Abstract
Reptiles are a rare model object for space research. However, some reptile species demonstrate effective adaptation to spaceflight conditions. The main scope of this review is a comparative analysis of reptile experimental exposure in weightlessness, demonstrating the advantages and shortcomings of this model. The description of the known reptile experiments using turtles and geckos in the space and parabolic flight experiments is provided. Behavior, skeletal bones (morphology, histology, and X-ray microtomography), internal organs, and the nervous system (morphology, histology, and immunohistochemistry) are studied in the spaceflight experiments to date, while molecular and physiological results are restricted. Therefore, the results are discussed in the scope of molecular data collected from mammalian (mainly rodents) specimens and cell cultures in the parabolic and orbital flights and simulated microgravity. The published data are compared with the results of the gecko model studies after the 12–44.5-day spaceflights with special reference to the unique peculiarities of the gecko model for the orbital experiments. The complex study of thick-toed geckos after three spaceflights, in which all geckos survived and demonstrated effective adaptation to spaceflight conditions, was performed. However, future investigations are needed to study molecular mechanisms of gecko adaptation in space.
Highlights
Space research into animal models may provide helpful information for the human space mission organization and data on the adaptive scopes and perspectives of various species
The heart showed a slight tendency of compensatory hypertrophy and high blood inflow, which still remained within the physiological norm in the Foton-M2 experiment flight group animals; there were no signs of compensatory hypertrophy in the Foton-M3 flight group geckos [32]
The fluorescence yield intensity from heavier elements was at the sensitivity limit of the detection system. Such a significant difference in the X-ray Fluorescence Analysis (XFA) and scanning Electron Microscopy (SEM) data on the chemical composition of the samples can be explained by the nonuniform distribution of elements in the samples; i.e., one may conclude that heavier elements are concentrated in the sample bulk, which is confirmed by X-ray microtomography data
Summary
Space research into animal models may provide helpful information for the human space mission organization and data on the adaptive scopes and perspectives of various species. The results of gecko spaceflight experiments, such as behavioral adaptations; skeletal bones morphology, histology, and X-ray microtomography; and internal organ and nervous system morphology; histology, and immunohistochemistry, are discussed with special reference to the unique peculiarities of the gecko model for the orbital experiments. These results are compared with the molecular data collected from mammalian (mainly rodents) specimens and cell cultures in the parabolic and orbital flights and simulated microgravity
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