Reversal of pressure-induced tremors in rats by step decompression and by inert gases.

A method for continuously recording the motor activity of pressurized rats was used to monitor their condition after 1) holding pressure constant after compression, 2) decompression, and 3) adding nitrogen prior to holding pressure constant. After procedures 1 and 2 the logarithm of activity plotted linearly against time in two distinct phases. A short initial decline was followed by a slower, longer decline that was incomplete after 5 h. The rate of the second, slower decline was inversely related to the holding pressure and unaffected by prior convulsions. The addition of 4.8 atm N2 was very effective at decreasing the activity at constant pressure compared to a large (43%) decompression step. The slopes obtained from plots of activity against pressure, which provide a measure of the sensitivity of the animal to compression, were unaltered by the early inclusion of 4.8 atm N2 or 0.19 atm N2O but were displaced to higher pressures. Activity appears to be the net result of activity-generating and accommodation processes, and there was no evidence that it was in equilibrium with pressure.