Study Of Brain Structures And Functions Of Bats Using Magnetic Resonance Technique

Magnetic resonance (MR) images of the brain of five species of wild bats, including three species of Microchiroptera(Rhinolophus ferrumequinum, Myotis ricketti, Myotis chinensis), one species of echolocating Megachiroptera(Rousettus leschenaultii)and one species of non-echolocating Megachiroptera(Cynopterus sphinx), were obtained in vivo. The relative volumes of inferior colliculus (IC) and superior colliculus (SC) to brainstem were derived from the MR images and compared among different species. In general, the relative size of IC was much larger in Microchiropteras than in Megachiropteras, and in echolocating Megachiroptera than in non-echolocating Megachiroptera. The relative size of SC was similar in these two suborders. Agreeing with the previous results and consistent with the current hypothesis that Megachiropterans originated from Microchiropterans, the results suggest that IC of Megachiropterans tends to degenerate during the process of evolution, as these fruit bats use more vision and smelling than hearing when they forage. The results also demonstrate that magnetic resonance imaging can be used to study the neuroanatomy of wild bats noninvasively.The cerebral blood flow (CBF) of bats was measured with spin echo Continuous Arial Spin labeling (CASL). R2* mapping was conducted with the optimized multiple gradient echo sequence to reduce the macroscopic susceptibility effect. Semi-quantitative CBF and R2* value were calculated to study the change of brain functions with the depression of body temperature(Tb). We found that Tb of both Megachiropteran and Microchiropteran depressed with the degression of ambient temperature. And the lowest Tb of Microchiropteran was around 10℃, compared to the lowest of Megachiropteran's was around 24℃. The CBF of both Megachiropteran and Microchiropteran decreased with the depression of Tb. The CBF of Megachiropteran's thalamus significantly decreased, but the decrease of the CBF of cortex was not significant. At the same time, R2* value of both cortex and thalamus of Megachiropteran had no significant decrease. In contrast, the CBF and R2* value of both cortex and thalamus of Microchiropteran significantly decreased. This showed that Microchiropteran could enter into a deep torpor state as well as hibernation. Even Megachiropteran also could enter into torpor state, its ability of coping low ambient temperature was very restricted.