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BACKGROUND Volatile anesthetic exposure during development leads to long-term cognitive deficits in rats which are dependent on age and sex. Female rats are protected relative to male rats for the same exposure on postnatal day 7. Here we test our hypothesis that androgens can modulate chloride cotransporter expression to alter the susceptibility to neurotoxicity from GABAergic drugs using female rats with exogenous testosterone exposure. METHODS Female rats were injected with testosterone (100 μg/animal) or vehicle on postnatal days 1 to 6. On postnatal day 7, the animals were randomized to either isoflurane exposure or sham. Spatial memory was assessed with the Barnes maze starting on postnatal day 41. Western blots were run from testosterone treated postnatal day 7 animals to measure levels of chloride cotransporters sodium-potassium-chloride symporter (NKCC1) and chloride-potassium symporter 5 (KCC2). RESULTS Exogenous testosterone modulated isoflurane anesthetic neurotoxicity in female rats based on poor performance in the probe trial of the Barnes Maze. By contrast, females with vehicle and isoflurane exposure were able to differentiate the goal position. These behavioral differences corresponded to differences in the protein levels of NKCC1 and KCC2 after exogenous testosterone exposure, with NKCC1 increasing (P

Direct electrical motor cortex stimulation with short-train high-frequency stimulation (HFS) for motor evoked potentials (MEPs) has been used intraoperatively during supratentorial surgeries, but the safety threshold is poorly defined. The goal of this study is to establish a rat model for the investigation of neural damage in the cerebral cortex caused by high current HFS to aid in defining safety thresholds. We performed bilateral craniotomy on 12 rats. Cerebral sensory-motor cortex was stimulated with a high-frequency current for 100 times. The rats were sacrificed and the brains were sliced for Nissl, DAPI, and IBA-1 staining. Severe neural damage of the cerebral cortex was found in all cases, including markedly shrunken and pyknotic cells. IBA-1 staining revealed reactive microglia morphology in the lesion area. DAPI staining showed nucleus degeneration and deformation. The cell density were significantly lower within the lesion area compared to the contralateral side. This study has established a brain lesion model caused by HFS on rats. These results suggest HFS may carry a risk of serious neural damage if repeatedly applied to the same brain site. More experiments are needed to fully understand the safety threshold of direct cortical stimulation with HFS for clinical use.

Background Cognitive deficits after perinatal anesthetic exposure are well established outcomes in animal models. This vulnerability is sex-dependent and associated with expression levels of the chloride transporters NKCC1 and KCC2. The hypothesis was that androgen signaling, NKCC1 function, and the age of isoflurane exposure are critical for the manifestation of anesthetic neurotoxicity in male rats. Methods Flutamide, an androgen receptor antagonist, was administered to male rats on postnatal days 2, 4, and 6 before 6 h of isoflurane on postnatal day 7 (ntotal = 26). Spatial and recognition memory were subsequently tested in adulthood. NKCC1 and KCC2 protein levels were measured from cortical lysates by Western blot on postnatal day 7 (ntotal = 20). Bumetanide, an NKCC1 antagonist, was injected immediately before isoflurane exposure (postnatal day 7) to study the effect of NKCC1 inhibition (ntotal = 48). To determine whether male rats remain vulnerable to anesthetic neurotoxicity as juveniles, postnatal day 14 animals were exposed to isoflurane and assessed as adults (ntotal = 30). Results Flutamide-treated male rats exposed to isoflurane successfully navigated the spatial (Barnes maze probe trial F[1, 151] = 78; P < 0.001; mean goal exploration ± SD, 6.4 ± 3.9 s) and recognition memory tasks (mean discrimination index ± SD, 0.09 ± 0.14; P = 0.003), unlike isoflurane-exposed controls. Flutamide changed expression patterns of NKCC1 (mean density ± SD: control, 1.49 ± 0.69; flutamide, 0.47 ± 0.11; P < 0.001) and KCC2 (median density [25th percentile, 75th percentile]: control, 0.23 [0.13, 0.49]; flutamide, 1.47 [1.18,1.62]; P < 0.001). Inhibiting NKCC1 with bumetanide was protective for spatial memory (probe trial F[1, 162] = 6.6; P = 0.011; mean goal time, 4.6 [7.4] s). Delaying isoflurane exposure until postnatal day 14 in males preserved spatial memory (probe trial F[1, 140] = 28; P < 0.001; mean goal time, 6.1 [7.0] s). Conclusions Vulnerability to isoflurane neurotoxicity is abolished by blocking the androgen receptor, disrupting the function of NKCC1, or delaying the time of exposure to at least 2 weeks of age in male rats. These results support a dynamic role for androgens and chloride transporter proteins in perinatal anesthetic neurotoxicity. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

