Basic studies on neurotoxicity of general anesthetics in the developing brain

Background Isoflurane is an inhaled anesthetic widely used in pediatric and obstetric operations, due to its advantages such as anesthesia depth which is easy to control and little influence on the circulation. Objective Recent reports showed that repeated or long-time exposure to anesthetics at the young stage may cause deficient memory in the future. Therefore, increasing attentions have been drawn on isoflurane's mechanism about neurological damages. Content This paper summarized the toxic mechanism of isoflurane in the recent five years, and synaptic plasticity damages can cause neurotoxicity, inhibit N-methyl-D-aspartate(NMDA) receptor and stimulate amino acid type A receptor (GABAAR) and affect long-term potentiation, calcium homeostasis, and activate neurotrophins to produce apoptotic pathway, and other possible toxic mechanisms. Trend This paper can further determine the research direction, providing references for transform of basic research data into clinical practice as well as for the research and development of new protective drugs. Key words: Isoflurane; Developmental brain; Apoptosis; Neurotoxicity; Synapsis

The number of pediatric surgery grows every year. Some studies found that long or repeated exposure to general anesthetics may affect the development of neurological system function in children. This finding is supported by a large number of animal researches currently, without sufficient clinical evidence. This review was to explore the effects of early anesthetic exposure on long-term neurodevelopment in children, so as to provide guidance to determine treatment method and surgery time. This review summarized the latest research progresses, and analyzed the association between early anesthetic exposure in childhood and long-term neurodevelopmental deficits and the sensitive period of the age exposed to anesthesia. At present, clinical researches involve different age populations and types of outcomes. Therefore, the interpretation of outcomes needs the combination of the age exposed to anesthesia, duration of exposure, sample size, outcome indicators, and other factors. It is found that anesthesia exposure in early childhood is associated with long-term neurological deficits, and affected by the frequency of anesthetic exposure to some extent. Key words: Children; Anesthesia; Neurotoxicity; Neurodevelopment

The FDA Warning on Anesthesia Drugs.

Compelling evidence in animal models that, under some conditions, general anesthetics and sedatives produce changes in the brain and persistent impairments in learning, memory, and behavior. The present review summarizes recent clinical studies investigating whether the use of these agents in children causes similar neurotoxicities. Although the results of retrospective studies are somewhat mixed, multiple exposures to general anesthesia were generally found to confer greater risk than single exposures with regard to learning disability, attention deficit hyperactivity disorder, school readiness, and academic achievement. Recent clinical studies, including a large randomized controlled trial, are consistent in confirming that a single exposure in infancy to general anesthesia lasting less than 1 h is not associated with neurodevelopmental impairments in later childhood. These studies do not, however, clarify the potential impacts of longer exposures or multiple exposures. Given that approximately half of the anesthetic exposures in young US children are 1 h or less in duration, the results of the recent clinical studies are reassuring. Because of the clinical necessity of administering general anesthetics and sedatives for longer periods for many surgical, procedural, or diagnostic purposes, the identification of adjuvants that prevent or reduce the potential neurotoxicity of these agents is an area of active research.

The present article is a conceptual discussion about cognitive neuroscience and its interface with human development. For this purpose, we begin with a brief history of cognitive neuroscience, emphasizing its interdisciplinary nature. Afterwards we discuss some concepts of neuropsychology such as perceptual and cognitive development, general development of the nervous system, the formation of the brain, synaptic plasticity and cellular and molecular bases of cognition. Finally we emphasize that there is no way to separate the behavior from its biological basis, understanding that the nervous system is a necessary condition for the occurrence of behavior, thoughts and feelings, though it may not be a sufficient condition for the emergence of consciousness and behavioral phenomena.

