Cardiorespiratory responses to glutamate microinjected into the medullary raphé

The involvement of the medullary raphé in modulating cardiorespiratory activity was examined by microinjecting L-glutamate (L-Glu) into the raphé of rats. Animals were vagotomized, paralyzed, artificially ventilated, maintained at 37 degrees C, and instrumented to record arterial blood pressure (BP) and phrenic nerve activity (PNA). Mock cerebrospinal fluid (mCSF, 10 nl, pH 7.4; control) and L-Glu dissolved in mCSF (10, 100, 1000 mM; 10 nl; pH 7.4; experimental) were microinjected into the raphé. L-Glu affected both BP and PNA in a dose dependent manner. Blood pressure was reduced by 6.30 +/- 0.97 and 12.98 +/- 1.29% by 100 and 1000 mM L-Glu, respectively, without affecting heart rate. PNA increased by 23 and 38% with 100 and 1000 mM L-Glu, respectively. Mock CSF and 10 mM L-Glu had no effect. It is concluded that there are sites in the medullary raphé that affect blood pressure only and other sites which can affect both blood pressure and respiration.