The effects of positive acceleration on the central nervous system.
The effects of positive acceleration on the CNS were studied by applying negative pressure to the lower body (LBNP) of unanesthetized rabbits. The LBNP which can simulate well the effects of positive acceleration induced high voltage slow bursts with amplitude 600-800 microV and frequency of 2-3 Hz in the EEG of the rabbits, which seemed to be quite similar to those observed by Adey et al. in the EEG of the centrifuged monkeys and cats. Because the physiological effects of LBNP as well as positive acceleration had been greatly attributed to disturbance of circulation in the CNS, much effort was made in this experiment to study the mechanisms triggering the slow bursts especially in relation to changes in hemodynamic cardiovascular measurements. By LBNP, both blood pressure and blood flow fell markedly and cerebral circulation was obstructed, but these changes were recovered to some extent approximately 10 seconds after the application of LBNP. These changes fell again until the release of LBNP, when cerebral blood flow was profoundly increased. The slow bursts seemed to be induced only in such periods when cerebral blood flow was profoundly increased after a failure of cardiovascular compensatory mechanisms such as a decrease of heart rate with irregular cardiac rhythm had occurred by repeated application of a greater LBNP. These results suggest that the necessary important change inducing the slow bursts is a sudden rush of blood to the anoxic CNS and is not only an anoxic condition of the CNS during LBNP, and the bursts may possibly be triggered by mechanical distortion of the neuronal network by a sudden fluid movement within the anoxic brain or change in permeability of blood vessels and the glial cells which might greatly modulate neuronal excitability by such sudden return of blood to the anoxic CNS.
Mitarai
G
G
Nagoya University, Nagoya, Japan.
Nagasaka
T
T
Mori
S
S
Takagi
S
S
D000054:Acceleration; D000818:Animals; D001794:Blood Pressure; D002490:Central Nervous System / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004569:Electroencephalography; D006339:Heart Rate; D008150:Lower Body Negative Pressure; D011817:Rabbits; D012640:Seizures / Q000209:etiology*