No abstract

No abstract

Fast-scan cyclic voltammetry, a demonstrated analytical method for the in vivo detection of catecholamine neurotransmitters, is extended to the simultaneous determination of molecular oxygen (O2). Cyclic voltammograms were recorded at a scan rate of 400 V/s at carbon-fiber disk electrodes coated with a perfluorinated ion-exchange material. The peak current for O2 occurs near -1.2 V under these conditions. In flow-injection experiments, these electrodes respond to step changes in dopamine and O2 with a half-rise time of less than 200 ms. The voltammetric peak current is independent of flow rate, indicating a diffusion-limited response unaffected by convection. Several compounds present in the in vivo matrix (adenosine, glutathione, and NAD and glutamic, lactic, and uric acids) were tested and shown not to interfere with the voltammetric signal for O2. These electrodes maintain a stable response in vivo for at least 6 h. They have been used to measure transient increases in both dopamine and O2 in the extracellular fluid of the caudate nucleus of an anesthetized rat in response to an electrical stimulus.

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 alpha-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.

No abstract