Respiratory depression produced by glycine injected into the cisterna magna of cats

Glycine (0.8-64.8 mumol) was administered into the cisterna magna of alpha-chloralose anesthetized cats to determine its effect on ventilation. Glycine caused a dose-related decrease in respiratory minute volume with the highest dose resulting in a decrease from 454 +/- 35 to 159 +/- 44 ml/min (p less than 0.05). This decrease was due primarily to a reduction in tidal volume which decreased from 31 +/- 2 to 12 +/- 2 ml (p less than 0.05). The two largest doses tested (21.6 and 64.8 mumol) also produced a decrease in respiratory rate from 14 +/- 1 to 11 +/- 1 and from 15 +/- 1 to 12 +/- 1 breaths/min (p less than 0.05), respectively. Apnea occurred in 2 of 7 animals given 64.8 mumol of glycine. No consistent dose-related changes in inspiratory and expiratory durations were observed. Intravenous administration of glycine (64.8 mumol) did not affect respiratory activity. These results indicate that glycine causes respiratory depression by an action in the central nervous system.