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Anesthesiology:
doi: 10.1097/ALN.0b013e31818a379a
Perioperative Medicine

Sevoflurane Anesthesia Alters Exploratory and Anxiety-like Behavior in Mice Lacking the β2 Nicotinic Acetylcholine Receptor Subunit

Wiklund, Andreas M.D., Ph.D.*; Granon, Sylvie Ph.D.†; Cloëz-Tayarani, Isabelle Ph.D.‡; Faure, Philippe Ph.D.‡; le Sourd, Anne-Marie§; Sundman, Eva M.D., Ph.D.∥; Changeux, Jean-Pierre Ph.D.#; Eriksson, Lars I. M.D., Ph.D.**

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Abstract

Background: Preexisting cognitive impairment and advanced age are factors that increase the risk of developing postoperative cognitive dysfunction. Because anesthetic agents interfere with cholinergic transmission and as impairment of cholinergic function is associated with cognitive decline, the authors studied how the volatile anesthetic sevoflurane affects exploratory and anxiety-like behavior in young and aged animals with a genetically modified cholinergic system.
Methods: Young and aged wild-type and mutant mice lacking the β2 subunit of the nicotinic cholinergic receptor (β2KO) were anesthetized for 2 h with 2.6% sevoflurane in oxygen and compared with nonanesthetized controls. Locomotor activity and organization of movement in the open field model were assessed before and 24 h after anesthesia. Locomotor activity and anxiety-like behavior in the elevated plus maze were assessed 24 h after anesthesia. High- and low-affinity nicotinic receptor and cholinergic uptake site densities were evaluated in the hippocampus, amygdala, and forebrain regions using receptor autoradiography.
Results: Sevoflurane anesthesia significantly reduced locomotor activity, altered temporospatial organization of trajectories, and increased anxiety-like behavior in young β2KO mice, whereas no such changes were observed in young wild-type mice. Aged wild-type and β2KO mice displayed reactions that were similar, but not identical, to the reactions of young mice to sevoflurane anesthesia. However, behavioral changes were not associated with differences in nicotinic receptor or cholinergic uptake site densities.
Conclusion: In conclusion, sevoflurane anesthesia altered exploratory and anxiety-like behavior in mice lacking the β2 nicotinic acetylcholine receptor subunit.
CHOLINERGIC neurotransmission is involved in the orchestration of cognitive functions in the central nervous system,1,2 and alteration of cholinergic functions has been suggested to play an important role in cognitive deterioration in aging and neurodegenerative disorders such as Alzheimer disease.3,4 Moreover, pharmacologic modulation of nicotinic cholinergic functions in various psychiatric disorders can modify cognitive function and reduce symptoms.5–7
Regarding postoperative cognitive dysfunction, several risk factors, such as advanced age8 and preoperative cognitive impairment,9 in combination with general or regional anesthesia have been associated with an increased incidence.9,10 Although impaired cholinergic neurotransmission has been proposed to play a key role in postoperative cognitive dysfunction,11 the underlying mechanisms remain obscure.12
Volatile anesthetics such as sevoflurane have a high affinity to nicotinic acetylcholine receptors (nAChRs) and may thus interfere with cholinergic nicotinic neurotransmission.13–17 Furthermore, recent studies link exposure to volatile anesthetics to enhanced aggregation and toxicity of the Alzheimer disease–associated amyloid β protein.18,19
Mice lacking the β2 subunit of the nAChR (β2KO) have a preexisting cholinergic dysfunction and display a distinct behavioral phenotype.20–24 Consequently, β2KO mice have been proposed to serve as a suitable animal model for the study of cognitive deficits, particularly those influenced by nicotinic cholinergic transmission.22,25,26
The aim of this investigation was to study sevoflurane-induced alterations of exploratory and anxiety-like behavior in young and aged mice with preexisting nicotinic cholinergic dysfunction.
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Materials and Methods

