Isoflurane Differentially Affects Neurogenesis and Long-term Neurocognitive Function in 60-day-old and 7-day-old Rats

Background: Anesthetic agents cause cell death in the developing rodent brain and long-term, mostly hippocampal-dependent, neurocognitive dysfunction. However, a causal link between these findings has not been shown. Postnatal hippocampal neurogenesis affects hippocampal function into adulthood; therefore, the authors tested the hypothesis that isoflurane affects long-term neurocognitive function via an effect on dentate gyrus neurogenesis. Methods: The S-phase marker 5-bromodeoxyuridine was administered at various times before, during, and after 4 h of isoflurane given to postnatal day (P)60 and P7 rats to assess dentate gyrus progenitor proliferation, early neuronal lineage selection, and long-term survival of new granule cell neurons. Fear conditioning and spatial reference memory was tested at various intervals from 2 weeks until 8 months after anesthesia. Results: in 1160 rats, isoflurane increased early neuronal differentiation as assessed by BrdU/NeuroD costaining, decreased progenitor proliferation for 1 day, and subsequently increased progenitor proliferation 5-10 days after anesthesia. In P7 rats, isoflurane did not induce neuronal lineage selection but decreased progenitor proliferation until at least 5 days after anesthesia. Isoflurane improved spatial reference memory of P60 rats long-term, but it caused a delayed-onset, progressive, persistent hippocampal deficit in P7 rats in fear conditioning and spatial reference memory tasks. Conclusion: The authors conclude that isoflurane differentially affects; both neurogenesis; and long-term neurocognitive function in P60 and P7 rats. Neurogenesis might mediate the long-term neurocognitive outcome after isoflurane at different ages.