Temperature-Induced Changes in the Number of Vesicles in the Free Nerve Endings of Temperature Neurons of the Snake

By observing ultrastructural changes under the electron microscope, we illustrated exocytosis and recycling of vesicles in the infrared receptor, a kind of free nerve ending in the pit organ of the crotaline snake, Trimeresurus flavoviridis. While maintaining the snake pit organs at stable temperatures of 15 degrees C, 25 degrees C, and 30 degrees C, we fixed them by perfusion and then processed them for transmission electron microscopy. The largest number of clear and coated vesicles appeared in the terminals at the lowest temperature. The perimeter and area of a terminal were enlarged at 30 degrees C, and "opening waves" on the plasma were prominently found at the highest temperature. We also observed coated vesicles that budded from the plasma membrane in the terminals. The configuration of mitochondria in the terminals was quantitatively different between lower and higher temperatures. The data suggest that exocytosis and endocytosis in these terminals operate in a manner similar to that observed in other cell types.