Repeated brief isoflurane anesthesia during early postnatal development produces negligible changes on adult behavior in male mice

Behavioral Voluntary and Social Bioassays Enabling Identification of Complex and Sex-Dependent Pain-(-Related) Phenotypes in Rats with Bone Cancer

Cancer-induced bone pain (CIBP) is a common and devastating symptom with limited treatment options in patients, significantly affecting their quality of life. The use of rodent models is the most common approach to uncovering the mechanisms underlying CIBP; however, the translation of results to the clinic may be hindered because the assessment of pain-related behavior is often based exclusively on reflexive-based methods, which are only partially indicative of relevant pain in patients. To improve the accuracy and strength of the preclinical, experimental model of CIBP in rodents, we used a battery of multimodal behavioral tests that were also aimed at identifying rodent-specific behavioral components by using a home-cage monitoring assay (HCM). Rats of all sexes received an injection with either heat-deactivated (sham-group) or potent mammary gland carcinoma Walker 256 cells into the tibia. By integrating multimodal datasets, we assessed pain-related behavioral trajectories of the CIBP-phenotype, including evoked and non-evoked based assays and HCM. Using principal component analysis (PCA), we discovered sex-specific differences in establishing the CIBP-phenotype, which occurred earlier (and differently) in males. Additionally, HCM phenotyping revealed the occurrence of sensory-affective states manifested by mechanical hypersensitivity in sham when housed with a tumor-bearing cagemate (CIBP) of the same sex. This multimodal battery allows for an in-depth characterization of the CIBP-phenotype under social aspects in rats. The detailed, sex-specific, and rat-specific social phenotyping of CIBP enabled by PCA provides the basis for mechanism-driven studies to ensure robustness and generalizability of results and provide information for targeted drug development in the future.

Consequences of General Anesthesia in Infancy on Behavior and Brain Structure

BACKGROUND

One in 7 children will need general anesthesia (GA) before the age of 3. Brain toxicity of anesthetics is controversial. Our objective was to clarify whether exposure of GA to the developing brain could lead to lasting behavioral and structural brain changes.

METHODS

A first study was performed in mice. The behaviors (fear conditioning, Y-maze, and actimetry) and brain anatomy (high-resolution magnetic resonance imaging) of 6- to 8-week-old Swiss mice exposed or not exposed to GA from 4 to 10 days old were evaluated. A second study was a complementary analysis from the preexisting APprentissages EXécutifs et cerveau chez les enfants d'âge scolaire (APEX) cohort to assess the replicability of our data in humans. The behaviors (behavior rating inventory of executive function, emotional control, and working memory score, Backward Digit Span, and Raven 36) and brain anatomy (high-resolution magnetic resonance imaging) were compared in 102 children 9 to 10 years of age exposed or not exposed to a single GA (surgery) during infancy.

RESULTS

The animal study revealed chronic exacerbated fear behavior in the adult mice (95% confidence interval [CI], 4-80; P = .03) exposed to postnatal GA; this was associated with an 11% (95% CI, 7.5-14.5) reduction of the periaqueductal gray matter (P = .046). The study in humans suggested lower emotional control (95% CI, 0.33-9.10; P = .06) and a 6.1% (95% CI, 4.3-7.8) reduction in the posterior part of the right inferior frontal gyrus (P = .019) in the children who had been exposed to a single GA procedure.

CONCLUSIONS

The preclinical and clinical findings of these independent studies suggest lasting effects of early life exposure to anesthetics on later emotional control behaviors and brain structures.

