Anaesthesia and cognition

Anaesthesia is an essential component of many clinical and scientific procedures. It is well-established that anaesthesia has short-term effects on cognition but an increasing body of work suggests that anaesthesia may have longer-term effects on learning and memory, beyond the point at which the drugs are eliminated from the body. Experiments were conducted, in adult rats, to better understand the behavioural phenotype of anaesthetic-induced cognitive impairment. A two-hour exposure to isoflurane/nitrous oxide anaesthesia in the absence of surgery was sufficient to impair win-shift spatial memory on the radial arm maze, despite intact spontaneous spatial novelty preference, a candidate psychological process for radial maze performance. Impairment in attentional processing might also affect spatial memory. The same anaesthetic regime, but not an injectable anaesthetic combination of propofol/fentanyl, impaired some aspects of attention, as assessed with the 5-choice serial-reaction-time task and the sustained attention task (SAT). However, in contrast to the spatial memory impairment, the magnitude of attentional impairment was not increased following successive anaesthetic exposures. A similar pattern of spatial memory impairment dependent on the number of anaesthetic episodes was seen in rats exposed to isoflurane during development and tested in adulthood. Developmental exposure to a similar anaesthetic, sevoflurane, did not impair attention in adulthood as assessed with the SAT and the intradimensional/extradimensional shift task. With the aim of better understanding the neuronal mechanisms underlying the spatial memory impairment, laser confocal microscopy was used to examine the dendritic ultrastructure of hippocampal neurons from rats exposed to isoflurane/nitrous oxide during adulthood. Results did not provide compelling evidence for changes in dendritic ultrastructure. These results highlight that anaesthesia is not benign and is a critical variable that should be considered when designing animal behavioural neuroscience experiments. In addition they contribute to a larger literature regarding the potential long-term effects of anaesthesia on human health.