Continuous intracellular recording from mammalian neurons exposed to hyperbaric helium, oxygen, or air

We developed a hyperbaric chamber for intracellular recording in rat brain stem slices during continuous compression and decompression of the tissue b ath with the inert gas helium. Air, rather than helium, was also used as th e compression medium in some cases to increase tissue nitrogen levels. An i mportant feature is the chamber door, which opens or closes rapidly at 1 at mosphere absolute (ATA) for increased accessibility of the microelectrode. The door also closes and seals smoothly without disrupting the intracellula r recording. Hyperbaric oxygen was administered during helium compression u sing a separate pressure cylinder filled with perfusate equilibrated with 2 .3-3.3 ATA oxygen. Measurements of tissue/bath Po-2 and pH confirmed that t he effects of compression using helium or air could be differentiated from those due to increased Po-2. One hundred and thirteen neurons were studied during 375 compression cycles ranging from 1 to 20 ATA (mode 3.0 ATA). We c onclude that it is technically feasible to record intracellularly from the same mammalian neuron while changing ambient pressure over a physiologicall y important range. These techniques will be useful for studying how various hyperbaric environments affect neurophysiological mechanisms.