Neonatal Isoflurane Exposure in Rats Impairs Short-Term Memory, Cell Viability, and Glutamate Uptake in Slices of the Frontal Cerebral Cortex, But Not the Hippocampus, in Adulthood

Neonatal exposure to general anesthetics has been associated with neurotoxicity and morphologic changes in the developing brain. Isoflurane is a volatile anesthetic widely used in pediatric patients to induce general anesthesia, analgesia, and perioperative sedation. In the present study, we investigated the effects of a single neonatal isoflurane (3% in oxygen, 2 h) exposure in rats at postnatal day (PND) 7, in short-term (24 h - PND8) and long-term (adulthood) protocols. In PND8, ex vivo analysis of hippocampal and frontal cortex slices evaluated cell viability and susceptibility to in vitro glutamate challenge. In adult rats, behavioral parameters related to anxiety-like behavior, short-term memory, and locomotor activity (PND60-62) and ex vivo analysis of cell viability, membrane permeability, glutamate uptake, and susceptibility to in vitro glutamate challenge in hippocampal and cortical slices from PND65. A single isoflurane (3%, 2 h) exposure at PND7 did not acutely alter cell viability in cortical and hippocampal slices of infant rats (PND8) per se and did not alter slice susceptibility to in vitro glutamate challenge. In rat's adulthood, behavioral analysis revealed that the neonatal isoflurane exposure did not alter anxiety-like behavior and locomotor activity (open field and rotarod tests). However, isoflurane exposure impaired short-term memory evaluated in the novel object recognition task. Ex vivo analysis of brain slices showed isoflurane neonatal exposure selectively decreased cell viability and glutamate uptake in cortical slices, but it did not alter hippocampal slice viability or glutamate uptake (PND65). Isoflurane exposure did not alter in vitro glutamate-induced neurotoxicity to slices, and isoflurane exposure caused no significant long-term damage to cell membranes in hippocampal or cortical slices. These findings indicate that a single neonatal isoflurane exposure did not promote acute damage; however, it reduced cortical, but not hippocampal, slice viability and glutamate uptake in the adulthood. Additionally, behavioral analysis showed neonatal isoflurane exposure induces short-term recognition memory impairment, consolidating that neonatal exposure to volatile anesthetics may lead to behavioral impairment in the adulthood, although it may damage brain regions differentially.

Sevoflurane-Induced Neurotoxicity in the Developing Hippocampus via HIPK2/AKT/mTOR Signaling

Sevoflurane (Sev) is a widely used inhalational anesthetic for general anesthesia in children. Previous studies have confirmed that multiple exposures to inhaled anesthetic can induce long-term neurotoxicity in newborn mice. However, the underlying mechanisms remain elusive. In this study, we investigated the role of homeodomain interacting protein kinase 2 (HIPK2), a stress activating kinase involved in neural survival and synaptic plasticity, and its underlying mechanism in sevoflurane-induced neurotoxicity. Empirical study showed that neuronal apoptosis was elevated after exposure to sevoflurane. Meanwhile, up-regulation of HIPK2 and AKT/mTOR signaling was observed in primary hippocampal neurons and hippocampus in mice upon anesthetic exposure. A64, antagonist of HIPK2, could significantly reduce increased apoptosis and activation of AKT/mTOR induced by sevoflurane. AKT antagonist MK2206 partially alleviated neuronal apoptosis without affecting the expression of HIPK2. Experimental results demonstrated a crucial role of HIPK2/AKT/mTOR signaling in neurotoxicity of sevoflurane. Thus, HIPK2/AKT/mTOR signaling can serve as a potential target for the protection of inhalation anesthesia-induced cytotoxicity in the future.

NLRP3 deficiency-induced hippocampal dysfunction and anxiety-like behavior in mice

