Intracellular protein kinase and calcium inward currents in perfused neurones of the snail Helix pomatia

Changes in the amplitude of the calcium inward current caused by intracellular administration of tolbutamide (an inhibitor of the cyclic AMP-dependent protein kinase activity) or catalytic subunits of cAMP-dependent protein kinases from rabbit myocardium were studied on internally perfused nerve cells of the snail, Helix pomatia. Intracellular administration of 7 mM tolbutamide caused a rapid decline of the amplitude of the calcium current that had been stabilized by theophylline; the effect was practically completely reversible. In contrast, addition to the perfusing solution of exogenous catalytic subunits of cyclic AMP-dependent protein kinases (about 0.7 microM of protein) together with 2 mM adenosine 5'-triphosphate and 3 mM MgCl2, led to stabilization of the calcium conductance of the cell membrane or restored it if it had declined during the perfusion with basic solution. The effect depended largely on the presence of adenosine 5'-triphosphate. Its time course was very slow (dozens of minutes) due probably to slow diffusion of the protein inside the cell. Heat-inactivated catalytic subunits did not produce such a stabilizing or restoring action on the calcium conductance. The results substantiate the suggestion that the normal functioning of calcium channels depends on phosphorylation catalyzed by cyclic AMP-dependent protein kinases.

Role of histone acetylation in long-term neurobehavioral effects of neonatal Exposure to sevoflurane in rats

Human studies, and especially laboratory studies, provide evidence that early life exposure to general anesthesia may affect neurocognitive development via largely unknown mechanisms. We explored whether hippocampal histone acetylation had a role in neurodevelopmental effects of sevoflurane administered to neonatal rats. Male Sprague-Dawley rats were exposed to 3% sevoflurane or were subjected to maternal separation only for 2h daily at postnatal days 6, 7, and 8. The histone deacetylase inhibitor, sodium butyrate (250mg/kg, intraperitoneally), or saline was administered starting 2h prior to anesthesia or maternal separation and continued daily until the end of behavioral tests, which were performed between postnatal days 33 and 50. Upon completion of the behavioral tests, the brain tissues were harvested for further analysis. Rats neonatally exposed to sevoflurane exhibited decreased freezing time in the fear conditioning contextual test and increased escape latency, decreased time in target quadrant, and number of platform crossings in the Morris water maze test. The sevoflurane-exposed rats had lower hippocampal density of dendritic spines, reduced levels of the brain-derived neurotrophic factor, c-fos protein, microtubule-associated protein 2, synapsin1, postsynaptic density protein 95, pCREB/CREB, CREB binding protein, and acetylated histones H3 and H4, and increased levels of histone deacetylases 3 and 8. These neurobehavioral abnormalities were normalized in the sevoflurane-exposed rats treated with sodium butyrate. Our findings provide evidence that neonatal exposure to sevoflurane induces neurobehavioral abnormalities and long-lasting alterations in histone acetylation; normalization of histone acetylation may alleviate the neurodevelopmental side effects of the anesthetic.

Anesthesia with sevoflurane in neonatal rats: Developmental neuroendocrine abnormalities and alleviating effects of the corticosteroid and Cl(-) importer antagonists

BACKGROUND

1.5 million children under 12 months of age are exposed to general anesthesia annually in the United States alone. Human and especially animal studies provide evidence that exposure to general anesthesia during the early postnatal period may lead to long-term neurocognitive abnormalities via poorly understood mechanisms. We investigated whether an immature stress response system and γ-aminobutyric acid (GABA) type A receptor activities are involved in mediating these abnormalities.

METHODS

Sprague-Dawley rats at postnatal days 4, 5 or 6 were anesthetized with 2.1% sevoflurane for 6h; maternally separated and house reared rats served as controls.

RESULTS

Sevoflurane anesthesia markedly increased corticosterone levels in rat pups of both genders. In adulthood, these rats responded to stress with heightened secretion of corticosterone and a greater increase in corticosterone levels in males versus females. Only male rats, previously exposed to neonatal sevoflurane, had a higher frequency of miniature inhibitory postsynaptic currents in CA1 neurons, spent a shorter time in open arms of the elevated plus maze (EPM) and exhibited impaired prepulse inhibition (PPI) of startle. Pretreatment of male rats prior to sevoflurane with the Na(+)-K(+)-2Cl(-) cotransporter inhibitor, bumetanide, or the mineralocorticoid receptor antagonist, RU28318, normalized endocrine responses to stress and the EPM behavior in adulthood, while only those pretreated with bumetanide exhibited normalized PPI of startle responses. Neither bumetanide nor RU28318 altered the effect of sevoflurane on synaptic activity.

