Comparative physiology of the high-pressure neurological syndrome--compression rate effects.

The effect of compression rate on onset of high-pressure convulsions has been studied in 14 vertebrate species, as well as in 10 mouse strains and 4 rat strains. Compression rate effects were observed in 9 of the 14 species. They appear to be independent of exposure temperature, correlate only very loosely with phylogenetic position, and appear to reflect species-specific compensatory mechanisms grafted onto an underlying convulsion-producing effect of high hydrostatic pressure.

Interaction of central nervous system effects of high pressures with barbiturates.

The interactions of phenobarbital, barbital, and pentobarbital with high pressures of heliox were explored. Principal features of the complex results include: double peaks in the time course of convulsion thresholds (Pc); an early peak and a shoulder in the time course of pressures reversing anesthesia (Pa); far steeper dose-response curves for Pa than for Pc; selectively greater anticonvulsant effect for phenobarbital than for the other barbiturates; and enhancement of Pa with simultaneous depression of Pc by reserpine in phenobarbital-pretreated mice. The data indicate the existence of at least two discrete sites of interaction between barbiturates and high pressure, reflected by Pc and Pa.

Time, rate, and temperature factors in the onset of high-pressure convulsions.

An interrupted compression profile technique was used to develop data to separate the effects of time and pressure factors governing increase of high-pressure neurological syndrome (HPNS) convulsion threshold pressures (the compression rate effect) during different compression profiles. A single differential equation fits all data available to date for compression rate effect on convulsion thresholds of CD-1 mice (three distinct types of compression profile; mean compression rates 12-1,000 atm/h). The process leading to increase in HPNS convulsion pressure is initiated at the very beginning of compression, proceeds at increasingly rapid rates as higher pressures are attained, and approaches a limiting upper convulsion pressure.