Cognitive deficits after general anaesthesia in animal models: a scoping review

Association between surgical admissions, cognition, and neurodegeneration in older people: a population-based study from the UK Biobank

BACKGROUND

Previous studies have shown that major surgical and medical hospital admissions are associated with cognitive decline in older people (aged 40-69 years at recruitment), which is concerning for patients and caregivers. We aimed to validate these findings in a large cohort and investigate associations with neurodegeneration using MRI.

METHODS

For this population-based study, we analysed data from the UK Biobank collected from March 13, 2006, to July 16, 2023, linked to the National Health Service Hospital Episode Statistics database, excluding participants with dementia diagnoses. We constructed fully adjusted models that included age, time, sex, Lancet Commission dementia risk factors, stroke, and hospital admissions with a participant random effect. Primary outcomes were hippocampal volume and white matter hyperintensities, both of which are established markers of neurodegeneration, and exploratory analyses investigated the cortical thickness of Desikan-Killiany-Tourville atlas regions. The main cognitive outcomes were reaction time, fluid intelligence, and prospective and numeric memory. Surgeries were calculated cumulatively starting from 8 years before the baseline evaluation.

FINDINGS

Of 502 412 participants in the UK Biobank study, 492 802 participants were eligible for inclusion in this study, of whom 46 706 underwent MRI. Small adverse associations with cognition were found per surgery: reaction time increased by 0·273 ms, fluid intelligence score decreased by 0·057 correct responses, prospective memory (scored as correct at first attempt) decreased (odds ratio 0·96 [95% CI 0·95 to 0·97]), and numeric memory maximum correct matches decreased by 0·025 in fully adjusted models. Surgeries were associated with smaller hippocampal volume (β=-5·76 mm³ [-7·89 to -3·64]) and greater white matter hyperintensities volume (β=100·02 mm³ [66·17 to 133·87]) in fully adjusted models. Surgeries were also associated with neurodegeneration of the insula and superior temporal cortex.

INTERPRETATION

This population-based study corroborates that surgeries are generally safe but cumulatively are associated with cognitive decline and neurodegeneration. Perioperative brain health should be prioritised for older and vulnerable patients, particularly those who have multiple surgical procedures.

FUNDING

The Australian and New Zealand College of Anaesthetists (ANZCA) Foundation and the University of Sydney.

No negative effects of intra-abdominal bio-logger implantation under general anaesthesia on spatial cognition learning in a hibernator the edible dormouse

The effect of hibernation on cognitive capacities of individuals is not fully understood, as studies provide conflicting results. Most studies focus on behavioural observations without taking the physiological state of individuals to account. To mechanistically understand the effect of hibernation on the brain, physiological parameters need to be included. The implantation of bio-loggers can provide insights on i.e. body temperature without further manipulation of the animals. Surgeries and anaesthesia, however, can harm animals' health and cause cognitive dysfunction, potentially biasing data collected through bio-loggers. We investigated the effects of bio-logger implantation surgery on cognitive performance and learning, controlling for animal and study design characteristics. First, juvenile dormice successfully learned to solve a spatial cognition task using a vertical maze. Distance, transitions, velocity, and duration were measured as indicators for performance. After training, bio-loggers were implanted intra-abdominally under general anaesthesia. Animals were re-tested in the maze two weeks after. We found no effect of bio-logger implantation and surgery on performance. This study is the first to show spatial cognition learning in edible dormice and provides a full description of the peri-anaesthetic management and a protocol for bio-logger implantation surgery in dormice. Importantly, measures were taken to mitigate common anaesthetic complications that could lead to post-operative cognitive dysfunction and influence animal behaviour. By pairing physiological measurements through bio-logger implantation with behaviour and cognition measurements, future research will significantly advance the understanding on mechanisms of learning and behaviour.

Interleukin-33 ameliorates perioperative neurocognitive disorders by modulating microglial state

Perioperative neurocognitive disorders (PND) are cognitive dysfunctions that usually occur in elderly patients after anesthesia and surgery. Microglial overactivation is a key underlying mechanism. Interleukin-33 (IL-33) is a member of the IL-1 family that orchestrates microglial function. In the present study, we explored how IL-33, which regulates microglia, contributes to cognitive improvement in a male mouse model of PND. An exploratory laparotomy was performed to establish a PND model. The expression levels of IL-33 and its receptor ST2 were evaluated using Western blot. IL-33/ST2 secretion, microglial density, morphology, phagocytosis of synapse, and proliferation, and dystrophic microglia were assessed using immunofluorescence. Synaptic plasticity was measured using Golgi staining and long-term potentiation. The Morris water maze and open field test were used to evaluate cognitive function and anxiety. Hippocampal expression of IL-33 and ST2 were elevated on postoperative day 3. We confirmed that IL-33 was secreted by astrocytes and neurons, whereas ST2 mainly colocalized with microglia. IL-33 treatment induced microgliosis after anesthesia and surgery. These microglia had larger soma sizes and shorter and fragmented branches. Compared to the Surgery group, IL-33 treatment reduced the synaptic phagocytosis of microglia and increased microglial proliferation and dystrophic microglia. IL-33 treatment also reversed the impaired synaptic plasticity and cognitive function caused by anesthesia and surgery. In conclusion, these results indicate that IL-33 plays a key role in regulating microglial state and synaptic phagocytosis in a PND mouse model. IL-33 treatment has a therapeutic potential for improving cognitive dysfunction in PND.