CONCLUSIONS

Sevoflurane-enhanced neuronal excitation and elevated corticosteroid levels at the time of anesthesia contribute to the mechanisms initiating neonatal sevoflurane-induced long-term endocrine and neurobehavioral abnormalities.

Role of epigenetic mechanisms in transmitting the effects of neonatal sevoflurane exposure to the next generation of male, but not female, rats

BACKGROUND

Clinical studies report learning disabilities and attention-deficit/hyperactivity disorders in those exposed to general anaesthesia early in life. Rats, primarily males, exposed to GABAergic anaesthetics as neonates exhibit behavioural abnormalities, exacerbated responses to stress, and reduced expression of hypothalamic K+-2Cl- Cl- exporter (Kcc2). The latter is implicated in development of psychiatric disorders, including male predominant autism spectrum disorders. We tested whether parental early life exposure to sevoflurane, the most frequently used anaesthetic in paediatrics, affects the next generation of unexposed rats.

METHODS

Offspring (F1) of unexposed or exposed to sevoflurane on postnatal day 5 Sprague-Dawley rats (F0) were subjected to behavioural and brain gene expression evaluations.

RESULTS

Male, but not female, progeny of sevoflurane-exposed parents exhibited abnormalities in behavioural testing and Kcc2 expression. Male F1 rats of both exposed parents exhibited impaired spatial memory and expression of hippocampal and hypothalamic Kcc2. Offspring of only exposed sires had abnormalities in elevated plus maze and prepulse inhibition of startle, but normal spatial memory and impaired expression of hypothalamic, but not hippocampal, Kcc2. In contrast to exposed F0, their progeny exhibited normal corticosterone responses to stress. Bisulphite sequencing revealed increased CpG site methylation in the Kcc2 promoter in F0 sperm and F1 male hippocampus and hypothalamus that was in concordance with the changes in Kcc2 expression in specific F1 groups.

CONCLUSIONS

Neonatal exposure to sevoflurane can affect the next generation of males through epigenetic modification of Kcc2 expression, while F1 females are at diminished risk.

Impaired glutamatergic synaptic transmission in the PKU brain

This paper reviews recent results of our investigation of the mechanisms whereby hyperphenylalaninemia may cause brain dysfunction in classical phenylketonuria (PKU). Acute applications of L-Phe in rat and mouse hippocampal and cerebrocortical cultured neurons, at a range of concentrations found in PKU brain, significantly and reversibly depressed glutamatergic synaptic transmission by a combination of pre- and postsynaptic actions: (1) competition for the glycine-binding site of the N-methyl-D-aspartate (NMDA) receptors; (2) attenuation of neurotransmitter release; (3) competition for the glutamate-binding site of (RS)-amino-3-hydroxy-5-methyl-4-isoxazolepropioinic acid and kainate (AMPA/kainate) receptors. Unlike L-Phe, its non-tyrosine metabolites, phenylacetic acid, phenylpyruvic acid, and phenyllactic acid, did not produce antiglutamatergic effects. L-Phe did not affect inhibitory gamma-aminobutyric (GABA)-ergic transmission. Consistent with this specific pattern of effects caused by L-Phe in neuronal cultures, the expression of NMDA receptor NR2A and AMPA receptor Glu1 and Glu2/3 subunits in brain of hyperphenylalaninemic PKU mice (Pah(enu2) strain) was significantly increased, whereas expression of the NMDA receptor NR2B subunit was decreased. There was no change in GABA alpha1 subunit expression. Considering the important role of glutamatergic synaptic transmission in normal brain development and function, these L-Phe-induced changes in glutamatergic synaptic transmission in PKU brain may be a critical element of the neurological symptoms of PKU.

