Squeezing nerve fibers causes axoplasm to accumulate on both sides, showing that nerve-fiber axoplasm flows {axon flow} in both directions.
Techniques {Nauta technique} can stain degenerating axons with silver. First, electrodes stimulate neurons with electric current, or fine pipettes stimulate neurons with chemicals. Then fine pipettes inject dye into cells. After axon cutting, dye blackens dying-axon branches.
Techniques {positron emission tomography} (PET) can use radioactive oxygen or carbon isotopes to measure cerebral blood flow or metabolic activity. Oxygen isotopes in glucose or neurotransmitters emit positrons as they decay. Patients receive radioactive tracers by injection or in food. Scanners localize radioactivity to within several millimeters and within one minute. Localized radioactivity shows increased oxygen-metabolism and glucose-metabolism sites. Brain blood flow varies with metabolic activity, so PET indicates locations with increased blood flow.
xenon
Alternatively, patients can receive radioactive xenon by injection into blood. The most active neurons become the most radioactive.
carbon 14
Carbon(14) 2-deoxyglucose is similar to glucose. Neurons can absorb the radioactive compound but cannot metabolize it. Neurons that absorb the most radioactivity are the most metabolically active.
Techniques {immunohistofluorescence} {retrograde marking} [1970] can stain neurons backward from injection site using horseradish peroxidase, colloidal gold wheat-germ agglutin, and fluorescent dyes.
Techniques {single channel recording} {patch clamping} can measure single-neuron electrical activity.
Techniques {single photon emission computed tomography} (SPECT) can measure cerebral blood flow or metabolic activity, using light.
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Date Modified: 2022.0225