Effect of electrical and chemical stimulation of the raphe obscurus on phrenic nerve activity in the cat.

The effect of electrical and chemical (L-glutamate) stimulation of the raphe obscurus on phrenic nerve activity was examined in the cat. Phrenic nerve activity was recorded from a C5 nerve root in anesthetized, paralyzed and artificially ventilated cats. Neural discharge was quantitated by integrating the phrenic nerve activity. The respiratory frequency was determined from the integrated nerve signal. Focal electrical stimulation (18-144 microA; 5-40 Hz; 100 microseconds pulse duration) resulted in significant (P less than 0.05) increases in both integrated phrenic nerve (IPN) amplitude and respiratory frequency. These changes were dependent upon current intensity and frequency of stimulation. The largest increases in IPN amplitude and respiratory frequency were 47 +/- 17% and 146 +/- 8%, respectively. To insure that the changes in integrated phrenic nerve activity (IPNA) were the result of stimulation of cell bodies and not axons of passage, L-glutamate (100, 200 nmol) was microinjected (100 nl) into the raphe obscurus. Significant (P less than 0.05) dose-related changes occurred in integrated phrenic nerve amplitude with an increase of 44 +/- 13% at 100 nmol and 80 +/- 13% at 200 nmol L-glutamate. No significant increase in respiratory frequency was observed with L-glutamate microinjection. The results suggest that the raphe obscurus may be involved in respiratory control.