Neuronal Mechanisms and Bloodflow Control of Infrared Reception in Snakes

摘要

The infrared pit organs of pit vipers and pythons were studied with emphasis on bloodflow in the capillary bed and its possible role as a cooling mechanism for the pit receptors stimulated by infrared (= heat) radiation to improve image resolution. Fluorescein isothiocyanate (FlTC) dextran together with fluorescent microspheres was introduced into the blood stream and pit bloodflow was viewed with a fluorescence microscope and CCD camera. Output of the camera was recorded before, during, and after infrared laser stimulation with a high-speed video system at 250 frames/sec. The FlTC rendered all the pit blood vessels visible without interfering with the visibility of the microspheres. After recording, the course and speed of individual microspheres were traced with proprietary software and analyzed by one-way ANOVA and other statistical tests. In pit areas directly irradiated by the laser, bloodflow speed was remarkably increased in the capillaries, but not in the arterioles or venules, during stimulation at a statistical significance of P=O.0002 as compared with the speed before and after stimulation. This phenomenon lends credibility to the theory that capillary bloodflow in the pits is used directly by the receptors as a coolant mechanism for fine-tuning image resolution.