Neurobehavioural abnormalities induced by repeated exposure of neonatal rats to sevoflurane can be aggravated by social isolation and enrichment deprivation initiated after exposure to the anaesthetic

BACKGROUND

We tested the hypothesis that developmental effects of repeated neonatal exposure to sevoflurane in rats are exacerbated by stressful experiences received later in life.

METHODS

Sprague-Dawley male rats received sequential exposures to 3% sevoflurane for two h on postnatal days (P) six, seven, and eight. After weaning at P21, rats were housed either in pairs in an enriched environment (EE) or singly in an enrichment-deprived environment (an adverse environment, AE). The hippocampal concentrations of brain-derived neurotrophic factor (BDNF), and synaptic markers were assessed at P8 and P53. The dentate gyrus neural progenitor proliferation was evaluated at P11 and P53 after administration of bromodeoyuridine (BrdU) at P8 to P10 and at P22 to P27, respectively. Neurobehavioural evaluations were performed at P49 to P53.

RESULTS

Repeated sevoflurane exposure acutely reduced concentrations of BDNF, synaptic markers and neural progenitor proliferation. The sevoflurane group housed in the AE conditions (sevoflurane+AE) had decreased concentrations of BDNF and synaptic markers, and survival of new granule cells and impaired cognitive function compared with the control+AE, control+EE, and sevoflurane+EE groups. The neurobehavioural parameters in the sevoflurane+EE and control+EE groups were similar.

CONCLUSIONS

Neurocognitive abnormalities induced by repeated neonatal exposure to sevoflurane can be aggravated by stressful conditions such as social isolation and enrichment deprivation.

Long-term changes in glutamatergic synaptic transmission in phenylketonuria

The cellular mechanisms that underlie impaired brain function during phenylketonuria (PKU), the most common biochemical cause of mental retardation in humans, remain unclear. Acute application of L-Phe at concentrations observed in the PKU brain depresses glutamatergic synaptic transmission but does not affect GABA receptor activity in cultured neurons. If these depressant effects of L-Phe take place in the PKU brain, then chronic impairment of the glutamate system, which may contribute to impaired brain function, could be detected as changes in postsynaptic glutamate receptors. This hypothesis was tested by using a combination of liquid chromatography-mass spectrometry, patch-clamp, radioligand binding and western blot approaches in forebrain tissue from heterozygous and homozygous (PKU) Pah(enu2) mice. Brain concentrations of L-Phe were nearly six-fold greater in PKU mice (863.12 +/- 17.96 micromol/kg) than in their heterozygous counterparts (149.32 +/- 10.23 micromol/kg). This concentration is significantly higher than the K(B) of 573 microM for L-Phe to compete for N-methyl-D-aspartate (NMDA) receptors. Receptor binding experiments with [3H]MK-801 showed significant up-regulation of NMDA receptor density in PKU mice. Consistent with the depressant effects of L-Phe, expression of NMDA receptor NR2A and (RS)-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor Glu1 and Glu2/3 subunits was significantly increased, whereas expression of the NR2B subunit was decreased. There was no change in GABA alpha1 subunit expression. Given the role of the glutamatergic system in brain development and function, these changes may, at least in part, explain the brain disorders associated with PKU.

Specific inhibition of N-methyl-D-aspartate receptor function in rat hippocampal neurons by L-phenylalanine at concentrations observed during phenylketonuria

Hippocampal N-methyl-D-aspartate receptors (NMDARs) are thought to be involved in the regulation of memory formation and learning. Investigation of NMDAR function during experimental conditions known to be associated with impaired cognition in vivo may provide new insights into the role of NMDARs in learning and memory. Specifically, the mechanism whereby high concentrations of L-phenylalanine (L-Phe) during phenylketonuria (>1.2 mM) cause mental retardation remains unknown. Therefore, the effects of L-Phe on NMDA-activated currents (I(NMDA)) were studied in cultured hippocampal neurons from newborn rats using the patch-clamp technique. L-Phe specifically and reversibly attenuated I(NMDA) in a concentration-dependent manner (IC(50) = 1.71 +/- 0.24 mM). In contrast, L-tyrosine (L-Tyr), an amino acid synthesized from L-Phe in normal subjects, did not significantly change I(NMDA). Although the L-Phe-I(NMDA) concentration-response relationship was independent of the concentration of NMDA, it was shifted rightward by increasing the concentration of glycine. Consistent with an effect of L-Phe on the NMDAR glycine-binding site, L-Phe (1 mM) did not attenuate I(NMDA) in the presence of D-alanine (10 microM). Furthermore, L-Phe significantly attenuated neither glutamate-activated current in the presence of MK-801, nor current activated by AMPA. The finding that L-Phe inhibits specifically NMDAR current in hippocampal neurons by competing for the glycine-binding site suggests a role for impaired NMDAR function in the development of mental retardation during phenylketonuria and accordingly an important role for NMDARs in memory formation and learning.

