VISUALIZATION OF CHANGES IN REGIONAL CEREBRAL BLOOD-FLOW (RCBF) PRODUCED BY KETAMINE USING LONG TE GRADIENT-ECHO SEQUENCES - PRELIMINARY-RESULTS

Autoradiographic studies have shown that Low dose ketamine produces in creases in regional glucose utilisation and blood flow in the hippocam pus, cerebral cortex, and olfactory lobe in the rat brain, probably du e to antagonism at the NMDA receptor. Functional MRI using deoxyhaemog lobin contrast can be used to study changes in regional cerebral blood flow (rCBF). Long TE gradient-echo sequences were used to study chang es in rCBF produced by low dose ketamine in rats anaesthetised with ni trous oxide, supplemented with either halothane (HAL) or fentanyl/flua nisone/midazolam (FFM) combination. Images from rats in the FFM group showed a 10-14% increase in signal intensity in the hippocampus, cereb ral cortex, and olfactory lobe following either a single bolus or a lo w dose infusion of ketamine (p < .05). These changes were significantl y reduced in the HAL group (p < .005). Halothane is known to attenuate the changes in regional glucose utilisation produced by the noncompet itive NMDA antagonist dizocilpine (MK-801), and its effects on ketamin e-induced changes in rCBF seen in this study may be due to a similar e ffect. The potential nse of functional MRI in studying the effect of p harmacological interventions on rCBF is discussed.