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Sensory transmission in dorsal column nuclei is inhibited during voluntary movement in experimental animals. We have studied the human response by recording spine and scalp somatosensory evoked potentials. Finger movement attenuated the amplitude and duration of the cervical N13 and the scalp N18 and N20 waves. Foot movement did not alter the lumbar N22 after foot stimulation, but the scalp P38 was attenuated. N22 results solely from activation of interneurons in the dorsal gray of the cord at the root entry zone, but N13 may receive contributions from the nucleus cuneatus. Therefore, the movement-induced attenuation of N13 is attributed to decreased contribution from the nucleus cuneatus.

Effects of high energy, heavy particle (HZE) radiation were studied in the brain of the fruit fly (Drosophila melanogaster) exposed to argon (40Ar) or krypton (84Kr) ions. In the flies exposed to argon the fluence ranged from 6 X 10(4) to 8 X 10(7) particles/cm2. The insects were killed 35 days after exposure. Extensive tissue fragmentation was observed at the higher fluence employed. At fluences ranging from 5 X 10(6) (one hit/two cell bodies) to 9 X 10(4) (one hit/90 cell bodies) particles/cm2, swelling of the neuronal cytoplasm and focally fragmented membranes was observed. Marked increase of glial lamellae around nerve cell processes was seen at fluences ranging from one hit/six to one hit/135 cell bodies. In the flies irradiated with krypton, the fluences employed were 5.8 X 10(3) and 2.2 X 10(6) particles/cm2. Acute and late effects were evaluated. In the flies killed 36 hours after exposure (acute effects) to either fluence, glycogen particles were found in the neuroglial compartment. The granules were no longer present in flies killed 35 days later (late effects). As in the flies exposed to argon, neuronal swelling and membrane disruption were observed 35 days after exposure to both fluences. From these studies it appears that the Drosophila brain is a useful model to investigate radiation damage to mature neurons, neuroglia, and therefore, to the glio-neuronal metabolic unit. In a separate study, the synaptic profiles of the neuropil in layers II-III of the frontal cerebral cortex of anesthesized adult LAFl mice were quantitatively appraised after exposure to argon (40Ar) particles. The absorbed dose ranged from 0.05 to 5 gray (Gy) plateau. It was determined that the sodium pentobarbital anesthesia per se results in a significant decrease in synaptic profile length one day after anesthetization, with return to normal values after 2-28 days. Irradiation with 0.05-5 Gy argon particles significantly inhibited the synaptic shortening effect of anesthesia at one day after exposure.

Histological preparations of brains from rabbits and mice exposed to different doses of various HZE particles or to low-LET photons have been subjected to preliminary quantitation of radiation-induced morphometric changes. Computer assisted measurements of several brain structures and cell types have been made using the KONTRON Automated Interactive Measurement System (IBAS, Carl Zeiss, Inc., Thornwood, N.Y. 10594 U.S.A.). New Zealand white rabbits irradiated at approximately 6 weeks of age were euthanatized 6.5-25 months after exposure to 60Co gamma photons (LET infinity = approximately 0.3 keV/micrometer, 20Ne particles (LET infinity = 35 +/- 3 keV/micrometer), or 40Ar particles (LET infinity = 90 +/- 5 keV/micrometer). Measurements of stained sections of the olfactory bulbs of those animals indicate that the mean size (volume) of olfactory glomeruli is reduced in a dose-dependent (and perhaps an LET-dependent) manner as soon as 6.5 months after irradiation. Differences between mean volumes of additional structures have been noted when histological preparations of control mouse brains were compared with irradiated specimens. Quantitation of intermediate and late changes in nervous (and other) tissues exposed to low- and high-LET radiations will improve our ability to predict late effects in tissues of astronauts and others exposed to the radiation hazards of the space environment.

Tissue reactions were found around the monitor (dosimeter) assemblies that had been implanted beneath the scalp of the five pocket mice that flew on Apollo XVII. Mitosis in the dentate gyrus of the hippocampal formation was considerably reduced in comparison with that in control animals. Otherwise the brain tissue as well as the menings in the flight animals appeared unaltered. Since the animals were exposed primarily to high Z-high energy (HZE) cosmic ray particles at the lower end of the high LET spectrum, the lack of changes in the brain cannot be taken as evidence that the brain will suffer no damage from the heavier HZE particles on prolonged manned missions.

Fruit flies (Drosophila melanogaster) were exposed to high-LET krypton (84Kr) ions at low (4.2 rad) and high (1,584 rad) doses and killed to assess acute (36 h post-exposure) and late (35 days post-exposure) effects in the brain by means of electron microscopy. The main findings were: (a) glycogen granules appeared in the neuroglial compartment 36 h after exposure to either dose and were no longer present in flies killed 35 days later, (b) neuronal alterations (swelling and membrane disruption) were observed 35 days after exposure to both doses, (c) changes in the neuroglia (electron-dense masses of concentrically arranged membranous structures) were seen 35 days after exposure. The data are discussed in relation to previous research in the fruit fly using argon (40Ar) charged particles and to other radiation studies performed in the mammalian brain with the view of using the insect brain as a model for detailed study of radiation effects on neurons, neuroglia, and the neuron-neuroglia unit.

A study was made of tissues from 130 pocket mice after a single head-only exposure to high-LET 20Ne particle radiation at 1000, 100 or 10 rad (nominal surface dose) with the view of obtaining base"line data regarding the effectiveness of HZE (cosmic-ray) particles during spaceflight. First seen at 2-3 weeks after exposure, necrotic neurons in the cerebrum reached peak incidence (0 . 04 per cent at 1000 rad, 0 . 003 per cent at 100 rad and less than 0 . 0005 per cent at 10 rad) after 4-5 weeks and decreased to low levels thereafter. Incidence in the cerebellum was lower. Neuroglia, cells of the subependymal matrix and dentate gyrus precursor cells suffered acute damage at 1000 and at 100 rad. At 1000 rad, enlarged hyperchromatic neuroglia, first noted at 3 weeks, increased in number up to 7 months, then declined. Alterations in the retina and olfactory epithelium were seen at 1000 rad, and reaction in the scalp at 100 rad. Damage was incurred by dentinoblasts at 10 rad. Changes similar to those observed in pocket mice were found in the brains of gerbils and C57B1 mice.