Nitric oxide mediates the anti-adrenergic effect of adenosine on calcium current in isolated rabbit atrioventricular nodal cells

The aim of this study was to determine if adenosine exerts an anti-adrenergic effect on rabbit isolated atrioventricular (AV) nodal cells and, if so, the dependence of this effect on nitric oxide (NO) production. Inward Ca current, ICa, was measured in AV nodal cells, enzymatically isolated from rabbit hearts. Isoprenaline (0.1 microM) increased ICa from 676 +/-59 to 1102 +/-86 pA (n =25). This isoprenaline-induced increase in ICa(178 +/-15% of control) was abolished in the presence of 10 microM adenosine (ICa100 +/-2% of control, n =9, P <0.05). This effect of adenosine was completely blocked by the A1 receptor antagonist CPDPX (8-cyclopentyl l, 3-dipropylxanthine, 0.1 microM). In cells pre-treated with the NO synthase inhibitor, L-nitro-arginine methyl ester (L-NAME, 1 mM) the isoprenaline-induced increase in ICa(208 +/-39% of control, n=7) was not reduced by the addition of 10 microM adenosine (195 +/-32% of control). Co-incubation of cells in L-NAME with L-arginine (1 mM, the endogenous substrate of NO synthase) restored the adenosine-induced attenuation of ICa. In these cells, isoprenaline increased ICa (157 +/-7% of control, n =6), and, following addition of adenosine (10 microM) ICa was reduced to 107 +/-8% (P <0.05). The NO-releasing agent SIN-1 (3-morpholino-sydnonimine, 100 microM), inhibited ICa augmented by isoprenaline (n=5). It is concluded that adenosine exerts an anti-adrenergic effect on the AV node via A1 receptors to attenuate a catecholamine-stimulated increase in ICa and that this action involves the intracellular production of NO.

L-phenylalanine selectively depresses currents at glutamatergic excitatory synapses

To explore the hypothesis that L-phenylalanine (L-Phe) depresses glutamatergic synaptic transmission and thus contributes to brain dysfunction in phenylketonuria (PKU), the effects of L-Phe on spontaneous and miniature excitatory postsynaptic currents (s/mEPSCs) in rat and mouse hippocampal and cerebrocortical cultured neurons were studied using the patch-clamp technique. L-Phe depressed the amplitude and frequency of both N-methyl-D-aspartate (NMDA) and non-NMDA components of glutamate receptor (GluR) s/mEPSCs. The IC(50) of L-Phe to inhibit non-NMDAR mEPSC frequency was 0.98 +/- 0.13 mM, a brain concentration seen in classical PKU. In contrast, D-Phe had a significantly smaller effect, whereas L-leucine, an amino acid that competes with L-Phe for brain transporter, had no effect on mEPSCs. Unlike GluR s/mEPSCs, GABA receptor mIPSCs were not attenuated by L-Phe. A high extracellular concentration of glycine prevented the attenuation by L-Phe of NMDAR current, activated by exogenous agonist, and of NMDAR s/mEPSC amplitude, but not of NMDAR s/mEPSC frequency. On the other hand, L-Phe significantly depressed non-NMDAR current activated by low but not high concentrations of exogenous agonists. Glycine-independent attenuation of NMDAR s/mEPSC frequency suggests decreased presynaptic glutamate release caused by L-Phe, whereas decreased amplitudes of NMDAR and non-NMDAR s/mEPSCs are consistent with competition of L-Phe for the glycine- and glutamate-binding sites of NMDARs and non-NMDARs, respectively. The finding that GluR activity is significantly depressed at conditions characteristic of classical PKU indicates a potentially important contribution of impaired GluR function to PKU-related mental retardation and provides important insights into the potential physiological consequences of impaired GluR function.

