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 Plexiglas^TM 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.