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

Glycine (0.8–64.8 umol) was administered into the cisterna magna of α-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 < 0.05). This decrease was due primarily to a reduction in tidal volume which decreased from 31 ± 2 to 12 ± 2 ml (p < 0.05). The two largest doses tested (21.6 and 64.8 umol) also produced a decrease in respiratory rate from 14 ± 1 to 11 ± 1 and from 15 ± 1 to 12 ± 1 breaths/min (p < 0.05), respectively. Apnea occurred in 2 of 7 animals given 64.8 μmo1 of glycine. No consistent doserelated changes in inspiratory and expiratory durations were observed-Intravenous administration of glycine (64.8 umol) did not affect respiratory activity. These results indicate that glycine causes respiratory depression by an action in the central nervous system.