Pressure (< or=4 ATA) increases membrane conductance and firing rate in the rat solitary complex.
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 (<or=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 <or=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.
Mulkey
Daniel K
DK
Department of Anatomy and Physiology, Wright State University, Dayton, OH 45435, USA.
Henderson
Richard A
RA
Putnam
Robert W
RW
Dean
Jay B
JB
D000138:Acidosis / Q000503:physiopathology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001274:Atmospheric Pressure; D002118:Calcium / Q000494:pharmacology; D004594:Electrophysiology; D005609:Free Radicals; D006610:High Pressure Neurological Syndrome / Q000503:physiopathology*; D006931:Hyperbaric Oxygenation; D006935:Hypercapnia / Q000503:physiopathology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017552:Solitary Nucleus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D000975:Antioxidants; D005609:Free Radicals; D008274:Magnesium; D002118:Calcium