Isoflurane-induced depolarization of neural mitochondria increases with age

Development and Application of a Mitochondrial Genetically Encoded Voltage Indicator in Narcosis

Mitochondrial membrane potential (MMP) plays a crucial role in the function of cells and organelles, involving various cellular physiological processes, including energy production, formation of reactive oxygen species (ROS), unfolded protein stress, and cell survival. Currently, there is a lack of genetically encoded fluorescence indicators (GEVIs) for MMP. In our screening of various GEVIs for their potential monitoring MMP, the Accelerated Sensor of Action Potentials (ASAP) demonstrated optimal performance in targeting mitochondria and sensitivity to depolarization in multiple cell types. However, mitochondrial ASAPs also displayed sensitivity to ROS in cardiomyocytes. Therefore, two ASAP mutants resistant to ROS were generated. A double mutant ASAP3-ST exhibited the highest voltage sensitivity but weaker fluorescence. Overall, four GEVIs capable of targeting mitochondria were obtained and named mitochondrial potential indicators 1-4 (MPI-1-4). In vivo, fiber photometry experiments utilizing MPI-2 revealed a mitochondrial depolarization during isoflurane-induced narcosis in the M2 cortex.

Low neuronal metabolism during isoflurane-induced burst suppression is related to synaptic inhibition while neurovascular coupling and mitochondrial function remain intact

Deep anaesthesia may impair neuronal, vascular and mitochondrial function facilitating neurological complications, such as delirium and stroke. On the other hand, deep anaesthesia is performed for neuroprotection in critical brain diseases such as status epilepticus or traumatic brain injury. Since the commonly used anaesthetic propofol causes mitochondrial dysfunction, we investigated the impact of the alternative anaesthetic isoflurane on neuro-metabolism. In deeply anaesthetised Wistar rats (burst suppression pattern), we measured increased cortical tissue oxygen pressure (p_tiO₂), a ∼35% drop in regional cerebral blood flow (rCBF) and burst-associated neurovascular responses. In vitro, 3% isoflurane blocked synaptic transmission and impaired network oscillations, thereby decreasing the cerebral metabolic rate of oxygen (CMRO₂). Concerning mitochondrial function, isoflurane induced a reductive shift in flavin adenine dinucleotide (FAD) and decreased stimulus-induced FAD transients as Ca²⁺ influx was reduced by ∼50%. Computer simulations based on experimental results predicted no direct effects of isoflurane on mitochondrial complexes or ATP-synthesis. We found that isoflurane-induced burst suppression is related to decreased ATP consumption due to inhibition of synaptic activity while neurovascular coupling and mitochondrial function remain intact. The neurometabolic profile of isoflurane thus appears to be superior to that of propofol which has been shown to impair the mitochondrial respiratory chain.

Real-Time Amperometric Recording of Extracellular H₂O₂ in the Brain of Immunocompromised Mice: An In Vitro, Ex Vivo and In Vivo Characterisation Study

We detail an extensive characterisation study on a previously described dual amperometric H₂O₂ biosensor consisting of H₂O₂ detection (blank) and degradation (catalase) electrodes. In vitro investigations demonstrated excellent H₂O₂ sensitivity and selectivity against the interferent, ascorbic acid. Ex vivo studies were performed to mimic physiological conditions prior to in vivo deployment. Exposure to brain tissue homogenate identified reliable sensitivity and selectivity recordings up to seven days for both blank and catalase electrodes. Furthermore, there was no compromise in pre- and post-implanted catalase electrode sensitivity in ex vivo mouse brain. In vivo investigations performed in anaesthetised mice confirmed the ability of the H₂O₂ biosensor to detect increases in amperometric current following locally perfused/infused H₂O₂ and antioxidant inhibitors mercaptosuccinic acid and sodium azide. Subsequent recordings in freely moving mice identified negligible effects of control saline and sodium ascorbate interference injections on amperometric H₂O₂ current. Furthermore, the stability of the amperometric current was confirmed over a five-day period and analysis of 24-h signal recordings identified the absence of diurnal variations in amperometric current. Collectively, these findings confirm the biosensor current responds in vivo to increasing exogenous and endogenous H₂O₂ and tentatively supports measurement of H₂O₂ dynamics in freely moving NOD SCID mice.

