title: Intrinsic optical signals in the dorsal horn of rat spinal cord slices elicited by brief repetitive stimulation.
abstract: With repetitive electrical stimulation of the dorsal root (20 Hz for 1 s at C-fibre strength), intrinsic optical signals (IOSs), measured as changes in light transmittance, were recorded in the superficial dorsal horn of rat spinal cord slices using a photodiode array imaging device. The mechanism underlying the induction of IOSs was investigated. IOSs elicited by brief repetitive stimulation persisted for 1-2 min and were decreased by reducing external Cl- concentration or by cation-chloride cotransport inhibitors. Furosemide was most effective whilst bumetanide was least effective among the inhibitors tested. A 1-min elevation of external K+ concentration evoked IOSs in the dorsal horn in the absence of stimulation, and K+-induced IOSs were inhibited by furosemide. These results suggest that the uptake of excess K+ via the furosemide-sensitive, cation-chloride cotransporters underlies the induction of the IOSs. One-minute exposure to hypotonic solutions, which would cause cell swelling, induced IOSs in the superficial dorsal horn. Whilst osmotic-induced IOSs were not affected by furosemide, they were inhibited by HgCl2 in a 2-mercaptoethanol-sensitive manner. The stimulation-induced IOSs were similarly depressed by HgCl2. In contrast, voltage-sensitive dye signals and field potentials, evoked by single electrical stimuli, were significantly less affected by HgCl2. These results suggest that there is a specialized water transport pathway in the superficial dorsal horn, and that IOSs elicited by brief repetitive activation of C-fibres are attributable to cell swelling caused by water influx through this pathway, as an osmotic gradient is established by the uptake of K+ via the furosemide-sensitive cotransporters.
authors.affiliation: Department of Human and Artificial Intelligence Systems, Fukui University, 3-9-1 Bunkyo, Japan. asai@synapse.fuis.fukui-u.ac.jp
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Asai
authors.forename: Kei
authors.initials: K
authors.lastname: Kusudo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ikeda
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Murase
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002034:Bumetanide / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002712:Chlorides / Q000378:metabolism; D004558:Electric Stimulation; D001330:Electronic Data Processing; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D005942:Gluconates / Q000494:pharmacology; D007192:Indenes / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008623:Mercaptoethanol / Q000494:pharmacology; D008627:Mercuric Chloride / Q000494:pharmacology; D009412:Nerve Fibers / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009924:Organ Culture Techniques; D009997:Osmotic Pressure / Q000187:drug effects; D020671:Posterior Horn Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013126:Spinal Nerve Roots / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D027981:Symporters / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*; D000096922:K Cl- Cotransporters
chemical_list: D000085:Acetates; D002034:Bumetanide; D002712:Chlorides; D005665:Furosemide; D005942:Gluconates; D007192:Indenes; D008623:Mercaptoethanol; D008627:Mercuric Chloride; D011188:Potassium; D027981:Symporters; D000096922:K Cl- Cotransporters; C095651:((2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy)acetic acid; C030691:gluconic acid