Brain vessels in the rats exposed to primary and repeated tail-suspension. Minimization of structural changes after repeated exposure

The aim of study was histological examination of brain vessels in the rats exposed to repeated tail-suspension (TS). The rats were subjected to 30-day TS, then readapted to horizontal position for 30 days and again exposed to 14-day TS simultaneously with the rats which were underwent to 14-day TS for the first time. 30-day TS induced in brain vessels the adaptive changes hindering the excessive blood inflow to brain--spasm and hypertrophy of muscle-elastic valves in extra- and intracerebral arteries and also the destructive changes--loss of vascular tone in extra- and intracerebral arteries, plethora in extra- and intracerebral veins, intracerebral venules and capillaries, conglutination of erythrocytes in capillaries, plasmatization of veins and capillaries and edema of brain tissue pointing out in total the increase in blood inflow to the brain and difficulty of blood outflow. After 30-day readaptation of TS-rats to horizontal position only adaptive changes in extracerebral arteries and intracerebral capillaries (cell proliferation) and edema of brain tissue were revealed. After repeated, 14-day TS in spite of new redistribution of blood to the head, in contrast to the vessel alterations after primary 14-day TS, the adaptive and destructive changes in brain vessels were lack, excluding only moderate plethora of intracerebral veins, cell proliferation in capillaries and weak signs of edema.