Two anesthetic procedures, intercostal nerve block (ICNB) and general anesthesia, were evaluated in 45 female patients scheduled for minor breast surgery. The study was designed to compare ICNB with general anesthesia for breast surgery with respect to efficacy, surgical stress and postoperative analgesia and to evaluate epinephrine and ornipressin as vasoconstrictors in the local anesthetic solution. Thirty patients received ICNB of T3-T7 unilaterally using 2% lidocaine plus epinephrine (15 patients, Group A) and 2% lidocaine plus ornipressin (15 patients, Group B). The control group consisted of 15 patients receiving a general anesthetic. The highest median lidocaine plasma level was 2.8 micrograms/ml in those patients who received epinephrine and 5.3 micrograms/ml in those who received ornipressin. There were statistically significantly higher lidocaine plasma levels in Group B than in Group A after 10, 30 and 60 minutes from injection while the two groups did not differ significantly at the 20- and 90-minute time intervals. Before and during surgery, epinephrine and norepinephrine plasma levels were highest in the epinephrine group, whereas, postoperatively, the plasma levels of both catecholamines were highest in the patients receiving general anesthesia. The latter patients experienced significantly more nausea and vomiting than the regional anesthesia groups. Patients with regional anesthesia required significantly less analgesics postoperatively than the patients receiving general anesthesia.

The finding that exposure to general anesthetics (GAs) in childhood may increase rates of learning disabilities has raised a concern that anesthetics may interfere with brain development. The generation of neuronal circuits, a complex process in which axons follow guidance cues to dendritic targets, is an unexplored potential target for this type of toxicity. GA exposures were conducted in developing neocortical neurons in culture and in early postnatal neocortical slices overlaid with fluorescently labeled neurons. Axon targeting, growth cone collapse, and axon branching were measured using quantitative fluorescence microscopy. Isoflurane exposure causes errors in Semaphorin-3A-dependent axon targeting (n = 77 axons) and a disruption of the response of axonal growth cones to Semaphorin-3A (n = 2,358 growth cones). This effect occurs at clinically relevant anesthetic doses of numerous GAs with allosteric activity at γ-aminobutyric acid type A receptors, and it was reproduced with a selective agonist. Isoflurane also inhibits growth cone collapse induced by Netrin-1, but does not interfere branch induction by Netrin-1. Insensitivity to guidance cues caused by isoflurane is seen acutely in growth cones in dissociated culture, and errors in axon targeting in brain slice culture occur at the earliest point at which correct targeting is observed in controls. These results demonstrate a generalized inhibitory effect of GAs on repulsive growth cone guidance in the developing neocortex that may occur via a γ-aminobutyric acid type A receptor mechanism. The finding that GAs interfere with axon guidance, and thus potentially with circuit formation, represents a novel form of anesthesia neurotoxicity in brain development.

Brain-derived neurotrophic factor (BDNF) is important in supporting neuronal development. BDNF imbalance due to excessive neuronal inhibition can result in the apoptotic degeneration of developing neurons. Since general anesthetics cause profound depression of neuronal activity and are known to induce widespread degeneration in the developing brain, we studied their potential to activate BDNF-mediated developmental neuroapoptosis. When P7 rats (at the peak of brain development) were exposed to a commonly-used and highly pro-apoptotic anesthesia protocol (midazolam, isoflurane, nitrous oxide) for a period of 2, 4 or 6 h, we found that anesthesia modulates the key steps in BDNF-activated apoptotic cascade in two of the most vulnerable brain regions--cerebral cortex and thalamus in time-dependent fashion by activating both Trk-dependent (in thalamus) and Trk-independent p75NTR dependent (in cerebral cortex) neurotrophic pathways. beta-estradiol, a sex hormone that upregulates the protein levels of the activated Akt, protects against anesthesia-induced neuroapoptosis.

