Repeated Exposure to Propofol in the Neonatal Period Impairs Hippocampal Synaptic Plasticity and the Recognition Function of Rats in Adulthood

Anesthesia of neonates with propofol induces persistent behavioral abnormalities in adulthood. Although propofol-triggered apoptosis of neurons in the developing brain may contribute to the development of cognitive deficits, the mechanism of neurotoxicity induced by neonatal exposure to propofol remains unclear. In this study, the effects of neonatal propofol anesthesia on synaptic plasticity and neurocognitive function were investigated. Postnatal day 7 (PND-7) Sprague-Dawley rats were intraperitoneally injected with fat emulsion or 20, 40 or 60 mg/kg propofol for three consecutive days. The expression of brain-derived neurotrophic factor (BDNF), tropomyosin-related kinase B (TrkB) and postsynaptic density protein 95 (PSD-95) in the rat hippocampus at PND-10 and PND-12 was measured by Western blotting. The number of dendritic branches, total dendritic length and dendritic spine density were observed by Golgi-Cox staining 24 h and 72 h after the last propofol administration. Long-term potentiation (LTP) was measured electrophysiologically in hippocampus of PND-60 rats to evaluate the synaptic function. The learning and memory abilities of rats were evaluated by Morris water maze (MWM) experiments, Novel object recognition test (NORT) and Object location test (OLT) at PND-60. Our results showed that neonatal exposure to propofol significantly inhibited the expression of BDNF, TrkB and PSD-95 in the rat hippocampus. The number of dendritic branches, total dendritic length and dendritic spine density of neurons in the rat hippocampus were markedly reduced after neonatal propofol anesthesia. LTP was significantly diminished in hippocampus of PND-60 rats after repeated exposure to propofol in the neonatal period. Morris water maze experiments showed that repeated neonatal exposure to propofol significantly prolonged the escape latency and decreased the time spent in the target quadrant and the number of platform crossings. NORT and OLT showed that repeated neonatal exposure to propofol markedly reduced the Investigation Time for novel object or location. All of the results above indicate that repeated exposure to propofol in the neonatal period can impair hippocampal synaptic plasticity and the recognition function of rats in adulthood.