Perioperative Neurocognitive Disorder: State of the Preclinical Science.

The purpose of this article is to provide a succinct summary of the different experimental approaches that have been used in preclinical postoperative cognitive dysfunction research, and an overview of the knowledge that has accrued. This is not intended to be a comprehensive review, but rather is intended to highlight how the many different approaches have contributed to our understanding of postoperative cognitive dysfunction, and to identify knowledge gaps to be filled by further research. The authors have organized this report by the level of experimental and systems complexity, starting with molecular and cellular approaches, then moving to intact invertebrates and vertebrate animal models. In addition, the authors' goal is to improve the quality and consistency of postoperative cognitive dysfunction and perioperative neurocognitive disorder research by promoting optimal study design, enhanced transparency, and "best practices" in experimental design and reporting to increase the likelihood of corroborating results. Thus, the authors conclude with general guidelines for designing, conducting and reporting perioperative neurocognitive disorder rodent research

From the Cover: Volatile Anesthetics Transiently Disrupt Neuronal Development in Neonatal Rats

Volatile anesthetics can cause neuronal and glial toxicity in the developing mammalian brain, as well as long-term defects in learning and memory. The goals of this study were to compare anesthetics using a clinically relevant exposure paradigm, and to assess the anesthetic effects on hippocampal development and behavior. Our hypothesis was that volatile anesthetics disrupt hippocampal development, causing neurobehavioral defects later in life. Bromodeoxyuridine (BrdU) was administered to rats on postnatal day (P)1, and the rats were exposed to volatile anesthetics (isoflurane, sevoflurane, or desflurane) for 2 h on P2. On days P7 and P14, the BrdU-labeled cells were quantified in the hippocampal dentate gyrus using immunohistochemical assays and fluorescent microscopy. Caspase-3 positive cells were quantified on P2 to evaluate apoptosis. The remaining animals underwent behavioral testing at ages 6 weeks and 6 months, using the Morris Water Maze. Significantly fewer BrdU-positive cells were detected in the hippocampal dentate gyrus in both isoflurane and desflurane-treated animals compared with controls at P7, but there were no changes in cell numbers after sevoflurane exposure. Cell counts for all three anesthetics compared with controls were equivalent at P14. Isoflurane or desflurane exposure yielded slight differences in the behavioral tests at 6 weeks, but no differences at 6 months post-exposure. We conclude that a single 2-h exposure at P2 to either isoflurane or desflurane causes a transient disruption of hippocampal neuronal development with no significant detectable long-term effects on learning and memory, whereas the same exposure to sevoflurane has no effects

Differential general anesthetic effects on microglial cytokine expression.

Post-operative cognitive dysfunction has been widely observed, especially in older patients. An association of post-operative cognitive dysfunction with the neurodegenerative diseases, such as Alzheimer's disease, has been suggested. Neuroinflammation contributes to Alzheimer pathology, through elevated pro-inflammatory cytokines and microglial activation in the CNS leading to neuronal damage, synaptic disruption and ultimately cognitive dysfunction. We compare the effects of three different, clinically-used, anesthetics on microglial activation with, and without, the prototypical inflammatory trigger, lipopolysaccharide (LPS). Microglial BV-2 cell cultures were first exposed to isoflurane, sevoflurane (each at 2 concentrations) or propofol for 6 h, and cytokine levels measured in lysates and media. The same experiments were repeated after 1 h LPS pre-treatment. We found; 1) anesthetics alone have either no or only a small effect on cytokine expression; 2) LPS provoked a large increase in microglia cytokine expression; 3) the inhaled anesthetics either had no effect on LPS-evoked responses or enhanced it; 4) propofol nearly eliminated the LPS pro-inflammatory cytokine response and improved cell survival as reflected by lactate dehydrogenase release. These data suggest that propofol may be a preferred anesthetic when it is desirable to minimize neuroinflammation

Anesthetics had minimal effects on the resting microglial cytokine response.