Animals
Table 1
Table 1
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After approval by the Karolinska Institutet Ethical Committee on Animal Research (Stockholm, Sweden; Dnr N154/05), male wild-type C57BL/6JICO (WT) mice and male mutant knockout SOPF HO ACNB2 β2−/−2KO) mice were obtained from Charles Rivers Laboratories France (L'Arbresle Cedex, France). β2KO mice were backcrossed onto a C57BL/6 background for at least 19 generations. Young animals arrived to the animal facility at 10 weeks of age and were housed individually in cages 2 weeks before the start of the experiment. Aged mice (15–18 months) were group housed in cages in the animal facility from the age of 10 weeks until the time of the experiment. Animals were housed under standard conditions with food and water ad libitum and with a circadian light cycle of 12 h light–12 h dark in the housing room. All experiments were performed during the light cycle; between 10:00 am and 16:00 pm. Animal group characteristics are presented in table 1. At the end of the experiment, animals were killed with carbon dioxide. Brains were dissected and immediately frozen on dry ice. This study, including care of the animals involved, was conducted according to the official edict by the French Ministry of Agriculture (Paris, France) and the recommendations of the Declaration of Helsinki. Experiments were performed according to the European Community Council guidelines27 and in conformity to the guidelines in the Guide for the Care and Use of Laboratory Animals.28 Therefore, the experiments were conducted in an authorized laboratory and under supervision of authorized researchers (A.W. and S.G.).
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Anesthesia
Young mice were randomly assigned to control, sham, and anesthesia groups. On the day of anesthesia, control group mice remained in their cages. Mice in the sham groups were introduced into a clear plastic cylinder (Plexiglas®; Evonik Röhm GmbH, Darmstadt, Germany), 25 cm long and 7 cm in ID, in which they remained for 2 min, and were subsequently returned to their home cages. Mice in the anesthesia groups were introduced into the same plastic cylinder and remained there for 2 min, before administration of sevoflurane commenced. Mice were subsequently anesthetized for 2 h before being returned to their home cages. No significant behavioral differences were observed between the control and sham groups among young mice, which thus were merged into one single control group for each genotype. Hence, the old mice were randomly assigned to either control or anesthesia groups. Anesthesia was provided by administration of the volatile anesthetic sevoflurane (Sevorane®; Abbott France, Saint Remy sur Avre, France) via a calibrated vaporizer (Penlon Sigma Elite; Penlon Ltd., Abingdon, United Kingdom). Oxygen (100%) was fed through the vaporizer at a constant flow rate of 2 l/min, and the gas mixture was humidified before flushed into the plastic chamber. Sevoflurane concentration in the chamber was continuously measured (AION; Artema Medical AB, Stockholm, Sweden). During induction, the vaporizer was set to 8% for 30 s, and then to 5% for 3 min, and vaporizer settings were thereafter adjusted to maintain 2.6% sevoflurane in the inspired gas mixture during 2 h. The body temperature of anesthetized mice was monitored by a rectal probe (RET-3; Physitemp Instruments Inc., Clifton, NJ) connected to a thermometer (Kimo TK-2; Kimo, Montpon, France) and was maintained between 36° and 38° by the use of a heating lamp. The rectal probe was inserted after induction, as soon as the mice had lost the righting reflex. Respiratory rate was counted by observing chest movements every 15 min. After 2 h, sevoflurane administration was discontinued and mice were allowed to recover, breathing oxygen in the anesthesia chamber for 10 min. When moving spontaneously in the chamber, the mice were returned to their home cage for further recovery. Oxygen saturation was measured (Nonin 8500AV; Nonin Medical Inc., Plymouth, MN) in the hind limbs of two WT and two β2KO mice. Oxygen saturation remained above 95% throughout the anesthetic procedure.
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Behavioral Assessments
Spontaneous novelty exploration was assessed in a circular open field on two occasions, the first 24 h before anesthesia and the second 24 h after anesthesia. The open field (Manutan SA, Gonesse, France) was made of white opaque plastic material and measured 100 cm in diameter with 40-cm-high borders. Illumination was set to 110 lux in the center of the open field. Visual cues were placed on the walls of the room. Animals were originally placed in the center of the arena, and their trajectories were recorded during 30 min using an automated video tracking system (Videotrack; View-Point, Lyon, France). The speed at which the animal moved was used to break down the trajectory into navigation (speed > 11.8 cm/s), fast exploration (i.e., small movements with speed ranging from 6.8 to 11.8 cm/s) and slow exploration (i.e., very small movements at a speed below 6.8 cm/s), as previously described.23 An index of slow versus fast movements, denominated as the exploration index, was obtained by dividing time in slow exploration with time in navigation. Refined temporospatial analysis of the trajectories was performed using digitized video recordings taken at 25 frames/s. Trajectories within the open field were deconstructed into active (A) or inactive (I) periods, and peripheral (P) or central (C) positions. The center (C) was defined as a virtual area of 50 cm diameter, in the middle of the open field, and periphery (P) was the area outside of the center to the borders of the open field.
