The neurotoxic effect of isoflurane on age-defined neurons generated from tertiary dentate matrix in mice

Isoflurane-induced reduction in neurogenesis derived from the tertiary dentate matrix

Anesthetics-induced disruption of dentate neurogenesis in the young brain is strongly suggested to contribute to delayed neurocognitive deficit. In postnatal rodents, the neurogenesis of the dentate gyrus (DG) is sequentially derived from the secondary dentate matrix, tertiary dentate matrix and subgranular zone (SGZ). However, the effects of anesthetics on the dentate neurogenesis derived from specific sites are poorly understood. To trace the new cells generated from the postnatal secondary dentate matrix, peak stage of the tertiary dentate matrix and early stage of the SGZ after isoflurane exposure, mice at postnatal day 1 (P1), P7 and P31 were injected with BrdU at 12 h before the exposure. We found that isoflurane exposure significantly reduced the numbers of proliferating cells (1 day old), immature granule cells (21 days old) or mature granule cells (42 days old) derived from the peak stage of the tertiary dentate matrix and postnatal secondary dentate matrix, but not from the SGZ. Quantitative assessment of BrdU-/BrdU+NeuN-positive cells and cleaved caspase-3 level in the DG indicated that the reduction was correlated with cell loss rather than neuronal differentiation. Mechanistically, we demonstrated that the PI3K/Akt/GSK-3β pathway enriched by mRNA-sequencing is a requirement for the isoflurane-induced loss of 1-day-old proliferating cells generated from the tertiary dentate matrix. In addition, this study demonstrated that P1 and P7 mice, but not P31 mice exposure to isoflurane resulted in subsequent deficits in performance of the tasks of the Morris Water Maze.

Alfaxalone Alleviates Neurotoxicity and Cognitive Impairment Induced by Isoflurane Anesthesia in Offspring Rats

BACKGROUND

The anesthetic isoflurane can cause neurotoxicity in fetuses and offspring of rats, affecting their neurodevelopment. However, the underlying mechanisms and therapeutic targets of isoflurane-induced neurotoxicity remain to be identified. Alfaxalone (ALF) is a steroid anesthetic. Steroids have been reported to have neuroprotective effects. This study aimed to investigate whether ALF could alleviate the isoflurane-induced neurotoxicity in fetuses and offspring of rats.

METHODS

On gestation day 15 (G15), the pregnant SD rats were randomly assigned to 4 groups: control 1 (CTL1) + control 2 (CTL2), isoflurane (ISO) + CTL2, CTL1 + ALF, and ISO + ALF. To analyze the changes in the expression levels of inflammatory cytokines, apoptotic factors, and synaptophysin, the brain tissues from the G15 fetuses and offspring at postnatal day 7 (P7), postnatal day 14 (P14), and postnatal day 31 (P31) were collected. The newborn neurons in the rats' offspring at P7, P14, and P31 were counted using immunofluorescence techniques. The Morris water maze (MWM) test was performed to assess the learning and memory abilities of P31 offspring rats.

RESULTS

ALF significantly alleviated the isoflurane-induced increase in the expression levels of inflammatory cytokines and apoptotic factors, such as interleukin (IL)-6 (ISO + CTL2 versus ISO + ALF: 5.133 ± 0.739 versus 1.093 ± 0.213, P < .001) and Caspase-3 (6.457 ± 0.6 versus 1.062 ± 0.1, P < .001) in the G15 fetuses. In P31 offspring rats, the expression levels of synaptophysin (0.719 ± 0.04 versus 1.068 ± 0.072, P < .001) and the number of newborn neurons in the dentate gyrus of the hippocampus were significantly lower in the ISO + CTL2 group as compared to those in the ISO + ALF group (118 ± 6 versus 140 ± 7, P < .001). These changes also occurred in the rat offspring at P7 and P14. In the MWM test, the escape latency of CTL1 + ALF group rats was significantly lower than that of ISO + ALF group rats (41 ± 6 versus 31 ± 7, P < .001) at P31.

CONCLUSIONS

Based on these findings, this study suggested that isoflurane exposure during pregnancy in rats could cause neuroinflammation and death of embryos as well as impairment of cognitive function in the offspring rats. ALF can be used to counteract the negative effects of isoflurane.

The neurotoxic effect of isoflurane on age-defined neurons generated from tertiary dentate matrix in mice

INTRODUCTION

Recent animal studies showed that isoflurane exposure may lead to the disturbance of hippocampal neurogenesis and later cognitive impairment. However, much less is known about the effect of isoflurane exposure on the neurons generated form tertiary dentate matrix, even though a great increase of granule cell population during the infantile period is principally derived from this area.

METHODS

To label the new cells originated from the tertiary dentate matrix, the mice were injected with BrdU on postnatal day 6 (P6). Then, the mice were exposed to isoflurane for 4 hr at 1, 8, 21, and 42 days after BrdU injection, and the brains were collected 24 hr later. The loss of newly generated cells/neurons with different developmental stage was assessed by BrdU, BrdU + DCX, BrdU + NeuN, or BrdU + Prox-1 staining, respectively.

RESULTS

We found that the isoflurane exposure significantly decreased the numbers of nascent cells (1 day old) and mature neurons (42 days old), but had no effect on the immature (8 days old) and early mature neurons (8 and 21 days old, respectively).

CONCLUSION

The results suggested isoflurane exposure exerts the neurotoxic effects on the tertiary dentate matrix-originated cells with an age-defined pattern in mice, which partly explain the cognitive impairment resulting from isoflurane exposure to the young brain.