Neuroprotective action of halogenated derivatives of L-phenylalanine

BACKGROUND AND PURPOSE

The aromatic amino acid L-Phenylalanine (L-Phe) significantly and reversibly depresses excitatory glutamatergic synaptic transmission (GST) via a unique set of presynaptic and postsynaptic mechanisms. Therefore, we hypothesized that endogenous derivatives of L-Phe, which display potent antiglutamatergic activity, may safely and efficaciously protect the brain during conditions characterized by overactivation of glutamate receptors.

METHODS

We tested this hypothesis in vitro with a combination of patch-clamp and lactate dehydrogenase (LDH) analyses in rat cultured neurons exposed to simulated ischemia, and in vivo using a rat model of experimental stroke caused by transient middle cerebral artery occlusion (MCAO).

RESULTS

3,5-diiodo-L-tyrosine (DIT) and 3,5-dibromo-L-tyrosine (DBrT), endogenous halogenated derivatives of L-Phe, attenuated GST by similar mechanisms as L-Phe, but with greater potency. For example, the IC50s for DIT and DBrT to depress the frequency of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor-mediated mEPSCs were 104.6+/-14.1 micromol/L and 127.5+/-13.3 micromol/L, respectively. Depression of GST by DIT and DBrT persisted during energy deprivation. Furthermore, DBrT significantly reduced LDH release in neuronal cultures exposed to oxygen glucose deprivation. In rats subjected to transient MCAO, DBrT decreased the brain infarct volume and neurological deficit score to 52.7+/-14.1% and 57.1+/-12.0% of control values, respectively. DBrT neither altered atrioventricular nodal and intraventricular conduction in isolated heart, nor heart rate and blood pressure in vivo.

CONCLUSIONS

DBrT, an endogenous halogenated derivative of L-Phe, shows promise as a representative of a novel class of neuroprotective agents by exerting significant neuroprotection in both in vitro and in vivo models of brain ischemia.

Animal models of brain dysfunction in phenylketonuria

Phenylketonuria (PKU) is a metabolic disorder that results in significant brain dysfunction if untreated. Although phenylalanine restricted diets instituted at birth have clearly improved PKU outcomes, neuropsychological deficits and neurological changes still represent substantial problems. The specific mechanisms by which Phe affects the brains of individuals with PKU are yet fully determined. The use of animal models in PKU research significantly broadens the possibilities for investigating these mechanisms. This report presents an overview of findings from animal studies on the mechanisms of Phe action in the PKU brain, discussing the importance of changes in protein synthesis, transport of large neutral amino acids across the blood-brain barrier, synthesis of monoamine neurotransmitters, activity of glutamate receptors, animal behavior, and translation of animal behavioral data to patients with PKU. This report shows that great progress has been made in past years and demonstrates the importance of further animal research to understand the neuropathological mechanisms underlying brain dysfunction in PKU. A better understanding of these mechanisms will guide the development of optimal treatment strategies for PKU.

The Combination of Long-term Ketamine and Extinction Training Contributes to Fear Erasure by Bdnf Methylation

A combination of antidepressant drugs and psychotherapy exhibits more promising efficacy in treating fear disorders than either treatment alone, but underlying mechanisms of such treatments remain largely unknown. Here we investigated the role of DNA methylation of the brain-derived neurotrophic factor (Bdnf) gene in the therapeutic effects of ketamine in combination with extinction training in a mouse model of post-traumatic stress disorder (PTSD) induced by inescapable electric foot shocks (IFS). Male mice received ketamine for 22 consecutive days starting 1 h after the IFS (long-term ketamine treatment) or 2 h prior to the extinction training on days 15 and 16 after the IFS (short-term ketamine treatment). The Open Field (OF) and Elevated Plus Maze (EPM) tests were conducted on days 18 and 20. The spontaneous recovery and fear renewal tests were performed on day 23. Mice, subjected to IFS, exhibited anxiety-like behavior and fear relapse, accompanied by the increased levels of DNA methyltransferases, hyper-methylation of Bdnf gene, and decreased BDNF mRNA expression in the medial prefrontal cortex (mPFC) and hippocampus (HIP). Long-term treatment with ketamine combined with extinction training alleviated the IFS-induced abnormalities. These results suggest that long-term ketamine treatment in combination with extinction training may ameliorate fear relapse in the murine model of PTSD, at least in part, by normalizing DNA methylation of Bdnf gene.

