Flat-floored Air-lifted Platform: A New Method for Combining Behavior with Microscopy or Electrophysiology on Awake Freely Moving Rodents

Abstract

It is widely acknowledged that the use of general anesthetics can undermine the relevance of electrophysiological or microscopical data obtained from a living animal's brain. Moreover, the lengthy recovery from anesthesia limits the frequency of repeated recording/imaging episodes in longitudinal studies. Hence, new methods that would allow stable recordings from non-anesthetized behaving mice are expected to advance the fields of cellular and cognitive neurosciences. Existing solutions range from mere physical restraint to more sophisticated approaches, such as linear and spherical treadmills used in combination with computer-generated virtual reality. Here, a novel method is described where a headfixed mouse can move around an air-lifted mobile homecage and explore its environment under stress-free conditions. This method allows researchers to perform behavioral tests (e.g., learning, habituation or novel object recognition) simultaneously with two-photon microscopic imaging and/or patch-clamp recordings, all combined in a single experiment. This video-article describes the use of the awake animal head fixation device (mobile homecage), demonstrates the procedures of animal habituation, and exemplifies a number of possible applications of the method.

An animal-actuated rotational head-fixation system for 2-photon imaging during 2-d navigation

“…This axial constraint system is then combined with a separate system that allows the animal to locomote. Here we use a 2-D air maze 25,26 that is rotationally constrained (can translate in x and y, but not rotate -see Fig.9 for details). Through the combination of the 1 degree-of-freedom headpost and the 2 degrees-of-freedom air maze, animals are now free to translate and rotate their heads and bodies, completely removing the visual/motor/vestibular mismatch of current VR systems 20 .…”

“…B: Schematic of conventional head-fixed VR systems that allow 2d-navigation. Mice are head-fixed and the floor they locomote on, either a floating flat arena 25,26 or a spherical treadmill 45 rotates under them. C: Schematic of head rotation systems.…”

“…Some behavioral choice tasks can be performed in relatively small behavior chambers 40,43 , while some sensory decision making and navigation tasks require large arenas 98 . We have developed our head-rotation system using a variation of an existing 2-D air 'maze'/arena method 25,26 , with the central modification being that our method does not rotate the arena itself. This significantly reduces the problems caused by the inertia of the rapidly spinning arena in current approaches 25,26 , which will make it possible to use large arenas.…”

“…The predominant approach to circumventing the shortcomings of head-fixed behaviors is to place head-fixed rodents in a virtual reality (VR) environment 19,20 . Animals are placed on a running wheel 21 , disc 22,23 , a floating omnidirectional ball treadmill 24 , or a flat arena on an air cushion 25,26 , and allowed to locomote. Despite the groundbreaking progress of these systems, current VR behaviors lack vestibular inputs, raising questions about whether rodents accept the VR environment as real or whether they merely learn to interact with it 20 .…”

Social Ultrasonic Vocalization in Awake Head-Restrained Mouse

“…However, tonic stress level, which could be a confounding factor in many of these behaviors, is often not quantified as mice produced no stress related sonic vocalizations while head restrained. It is currently unknown how different platforms for head-fixation such as a tube, a floating ball, a running wheel, a treadmill or a floating cage (Crochet and Petersen, 2006; Dombeck et al, 2007; Niell and Stryker, 2010; Kislin et al, 2014; Vinck et al, 2015) affect the stress level of the subject mouse. It would be interesting to test which of these methods would permit social interaction related vocalization emission following habituation.…”