BackgroundEarly life anesthesia exposure results in long-term cognitive deficits in rats. Environmental enrichment consisting of social housing, a stimulating environment, and voluntary exercise can rescue this deficit. We hypothesized that exercise alone is sufficient to rescue the cognitive deficit associated with perinatal anesthesia.MethodsPostnatal day 7 male rats (P7) underwent isoflurane (Iso) or sham exposure and were subsequently weaned at P21. They were then singly housed in a cage with a running wheel or a fixed wheel. After 3 weeks of exercise, animals underwent behavioral testing for spatial and recognition memory assessments. Animals were killed at various time points to accomplish either bromodeoxyuridine (BrdU) labeling or quantitative real-time polymerase chain reaction (qRT-PCR) to quantify brain-derived neurotrophic factor (BDNF) messenger ribonucleic acid (mRNA) levels.ResultsPostweaning voluntary exercise rescued the long-term spatial memory deficit associated with perinatal Iso exposure. Iso-sedentary animals did not discriminate the goal quadrant, spending no more time than chance during the Barnes maze probe trial (1-sample t test, P = .524) while all other groups did (1-sample t test, PIso-exercise = .033; Pcontrol [Con]-sedentary = .004). We did not find a deficit in recognition memory tasks after Iso exposure as we observed previously. BrdU incorporation in the adult hippocampus of Iso-sedentary animals was decreased compared to sedentary controls (Tukey P = .005). Exercise prevented this decrease, with Iso-exercise animals having more proliferation than Iso-sedentary (Tukey P < .001). There was no effect of exercise or Iso on BDNF mRNA in either the cortex or hippocampus (cortex: FExercise[1,32] = 0.236, P = .631; FIso [1,32] = 0.038, P = .847; FInteraction [1,32] = 1.543, P = .223; and hippocampus: FExercise[1,33] = 1.186, P = .284; FIso [1,33] = 1.46, P = .236; FInteraction[1,33] = 1.78, P = .191).ConclusionsExercise restores BrdU incorporation and rescues a spatial memory deficit after early life anesthesia exposure. This demonstrates sufficiency of exercise alone in the context of environmental enrichment to recover a behavioral phenotype after a perinatal insult.

Background Preclinical investigations of the effects of general anesthesia on the young brain show differences in vulnerability of males and females to anesthetic exposure at different times during development. However, the mechanism underlying this sex difference is poorly understood. Perinatal testosterone is the primary determinant of sexual differentiation and likely plays an important role in defining the period of susceptibility to anesthetic injury. We investigated whether the removal of testosterone through gonadectomy shortly after birth would improve cognitive outcomes in male rodents after early anesthesia exposure. Methods Male Sprague Dawley rats underwent gonadectomy at postnatal day 2 (P2), followed by exposure to 6 hours of isoflurane at P7. A control cohort of gonad-intact male littermates was simultaneously exposed. All rats were subjected to a series of object recognition and association tasks beginning at P42. Cell death in the thalamus and hippocampus was assessed in a separate cohort. Results All groups performed similarly on the Novel Object Recognition task; however, the gonad-intact isoflurane group exhibited decreased performance in the more difficult tasks. This deficit was ameliorated in the gonadectomized group. Cell death was similar between both isoflurane-exposed groups, regardless of gonadectomy. Conclusions The absence of testosterone does not block cell death after anesthesia in specific brain regions of interest; however, does provide some neuroprotection as evidenced by the improved cognitive test performance during adulthood. These findings suggest that testosterone may be mechanistically involved in the sex-specific effects of anesthetic injury on the developing brain by extending the vulnerable period in male rats.