Active and inactive periods were defined by the instantaneous velocity of the mouse within the open field, averaged over time windows of 0.2 s. Each time frame was thus associated with two symbols, which when combined formed a four-symbol code (PI, CI, PA, and CA) describing the state of the mouse at each time point of the experiment. Each individual experiment was then transformed into a sequence of 45,000 state symbols (30 min at 25 frames/s), which was subsequently reduced to a matrix of state transitions. This conditional matrix lists the probability of entering one state from another. The method has previously been described in detail.24,29 The open field apparatus was thoroughly wiped with a moist cloth between every animal, to smear out any olfactory cues left by previous mice.
Anxiety levels were assessed using an elevated plus maze, consisting of a cross-shaped platform with two arms without walls (open arms) and two arms with walls (closed arms), elevated 60 cm above the ground. The elevated plus maze provides independent measures of anxiety-like behavior (time spent on open arms) and activity (number of transitions between closed arms).30 Light intensity in the room was set to 300 lux, and the animal was gently placed in the middle of the platform. Using a video camera mounted in the ceiling, mice's reactions to anxiogenic apparatus were stored on video tapes for off-line analysis. Time spent on the open arms and time spent at the end of the open arms was recorded, as well as the number of transitions between the walled arms. Each mouse remained in the plus maze for 10 min, and the experiment was performed only once, after the second open field test, 24 h after anesthesia.
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Receptor Density
Radioligand binding of high-affinity nAChRs was performed on coronal brain sections (20 μm, cut in cryostat at −20°C) incubated at room temperature with 200 pm [125I]-epibatidine (PerkinElmer Inc., Waltham, MA; specific activity 2,200 Ci/mmol) in 50 mm Tris (pH 7.4) for 60 min. After incubation sections were rinsed 2 × 5 min in the same buffer and briefly in distilled water. Sections were exposed on Kodak Biomax® MS films (Eastman Kodak Company, Rochester, NY) for 24 h. Nonspecific binding was measured in the presence of 10 μm nicotine and was not distinguishable from film background. For labeling of low-affinity nAChRs, [125I]-α-bungarotoxin binding was performed. Brain sections were preincubated with 50 mm Tris (pH 7.4) with 0.1% BSA for 30 min, and then incubated with 2.5 nm [125I]-α-bungarotoxin (PerkinElmer Inc.; specific activity 238 Ci/mmol) in Tris 50 mm (pH 7.4) with 0.1% BSA for 2 h. Nonspecific binding was assessed in presence of 1 mm nonlabeled nicotine. After incubation, sections were rinsed 6 × 30 min in 50 mm Tris (pH 7.4) at 4°C and briefly in distilled water. Sections were then exposed on Kodak Biomax® MS films for 8 days. For labeling of high-affinity choline uptake sites, [3H]-hemicholinium binding was performed. Brain sections (20 μm) were incubated with 8 nm [3H]-hemicholinium (PerkinElmer Inc.; specific activity 140 Ci/mmol) at 4°C for 60 min in 50 mm Tris (pH 7.4) containing 300 mm NaCl. Nonspecific binding was performed in presence of 100 μm nonlabeled hemicholinium-3. After incubation, sections were rinsed 6 × 1 min each in ice-cold 50 mm Tris (pH 7.4) and briefly in distilled water. Sections were then exposed on Kodak Biomax® MS films for 21 days. Optical density in specific brain regions was determined for each radioactive ligand by using the public domain ImageJ program†† and appropriate radioactive standards. All autoradiographic data sets were expressed in arbitrary units ± interquartile range.
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Statistics
Statistical analysis was performed using Statistica 7.1 software (StatSoft Inc., Tulsa, OK). For data obtained in the open field, we used Generalized Linear Models with baseline values as covariate for each dependent variable (distance, exploration index, %PA-CA, #PA-CA-PA). Data were normally distributed according to Kolmogorov–Smirnov tests. Planned comparisons were performed to determine significant differences between groups. For the results in the elevated plus maze test, factorial analysis of variance was used to evaluate the effect of genotype (WT vs. β2KO), group (control vs. sham vs. anesthesia), and age (young vs. aged). One-way analysis of variance was used for comparisons between groups, recovery time, body weight, and respiratory rate. Post hoc analyses were performed, when appropriate, by Tukey honestly significant difference test. Autoradiographic data were analyzed using the Mann–Whitney U test. Normally distributed data are plotted as mean ± SEM. Results from nonparametric tests are plotted as median ± interquartile range.
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Results

