Effect of exposure to high temperatures during early pregnancy on hippocampal-dependent learning and memory integrity in neonatal rats.

To explore the influence of short-term (0, 30 and 60 min) exposure to high temperatures on the integrity of hippocampal-dependent learning and memory in neonatal rats. Confocal laser scanning microscopy (CLSM) was used to observe neuronal apoptosis in the hippocampi of neonatal rats. In situ hybridization was conducted for the detection of hippocampal c-fos messenger RNA (mRNA) expression, and reverse transcription-polymerase chain reaction was performed to test the expression of NR1 (an N-methyl-D-aspartate receptor [NR] subunit) gene in the hippocampus. Finally, the Morris water maze (MWM) was used to evaluate hippocampal-dependent learning and memory. The number of c-fos mRNA-positive cells in the hippocampus was positively correlated with increasing heat exposure times. NR1 mRNA expression in the hippocampal CA1 area was positively correlated with the proportion of dead and apoptotic cells. In addition, neonatal rats exposed to high temperatures had significantly reduced platform crossings in the MWM compared to controls. The duration of heat exposure during early pregnancy was correlated with severe deficits in hippocampal-dependent learning and memory in neonatal rats.