Background The factors determining peak susceptibility of the developing brain to anaesthetics are unclear. It is unknown why postnatal day 7 (P7) male rats are more vulnerable to anaesthesia-induced memory deficits than littermate females. Given the precocious development of certain regions in the female brain during the neonatal critical period, we hypothesised that females are susceptible to anaesthetic brain injury at an earlier time point than previously tested. Methods Female rats were exposed to isoflurane (Iso) 1 minimum alveolar concentration or sham anaesthesia at P4 or P7. Starting at P35, rats underwent a series of behavioural tasks to test their spatial and recognition memory. Cell death immediately after anaesthesia was quantified by Fluoro-Jade C staining in select brain regions, and developmental expression of the chloride transporters KCC2 and NKCC1 was analysed by immunoblotting in male and female rats at P4 and P7. Results Female rats exposed to Iso at P4 displayed impaired spatial, object-place, -context, and social recognition memory, and increased cell death in the hippocampus and laterodorsal thalamus. Female rats exposed at P7 exhibited only decreased performance in object-context compared with control. The ratio of NKCC1/KCC2 expression in cerebral cortex was higher in P4 females than in P7 females, and similar to that in P7 males. Conclusions Female rats exposed to Iso at P4 are sensitive to anaesthetic injury historically observed in P7 males. This is consistent with a comparably immature developmental state in P4 females and P7 males. The window of anaesthetic vulnerability correlates with sex-specific cortical expression of chloride transporters NKCC1 and KCC2. These findings suggest that both sex and developmental age play important roles in determining the outcome after early anaesthesia exposure.

Preclinical data suggest that general anaesthetics affect brain development. There is mixed evidence from cohort studies that young children exposed to anaesthesia can have an increased risk of poor neurodevelopmental outcome. We aimed to establish whether general anaesthesia in infancy has any effect on neurodevelopmental outcome. Here we report the secondary outcome of neurodevelopmental outcome at 2 years of age in the General Anaesthesia compared to Spinal anaesthesia (GAS) trial.In this international assessor-masked randomised controlled equivalence trial, we recruited infants younger than 60 weeks postmenstrual age, born at greater than 26 weeks' gestation, and who had inguinal herniorrhaphy, from 28 hospitals in Australia, Italy, the USA, the UK, Canada, the Netherlands, and New Zealand. Infants were randomly assigned (1:1) to receive either awake-regional anaesthesia or sevoflurane-based general anaesthesia. Web-based randomisation was done in blocks of two or four and stratified by site and gestational age at birth. Infants were excluded if they had existing risk factors for neurological injury. The primary outcome of the trial will be the Wechsler Preschool and Primary Scale of Intelligence Third Edition (WPPSI-III) Full Scale Intelligence Quotient score at age 5 years. The secondary outcome, reported here, is the composite cognitive score of the Bayley Scales of Infant and Toddler Development III, assessed at 2 years. The analysis was as per protocol adjusted for gestational age at birth. A difference in means of five points (1/3 SD) was predefined as the clinical equivalence margin. This trial is registered with ANZCTR, number ACTRN12606000441516 and ClinicalTrials.gov, number NCT00756600.Between Feb 9, 2007, and Jan 31, 2013, 363 infants were randomly assigned to receive awake-regional anaesthesia and 359 to general anaesthesia. Outcome data were available for 238 children in the awake-regional group and 294 in the general anaesthesia group. In the as-per-protocol analysis, the cognitive composite score (mean [SD]) was 98.6 (14.2) in the awake-regional group and 98.2 (14.7) in the general anaesthesia group. There was equivalence in mean between groups (awake-regional minus general anaesthesia 0.169, 95% CI -2.30 to 2.64). The median duration of anaesthesia in the general anaesthesia group was 54 min.For this secondary outcome, we found no evidence that just less than 1 h of sevoflurane anaesthesia in infancy increases the risk of adverse neurodevelopmental outcome at 2 years of age compared with awake-regional anaesthesia.Australia National Health and Medical Research Council (NHMRC), Health Technologies Assessment-National Institute for Health Research UK, National Institutes of Health, Food and Drug Administration, Australian and New Zealand College of Anaesthetists, Murdoch Childrens Research Institute, Canadian Institute of Health Research, Canadian Anesthesiologists' Society, Pfizer Canada, Italian Ministry of Heath, Fonds NutsOhra, and UK Clinical Research Network (UKCRN).