NEUROPROTECTION OF MILD HYPOTHERMIA - DIFFERENTIAL-EFFECTS

To estimate whether mild hypothermia during repetitive hypoxia provide s a neuroprotective effect on brain tissue, hippocampal slice preparat ions were subjected to repetitive hypoxic episodes under different tem perature conditions. Slices of guinea pig hippocampus (n = 40) were pl aced at the interface of artificial cerebrospinal fluid (aCSF) and gas (normoxia: 95% O-2 5% CO2; hypoxia: 95% N-2, 5% CO2). Evoked potentia ls (EP) and direct current (DC) potentials were recorded from hippocam pal CAl region. Slices were subjected to two repetitive hypoxic episod es under the following temperature conditions: (A) 34 degrees C/34 deg rees C, (B) 30 degrees C/30 degrees C and (C) 34 degrees C/30 degrees C. Hypoxic phases lasted until an anoxic terminal negativity (ATN) occ urred. The recovery after first hypoxia lasted 30 min. Tissue function was assessed regarding the latency of ATN and the recovery of evoked potentials. The ATN latencies with protocol A (n = 25) for the first a nd second hypoxia were 5.9 +/- 1.3 min (mean +/- S.E.M., Ist hypoxia) and 2.4 +/-: 0.9 min (2nd hypoxia), with protocol B the latencies (n = 7) were significantly longer: 25.2 +/- 7.1 min and 15.6 +/- 7.7 min. With protocol C (n = 8), the latencies were 5.6 +/- 1.8 and 3.3 +/- 0. 5 min. No differences were seen in the recovery of the EPs with protoc ols A-C. Our results suggest that a mild hypothermia is only neuroprot ective if applied from an initial hypoxia onwards. (C) 1998 Elsevier S cience B.V.