Abstract
A large number of studies have analyzed social and sexual interactions between rodents in relation to neural activity. Computerized video analysis has been successfully used to detect numerous behaviors quickly and objectively; however, to date only 2D video recording has been used, which cannot determine the 3D locations of animals and encounters difficulties in tracking animals when they are overlapping, e.g., when mounting. To overcome these limitations, we developed a novel 3D video analysis system for examining social and sexual interactions in rats. A 3D image was reconstructed by integrating images captured by multiple depth cameras at different viewpoints. The 3D positions of body parts of the rats were then estimated by fitting skeleton models of the rats to the 3D images using a physics-based fitting algorithm, and various behaviors were recognized based on the spatio-temporal patterns of the 3D movements of the body parts. Comparisons between the data collected by the 3D system and those by visual inspection indicated that this system could precisely estimate the 3D positions of body parts for 2 rats during social and sexual interactions with few manual interventions, and could compute the traces of the 2 animals even during mounting. We then analyzed the effects of AM-251 (a cannabinoid CB1 receptor antagonist) on male rat sexual behavior, and found that AM-251 decreased movements and trunk height before sexual behavior, but increased the duration of head-head contact during sexual behavior. These results demonstrate that the use of this 3D system in behavioral studies could open the door to new approaches for investigating the neuroscience of social and sexual behavior.
Highlights
A large number of studies have examined the various neural functions associated with social and sexual interactions in rodents [1,2,3,4,5,6]
We found that AM-251 had significant effects on male sexual behavior, which could be detected through 3D spatial measurements of the body parts
We aimed to extend this approach into 3D, i.e., to track the 3D positions of 4 body parts of each rat and to recognize behaviors based on the spatio-temporal patterns of the 3D positions
Summary
A large number of studies have examined the various neural functions associated with social and sexual interactions in rodents [1,2,3,4,5,6]. Previous computerized video analysis systems (e.g., MiceProfiler [7]; SocialScan, Cleversys; Ethovision, Noldus; VideoTrack, Viewpoint) have used 2D top-view video recording and detected behaviors as follows: first, silhouettes of the animals in the video frames were extracted based on the animals’ colors; the positions of the body parts (head, trunk, etc.) of the animals were estimated based on these silhouettes; and behaviors were recognized based on the spatio-temporal patterns of these positions. Such 2D video analyses have notable limitations. This problem could be avoided by painting the animals different colors, such manipulations may bias the animals’ behaviors and the positions of the occluded body parts could still not be estimated (see Supplementary Notes 2 and 3 in [7] for further details of these limitations)
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