Peripheral vasoconstriction in the rat in response to sound. II. Dependence on rate of change of sound level.

Vasoconstrictions elicited by sound were studied in the non-anaesthetized rat. Arterial pulsations in the tail were recorded by a non-invasive technique. On slightly heating the animal, the tail vessels became dilated. An 80 dB SPL noise burst caused a decrease in pulse amplitude, usually to less than 10% of the pre-stimulus value. It was found that 4 s bursts of 80 dB SPL noise with rise times 1, 10, or 100 ms were equally efficient in producing vasoconstriction. If the rise time was longer, 1 s, the vasconstriction was significantly smaller. It was pointed out that the feedback control of the stimulus noise provided by the acoustic middle ear reflex would contribute to enhancing rapid variations in sound level, and thereby form part of a physiological explanation for the present findings.