actual and set point temperature.

Results: Our tempering system allows operation from 10°C to 45°C with a control error in steady state between 0.052°C (RMSE) and 0.115°C (RMSE). To document the versatility of our system, we performed extracellular MEA recordings from retinal ganglion cells of isolated retina under different temperature conditions. We found strong influences on light response properties, even for small temperature changes.

Comparison With Existing Methods: Currently used heating systems that allow top and bottom side optical access to a preparation typically exhibit low temperature accuracy, precision or homogeneity.

Conclusions: Our system is adequate not only for experiments on a variety of species under physiological temperature conditions but also for studies on temperature effects on physiology in general. Though the setup was developed for the context of MEA recordings from retina it may be useful in other cases where optical access to the preparation from both, top and bottom side is required.