Neuroinflammation has been classified as a trigger of behavioral alterations and cognitive impairments in many neurological conditions, including Alzheimer's disease, major depression, anxiety and others. Regardless of the cause of neuroinflammation, key molecules, which sense neuropathological conditions, are intracellular multiprotein signaling inflammasomes. Increasing evidence shows that the inflammatory response, mediated by activated nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasomes, is associated with the onset and progression of a wide range of diseases of the CNS. However, whether the NLRP3 inflammasome in the CNS is involved in the learning, development of anxiety and adult neurogenesis remains elusive. Therefore, the present study was designed to assess NLRP3 inflammasome contribution in anxiety and reveal its potential involvement in the experimental acquisition of fear responses and hippocampal neurogenesis. Behavioral, immunohistochemical and electrophysiological alterations were measured to evaluate role of neuroinflammation in the limbic system of mice. In this study, we describe interrelated neurophysiological mechanisms, which culminate in absence of NLRP3 inflammasome in young 4 months mice. These include the following: anxious behavior and deterioration in learning and memory of fear conditioning; impairment of adult neurogenesis; reduction and altered morphology of astrocytes in the brain; hyperexcitability in basolateral amygdala (BLA); impaired activation in axons of pyramidal cells of CA1 hippocampal zone in NLRP3 KO mice particularly via the Schaffer collateral pathway; and impaired synaptic transduction in pyramidal cells mediated by an embarrassment of neurotransmitter release from presynaptic site in CA3 hippocampal zone. The present study has demonstrated the novel findings that basal level of NLRP3 inflammasome in the brain of young mice is required for conditioning-induced plasticity in the ventral hippocampus and the basolateral amygdala. The deletion of NLRP3 impair synaptic transduction and caused anxiety-like behavior and labored fear learning, suggesting that low grade inflammation, mediated by NLRP3 expression, play a key role in memory consolidation.

Laminin degradation by matrix metalloproteinase 9 promotes ketamine-induced neuronal apoptosis in the early developing rat retina

AIMS

During early development, laminin degradation contributes to the death of neurons. This study aims to investigate the role and regulation of laminin in ketamine-induced apoptosis.

METHODS

We performed terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) and immunohistochemical assays to investigate the roles of the non-integrin laminin receptor, matrix metalloproteinase 9 (MMP9) in ketamine-induced neuronal apoptosis. In situ zymography, Western blot, and immunofluorescence were used to explore the relationships between laminin, MMP9 activity, and Zn2+ . Experiments were performed using whole-mount retinas dissected from Sprague Dawley rats.

RESULTS

The TUNEL and immunohistochemical assays indicated that ketamine-induced neuronal apoptosis in early developing rat retina. Blockade of non-integrin laminin receptor promoted ketamine-induced apoptosis, while non-integrin laminin receptor activation attenuated ketamine-induced apoptosis. Ketamine-induced laminin degradation, possibly by enhancing the activity of MMP9. MMP9 inhibition reduced ketamine-induced apoptosis by reducing laminin degradation. Downregulation of Zn2+ attenuated the increased MMP9 activity, laminin degradation caused by ketamine and significantly reduced ketamine-induced neuronal apoptosis.

CONCLUSION

Laminin degradation by MMP9 promoted ketamine-induced neuronal apoptosis in early developing rat retina. The non-integrin laminin receptor may be a pathway involved in ketamine-induced apoptosis. Zn2+ downregulation may play a protective role against ketamine-induced neuronal apoptosis through inhibiting MMP9 activity.

Intraperitoneal Alfaxalone and Alfaxalone-Dexmedetomidine Anesthesia in Sprague-Dawley Rats (Rattus norvegicus)

Due to their unpredictability and variable effects, injectable anesthetic regimens in laboratory rodent species warrant refinement. In our study we sought to evaluate alfaxalone, which has gained recent popularity in veterinary medicine, alone and in combination with dexmedetomidine to evaluate their anesthetic ability in Sprague-Dawley rats when administered intraperitoneally. Three doses of alfaxalone only and 4 dose combinations of alfaxalone-dexmedetomidine were tested in males and female rats. The time to induction, anesthetic duration, pulse rate, respiratory rate, temperature, and time to recovery were recorded by a blind observer. The level of anesthesia induced by the various anesthetic protocols was assessed by using pedal withdrawal reflex to a noxious stimulus and scored according to the response. Dependent on the treatment group, atipamezole or saline was administered intraperitoneally once animals reached 60 min of anesthesia. Regardless of the dose, alfaxalone alone achieved only a sedative level of anesthesia, whereas all alfaxalone-dexmedetomidine combinations led to a surgical level of anesthesia in all animals. Anesthesia regimens using alfaxalone alone and in combination with dexmedetomidine demonstrated sex-associated differences, with female rats maintaining longer durations of sedation or anesthesia than their male counterparts. Both male and female rats displayed decreases in physiologic parameters consistent with the effects of dexmedetomidine. Given the results described herein, we recommend 20 mg/kg alfaxalone for sedation and 30 mg/kg alfaxalone combined with 0.05 mg/kg dexmedetomidine for surgical anesthesia in female rats. Appropriate doses of alfaxalone only and alfaxalone-dexmedetomidine for male rats were not determined in this study and need further evaluation.