Dexmedetomidine nasal administration improves perioperative sleep quality and neurocognitive deficits in elderly patients undergoing general anesthesia

OBJECTIVE

To investigate the improvement of perioperative sleep quality and neurocognitive impairment in elderly patients under general anesthesia by nasal administration of dexmedetomidine.

METHODS

One hundred and twenty patients admitted to our hospital for various laparoscopic elective gynecological surgeries lasting more than 1 h under general anesthesia from July 2021 to March 2023 were selected. All subjects were divided into 3 groups according to the random number table method. From 21:00 to 21:30 every night from one day before to 5 days after surgery, group A was given alprazolam 0.4 mg orally; group B was given dexmedetomidine 1.5ug/kg nasal drip; group C was given saline nasal drip. All subjects were observed for general information, sleep quality, postoperative cognitive function, anxiety status, sleep quality, adverse effects and complication occurrence.

RESULTS

The difference in general information between the three groups was not statistically significant, P > 0.05; the sleep quality scores of the three groups on admission were not statistically significant, P > 0.05. At the Preoperative 1d, postoperative 1d, 3d and 5d, the RCSQ scores of the subjects in group A and group B were higher than those in groups C, and with the postoperative RCSQ scores of subjects in group B were higher as the time increased; the assessment of anxiety status in the three groups 1d before surgery was not statistically significant, P > 0.05. The cognitive function scores of subjects in the three groups were not statistically significant in the preoperative 1d, P > 0.05. The postoperative 1d (24.63 ± 2.23), 3d (25.83 ± 2.53), and 5d (26.15 ± 2.01) scores of the subjects in group B were higher than those in groups A and C (P < 0.05), and the subjects in group B had better recovery of postoperative cognitive function with increasing time; the occurrence of postoperative delirium (POD) in group B (12.5%) were lower on postoperative 5d than those in groups A (37.5%) and C (32.5%) (P < 0.05). There was no statistical significance in the evaluation of anxiety state of the three groups on the first day before operation (P > 0.05). The scores in group B were lower than those in group C on the postoperative 1d, 3d, 5 d (P < 0.05). The overall incidence of adverse reactions and complications in subjects in group B was 17.5% significantly lower than that in groups A and C (P < 0.05).

CONCLUSION

Dexmedetomidine can effectively improve the sleep disorder of elderly general anesthesia patients, reduce the damage to their neurocognitive function and the occurrence of POD, effectively reduce the anxiety of patients and the occurrence of adverse reactions and complications, and has better sedative, improve postoperative cognitive function and anti-anxiety effects, with a high drug safety, worthy of clinical application and promotion.

Cell-surface biotinylation of GABAA receptors in mouse hippocampal slices after sevoflurane anesthesia

Here, we present a protocol for studying the cell-surface proteins in hippocampal slices after in vivo administration of sevoflurane, an inhaled general anesthetic drug, to mice. We describe steps for anesthetic delivery, hippocampal slice preparation, and cell-surface biotinylation. We then detail the isolation of surface proteins and their quantification through Western blotting. This protocol can be adapted to study changes in other surface proteins following exposure to various general anesthetic drugs. For complete details on the use and execution of this protocol, please refer to Wang et al. (2012),1 Zurek et al. (2014),2 and Yu et al. (2019).3.

Reduced excitatory neurotransmission in the hippocampus after inflammation and sevoflurane anaesthesia

Background

Inflammation and general anaesthesia likely contribute to perioperative neurocognitive disorders, possibly by causing a neuronal imbalance of excitation and inhibition. We showed previously that treatment with lipopolysaccharide (LPS) and sevoflurane causes a sustained increase in a tonic inhibitory conductance in the hippocampus; however, whether excitatory neurotransmission is also altered remains unknown. The goal of this study was to examine excitatory synaptic currents in the hippocampus after treatment with LPS and sevoflurane. Synaptic plasticity in the hippocampus, a cellular correlate of learning and memory, was also studied.

Methods

Mice were injected with vehicle or LPS (1 mg kg-1 i.p.), and after 24 h they were then exposed to vehicle or sevoflurane (2.3%; 2 h). Hippocampal slices were prepared 48 h later. Excitatory synaptic currents were recorded from pyramidal neurones. Long-term potentiation (LTP) and long-term depression (LTD) were studied in the Schaffer collateral-cornu ammonis 1 pathway.

Results

The amplitude of miniature excitatory postsynaptic currents (EPSCs) was reduced after LPS+sevoflurane (P<0.001), whereas that of spontaneous EPSCs was unaltered, as evidenced by cumulative distribution plots. The frequency, area, and kinetics of both miniature and spontaneous EPSCs were unchanged, as were LTP and LTD.

Conclusions

The reduced amplitude of miniature EPSCs, coupled with the previously reported increase in tonic inhibition, indicates that the combination of LPS and sevoflurane markedly disrupts the balance of excitation and inhibition. Restoring this balance by pharmacologically enhancing excitatory neurotransmission and inhibiting the tonic current may represent an effective therapeutic option for perioperative neurocognitive disorders.