Dopamine and oxygen (O2) were measured in the caudate nucleus of anesthetized rats and in striatal slices during electrical stimulation. Simultaneous electrochemical detection of dopamine and O2 was accomplished with fast-scan cyclic voltammetry at a Nafion-coated carbon-fiber microelectrode. Stimulation of the medial forebrain bundle resulted in synaptic overflow of dopamine in the caudate nucleus. At the same time, O2 concentration increased in the extracellular fluid with two separate phases. The amplitude of the initial increase directly correlated with the frequency of the stimulus, with the time of maximum concentration reproducible across a range of frequencies. The second increase occurred at later times with a more random amplitude and with a broad, variable shape. Agents which blocked vasodilation affected both phases: Atropine attenuated the initial increase, while the second feature was nearly absent after theophylline. Yohimbine and α-methyl- p-tyrosine did not affect the O2 responses. Local electrical stimulation of the slice preparation also resulted in dopamine overflow, but a prolonged decrease in O2 concentration accompanied this event. Striatal field stimulation in vivo produced changes in O2 concentration dependent on the relative position of the stimulating and working electrodes, but none of the responses resembled that seen in the caudate slice. Thus, while measurements in brain slices show O2 consumption as a result of stimulated neuronal activity, an apparent elevation of local cerebral blood flow during and after stimulation dominate the in vivo response.
Interpretive monitoring in the caudate nucleus