A complete pupillometry toolbox for real-time monitoring of locus coeruleus activity in rodents

Abstract

The locus coeruleus (LC) is a region in the brainstem that produces noradrenaline and is involved in both normal and pathological brain function. Pupillometry, the measurement of pupil diameter, provides a powerful readout of LC activity in rodents, primates and humans. The protocol detailed here describes a miniaturized setup that can screen LC activity in rodents in real-time and can be established within 1-2 d. Using low-cost Raspberry Pi computers and cameras, the complete custom-built system costs only 300 euros, is compatible with stereotaxic surgery frames and seamlessly integrates into complex experimental setups. Tools for pupil tracking and a user-friendly Pupillometry App allow quantification, analysis and visualization of pupil size. Pupillometry can discriminate between different, physiologically relevant firing patterns of the LC and can accurately report LC activation as measured by noradrenaline turnover. Pupillometry provides a rapid, non-invasive readout that can be used to verify accurate placement of electrodes/fibers in vivo, thus allowing decisions about the inclusion/exclusion of individual animals before experiments begin.

MEYE: Web-app for translational and real-time pupillometry

“…Our code can be used in two different ways, to satisfy many needs. [33,34]. One of these papers [33] assessed pupil dilation in mice through DeepLabCut [44], a technique for 3D markerless pose estimation based on transfer learning.…”

“…Available open source methods require complicated steps for the installation and configuration of custom software not suitable for non-technical operators. Moreover, these tools were tested exclusively in one species (mice [33], humans [34] ), and none of them were applied in cognitive experiments that usually involve small pupil changes associated with high variability.…”

Voluntary alcohol consumption disrupts coupling of prefrontal cortical activity to arousal

“…1E, F). In addition, we used high-speed videography to measure changes in the pupil diameter as a proxy for momentary fluctuations in arousal 26,63,64 . Together with the high-resolution readout of licking behavior, this HFD paradigm allowed us to assess the effect of voluntary ethanol consumption on ACC activity as well as its coupling to simultaneously measured changes in arousal ( Fig.…”

Real-time, low-latency closed-loop feedback using markerless posture tracking

“…Using this forward-prediction module, we were able to provide ultra-low latency feedback to an animal (even down to sub-zero ms delay). Such short latencies have only been approachable in marked animals ( Sehara et al, 2019 ), but have not been achieved to the best of our knowledge previously with markerless pose estimation ( Zhao et al, 2019 ; Forys et al, 2020 ; Štih et al, 2019 ; Schweihoff et al, 2019 ; Privitera et al, 2020 ).…”