CEREBRAL EXTRACELLULAR LACTATE CONCENTRATION AND BLOOD-FLOW DURING CHEMICAL-STIMULATION OF THE NUCLEUS-TRACTUS-SOLITARII IN ANESTHETIZED RATS

The extracellular lactate concentration and blood flow in the cerebral cortex of urethane-anesthetized, paralyzed and artificially ventilate d rats were monitored continuously and simultaneously using an enzyme electrode and a laser Doppler flowmeter (LDF), respectively, during ch emical stimulation of the nucleus tractus solitarii (NTS) by microinje ction of L-glutamate (1.7 nmol 50 nl). Chemical stimulation of the NTS significantly decreased the arterial blood pressure (ABP) from 85 +/- 17 to 68 +/- 14 mmHg, heart rate from 418 +/- 13 to 402 +/- 19 beats min(-1) and cerebral blood flow (CBF) by 17.9 +/- 6.2% (P < 0.001). Ho wever, chemical stimulation of the NTS significantly increased the lac tate concentration by 58.9 +/- 17.3 mu M (P < 0.001). Barostat maneuve r, which held systemic ABP constant during chemical stimulation of the NTS attenuated the responses in CBF and lactate concentration by 30 a nd 27%, respectively. The onset of the increase in lactate concentrati on was delayed about 19 s after that of the CBF decrease. Circulatory lactate produced no significant change in the cerebral extracellular l actate concentration. These results indicate that chemical stimulation of the NTS induces an increase in extracellular lactate concentration in the cerebral cortex through a decrease in CBF via cerebral vasocon striction.