| Summary: | 碩士 === 國立臺灣師範大學 === 生命科學研究所 === 96 === In order to climb without brain hypotension, arboreal snakes tend to maintain a higher (40～70) blood pressure (BP) than other snakes when measured in a plastic tube. Moreover, when passive tilted head up to 90°, the BP of head is still maintained at 50～90 % of pre tilt value. Terrestrial and aquatic snakes frequently drop bellow 0 % when treated as the same way. The Chinese cobra (Naja atra) raise it’s head up quickly when threatened. Although it is a terrestrial snake, the circulation problem of orthostatic posture is the same as climbing behavior of arboreal snakes. Consequently, I speculate that the cardiovascular and BP characteristics of cobras may be similar to that of arboreal snakes. If the speculation is not true, then, the cobra should be able to increase the BP largely and quickly when raising their heads during defending. Another terrestrial snake, banded krait (Bungarus multicinctus multicinctus) and two well climbing snakes, beauty snake (Elaphe taeniura) and rat snake (Ptyas mucosus) were selected for comparison species in this experiment.
Unlike arboreal snakes, the BP of cobra measured in a plastic tube is not high, only 39 mmHg, so did banded krait (33 mmHg). Whereas The BPs were higher in the other two well climbing snakes (48 and 46 mmHg). When the head was passively tilted up at 90°, the head BP of cobra was dropped to the lowest level among four species, and the average BP of head is only 32 % of pre tilt value, significantly lower than beauty snake and rat snake (70 and 80 %).
When the cobras were stressed by tapping their heads, the BP increased quickly to two times of the resting value (average, 70 mmHg), which is significantly higher than that of banded krait and faster than that of beauty snake and rat snake. A large and quick increase in BP seen in the cobra was also observed at active head raising. In this situation, the BP at head level was maintained above 40 mmHg. Nevertheless, when the cobra was settled in a plastic tube, the average BP of head is only 22 mmHg during a passive front body tilt without any visual stress. When pretreated with α and β sympathetic inhibitors, increasing in BP seen in the cobra during active head raising was abolished and the height of head raising was low. These results indicate that the mechanism of BP increase in the cobra during head raising is probably dependent on sympathetic excitation induced by mental stress and that blood supply to the head by way of BP increase may play a role in maintaining the height of head raising during defense reaction.
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