Midazolam selectively potentiates the A(2A) - but not A1- receptor--mediated effects of adenosine: role of nucleoside transport inhibition and clinical implications

BACKGROUND

Inhibition of adenosine metabolism offers a unique approach to harness the cardioprotective properties of adenosine in a site- and event-specific manner. Benzodiazepines inhibit adenosine metabolism by blocking nucleoside transporter. Therefore, the authors studied the binding affinities of structurally different benzodiazepines to nucleoside transporter and benzodiazepine-induced potentiation of A1-adenosine (negative dromotropy) and A2A-adenosine (coronary vasodilation) receptor-mediated effects.

METHODS

In membranes from porcine striatum and guinea pig ventricle, competition binding assays to displace [3H]nitrobenzylmercaptopurine riboside ([3H]NBMPR) from nucleoside transporter were performed using alprazolam, chlorodiazepoxide, diazepam, flurazepam, and midazolam. The augmentation by the most potent benzodiazepine of A1- and A2A-adenosine receptor-mediated responses, elicited by exogenous administration of adenosine or brief periods of global hypoxia, was subsequently studied in guinea pig Langendorff-perfused hearts.

RESULTS

All benzodiazepines completely displaced [3H]NBMPR in a concentration-dependent manner with Hill coefficients not significantly different from unity in both striatal and ventricular membranes. Midazolam was the most potent inhibitor of nucleoside transporter (ventricle:pKi = 5.22+/-0.41, Ki = 6 microM). In isolated hearts, midazolam (5, 10, 20 microM) significantly augmented coronary flow in a concentration-dependent manner in the presence of adenosine (30 nM), an effect reversed by ZM 241385, a selective A2A-receptor antagonist. In contrast, midazolam did not increase the effect of adenosine (30 nM) on atrioventricular conduction. Similarly, midazolam potentiated A2A- but not A1-receptor-mediated effects of endogenous adenosine released during hypoxia.

CONCLUSIONS

Structurally distinct benzodiazepines inhibit nucleoside transporter to different degrees. Midazolam selectively augments A2A- but not A1-receptor-mediated effects of adenosine by inhibiting nucleoside transporter.

Role of environmental stressors in determining the developmental outcome of neonatal anesthesia

BACKGROUND

The majority of studies evaluating neurocognition in humans who had procedures under anesthesia early in life found long-term deficits even though the typical anesthesia duration normalized to the human life span is much shorter than that shown to induce developmental abnormalities in rodents. Therefore, we studied whether subsequent environmental stressors contribute to deficiencies programmed by a brief neonatal etomidate exposure.

METHODS

Postnatal days (P) 4, 5, or 6, Sprague-Dawley rats, pretreated with vehicle or the Na+-K+-2Cl- (NKCC1) inhibitor, bumetanide, received two injections of etomidate resulting in anesthesia for 2h. To simulate stress after anesthesia, the animals were exposed to a single maternal separation for 3h at P10. 3-7days after exposure to etomidate the rats had increased hypothalamic NKCC1 mRNA and corticotropin releasing hormone (CRH) mRNA and decreased K+-2Cl- (KCC2) mRNA levels with greater changes in males. In rats neonatally exposed to both etomidate and maternal separation, these abnormalities persisted into adulthood. These animals also exhibited extended corticosterone responses to restraint stress with increases in total plasma corticosterone more robust in males, as well as behavioral abnormalities. Pretreatment with the NKCC1 inhibitor ameliorated most of these effects.

CONCLUSIONS

Post-anesthesia stressors may exacerbate/unmask neurodevelopmental abnormalities even after a relatively short anesthetic with etomidate, leading to dysregulated stress response systems and neurobehavioral deficiencies in adulthood. Amelioration by bumetanide suggests a mechanistic role for etomidate-enhanced gamma-aminobutyric acid type A receptor-mediated depolarization in initiating long-lasting alterations in gene expression that are further potentiated by subsequent maternal separation.

