CEREBRAL BLOOD-FLOW DECREASES FOLLOWING MICROINJECTION OF SODIUM-NITROPRUSSIDE INTO THE NUCLEUS-TRACTUS-SOLITARII OF ANESTHETIZED RATS

The present study was undertaken to examine the effects of microinject ion of sodium nitroprusside (SNP), which releases nitric oxide (NO) sp ontaneously, into the nucleus tractus solitarii (NTS) on cerebral circ ulation. Cerebral blood flow (CBF) was measured in urethane-anesthetiz ed (1.5 g . kg(-1), i.p.), paralysed and artificially ventilated rats using labeled microspheres or laser Doppler flowmetry. The CBF was sig nificantly decreased by microinjectiou of SNP (5 mmol, n=10, microsphe re technique; 0.5 mnol, n=6, laser Doppler flowmetry) into the unilate ral NTS. Microinjection of N-G-monomethyl-L-arginine (L-NMMA), an inhi bitor of the formation of NO, prevented cerebral vasoconstrictor respo nses induced by microinjection of L-glutamate into the NTS (n=10). Mic roinjection of N-G-monomethyl-D-arginine (D-NMMA) had no effect on the cerebral vasoconstrictor responses induced by L-glutamate (n=11). Uni lateral microinjections of L-NMMA into the NTS (n=9), of SNP into the area adjacent to the NTS (n=9), of vehicle solution into the NTS (n=10 ), and of light-inactivated SNP into the NTS (n=6) had no effect on ce rebral circulation. Cerebral autoregulation was well maintained in our protocols (n=9). These results indicate that microinjection of SNP, a n NO donor, into the NTS decreases CBF.