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Changes in extracellular space volume and geometry induced by cortical spreading depression in immature and adult rats.
Mazel T, Richter F, Vargova L, Sykova E.
Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic, sykova@biomed.cas.cz
Changes in extracellular space (ECS) diffusion parameters, DC potentials
and extracellular potassium concentration were studied during single and
repeated cortical spreading depressions (SD) in 13-15 (P13-15), 21 (P21)
and 90-day-old (adult) Wistar rats. The real-time iontophoretic method
using tetramethylammonium (TMA+)-selective microelectrodes was employed
to measure three ECS parameters in the somatosensory cortex: the ECS volume
fraction a (a = ECS
volume/total tissue volume), ECS tortuosity l
(increase in diffusion path length) and the nonspecific TMA+ uptake k'.
SD was elicited by needle prick. SD was significantly longer at P13-15
than at P21 and in adults. During SD, a in all
age groups decreased from 0.21-0.23 to 0.05-0.09; l
increased from 1.55-1.65 to 1.95-2.07. Ten minutes after SD, a
(in adults) and l (all age groups) increased
compared to controls. This increase persisted even 1 hour after SD. When
SD was repeated at 1 hour intervals, both a and
l showed a gradual cumulative increase with
SD repetition. Our study also shows that cortical SD is, as early as P13,
accompanied by severe ECS shrinkage and increased diffusion path length
(tortuosity) with values similar to adults, followed by a long-lasting
increase in ECS volume and tortuosity when compared to pre-SD values.
