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Fig. 4. The effects of polyethylene glycol (PEG) on CAP recovery following
ischemia/acrolein reperfusion. (A) The double-sucrose gap-recording chamber.
The device is constructed of PlexiglasTM with five separate chambers, all
linked together by a narrow slot. Three large chambers are shown; the two end
ones filled with KCl and the middle chamber with a physiological medium (a
modified Krebs' solution), where a constant flow of medium through the chamber
is carried out. The delivery to an `antechamber' reduces any turbulence or
artifacts based on flow of medium through and out of the device. A delivery
and an aspiration tube (that sets the fluid level) are shown for the central
chamber and one of the small sucrose chambers to its right. A constant flow of
sucrose significantly reduces the mixing of the KCl solution in the end
chambers with the center one. A full length (
40 mm) of guinea pig spinal
cord or a wedge-shaped long strip of only ventral white matter was placed
across and within all five chambers. The ends of the dissected cord are then
near intracellular potential, while the center of the cord is near
extracellular potential. Bipolar stimulating electrodes fire compound action
potentials (CAPs) at one end of the cord, and these are recorded arriving at
the other end with bipolar recording electrodes. This arrangement provides a
very precise recording of CAPs in cord for many hours at a time. It also
allows the addition of test drugs or other interventions to be carried out in
the central chamber. (B) The CAP amplitude profile in (a) the presence of
oxygen and glucose deprivation (OGD), (b) OGD plus acrolein, and (c) OGD plus
acrolein plus PEG. This graph displays the CAP amplitude recorded over a
period of time. The values were normalized. Note the similarity in CAP
amplitude recovery during the reperfusion period for groups (b) and (c). (C)
The CAP waveforms are shown at three time points, (a) pre OGD, (b) at the end
of OGD and (c) at the end of reperfusion, as indicated in B. Note there is
little difference from the initial CAPs and the ones recorded following
recovery from ischemia in OGD group. However, the amplitude is reduced to a
half of pre-OGD levels in both groups (b) and (c). Scale bars, 1 mV, 1 ms.
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