Comparing amyloid-β deposition, neuroinflammation, glucose metabolism, and mitochondrial complex I activity in brain: a PET study in aged monkeys

PURPOSE

The aim of the present study was to compare amyloid-β (Aβ) deposition, translocator protein (TSPO) activity, regional cerebral metabolic rate of glucose (rCMRglc), and mitochondrial complex I (MC-I) activity in the brain of aged monkeys.

METHODS

PET scans with (11)C-PIB (Aβ), (18)F-BCPP-EF (MC-I), (11)C-DPA-713 (TSPO), and (18)F-FDG (rCMRglc) were performed in aged monkeys (Macaca mulatta) in the conscious state and under isoflurane anaesthesia. (11)C-PIB binding to Aβ and (11)C-DPA-713 binding to TSPO were evaluated in terms of standard uptake values (SUV). The total volume of distribution (V T) of (18)F-BCPP-EF and rCMRglc with (18)F-FDG were calculated using arterial blood sampling.

RESULTS

Isoflurane did not affect MC-I activity measured in terms of (18)F-BCPP-EF uptake in living brain. There was a significant negative correlation between (18)F-BCPP-EF binding (V T) and (11)C-PIB uptake (SUVR), and there was a significant positive correlation between (11)C-DPA-713 uptake (SUV) and (11)C-PIB uptake. In contrast, there was no significant correlation between rCMRglc ratio and (11)C-PIB uptake.

CONCLUSION

(18)F-BCPP-EF could be a potential PET probe for quantitative imaging of impaired MC-I activity that is correlated with Aβ deposition in the living brain.

Isoflurane causes neocortical but not hippocampal-dependent memory impairment in mice

BACKGROUND

The aim of this study is to investigate the effect of general anaesthesia induced by isoflurane with buprenorphine on hippocampus-dependent and neocortex-dependent memory, respectively, in mice, and in addition, to compare the effects of such anaesthesia on these memory processes with the effects induced by lipopolysaccharide (LPS) administration on the same memory processes.

METHODS

To assess hippocampus-dependent memory, isoflurane (for 15 min) after buprenorphine injection, or LPS 100 μg/kg (intraperitoneally) was administered 24 h before or after fear conditioning. The effect of these treatments on hippocampus-dependent memory was assessed using contextual fear-conditioning tasks at day 4. To assess neocortex-dependent memory, isoflurane anaesthesia or LPS was given 72 h after contextual fear conditioning. Neocortex-dependent memory assessment was performed at day 32.

RESULTS

Unlike LPS injection, isoflurane with buprenorphine-induced anaesthesia does not impair freezing responses in hippocampus-dependent fear-conditioning memory tasks. On anterograde amnesia assessment: 49.67 ± 6.87% for the anaesthesia group and 54.5 ± 4.12% for the control group. On retrograde amnesia assessment: 47.16 ± 8.71% for the anaesthesia group and 54.5 ± 4.12% for control group; P > 0.05. Thus, neither isoflurane nor buprenorphine impair hippocampus-dependent memory. However, on the neocortex-dependent memory task, both isoflurane-induced anaesthesia and LPS-induced inflammation result in reduced freezing responses: 62.13 ± 5.80% for the anaesthesia group, 74.63 ± 5.69% for the LPS group, and 81.75 ± 3.26% for the control group; P < 0.05 compared with control group.

CONCLUSION

General anaesthesia induced by isoflurane with buprenorphine may result in impairment of neocortex-dependent memory in mouse. However, general anaesthesia so induced does not impair hippocampus-dependent memory in mouse in our experimental conditions.