Effects on Locomotor Activity and Temporospatial Organization of Trajectories
Exposure to sevoflurane for 2 h caused significant alteration in the locomotor activity 24 h after anesthesia in both young and aged mice lacking the β2-containing nicotinic receptor subunit. In contrast, young and aged WT mice exposed to sevoflurane did not display changes in locomotor activity after 24 h, when compared with their respective control group.
Fig. 1
Fig. 1
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In young β2KO mice, spontaneous locomotor activity decreased both in the open field (P < 0.01; fig. 1A) and in the plus maze (P < 0.05), whereas in the latter, it was observed as a reduction in the number of transitions between the closed arms in the apparatus (fig. 1B). Anesthesia provoked alterations in the characteristics of exploration in young β2KO mice and caused alterations in three of the patterns used to define temporospatial organization of trajectories in the open field (fig. 1C). As illustrated in figure 1D, anesthesia increased the amount of slow velocity exploration (explo index) in young β2KO mice compared with controls (P < 0.01). Second, the probability to venture into the center of the open field (%PA-CA) was reduced (P < 0.05), and third, the total number of large movements across the center (#PA-CA-PA) was reduced (P < 0.05) in young anesthetized β2KO mice compared with controls.
Fig. 2
Fig. 2
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In aged β2KO mice, the level of locomotor activity in the open field was also reduced by anesthesia (P < 0.05; fig. 2A). However, in the plus maze test, we were unable to detect any difference in activity levels between the different groups of aged mice (aged WT control mean = 22 [95% confidence interval (CI), 15–29]; aged WT anesthesia mean = 20 [95% CI, 15–25]; aged KO control mean = 19 [95% CI, 15–24]; aged KO anesthesia mean = 18 [95% CI, 14–24]; fig. 2B).
Nevertheless, in aged β2KO mice, the amount of slow velocity exploration (explo index) (P < 0.05) and the probability to venture into the center (%PA-CA) (P < 0.05) were changed 24 h after anesthesia compared with controls (fig. 2C).
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Effects on Anxiety-like Behavior
Fig. 3
Fig. 3
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Anesthesia increased anxiety-like behavior in young β2KO mice, as indicated by a reduction in the time venturing out on the open arms of the plus maze (P < 0.05; fig. 3A). In contrast, we were unable to detect effects on anxiety-like behavior induced by sevoflurane anesthesia in young WT (young WT control mean = 78 [95% CI, 65–91]; young WT anesthesia mean = 82 [95% CI, 62–102]; fig. 3A). We did not detect any significant differences in anxiety-like behavior in aged WT mice or in aged β2KO mice (aged WT control mean = 71 [95% CI, 25–116]; aged WT anesthesia mean = 92 [95% CI, 52–132]; aged KO control mean = 62 [95% CI, 43–81]; aged KO anesthesia mean = 45 [95% CI, 31–58]; fig. 3B).
Time spent on the open arms of the elevated plus maze did not differ significantly between young or aged WT and β2KO control groups, indicating that neither age nor preexisting nicotinic cholinergic dysfunction per se had any effect on anxiety levels.
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Effects of Age and Repeated Measurements and Genotype on Locomotor Activity
Fig. 4
Fig. 4
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As opposed to WT, there was a significant effect of age in the β2KO mice, as illustrated by a reduction of locomotor activity in aged β2KO mice compared with young β2KO mice (P < 0.001; fig. 4A). This was confirmed in the plus maze test, where aged β2KO mice displayed lower activity levels than did young β2KO mice (P < 0.001; fig. 4B). We did not detect any significant effect of age on baseline activity levels in WT mice (young WT control mean = 197 [95% CI, 185–210]; aged WT control mean = 188 [95% CI, 162–214]; figs. 4A and B).
Repeating the open field test revealed an effect of habituation, i.e., locomotor distance during the second session was reduced as compared with the first session, in young WT (P < 0.01), young β2KO (P < 0.05), aged WT (P < 0.01), and aged β2KO (P < 0.01) mice (figs. 4C and D).
We observed a significant effect of genotype on baseline locomotor activity in young mice (P < 0.01), whereas this was not found in aged animals (aged WT control mean = 197 [95% CI, 185–210]; aged KO control mean = 200 [95% CI, 181–221]). That is, young β2KO mice had higher locomotor activity in the open field (fig. 4A) and in the plus maze (fig. 4B) compared with young WT mice.
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Receptor Density
Fig. 5
Fig. 5
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Anesthesia was not associated with changes in nicotinic receptor density (fig. 5A) either in [125I]-epibatidine–labeled, high-affinity receptors (fig. 5B) or in [125I]-α-bungarotoxin–labeled, low-affinity receptors (fig. 5C). Nor was any effect of anesthesia observed in [3H]-hemicholinium–labeled, high-affinity choline uptake sites (fig. 5D).
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Anesthesia
The recovery time, expressed as time to return of the righting reflex, was significantly longer (P < 0.05) in young β2KO mice (178 ± 130 s) compared with young WT mice (78 ± 78 s). Among elderly mice, no significant difference in recovery time was observed between the genotypes. During anesthesia, no differences regarding animal body temperature, sevoflurane concentration, or respiratory rate were observed between genotypes or age groups (table 1).
Two young β2KO mice and one young WT mouse were excluded because of behavioral abnormalities before experiments. Among old mice, one β2KO mouse was excluded because of unexpected disturbing sounds in the animal facility during experiments.
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Discussion

