Effects of gestational isoflurane exposure on postnatal memory and learning in rats

A maternal fetal rat model was developed to study the effects of gestational isoflurane exposure on postnatal memory and learning and investigate the potential mechanisms. Pregnant rats at gestational day 14 were exposed to 1.3% isoflurane for 4 h. Spatial learning and memory of the offspring were examined using the Morris Water Maze. The expression levels of C/EBP homologous transcription factor protein (CHOP) and caspase-12 in the hippocampus of the pups were determined by immunohistochemistry and western blot analysis. Simultaneously, the ultrastructure changes of synapse in the hippocampal CA1 and dentate gyrus region were also observed by transmission electron microscopy (TEM). Prenatal exposure to isoflurane impaired postnatal spatial memory and learning in the offspring rats as shown by the longer escape latency and the fewer times of original platform crossing in the Morris Water Maze test. The number of CHOP and caspase-12 positive neurons significantly increased by 138% and 147% respectively in the hippocampus of isoflurane-exposed pups, as well as the levels of CHOP and caspase-12 protein. Furthermore, TEM studies showed changes of synaptic ultrastructure in isoflurane-exposed hippocampus characterized by the decreased synapse number, the widened synaptic cleft and the thinned postsynaptic densities. These results demonstrate that gestational exposure to a clinically relevant concentration of isoflurane could cause neuron apoptosis, changes of synaptic structure, and postnatal spatial memory and learning impairments in offspring. Our study further showed that the up-regulation of CHOP and caspase-12 may contribute to isoflurane-induced neuron apoptosis.