Sulphur dioxide block of laryngeal receptors in rabbits.

In 6 rabbits moving average of activity of superior laryngeal nerve(SLN) increased when pressure in upper airways (Pua) was positive and decreased when it was negative. After SO2 exposure of upper airways SLN activity at Pua = 0 decreased to 40% and was no longer affected by changes in Pua. Activity of 67 fibers of SLN was recorded in 11 rabbits: 35 came from 'pressure' receptors, 27 from 'drive', and 5 from 'flow'. Thirty-three pressure receptors discharged at Pua = 0: 32 increased their firing rate with positive Pua and decreased it with negative Pua, one did the reverse. One pressure receptor silent at Pua = 0 fired with positive Pua, the other with negative Pua. Pressure receptors were slowly adapting. SO2 blocked within 3-9 min 84% of pressure receptors, 56% of drive receptors, and 4 out of 5 flow receptors. The receptors recovered control activity within 5-10 min after SO2 removal. SO2 block of laryngeal receptors may represent a convenient experimental tool for studies of laryngeal reflexes.