Our study is the first to demonstrate that cognitive processes are affected by a single sevoflurane anesthesia in mutant mice lacking the β2 subunit–containing high-affinity nAChR, whereas these processes remain unaffected in WT mice.
The β2-containing nAChR is the most widespread cholinergic receptor in the central nervous system and is implicated in modulation of cognitive function.1 β2KO mice have been proposed as a suitable animal model for studies related to human behavior pathology, such as attention deficit hyperactivity disorder, physiologic ageing, nicotine addiction, and Alzheimer disease.22,24,26 In this context, β2KO mice have undergone extensive behavioral testing and have been used for the study of pharmacologically induced behavioral alterations.22–24,26 The β2KO mice used in our experiment carried the gene deletion since fertilization. It is therefore possible that compensatory phenomena in the expression of various nAChR subunit genes together with possible reorganization of neuronal circuits might have taken place. However, β2 subunit gene re-expression experiments have shown that the neuronal, physiologic, and behavioral phenotypes are not caused by the actual absence of β2-containing nAChRs, but rather by their deficit in defined circuits involving, in particular, dopaminergic neurons in the ventral tegmental area.24
We wanted to study the effects of anesthesia also in aged WT and β2KO mice because, in humans, the risk of developing postoperative cognitive dysfunction increases with age.8 Our assumption before the experiment was that aging would further accentuate the characteristic hyperactive phenotype of β2KO mice. Instead, hyperactivity became attenuated with increasing age. It has previously been demonstrated that β2KO mice display accelerated neurodegeneration upon aging, unrelated to the amount of other cholinergic receptor subtypes.22 We therefore speculate that age-dependent neurodegenerative processes counteract the hyperactive phenotype in mutant mice, making their exploratory and anxiety-like behavior more similar to that of their WT counterparts.
Because all of the observed behavioral changes after sevoflurane anesthesia have been restricted to β2KO mice, normally functioning cholinergic neurotransmission seems to play a protective role on cognitive function after anesthesia, as illustrated by the lack of behavioral changes after sevoflurane anesthesia in WT mice. Alternatively, the lack of β2-containing nAChRs might facilitate or permit sevoflurane-induced disturbances in neurotransmission.
One distinct characteristic phenotype in β2KO mice is increased and disorganized locomotion in the open field.23,24,29 In our study, exposure to sevoflurane attenuated the hyperactive phenotype of young β2KO mice, which seemingly restored their normal behavior. Not only did sevoflurane anesthesia reduce their overall exploratory activity to levels similar to those of WT mice, but it also affected some patterns of sequential organization of trajectories, robustly modified in β2KO animals as compared with WT mice. A similar, although not necessarily identical, compensatory process has previously been proposed in β2KO mice upon chronic nicotine exposure and was interpreted as resulting from the enhancement of an opposing process mobilizing α7 nAChR–mediated cholinergic transmission.29
On the surface, it might seem paradoxical that an agonist of the nicotinic system and a nonselective antagonist, acting also on several other receptor systems, would induce similar behavioral changes. However, nicotinic agonists primarily act indirectly via nAChRs located on or near nerve terminals where they mediate calcium-dependent release of neurotransmitters including dopamine, norepinephrine, glutamate, γ-aminobutyric acid, and acetylcholine.2 Furthermore, nicotine administration has been shown to increase or decrease locomotor activity depending on dose, species, and strain.31 A nonselective antagonist, such as sevoflurane, can act by directly suppressing the same systems,13 and we therefore consider it possible for a nonselective antagonist to cause behavioral changes similar to those of a nicotinic agonist.
However, at this stage, and still as a working hypothesis, we suggest that the long-term effect of sevoflurane anesthesia may be due to action on the balance between nicotinic subtypes in cholinergic neurotransmission. Such intrinsic cholinergic balance is important to the proper functioning of the entire nervous system, and the absence of the β2 subunit in β2KO mice has created a cholinergic balance different from that of WT mice.29 In many aspects, the β2KO mice compensate for this aberrant receptor content, but nevertheless display a distinct behavioral phenotype.20,21,23 Others have proposed that the role of β2-containing nAChRs in the modulation of cognitive processes might be compensated in the normal adult brain, and that the contribution of β2-containing nAChRs would become apparent only in the presence of other deficits22 or in challenging cognitive situations.20,21,23 We suggest that sevoflurane anesthesia elicits changes in neurotransmission that are unveiled only in β2KO mice already having a preexisting nicotinic cholinergic dysfunction. That is, sevoflurane might possibly act, among other mechanisms, as a modulator of α7 nicotinic receptor transmission, as has previously been suggested for isoflurane.15 On the other hand, mice with normal nicotinic cholinergic neurotransmission seem to be able to compensate for the effects of sevoflurane anesthesia and therefore do not display detectable behavioral changes in our model.
Interestingly, simultaneously to the reduced activity observed in anesthetized β2KO mice, an increase in anxiety-like behavior was found. Although β2KO mice show higher levels of circulating stress hormones, they display normal anxiety levels.22,23 The current study shows that exposure to sevoflurane anesthesia increases anxiety-like behavior selectively in β2KO mice but not in WT mice. One plausible hypothesis is that the observed increase in anxiety-like behavior seen in β2KO mice after anesthesia is due to sevoflurane-induced changes in nicotinic cholinergic transmission of neuronal circuits regulating anxiety. Indeed, nicotinic cholinergic receptors modulate γ-aminobutyric acid–mediated interneurons in the hippocampus and nucleus accumbens,32 and in dorsal hippocampal regions, anxiety is modulated by interaction between serotonergic and cholinergic neurons.33 Cholinergic tone in these regions mediates anxiolytic effects,34 and both α7 and α4 β2 nAChRs are proposed to participate in the maintenance of this balance.35 The observed increase in anxiety-like behavior seen in β2KO mice after anesthesia may be due to sevoflurane-induced changes in α7 nAChR–mediated cholinergic transmission and/or muscarinic receptors of neuronal circuits regulating anxiety. Such hypothesis would require further pharmacologic manipulation to be tested.
Exposure to sevoflurane or desflurane for 3 h can induce long-lasting alterations in protein level expressions.36 Such changes are proposed to contribute both to short- and long-term effects such as memory alteration and neurocognitive reactions.37 In our study, we did not observe any changes in density of either β2-containing nAChRs, α7-containing nAChRs, or choline uptake sites. Whereas the direct effects of volatile anesthetics on nAChRs are well described,38–40 the downstream intracellular effects are more obscure. We propose that the behavioral effects noted in our study are most likely due to sevoflurane-induced changes in signaling pathways involving this receptor subtype.41,42
Anesthetic sensitivity of β2KO mice has been shown to be similar to that of WT mice.43 In our study, we maintained constant sevoflurane concentration at 2.6%, corresponding to 1 minimal alveolar concentration in mice,44 which provided adequate anesthesia without severe respiratory depression. We also maintained normal animal body temperature during the 2-h anesthesia. Respiratory rate during anesthesia was not different between the genotypes, also indicating similar levels of anesthetic depth. We observed that after anesthesia, the time to return of the righting reflex was significantly longer in young β2KO mice. However, young β2KO animals weighed slightly more than WT mice did, which could account for some of the prolonged recovery time, but there is still a possibility that β2-containing nAChRs might be involved in the recovery after anesthesia. It also suggests a role for nAChR agonists for enhanced recovery after general anesthesia. Because behavioral testing was performed 24 h after recovery and the difference in recovery time was measured in seconds, we consider it unlikely that a slower recovery from anesthesia would explain the behavioral differences noted.
We chose to evaluate locomotor activity and anxiety-like behavior 24 h after anesthesia, to ascertain that the effects were not due to lingering concentrations of sevoflurane. Hence, behavioral changes observed by this time could not be attributed to an acute sevoflurane effect but were regarded as long-term effects of anesthesia. Furthermore, to address the effects of anesthesia per se, we avoided all surgical manipulation or painful stimuli to the animals during anesthesia. The observed behavioral effects are thus likely to be due solely to interaction between sevoflurane anesthesia and the particular β2KO phenotype, because WT animals did not display behavioral changes related to sevoflurane anesthesia exposure. Behavioral effects of repeated open field testing in young and aged WT mice is a phenomenon previously described.45 By comparing anesthetized mice with control mice, we were able to control for this effect.
In conclusion, sevoflurane anesthesia altered exploratory and anxiety-like behavior in mice lacking the β2 nAChR subunit. The duration of this effect, its cellular origin, and possible modulation by pharmacologic intervention remain to be determined. The current behavioral results suggest that brain circuits involved in organization of locomotor behavior or anxiety should be further investigated.
The authors thank Per Lindestam, M.Sc. Phys. (Artema Medical AB, Stockholm, Sweden), for lending the gas analyzer and Anne Cormier, Ph.D. (Research Assistant, Département de Neuroscience, Institut Pasteur, Paris, France), for excellent technical assistance.
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References