<p>The cytokine response to anesthetic exposures was evaluated in the cell lysate and supernatant fractions of cultured BV-2 microglial cells. In the cell lysates, no changes were found in IL-6 (A) or IL-1β (C) levels after the anesthetic exposures. However, TNF-α levels significantly declined after exposures to 1.2% and 2.4% isoflurane (Iso) and 2% sevoflurane (Sevo) but were significantly elevated after propofol (Prop) (B). IL-10 levels were significantly reduced only with 4% sevoflurane. In the supernatant, significant increases were found in both IL-6 after exposure to 1.2% isoflurane (E), and in TNF-α levels after 4% sevoflurane and propofol (F) and in IL-10 levels after 1.2% isoflurane and 4% sevoflurane (H). No changes were found in IL-1β levels (G). For all graphs, data are expressed as means ± SEM. For all anesthetics, n = 3 culture plates. No significant differences were found between the air controls and the air controls with DMSO and the control data were combined (n = 6). Significance was determined for both analyses by 1-way analysis of variance with Dunnett's multiple comparison test (control compared to all columns). *P<0.05, **P<0.01, ***P<0.001. SEM indicates standard error of the mean.</p

Propofol muted the LDH release after LPS pre-treatment.

<p>LDH release is significantly enhanced after isoflurane and propofol exposures (A). When microglial cultures are pre-treated with LPS, only propofol significantly reduces LDH release (B).</p

The inhaled anesthetics had minimal effects on the microglial cytokine response to LPS stimulation.

<p>Compared to LPS alone, the addition of volatile anesthetics significantly elevated the IL-6 (A) and IL-1β (C) response after exposure to both 4% sevoflurane and LPS. TNF-α (B) and IL-10 (D) levels were unchanged in the cell lysate fraction. In the supernatant fraction, only IL-6 (E) levels were significantly elevated after 4% sevoflurane and LPS exposure, while TNF-α (F), IL-1 β (G) and IL-10 (H) remained unchanged. For all graphs, data are expressed as means ± SEM and n = 3 culture plates. Significance was determined for both analyses by 1-way analysis of variance with Dunnett's multiple comparison test (control compared to all columns). *P<0.05, **P<0.01, ***P<0.001. SEM indicates standard error of the mean.</p

Propofol mitigated the effect of LPS pre-treatment.

<p>Cytokine levels are all significantly reduced with the addition of propofol compared to controls plus DMSO (vehicle) for IL-6 (A), TNF-α (B) and IL-1β (C) in both the cell lysate and supernatant fractions (E–G, respectively). There were no changes in the IL-10 levels after the addition of propofol to LPS in either the cell lysate (D) or supernatant (H) fractions. For all graphs, data are expressed as means ± SEM and n = 3 culture plates. Statistical significance was determined by unpaired t-tests. *P<0.05, **P<0.01, ***P<0.001. SEM indicates standard error of the mean.</p

Macroscopic and macromolecular specificity of alkylphenol anesthetics for neuronal substrates.

We used a photoactive general anesthetic called meta-azi-propofol (AziPm) to test the selectivity and specificity of alkylphenol anesthetic binding in mammalian brain. Photolabeling of rat brain sections with [(3)H]AziPm revealed widespread but heterogeneous ligand distribution, with [(3)H]AziPm preferentially binding to synapse-dense areas compared to areas composed largely of cell bodies or myelin. With [(3)H]AziPm and propofol, we determined that alkylphenol general anesthetics bind selectively and specifically to multiple synaptic protein targets. In contrast, the alkylphenol anesthetics do not bind to specific sites on abundant phospholipids or cholesterol, although [(3)H]AziPm shows selectivity for photolabeling phosphatidylethanolamines. Together, our experiments suggest that alkylphenol anesthetic substrates are widespread in number and distribution, similar to those of volatile general anesthetics, and that multi-target mechanisms likely underlie their pharmacology