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Pressure (4 ATA) increases membrane conductance and firing rate in the rat solitary complex

¹Department of Physiology and Biophysics, Environmental and Hyperbaric Cell Biology Facility, and ²Department of Community Health, Wright State University School of Medicine, Dayton, Ohio 45435

Submitted 20 September 2002 ; accepted in final form 4 April 2003

Neuronal sensitivity to pressure, barosensitivity, is illustrated by high-pressure nervous syndrome, which manifests as increased central nervous system excitability when heliox or trimix is breathed 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 in rat brain stem 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 among CO₂/H⁺-chemosensitive and -insensitive neurons; in CO₂/H⁺-chemosensitive neurons, pressure did not significantly reduce neuronal chemosensitivity. We conclude that moderate pressure stimulates certain solitary complex neurons by a mechanism that possibly involves an increased cation conductance, but that does not involve free radicals. Neuronal barosensitivity to 4 ATA may represent a physiological adaptive response to increased pressure or a pathophysiological response that is the early manifestation of high-pressure nervous syndrome.

brain slice; intracellular recording; cardiorespiratory control; high-pressure nervous syndrome; hyperbaric helium; hypercapnia; hyperoxia; neuron

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