1. Changeux J-P, Edelstein S: Chapter 12, Nicotinic Acetylcholine Receptors: From Molecular Biology to Cognition. New York, Odile Jacob, 2005, pp 192–213

2. Hogg RC, Raggenbass M, Bertrand D: Nicotinic acetylcholine receptors: From structure to brain function. Rev Physiol Biochem Pharmacol 2003; 147:1–46

3. Bohnen NI, Kaufer DI, Ivanco LS, Lopresti B, Koeppe RA, Davis JG, Mathis CA, Moore RY, DeKosky ST: Cortical cholinergic function is more severely affected in parkinsonian dementia than in Alzheimer disease: An in vivo positron emission tomographic study. Arch Neurol 2003; 60:1745–8

4. Nordberg A: Emerging biology of the cholinergic system across the spectrum of Alzheimer's disease. Int Psychogeriatr 2006; 18(suppl 1):S3–16

5. Araki H, Suemaru K, Gomita Y: Neuronal nicotinic receptor and psychiatric disorders: Functional and behavioral effects of nicotine. Jpn J Pharmacol 2002; 88:133–8

6. Poirier MF, Canceil O, Bayle F, Millet B, Bourdel MC, Moatti C, Olie JP, Attar-Levy D: Prevalence of smoking in psychiatric patients. Prog Neuropsychopharmacol Biol Psychiatry 2002; 26:529–37

