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4 ATA) INCREASES MEMBRANE CONDUCTANCEAND FIRING RATE IN THE RAT SOLITARY COMPLEX
1 Department of Physiology and Biophysics, Environmental and Hyperbaric Cell Biology Facility, Wright State University School of Medicine, Dayton, OH, USA
2 Department of Physiology and Biophysics, Environmental and Hyperbaric Cell Biology Facility, Wright State University School of Medicine, Dayton, OH, USA; Department of Community Health, Wright State University School of Medicine, Dayton, OH, USA
* To whom correspondence should be addressed. E-mail: jay.dean{at}wright.edu.
Neuronal sensitivity to pressure-barosensitivity-is illustrated by high pressure nervous syndrome (HPNS), which manifests as increased CNS excitability when breathing Heliox or Trimix at >15 atmospheres absolute (ATA). We have tested the hypothesis that smaller levels of pressure (
4 ATA) also increase neuronal excitability. The effect of hyperbaric helium, which mimics increased hydrostatic pressure, was determined on putative CO2/H+-chemoreceptor neurons in the solitary complex (SC) in rat brainstem slices by intracellular recording. Pressure stimulated firing rate in 31% of neurons (barosensitivity) and decreased input resistance. Barosensitivity was retained during synaptic blockade and was unaffected by antioxidants. Barosensitivity was distributed amongst CO2/H+-chemosensitive and CO2/H+-insensitive neurons; in CO2/H+-chemosensitive neurons, pressure did not significantly reduce neuronal chemosensitivity. We conclude that moderate pressure stimulates certain SC neurons by a mechanism that possibly involves an increased cation conductance, but which does not involve free radicals. Neuronal barosensitivity to 4 ATA may represent a physiological adaptive response to increased pressure or an early pathophysiological response that is the early manifestation of HPNS.
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