Central and spinal effects of sodium cyanide on respiratory activity.

The pharmacological actions of cyanide on respiratory activity have been known for some time and are attributed mainly to effects on peripheral chemoreceptors. In the studies reported here, we have examined the acute central effects of cyanide when applied topically to the ventral surface of the medulla (VMS) and when administered into the spinal intrathecal space at the C5-T3 level on activities of the phrenic nerve, diaphragm, parasternal intercostal, triangularis sterni, and transversus abdominis muscles. Topical application of 10-100 micrograms (10 microliters of 1-10 mg/ml) cyanide to the intermediate area of the VMS decreased respiratory activity by > 50%, and expiratory muscles were more sensitive to inhibition than inspiratory muscles. The onset of depression of phrenic nerve or respiratory muscle activity occurred within 20 s of administration, and the effects reversed after washout. In contrast, intrathecal administration of cyanide in doses of 10-100 micrograms (100 microliters of 0.1-1 mg/ml) increased electrical activity of the respiratory muscles. Diaphragm activity changed from 17 +/- 2 to 42 +/- 8 (SE) units (P < 0.01), parasternal intercostal activity increased from 18 +/- 3 to 46 +/- 9 units (P < 0.01), and expiratory activity of the chest wall and abdominal muscles increased from 9 +/- 2 to 39 +/- 10 units (P < 0.05). Both topical application on the VMS and intrathecal administration of cyanide caused an increase in arterial blood pressure and a slight insignificant acceleration of heart rate. These data suggest that cyanide acting on the VMS causes respiratory depression and enhancement of sympathetic outflow.(ABSTRACT TRUNCATED AT 250 WORDS)