[MORPHOLOGICAL ASPECTS OF CHANGES IN THE SPINAL GRAY MATTER DUE TO G-LOADS IN EXPERIMENT]

To study changes in spinal cord structures brought about by g-loads, laboratory animals (rats) were rotated on a centrifuge following a special procedure. Systematic g-loads along the craniocaudal axis resulted in reactive alterations, and also obvious destructive processes in the spinal gray matter (SGM). Light optical microscopy discovered that part of neurons had bodies with less intensive dying. Electron microscopy showed that among the cytoplasmic structures mitochondria were particularly sensitive to g-loads, which could affect mitochondrial oxidation. In the lumbar, these changes were observed in every segment under study; they were more significant in comparison with those found in cervical and thoracic segments of the spinal cord. Interneuron disintegration at neural centers revealed itself by the "light" type degeneration of synapses. Changes in capillaries included nuclei deformations and destruction of organelles in endotheliocytes, pericapillary edema, and erythrocytes sludge in the lumen. Inequality of spinal cord changes suggests the mosaic pattern of their distribution. Furthermore, their manifestation grew with the cranicaudal gradient so that the most conspicuous destructive developments occurred in the lumbar but not in the thoracic let alone the cervical segment. Acute g-loads gave rise to reactive changes in neurons and interneuron synapses that were the morphological markers of increased functional activity of neurons and activation of interneuron firing. In addition to the reactive changes, chronic g-loading also produced destructive disorders in GSM structures. These changes were not observed following acute g-loads and, therefore, resulted from multiple g-exposures and were cumulative.