Functional neuroimaging relies on the robust coupling between neuronal activity, metabolism and cerebral blood flow (CBF), but the physiological basis of the neuroimaging signals is still poorly understood. We examined the mechanisms of activity-dependent changes in tissue oxygenation in relation to variations in CBF responses and postsynaptic activity in rat cerebellar cortex. To increase synaptic activity we stimulated the monosynaptic, glutamatergic climbing fibres that excite Purkinje cells via AMPA receptors. We used local field potentials to indicate synaptic activity, and recorded tissue oxygen partial pressure (P tiss,O 2 ) by polarographic microelectrodes, and CBF using laser-Doppler flowmetry. The disappearance rate of oxygen in the tissue increased linearly with synaptic activity. This indicated that, without a threshold, oxygen consumption increased as a linear function of synaptic activity. The reduction in P tiss,O 2 preceded the rise in CBF. The time integral (area) of the negative P tiss,O 2 response increased non-linearly showing saturation at high levels of synaptic activity, concomitant with a steep rise in CBF. This was accompanied by a positive change in P tiss,O 2 . Neuronal nitric oxide synthase inhibition enhanced the initial negative P tiss,O 2 response ('dip'), while attenuating the evoked CBF increase and positive P tiss,O 2 response equally. This indicates that increases in CBF counteract activity-induced reductions in P tiss,O 2 , and suggests the presence of a tissue oxygen reserve. The changes in P tiss,O 2 and CBF were strongly attenuated by AMPA receptor blockade. Our findings suggest an inverse relationship between negative P tiss,O 2 and CBF responses, and provide direct in vivo evidence for a tight coupling between activity in postsynaptic AMPA receptors and cerebellar oxygen consumption.

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Cortical spreading depression (CSD) is associated with release of arachidonic acid, impaired neurovascular coupling, and reduced cerebral blood flow (CBF), caused by cortical vasoconstriction. We tested the hypothesis that the released arachidonic acid is metabolized by the cytochrome P450 enzyme to produce the vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE), and that this mechanism explains cortical vasoconstriction and vascular dysfunction after CSD. CSD was induced in the frontal cortex of rats and the cortical electrical activity and local field potentials recorded by glass microelectrodes, CBF by laser Doppler flowmetry, and tissue oxygen tension (tpO 2 ) using polarographic microelectrodes. 20-HETE synthesis was measured in parallel experiments in cortical brain slices exposed to CSD. We used the specific inhibitor HET0016 (N-hydroxy-NЈ-(4-n-butyl-2-methylphenyl)formamidine) to block 20-HETE synthesis. CSD increased 20-HETE synthesis in brain slices for 120 min, and the time course of the increase in 20-HETE paralleled the reduction in CBF after CSD in vivo. HET0016 blocked the CSD-induced increase in 20-HETE synthesis and ameliorated the persistent reduction in CBF, but not the impaired neurovascular coupling after CSD. These findings suggest that CSD-induced increments in 20-HETE cause the reduction in CBF after CSD and that the attenuation of stimulation-induced CBF responses after CSD has a different mechanism. We suggest that blockade of 20-HETE synthesis may be clinically relevant to ameliorate reduced CBF in patients with migraine and acute brain cortex injuries.

