Acidosis and blockade of orthodromic responses caused by anoxia in rat hippocampal slices at different temperatures.

Abstract

SUMMARY1. Interstitial pH (pH.) and field responses (to stratum radiatum stimulation) were recorded simultaneously with double-barrelled microelectrodes in the CAI region of hippocampal slices from Sprague-Dawley rats.2. Both the relative acidity and amplitude of field responses increased with depth, reaching a maximum near the centre of the slice. When the temperature was raised from 22 to 37°C, this pH. gradient was > 2 times steeper, but the field responses were much diminished.3. Standard anoxic tests (substituting 95 % N2 + 5 % CO2 for 95 % 02 + 5 % CO2, for 2 min) tended to reduce pH0 and population spikes, but these effects were highly temperature sensitive: at -22°C the blocking rate was only 12 3 + 4 6 % and ApHo -0018+0-0157 units, both per minute; corresponding changes at 34-35°C were 67-6 + 11 9 % and -0O065 + 0-0046 units per minute. Highly significant linear correlations between rates of block and ApHR gave a mean slope of 904 + 17-6 % per 0-1 unit of acid change.4. Anoxia caused similar temperature-dependent increases in acidity in stratum pyramidale and radiatum, but in the latter field responses (EPSPs) were much less depressed after 2 min of anoxia.5. When slices were superfused with acid medium (low [HCO3-j), much greater reductions in pHo were needed to depress responses, giving a mean slope of 17-7 % per 0.1 pH unit.6. In glucose-free medium, there was a slow alkaline shift in pHo (0-13 +0-036 units); population spikes and the acid transients evoked by anoxia disappeared.7. It was concluded that acidosis cannot be the immediate cause of the similar depressions of postsynaptic excitability seen during anoxia and hypoglyeaemia.8. In further tests, DL-p-hydroxyphenyl-lactic acid, a blocker of lactate transport, failed to diminish acid transients evoked by anoxia, indicating that these are not mediated principally by lactate transport.

Membrane potentials and microenvironment of rat dorsal vagal cells in vitro during energy depletion.

“…The extra-and intracellular pH decreases most probably result from anaerobic lactate production and H+ formation during oxygen depletion (Hansen, 1985;Chesler, 1990). This is confirmed by the observed blockade of the anoxia-related fall in pHo after removal of glucose as the substrate for lactate production, as has also been described for rat hippocampal slices (Krnjevic & Walz, 1990). The increase in pH0 baseline in glucose-free solutions further suggests that anaerobic metabolism is, at least partly, responsible for the rather acidic pH.…”

Acute neuroinflammation provokes intracellular acidification in mouse hippocampus

“…In our experiments, control pHi and pHo levels were about 7.1 and 7.3, respectively. These values are consistent with the measurements observed in other studies [3, 16, 47, 48] indicating that the slices were in good health in our experimental conditions. Acute neuroinflammation, induced by either i.p.…”

“…When measured in slice preparations, the level of pHo varies as a function of distance from the slice surface [16–18]. To measure such pHo profiles, the tip of a calibrated pH-sensitive micropipette was first placed at the “starting” position of 200 μm above the slice, at which position pHo = pHacsf, and then moved down by 20-μm steps, once in 5 s, till the position of 180 μm below the slice surface (Additional file 1: Figure S1B, “Vp,” see also a schematic on Fig.…”

Electrical coupling of astrocytes in rat hippocampal slices under physiological and simulated ischemic conditions

“…The extracellular pH in the ischemic lesion area can fall to 6.9-6.2 (Nedergaard et al, 1991;Smith et al, 1986) and the astrocytic intracellular pH to 6.8-5.3 (Kraig et al, 1985). In the conventional slice OGD model, the bath pH is maintained by the bicarbonate buffer that may even cause a small alkaline shift in hippocampal slices (Krnjevi c and Walz, 1990). We found that a 10-min exposure of slices to OGD had no effect on electrical coupling, suggesting a lack of significant intracellular acidification of astrocytes.…”