Development of intravital deep tissue imaging system and investigation of hippocampal mechanism for individual recognition

Abstract

[Development of intravital deep tissue imaging system] Obtaining high-dimensional information underlying deep tissue in vivo remains a key challenge in the bio-imaging field. Here, we developed different types of deep tissue imaging system based on customized confocal microscopy: endomicroscopy with 1) miniaturized side-viewing GRIN lens probes and 2) tissue-implantable window chamber.

By applying these newly developed deep tissue imaging system longitudinally and repetitively to various organs (e.g. breast tumor and brain tissue) of live animals in a minimally invasive manner, we successfully monitored long-term cellular activities, wide-range morphogenesis, and tumorigenesis with high spatiotemporal resolution. After the in vivo imaging session, histological analysis including tissue clearing technique was subsequently followed, thereupon the functionality of confocal endomicroscopy could be validated.

All types of endomicroscopy demonstrated in this study could be a versatile platform for investigating complex and dynamic phenomena arising from deep tissue in real-time.

[Investigation of hippocampal mechanism for individual recognition] In a social environment, animals frequently and repeatedly interact with other individuals. The ability to recognize the social counterpart as a unique individual and then process individual-specific information is highly essential for adaptive social behavior, however, neural mechanisms underlying individual recognition have not been rigorously investigated. Although the hippocampal formation has been widely implicated in social memory, how hippocampal neurons process individual-specific information remains uncovered yet. In this study, the hippocampal neural mechanism underlying individual recognition was investigated by combining a novel individual discrimination paradigm and in vivo two-photon imaging technique.

Through a brief nose-to-nose social interaction, mice could discriminate familiar conspecifics associated with reward and non-reward, which depended on the dorsal hippocampus. The social memory obtained during the behavioral task can be reliably maintained for a week. In vivo two-photon calcium imaging showed that subsets of dorsal CA 1 neurons accurately discriminate familiar conspecifics in both reward and non-reward category. Hippocampal population activity also decoded individual mice with high accuracy regardless of reward contingency. Furthermore, by monitoring activities of the same dorsal CA1 neurons for two consecutive days, we also found that the individual-specific activities are stably maintained over days in both single-cell and population level. These results elucidate the mechanisms of how dynamically and efficiently dorsal CA1 neurons encode social information to distinguish individual conspecifics.