title: The relationship between changes in intrinsic optical signals and cell swelling in rat spinal cord slices.
abstract: Changes in intrinsic optical signals could be related to cell swelling; however, the evidence is not compelling. We measured light transmittance, ECS volume fraction (alpha), and extracellular K+ in rat spinal cord slices during electrical stimulation and the application of elevated potassium, NMDA, or anisoosmotic solutions. Dorsal root stimulation (10 Hz/1 min) induced an elevation in extracellular K+ to 6-8 mM, a light transmittance increase of 6-8%, and a relative ECS volume decrease of less than 5%; all of these changes had different time courses. The application of 6 or 10 mM K+ or NMDA (10(-5) M) had no measurable effect on alpha, but light transmittance increased by 20-25%. The application of 50 or 80 mM K+ evoked a 72% decrease in alpha while the light transmittance increase remained as large as that in 6 or 10 mM K+. While the change in alpha persisted throughout the 45-min application, light transmittance, after peaking in 6-8 min, quickly returned to control levels and decreased below them. Astrocytic hypertrophy was observed in 6, 10, and 50 mM K+. The same results followed the application of 10(-4) M NMDA or hypotonic solution (160 mmol/kg). The elevation of extracellular K+ after NMDA application, corresponding to increased neuronal activity, had a similar time course as the light transmittance changes. Furosemide, Cl(-)-free, or Ca(2+)-free solution blocked or slowed down the decreases in alpha, while the light transmittance increases were unaffected. In hypertonic solution (400 mmol/kg), alpha increased by 30-40%, while light transmittance decreased by 15-20%. Thus, light transmittance changes do not correlate with changes in ECS volume but are associated with neuronal activity and morphological changes in astrocytes.
authors.affiliation: Department of Neuroscience, 2nd Medical Faculty, Charles University, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic. sykova@biomed.cas.cz
authors.forename: Eva
authors.initials: E
authors.lastname: Syková
authors.forename: Lýdia
authors.initials: L
authors.lastname: Vargová
authors.forename: Sárka
authors.initials: S
authors.lastname: Kubinová
authors.forename: Pavla
authors.initials: P
authors.lastname: Jendelová
authors.forename: Alexandr
authors.initials: A
authors.lastname: Chvátal
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000502:physiology*; D048429:Cell Size / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007124:Immunoenzyme Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008839:Microelectrodes; D008857:Microscopy, Interference; D016202:N-Methylaspartate / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology*; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
chemical_list: D005904:Glial Fibrillary Acidic Protein; D016202:N-Methylaspartate; D005665:Furosemide; D011188:Potassium