Modification of synaptic facilitation and bursting patterns in Aplysia californica by hyperbaric air

We have studied the effects of air pressure to 10 atmospheres absolute on several electrophysiological characteristics of identified neurons in Aplysia californica. These pressures did not affect the resting potential, rates of polarization, amplitude, or duration of action potentials in cell R2. Repetitive stimulation of the right pleurovisceral connective nerve produced a frequency-dependent train of unitary excitatory postsynaptic potentials (PSPs) in cell R15 which showed marked facilitation near the end of the train. The amount of facilitation of the last four PSPs increased significantly (approximately 20%) at 9 ATA air pressure. The amplitude of the first PSP was not altered by pressure. Changes in extracellular [Ca2+] or oxygen tension did not influence these pressure effects. Increases in air pressure also reduced the number of action potentials per burst, burst duration, and interburst interval of cell R15 but left the overall firing frequency unchanged. These results indicate that fundamental neurophysiological processes can be altered by increased gas tensions similar to those confronting animals experiencing narcotic symptoms at less than 300 ft of seawater.