7. Newhouse P, Singh A, Potter A: Nicotine and nicotinic receptor involvement in neuropsychiatric disorders. Curr Top Med Chem 2004; 4:267–82

8. Canet J, Raeder J, Rasmussen LS, Enlund M, Kuipers HM, Hanning CD, Jolles J, Korttila K, Siersma VD, Dodds C, Abildstrom H, Sneyd JR, Vila P, Johnson T, Munoz Corsini L, Silverstein JH, Nielsen IK, Moller JT: Cognitive dysfunction after minor surgery in the elderly. Acta Anaesthesiol Scand 2003; 47:1204–10

9. Ancelin ML, de Roquefeuil G, Ledesert B, Bonnel F, Cheminal JC, Ritchie K: Exposure to anaesthetic agents, cognitive functioning and depressive symptomatology in the elderly. Br J Psychiatry 2001; 178:360–6

10. Rasmussen LS, Johnson T, Kuipers HM, Kristensen D, Siersma VD, Vila P, Jolles J, Papaioannou A, Abildstrom H, Silverstein JH, Bonal JA, Raeder J, Nielsen IK, Korttila K, Munoz L, Dodds C, Hanning CD, Moller JT: Does anaesthesia cause postoperative cognitive dysfunction? A randomised study of regional versus general anaesthesia in 438 elderly patients. Acta Anaesthesiol Scand 2003; 47:260–6

11. Pratico C, Quattrone D, Lucanto T, Amato A, Penna O, Roscitano C, Fodale V: Drugs of anesthesia acting on central cholinergic system may cause post-operative cognitive dysfunction and delirium. Med Hypotheses 2005; 65:972–82

12. Newman S, Stygall J, Hirani S, Shaefi S, Maze M: Postoperative cognitive dysfunction after noncardiac surgery: A systematic review. Anesthesiology 2007; 106:572–90

13. Franks NP, Lieb WR: Molecular and cellular mechanisms of general anaesthesia. Nature 1994; 367:607–14

14. Violet JM, Downie DL, Nakisa RC, Lieb WR, Franks NP: Differential sensitivities of mammalian neuronal and muscle nicotinic acetylcholine receptors to general anesthetics. Anesthesiology 1997; 86:866–74

15. Flood P, Coates KM: Sensitivity of the alpha7 nicotinic acetylcholine receptor to isoflurane may depend on receptor inactivation. Anesth Analg 2002; 95:83–7

16. Tassonyi E, Charpantier E, Muller D, Dumont L, Bertrand D: The role of nicotinic acetylcholine receptors in the mechanisms of anesthesia. Brain Res Bull 2002; 57:133–50

17. Chiara DC, Dangott LJ, Eckenhoff RG, Cohen JB: Identification of nicotinic acetylcholine receptor amino acids photolabeled by the volatile anesthetic halothane. Biochemistry 2003; 42:13457–67

18. Eckenhoff RG, Johansson JS, Wei H, Carnini A, Kang B, Wei W, Pidikiti R, Keller JM, Eckenhoff MF: Inhaled anesthetic enhancement of amyloid-beta oligomerization and cytotoxicity. Anesthesiology 2004; 101:703–9

19. Xie Z, Dong Y, Maeda U, Alfille P, Culley DJ, Crosby G, Tanzi RE: The common inhalation anesthetic isoflurane induces apoptosis and increases amyloid beta protein levels. Anesthesiology 2006; 104:988–94

20. Picciotto MR, Zoli M, Lena C, Bessis A, Lallemand Y, Le Novere N, Vincent P, Pich EM, Brulet P, Changeux JP: Abnormal avoidance learning in mice lacking functional high-affinity nicotine receptor in the brain. Nature 1995; 374:65–7

21. Picciotto MR, Zoli M, Zachariou V, Changeux JP: Contribution of nicotinic acetylcholine receptors containing the beta 2-subunit to the behavioural effects of nicotine. Biochem Soc Trans 1997; 25:824–9

22. Zoli M, Picciotto MR, Ferrari R, Cocchi D, Changeux JP: Increased neurodegeneration during ageing in mice lacking high-affinity nicotine receptors. Embo J 1999; 18:1235–44

23. Granon S, Faure P, Changeux JP: Executive and social behaviors under nicotinic receptor regulation. Proc Natl Acad Sci U S A 2003; 100:9596–601

24. Maskos U, Molles BE, Pons S, Besson M, Guiard BP, Guilloux JP, Evrard A, Cazala P, Cormier A, Mameli-Engvall M, Dufour N, Cloez-Tayarani I, Bemelmans AP, Mallet J, Gardier AM, David V, Faure P, Granon S, Changeux JP: Nicotine reinforcement and cognition restored by targeted expression of nicotinic receptors. Nature 2005; 436:103–7

25. Lena C, Changeux JP: The role of beta 2-subunit-containing nicotinic acetylcholine receptors in the brain explored with a mutant mouse. Ann N Y Acad Sci 1999; 868:611–6