Clinically used general anesthetics, alone or in combination, are damaging to the developing mammalian brain. In addition to causing widespread apoptotic neurodegeneration in vulnerable brain regions, exposure to general anesthesia at the peak of synaptogenesis causes learning and memory deficiencies later in life. In vivo rodent studies have suggested that activation of the intrinsic (mitochondria-dependent) apoptotic pathway is the earliest warning sign of neuronal damage, suggesting that a disturbance in mitochondrial integrity and function could be the earliest triggering events. Because proper and timely mitochondrial morphogenesis is critical for brain development, the authors examined the long-term effects of a commonly used anesthesia combination (isoflurane, nitrous oxide, and midazolam) on the regional distribution, ultrastructural properties, and electron transport chain function of mitochondria, as well as synaptic neurotransmission, in the subiculum of rat pups. This anesthesia, administered at the peak of synaptogenesis, causes protracted injury to mitochondria, including significant enlargement of mitochondria (more than 30%, P < 0.05), impairment of their structural integrity, an approximately 28% increase in their complex IV activity (P < 0.05), and a twofold decrease in their regional distribution in presynaptic neuronal profiles (P < 0.05), where their presence is important for the normal development and functioning of synapses. Consequently, the authors showed that impaired mitochondrial morphogenesis is accompanied by heightened autophagic activity, decrease in mitochondrial density (approximately 27%, P < 0.05), and long-lasting disturbances in inhibitory synaptic neurotransmission. The interrelation of these phenomena remains to be established. Developing mitochondria are exquisitely vulnerable to general anesthesia and may be important early target of anesthesia-induced developmental neurodegeneration.

In many recent studies, the inhibitory transmitter gamma-aminobutyric acid has been shown to modulate the proliferation, differentiation and survival of neural stem cells. Most general anesthetics are partial or allosteric gamma-aminobutyric acid A receptor agonists, suggesting that general anesthetics could alter the behavior of neural stem cells. The neuroprotective efficacy of general anesthetics has been recognized for decades, but their effects on the proliferation of neural stem cells have received little attention. This study investigated the potential effect of midazolam, an extensively used general anesthetic and allosteric gamma-aminobutyric acid A receptor agonist, on the proliferation of neural stem cells in vitro and preliminarily explored the underlying mechanism. The proliferation of neural stem cells was tested using both Cell Counting Kit 8 and bromodeoxyuridine incorporation experiments. Cell distribution analysis was performed to describe changes in the cell cycle distribution in response to midazolam. Calcium imaging was employed to explore the molecular signaling pathways activated by midazolam. Midazolam (30–90 μM) decreased the proliferation of neural stem cells in vitro. Pretreatment with the gamma-aminobutyric acid A receptor antagonist bicuculline or Na-K-2Cl cotransport inhibitor furosemide partially rescued this inhibition. In addition, midazolam triggered a calcium influx into neural stem cells. The suppressive effect of midazolam on the proliferation of neural stem cells can be partly attributed to the activation of gamma-aminobutyric acid A receptor. The calcium influx triggered by midazolam may be a trigger factor leading to further downstream events.

The HNK-1 carbohydrate, which is recognized by anti-HNK-1 antibody, is well known to be expressed predominantly in the nervous system. The characteristic structural feature of the HNK-1 carbohydrate is 3-sulfo-glucuronyl residues attached to lactosamine structures (Gal beta1-4GlcNAc) on glycoproteins and glycolipids. The biosynthesis of the HNK-1 carbohydrate is regulated mainly by two glucuronyltransferases (GlcAT-P and GlcAT-S) and a sulfotransferase. In this study, we found that GlcAT-S mRNA was expressed at higher levels in the kidney than in the brain, but that both GlcAT-P and HNK-1 sulfotransferase mRNAs, which were expressed at high levels in the brain, were not detected in the kidney. These results suggested that the HNK-1 carbohydrate without sulfate (non-sulfated HNK-1 carbohydrate) is expressed in the kidney. We substantiated this hypothesis using two different monoclonal antibodies: one (anti-HNK-1 antibody) requires sulfate on glucuronyl residues for its binding, and the other (antibody M6749) does not. Western blot analyses of mouse kidney revealed that two major bands (80 and 140 kDa) were detected with antibody M6749, but not with anti-HNK-1 antibody. The 80- and 140-kDa band materials were identified as meprin alpha and CD13/aminopeptidase N, respectively. We also confirmed the presence of the non-sulfated HNK-1 carbohydrate on N-linked oligosaccharides by multistage tandem mass spectrometry. Immunofluorescence staining with antibody M6749 revealed that the non-sulfated HNK-1 carbohydrate was expressed predominantly on the apical membranes of the proximal tubules in the cortex and was also detected in the thin ascending limb in the inner medulla. This is the first study indicating the presence of the non-sulfated HNK-1 carbohydrate being synthesized by GlcAT-S in the kidney. The results presented here constitute novel knowledge concerning the function of the HNK-1 carbohydrate.