Functional neuroimaging and normal brain function rely on the robust coupling between neural activity and cerebral blood flow (CBF), that is neurovascular coupling. We examined neurovascular coupling in rat sensory cortex in response to direct stimulation of transcallosal pathways, which allows examination of brain regions inaccessible to peripheral stimulation techniques. Using laserDoppler flowmetry to record CBF and electrophysiologic recordings of local field potentials (LFPs), we show an exponential relation between CBF responses and summed LFP amplitudes. Hemodynamic responses were dependent on glutamate receptor activation. CNQX, an AMPA receptor blocker, strongly attenuated evoked CBF responses and LFP amplitudes at all stimulation frequencies. In comparison, N-methyl D-aspartate (NMDA) receptor blockade by MK801 attenuated CBF responses at high ( > 7 Hz) but not low ( < 7 Hz) stimulation frequencies, without affecting evoked LFP amplitudes. This shows the limitation of using LFP amplitudes as indicators of synaptic activity. 7-Nitroindazole, a neuronal nitric oxide synthase inhibitor, and indomethacin, a nonspecific cyclooxygenase inhibitor, attenuated the hemodynamic responses by 50%61% and 48%61%, respectively, without affecting LFP amplitudes. The data suggest that preserved activity of both AMPA and NMDA receptors is necessary for the full CBF response evoked by stimulation of rodent interhemispheric connections. AMPA receptor activation gives rise to a measurable LFP, but NMDA receptor activation does not. The lack of a measurable LFP from neural processes that contribute importantly to CBF may explain some of the difficulties in transforming extracellular current or voltage measurements to a hemodynamic response.

A continuous cell line, Se-Ax, from a patient with Sézary syndrome has been established. The Se-Ax cell line is IL-2 dependent, requires human serum for permanent growth, and has the following phenotype: CD1-, CD2+, CD3+, CD4-, CD5-, CD8-, CD20-, CD25+; it expresses the T9, T10, and HLA-DR antigens. This cell line reveals multiple chromosome aberrations as seen in the most abundant abnormal clone in peripheral blood. Therefore, it is not unlikely that it derives from tumor cells. A putative cytotoxic cell line derived from the same patient has only weak killer-cell activity against the autologous permanent cell line: this CD8+ cytotoxic cell line has a 14q+ chromosomal marker. The fact that the patient demonstrated no natural killer-cell or activated killer-cell activity against the Se-Ax cell line may in part explain the successful establishment of the continuous cell line from bulk culture.

Neuronal activity, cerebral blood flow, and metabolic responses are all strongly coupled, although the mechanisms behind the coupling remain unclear. One of the key questions is whether or not increases in spiking activity in the stimulated neurons are sufficient to drive the activity-dependent rises in cerebral blood flow (CBF) that form the basis of the signals used in functional neuroimaging such as the blood oxygen level-dependent (BOLD) signal. To this end the present study examined the effect of enhanced spike activity per se on CBF in rat cerebellar cortex under conditions of disinhibition, achieved by blocking GABA A receptors using either bicuculline or picrotoxin. Purkinje cell spiking activity and local field potentials were recorded by glass microelectrodes, and laser Doppler flowmetry was used to monitor CBF. Disinhibition increased Purkinje cell spiking rate to 200-300% of control without incurring any increase in basal CBF. This demonstrates that increased spike activity per se is not sufficient to affect basal CBF. The neurovascular coupling between excitatory synaptic activity and CBF responses evoked by inferior olive (climbing fibre) stimulation was preserved during disinhibition. Thus, the unchanged basal CBF in the presence of the dramatic rise in Purkinje cell spiking rate was not explained by impaired synaptic activity-CBF coupling. On the basis of our previous and the present studies, we conclude that increased spiking activity of principal neurons is neither sufficient nor necessary to elicit CBF responses and in turn BOLD signals, and that activation-dependent vascular signals reflect excitatory synaptic activity.

Our results showed no evidence of bacteria in vertebrae with Modic type I changes. The isolation of staphylococci from two patients probably represented contamination.

Summary.-Biopsy specimens from nasopharyngeal carcinomas (NPC) or salivarygland carcinomas (SGC) in Greenland Eskimoes were examined for the presence of Epstein-Barr virus (EBV) DNA and sera from the patients were tested for EBVspecific antibody titres. Six out of 7 NPCs and one from an undifferentiated SGC were positive for EBV DNA. The EBV-specific antibody spectra and titres of the patients with NPC or undifferentiated SGC conformed to the results of earlier studies in other high-incidence areas.