26. Granon S, Changeux JP: Attention-deficit/hyperactivity disorder: A plausible mouse model? Acta Paediatr 2006; 95:645–9

27. Dimas: Commission recommendation of 18 June 2007 on Guidelines for the Accommodation and Care of Animals Used for Experimental and Other Scientific Purposes (2007/526/EC). Official J Eur Union 2007:50

28. Institute of Laboratory Animal Research, Commission on Life Sciences, National Research Council: Chapters 2 and 3, Guide for the Care and Use of Laboratory Animals. Washington, DC, National Academies Press, 1996, pp 21–70

29. Besson M, Granon S, Mameli-Engvall M, Cloez-Tayarani I, Maubourguet N, Cormier A, Cazala P, David V, Changeux JP, Faure P: Long-term effects of chronic nicotine exposure on brain nicotinic receptors. Proc Natl Acad Sci U S A 2007; 104:8155–60

30. File SE: Factors controlling measures of anxiety and responses to novelty in the mouse. Behav Brain Res 2001; 125:151–7

31. Grady S, Salminen O, Laverty DC, Whiteaker P, McIntosh JM, Collins AC, Marks MJ: The subtypes of nicotinic acetylcholine receptors on dopaminergic terminals of mouse striatum. Biochem Pharmacol 2007; 74:1235–46

32. Potier B, Jouvenceau A, Epelbaum J, Dutar P: Age-related alterations of GABAergic input to CA1 pyramidal neurons and its control by nicotinic acetylcholine receptors in rat hippocampus. Neuroscience 2006; 142:187–201

33. Picciotto MR, Brunzell DH, Caldarone BJ: Effect of nicotine and nicotinic receptors on anxiety and depression. Neuroreport 2002; 13:1097–106

34. File SE, Kenny PJ, Cheeta S: The role of the dorsal hippocampal serotonergic and cholinergic systems in the modulation of anxiety. Pharmacol Biochem Behav 2000; 66:65–72

35. Tucci S, Genn RF, Marco E, File SE: Do different mechanisms underlie two anxiogenic effects of systemic nicotine? Behav Pharmacol 2003; 14:323–9

36. Futterer CD, Maurer MH, Schmitt A, Feldmann RE Jr, Kuschinsky W, Waschke KF: Alterations in rat brain proteins after desflurane anesthesia. Anesthesiology 2004; 100:302–8

37. Kalenka A, Hinkelbein J, Feldmann RE Jr, Kuschinsky W, Waschke KF, Maurer MH: The effects of sevoflurane anesthesia on rat brain proteins: A proteomic time-course analysis. Anesth Analg 2007; 104:1129–35

38. Flood P, Ramirez-Latorre J, Role L: Alpha 4 beta 2 neuronal nicotinic acetylcholine receptors in the central nervous system are inhibited by isoflurane and propofol, but alpha 7-type nicotinic acetylcholine receptors are unaffected. Anesthesiology 1997; 86:859–65

39. Flood P, Role LW: Neuronal nicotinic acetylcholine receptor modulation by general anesthetics. Toxicol Lett 1998; 100–101:149–53

40. Rada EM, Tharakan EC, Flood P: Volatile anesthetics reduce agonist affinity at nicotinic acetylcholine receptors in the brain. Anesth Analg 2003; 96:108–11

41. Zaugg M, Schaub MC: Signaling and cellular mechanisms in cardiac protection by ischemic and pharmacological preconditioning. J Muscle Res Cell Motil 2003; 24:219–49

42. Gomez RS, Guatimosim C, Gomez MV: Mechanism of action of volatile anesthetics: Role of protein kinase C. Cell Mol Neurobiol 2003; 23:877–85

43. Flood P, Sonner JM, Gong D, Coates KM: Heteromeric nicotinic inhibition by isoflurane does not mediate MAC or loss of righting reflex. Anesthesiology 2002; 97:902–5

44. Puig NR, Ferrero P, Bay ML, Hidalgo G, Valenti J, Amerio N, Elena G: Effects of sevoflurane general anesthesia: Immunological studies in mice. Int Immunopharmacol 2002; 2:95–104

45. Ammassari-Teule M, Fagioli S, Rossi-Arnaud C: Radial maze performance and open-field behaviours in aged C57BL/6 mice: Further evidence for preserved cognitive abilities during senescence. Physiol Behav 1994; 55:341–5

†† Developed at the US National Institutes of Health and freely available at: http://rsb.info.nih.gov/nih-image/. Accessed June 16, 2008. Cited Here...

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NeuroReport
Object memory in young and aged mice after sevoflurane anaesthesia
Wiklund, A; Granon, S; Faure, P; Sundman, E; Changeux, J; Eriksson, LI
NeuroReport, 20(16): 1419-1423.
10.1097/WNR.0b013e328330cd2b
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