Background Although emerging evidence shows that dexmedetomidine (Dex) has unique advantages in obstetric anesthesia & analgesia, clinical trials using Dex as an obstetric medication have been relatively rare in China. Objective To review and discuss the benefits and potential application of Dex in obstetric anesthesia & analgesia. Content Dex is demonstrated to be a safe general anesthetics with or without minor adverse effects to neonates, and it was also reported to reduce the toxic effects of sevoflurane and ketamine on neonates. Dex has been used in obstetrics for intravenous analgesia and intrathecal anesthesia. In these applications, Dex relieves symptoms commonly seen in pregnant women during perinatal period, such as shivering, nausea, and vomiting, and maintains normal contraction of uterus during labor under general anesthesia. Dex also possesses some properties allowing it suitable for anesthesia in tracheal intubation, including minor respiratory suppression, efficient sedative action, non-effect on wakefulness. However, it is still early to apply Dex as a routine medication in obstetric anesthesia & analgesia, and further investigations are warranted to verify its safety, indications, and contraindications. Trend Dex may be a new drug choice for optimizing obstetric anesthesia & analgesia. Key words: Dexmedetomidine; Obstetric anesthesia; Analgesia; Clinical study

Current technology in newborn universal hearing detection: Jacobson J.; Jacobson C.A.Semin. Hear. (USA) (1996) 17/2 (125–138)

Skilled management of sick premature babies and very young children has resulted in numerous exposures of their brains to a variety of anesthetic agents designed to achieve the substantial depth of neuronal inhibition required for complete loss of consciousness and insensitivity to pain. Unfortunately, our recent animal findings suggest that commonly used general anesthetics are damaging to developing neurons and cause significant neuronal deletion in vulnerable brain regions. In addition, emerging animal and human data suggest an association between early exposure to general anesthesia and long-term impairment of cognitive development. Consequently, the prudence of frequent anesthesia exposure of this population is now being scrutinized. It is important to note that on the basis of currently available information, there are still considerable differences of opinion regarding the clinical relevance of the animal findings. Since there is insufficient evidence establishing a clear association between animal and human findings, it would be premature to suggest major changes in current clinical practice.

Background: Isoniazid (INH), first line drug for antitubercular treatment, induces hepatic necrosis in some of human beings in normal doses and in experimental animals in toxic doses. Reactive toxic metabolites of INH are released which disrupt hepatocellular membrane and cause necrosis. So there is a need to find some hepatoprotective and antioxidant agent. Silymarin has been used as a raw extract from the seeds of Silybum marianum (carduimariae fructus) but now mixture of 4 flavonolignane isomers is available i.e. silybinin, isosilybinin, silidianin and silychristin. The data suggests that factor of antioxidation is important in the process of hepatoprotection by silymarin. In this study the role of silymarin against INH induced hepatotoxicity was observed in rabbit model. Methods: Study was conducted on oryctolagus cuniculus rabbits (1-1.5 kg) of either sex for a period of 11 days. Four groups of rabbits were formed at random with 6 animals per group. In group I liver function tests were recorded without any drug. In group II effects of silymarin (50 mg/kg/day p.o) was observed. In Group III isoniazid (50 mg/kg /day i.p) was administered. In group IV combined effects of isoniazid and silymarin were observed. Liver function tests including serum bilirubin, ALT and AST were performed on 12 th day. Rabbits were sacrificed on 12 th day for observing histopathological changes in liver. Results: In group I, II and IV there was no mortality and rabbits of group II and IV gained weight. Liver architecture remained almost intact in group II. In group III, bilirubin level increased (P<0.05). Histological picture revealed ballooning degeneration, portal inflammation and necrosis of hepatocytes which are signs of acute inflammation. In group IV there was significant improvement in liver architecture when compared with group III. So it can be concluded that INH induced biochemical and histopathological changes are well antagonized by concurrent administration of silymarin for 11days. Key Words: Hepatotoxicity, INH-induced hepatotoxicity, Silymarin, Liver function tests.