Ionic basis of the differential effects of intravenous anesthetics on erythromycin-induced prolongation of ventricular repolarization in the guinea pig heart

BACKGROUND

Dysrhythmias and death occur in patients with acquired long QT syndrome (LQTS). Little information exists regarding interactions between anesthetics and drugs that prolong ventricular repolarization. Therefore the effects of three commonly used intravenous anesthetics on ventricular repolarization were investigated in the setting of drug-induced, long QT syndrome.

METHODS

The effects of increasing concentrations (0, 10, 25, and 50 microM) of propofol, ketamine, and thiopental on ventricular repolarization were evaluated by measuring the monophasic action potential duration at 90% repolarization (MAPD90) in guinea pig Langendorff-perfused hearts in the absence or presence of erythromycin (100 microM). If an anesthetic enhanced erythromycin-induced prolongation of MAPD90, its effects on the delayed rectifier (I[K]) and inward rectifier (I[Kl]) potassium currents were measured using the whole-cell patch-clamp technique.

RESULTS

At clinically relevant concentrations, only thiopental significantly modulated erythromycin's effect on MAPD90. Thiopental at 10, 25, and 50 microM prolonged MAPD90 from a control of 163 +/- 6 ms by 18 +/- 4, 30 +/- 3, and 31 +/- 4 ms, respectively. In a separate group, erythromycin prolonged MAPD90 from 155 +/- 2 ms to 171 +/- 2 ms (n = 21, P < 0.001). In the presence of erythromycin, thiopental at 10, 25, and 50 microM caused significantly greater prolongation from a control of 171 +/- 2 ms by 39 +/- 2, 58 +/- 3, and 72 +/- 6 ms, respectively. Whole-cell patch-clamp experiments indicated that thiopental inhibited I(K) and I(Kl).

CONCLUSIONS

Intravenous anesthetics caused markedly different effects on ventricular repolarization. Thiopental, unlike propofol and ketamine, potentiated the effects of erythromycin on ventricular repolarization by inhibiting I(K) and I(Kl).

Epilepsy in Phenylketonuria: A Complex Dependence on Serum Phenylalanine Levels

PURPOSE

Phenylketonuria (PKU) is a disorder of phenylalanine (Phe) metabolism that frequently results in epilepsy if a low Phe diet was not implemented at birth. The mechanisms by which Phe affects the brain are poorly understood.

METHODS

Audiogenic seizures (AGS) were studied in female homozygous Pah(enu2) BTBR (PKU) mice.

RESULTS

Adult PKU mice, 18-20 weeks of age, in contrast to wild-type and heterozygous counterparts, exhibited a full range of AGS. Younger PKU mice, 5-7 weeks of age, had higher serum Phe levels (2.22 +/- 0.20 mM) in comparison with the adult animals (1.72 +/- 0.05 mM) and were not susceptible to AGS. Among adult mice, animals susceptible to AGS had significantly lower serum Phe levels (1.62 +/- 0.06 mM) in comparison with those resistant to AGS (1.86 +/- 0.07 mM). Susceptibility to AGS tended to increase in the afternoon when serum Phe concentration decreased in comparison to evening and morning. Normalization of serum Phe level by instituting a low Phe diet generally prevented susceptibility to AGS within 12 h. Although return to a standard diet raised Phe levels to hyperphenylalaninemic within 12 h in animals treated with a low Phe diet for 2 weeks, more than 7 weeks were needed for a complete resumption of AGS.

CONCLUSIONS

Transient decrease in Phe levels within hyperphenylalaninemic range may be a necessary condition for PKU-related seizures to occur. A low Phe diet prevents susceptibility to seizures, which can resume with the significant delay after termination of dietary treatment.