An inhalation anaesthesia approach for neonatal mice allowing streamlined stereotactic injection in the brain

BACKGROUND

Investigating brain function requires tools and techniques to visualise, modify and manipulate neuronal tissue. One powerful and popular method is intracerebral injection of customised viruses, allowing expression of exogenous transgenes. This technique is a standard procedure for adult mice, and is used by laboratories worldwide. Use of neonatal animals in scientific research allows investigation of developing tissues and enables long-term study of cell populations. However, procedures on neonatal mice are more challenging, due to the lack of reliable methods and apparatus for anaesthesia of these animals.

NEW METHOD

Here, we report an inhalation-based protocol for anaesthesia of neonatal (P0-2) mice and present a custom 3D-printed apparatus for maintenance of anaesthesia during surgical procedures. Our optimised method of anaesthesia enables a rapid method of stereotactic injection in neonatal mice for transduction of brain tissue.

RESULTS AND COMPARISON WITH EXISTING METHODS

This approach significantly enhances animal welfare and facilitates wider and simpler use of neonatal rodents in scientific research. We demonstrate this procedure for targeted labelling of specific brain regions, and in vivo modification of tissue prior to organotypic culture.

CONCLUSIONS

Our protocol for reliable delivery of inhalational anaesthetics can be readily adopted by any laboratory and will enable safer use of neonatal rodents across a diverse spectrum of scientific disciplines. Application to stereotactic injections allows a rapid and efficient method for modification of brain tissue.

Acetyl-l-carnitine does not prevent neurodegeneration in a rodent model of prolonged neonatal anesthesia

Many studies have shown that prolonged or repeated use of general anesthesia early in life can cause an increase in neurodegeneration and lasting changes in behavior. While short periods of general anesthesia appear to be safe, there is a concern about the neurotoxic potential of prolonged or repeated general anesthesia in young children. Unfortunately, the use of general anesthesia in children cannot be avoided. It would be a great benefit to develop a strategy to reduce or reverse anesthesia mitigated neurotoxicity. The mechanisms behind anesthesia related neurotoxicity are unknown, but evidence suggests that mitochondrial dysfunction and abnormal energy utilization are involved. Recent research suggests that a class of compounds known as carnitines may be effective at preventing anesthesia related neurotoxicity by influencing fatty acid metabolism in the mitochondria. However, it is unknown if carnitines can provide protection against changes in behavior associated with early life exposure to anesthesia. Accordingly, we evaluated the neuroprotective potential of acetyl-l-carnitine in 7-day old rats. Rat pups were exposed to 6 h of general anesthesia with sevoflurane or a control condition, with and without acetyl-l-carnitine. The oxygenation level of animals was continuously monitored during sevoflurane exposure, and any animal showing signs of hypoxia was removed from the study. Animals exposed to sevoflurane showed clear signs of neurodegeneration 2 h after sevoflurane exposure. The hippocampus, cortex, thalamus, and caudate putamen all had elevated levels of Fluoro-Jade C staining. Despite the elevated levels of Fluoro-Jade C, few behavioral changes were observed in an independent cohort of animals treated with sevoflurane. Furthermore, acetyl-l-carnitine had little impact on levels of Fluoro-Jade C staining in animals treated with sevoflurane. These data suggest that acetyl-l-carnitine may offer little protection again anesthesia related neurotoxicity in fully oxygenated animals.

