Background

Isoflurane exposure causes improvement in long-term neurocognitive function in young adult rats; this is associated with an increase in dentate gyrus (DG) progenitor proliferation 4 days after anesthesia. However, the number of new neurons that were born from cells that incorporated bromodeoxyuridine (BrdU) 4 days after anesthesia is not affected by anesthesia. We tested the hypothesis that progenitor proliferation continues to increase past 4 days, which would imply the possibility that the number of new neurons after anesthesia could be increased if BrdU labeling occurred at a later time point.

Methods

BrdU was injected at 0, 1, 2, 4, 9, 16 days after 4 hours of isoflurane exposure to 60-day old rats. Brains were harvested 2 hours later, immunohistochemically stained, and the number of BrdU+ cells in the DG was assessed microscopically.

Results

After 4 hours of exposure to isoflurane in 60-day old rats, the number of BrdU+ cells decreased on days 0 to 2, then increased on day 4 significantly, and regressed toward the control level on days 9 and 16.

Conclusions

Anesthesia-induced progenitor proliferation in the DG was not sustained 9 days after anesthesia. We interpret these results to signify that an anesthetic effect on neurogenesis likely does not play a critical role in the previously observed isoflurane-induced long-term improvement in neurocognitive function in 60-day old rats and that the transient increase in progenitor proliferation serves to replenish the pool of neural stem cells. The mechanism of anesthesia-induced improvement in cognition of young adult rats remains elusive.

Background

Propofol in the early postnatal period has been shown to cause brain cell death. One proposed mechanism for cognitive dysfunction after anesthesia is alteration of neural stem cell function and neurogenesis. We examined the effect of propofol on neural precursor or stem cells (NPCs) grown in vitro.

Methods

Hippocampal-derived NPCs from postnatal day 2 rats were exposed to propofol or Diprivan. NPCs were then analyzed for bromodeoxyuridine incorporation to measure proliferation. Cell death was measured by lactate dehydrogenase release. Immunocytochemistry was used to evaluate the expression of neuronal and glial markers in differentiating NPCs exposed to propofol.

Results

Propofol dose dependently increases the release of lactate dehydrogenase from NPCs under both proliferating and differentiating conditions at supraclinical concentrations (more than 7.1 µM). Both Diprivan and propofol had the same effect on NPCs. Propofol-mediated release of lactate dehydrogenase is not inhibited by blocking the γ-aminobutyric acid type A receptor or extracellular calcium influx and is not mediated by caspase-3/7. Direct γ-aminobutyric acid type A receptor activation did not have the same effect. In differentiating NPCs, 6 h of propofol at 2.1 µM increased the number neurons but not glial cells 4 days later. Increased neuronal differentiation was not blocked by bicuculline.

Conclusions

Only supraclinical concentrations of propofol or Diprivan kill NPCs in culture by a non-γ-aminobutyric acid type A, noncaspase-3 mechanism. Clinically relevant doses of propofol increase neuronal fate choice by a non-γ-aminobutyric acid type A mechanism.

Background

With growing evidence that anesthesia exposure in infancy affects cognitive development, it is important to understand how distinct anesthetic agents and combinations can alter long-term memory. Investigations of neuronal death suggest that combining anesthetic agents increases the extent of neuronal injury. However, it is unclear how the use of simultaneously combined anesthetics affects cognitive outcome relative to the use of a single agent.

Methods

Postnatal day 7 (P7) male rats were administered either sevoflurane as a single agent or the combined delivery of sevoflurane with nitrous oxide at 1 Minimum Alveolar Concentration for 4 h. Behavior was assessed in adulthood using the forced alternating T-maze, social recognition, and context-specific object recognition tasks.

Results

Animals exposed to either anesthetic were unimpaired in the forced alternating T-maze test and had intact social recognition. Subjects treated with the combined anesthetic displayed a deficit, however, in the object recognition task, while those treated with sevoflurane alone were unaffected.

Conclusion

A combined sevoflurane and nitrous oxide anesthetic led to a distinct behavioral outcome compared with sevoflurane alone, suggesting that the simultaneous use of multiple agents may uniquely influence early neural and cognitive development and potentially impacts associative memory.

Anesthesia in infancy impairs performance in recognition memory tasks in mammalian animals, but it is unknown if this occurs in humans. Successful recognition can be based on stimulus familiarity or recollection of event details. Several brain structures involved in recollection are affected by anesthesia-induced neurodegeneration in animals. Therefore, we hypothesized that anesthesia in infancy impairs recollection later in life in humans and rats. Twenty eight children ages 6-11 who had undergone a procedure requiring general anesthesia before age 1 were compared with 28 age- and gender-matched children who had not undergone anesthesia. Recollection and familiarity were assessed in an object recognition memory test using receiver operator characteristic analysis. In addition, IQ and Child Behavior Checklist scores were assessed. In parallel, thirty three 7-day-old rats were randomized to receive anesthesia or sham anesthesia. Over 10 months, recollection and familiarity were assessed using an odor recognition test. We found that anesthetized children had significantly lower recollection scores and were impaired at recollecting associative information compared with controls. Familiarity, IQ, and Child Behavior Checklist scores were not different between groups. In rats, anesthetized subjects had significantly lower recollection scores than controls while familiarity was unaffected. Rats that had undergone tissue injury during anesthesia had similar recollection indices as rats that had been anesthetized without tissue injury. These findings suggest that general anesthesia in infancy impairs recollection later in life in humans and rats. In rats, this effect is independent of underlying disease or tissue injury.