Using animal models to evaluate the functional consequences of anesthesia during early neurodevelopment

Fifteen years ago Olney and colleagues began using animal models to evaluate the effects of anesthetic and sedative agents (ASAs) on neurodevelopment. The results from ongoing studies indicate that, under certain conditions, exposure to these drugs during development induces an acute elevated apoptotic neurodegenerative response in the brain and long-term functional impairments. These animal models have played a significant role in bringing attention to the possible adverse effects of exposing the developing brain to ASAs when few concerns had been raised previously in the medical community. The apoptotic degenerative response resulting from neonatal exposure to ASAs has been replicated in many studies in both rodents and non-human primates, suggesting that a similar effect may occur in humans. In both rodents and non-human primates, significantly increased levels of apoptotic degeneration are often associated with functional impairments later in life. However, behavioral deficits following developmental ASA exposure have not been consistently reported even when significantly elevated levels of apoptotic degeneration have been documented in animal models. In the present work, we review this literature and propose a rodent model for assessing potential functional deficits following neonatal ASA exposure with special reference to experimental design and procedural issues. Our intent is to improve test sensitivity and replicability for detecting subtle behavioral effects, and thus enhance the translational significance of ASA models.

Repeated neonatal isoflurane exposures in the mouse induce apoptotic degenerative changes in the brain and relatively mild long-term behavioral deficits

Epidemiological studies suggest exposures to anesthetic agents and/or sedative drugs (AASDs) in children under three years old, or pregnant women during the third trimester, may adversely affect brain development. Evidence suggests lengthy or repeated AASD exposures are associated with increased risk of neurobehavioral deficits. Animal models have been valuable in determining the type of acute damage in the developing brain induced by AASD exposures, as well as in elucidating long-term functional consequences. Few studies examining very early exposure to AASDs suggest this may be a critical period for inducing long-term functional consequences, but the impact of repeated exposures at these ages has not yet been assessed. To address this, we exposed mouse pups to a prototypical general anesthetic, isoflurane (ISO, 1.5% for 3 hr), at three early postnatal ages (P3, P5 and P7). We quantified the acute neuroapoptotic response to a single versus repeated exposure, and found age- and brain region-specific effects. We also found that repeated early exposures to ISO induced subtle, sex-specific disruptions to activity levels, motor coordination, anxiety-related behavior and social preference. Our findings provide evidence that repeated ISO exposures may induce behavioral disturbances that are subtle in nature following early repeated exposures to a single AASD.

Anesthetics disrupt brain development via actions on the mTOR pathway

Experiments conducted in non-human primates have recently provided new evidence supporting a longstanding concern that exposure to general anesthesia during late intrauterine life or early childhood can cause lasting cognitive deficits through harmful effects on brain development. The mammalian target of rapamycin (mTOR) signaling system plays a key role in both normal brain development and in a wide range of developmental disorders that are characterized by cognitive deficits. Intriguingly, our recently published work shows that anesthetics can chronically alter mTOR signaling in the hippocampal dentate gyrus and that normalization of mTOR signaling can prevent anesthesia-induced perturbation of structure and function. In this addendum, we briefly discuss the putative role of mTOR in developmental anesthetic neurotoxicity.

Lipid profiling as an effective approach for identifying biomarkers/adverse events associated with pediatric anesthesia

Adverse effects related to central nervous system (CNS) function in pediatric populations may, at times, be difficult, if not impossible to evaluate. Prolonged anesthetic exposure affects brain excitability and anesthesia during the most sensitive developmental stages and has been associated with mitochondrial dysfunction, aberrant lipid metabolism and synaptogenesis, subsequent neuronal damage, as well as long-term behavioral deficits. There has been limited research evaluating whether and how anesthetic agents affect cellular lipids, the most abundant components of the brain other than water. Therefore, this review discusses: (1) whether the observed anesthetic-induced changes in lipid profiles seen in preclinical studies represents early signs of neurotoxicity; (2) the potential mechanisms underlying anesthetic-induced brain injury; and (3) whether lipid biomarker(s) identified in preclinical studies can serve as markers for the early clinical detection of anesthetic-induced neurotoxicity.