PKU is a reversible neurodegenerative process within the nigrostriatum that begins as early as 4 weeks of age in Pah(enu2) mice

Phenylketonuria (PKU) is a common genetic disorder in humans that arises from deficient activity of phenylalanine hydroxylase (PAH), which catalyzes the conversion of phenylalanine to tyrosine. There is a resultant hyperphenylalanemia with subsequent impairment in cognitive abilities, executive functions and motor coordination. The neuropathogenesis of the disease has not been completely elucidated, however, oxidative stress is considered to be a key feature of the disease process. Hyperphenylalanemia also adversely affects monoaminergic metabolism in the brain. For this reason we chose to evaluate the nigrostriatum of Pah(enu2) mice, to determine if alterations of monoamine metabolism resulted in morphologic nigrostriatal pathology. Furthermore, we believe that recent developments in adeno-associated virus (AAV)-based vectors have greatly increased the potential for long-term gene therapy and may be a viable alternative to dietary treatment for this metabolic disorder. In this study we identified neurodegenerative changes with regenerative responses in the nigrostriatum of Pah(enu2) mice that are consistent with oxidative injury and occurred as early as 4 weeks of age. These neuropathologic changes were reversed following portal vein delivery of a recombinant adeno-associated virus-mouse phenylalanine hydroxylase-woodchuck hepatitis virus post-transcriptional response element (rAAV-mPAH-WPRE) vector to Pah(enu2) mice and corresponded to rapid reduction of serum Phe levels.

Role of Steroids in Hyperexcitatory Adverse and Anesthetic Effects of Sevoflurane in Neonatal Rats

Recent studies have demonstrated that long-term developmental effects of neonatal anesthesia were more prominent in males. We tested whether steroids, in general, and sex steroids, in particular, are involved in the mediation of sevoflurane-caused paradoxical cortical seizures during the early postnatal period.

METHODS

Cortical electroencephalograms, hippocampal synaptic activity, serum levels of steroids and the loss of the righting reflex (LORR), a marker of anesthetic effect, were measured on postnatal days 4-6 in Sprague Dawley rats of both genders exposed to 2.1% sevoflurane.

RESULTS

Episodes of seizures, persistent spikes in electroencephalograms and increases in serum corticosterone were similar in both genders. In the order of increasing potency, the corticosteroid receptor antagonist RU 28318, the estradiol receptor antagonist ICI 182780 and the estradiol synthesis inhibitor formestane decreased sevoflurane-induced seizures. Exogenous estradiol increased sevoflurane-caused seizures, spikes and serum levels of corticosterone. These estradiol-enhanced seizures and spikes were depressed by ICI 182780 and the NKCC1 inhibitor, bumetanide, while RU 28318 decreased seizures only. In hippocampal CA1 neurons, estradiol increased the amplitude, rise time and area under the curve of gamma-aminobutyric acid type A receptor (GABAAR)-mediated miniature postsynaptic currents. Exogenous estradiol shortened, while ICI 182780 and formestane lengthened the time needed for sevoflurane to induce LORR.

CONCLUSION

These findings provide evidence for gender-independent acute electroencephalographic effects of sevoflurane at this age. Corticosterone and estradiol are involved in the mediation of sevoflurane-induced seizures. Estradiol, but not corticosterone, also contributes to sevoflurane-caused spikes, by enhancing GABAAR-mediated excitation in the cortex. By increasing GABAAR-mediated inhibition in more mature caudal regions of the brain, estradiol contributes to sevoflurane-induced LORR.

Role of nitric oxide, cyclic GMP and superoxide in inhibition by adenosine of calcium current in rabbit atrioventricular nodal cells

OBJECTIVE

To study the intracellular pathways which mediate the inhibitory actions of adenosine on isoprenaline-stimulated calcium current (ICa) in atrioventricular (AV) nodal myocytes.

METHODS

The whole-cell patch-clamp technique was used to record ICa from rabbit AV nodal cells, isolated by enzymatic and mechanical dispersion.

RESULTS

Isoprenaline, 0.1 microM, increased peak ICa from 0.58 +/- to 1.23 +/- 0.1 nA, and this increase was reversibly inhibited by adenosine, 10 microM (83 +/- 6%), which we have previously shown to be mediated by nitric oxide (NO) production. A membrane-permeable analogue of cyclic GMP, 8-Br-cGMP (300 microM), an inhibitor of cGMP-stimulated phosphodiesterase, prevented the effect of adenosine on ICa-Methylene blue (10 microM), an inhibitor of NO-sensitive guanylyl cyclase and a generator of superoxide (.02-), did not prevent, but increased, the inhibiting action of adenosine (49.5 +/- 6.6%, P < 0.01). Methylene blue (50 microM) caused a reduction of ICa, with further inhibition when combined with adenosine. A .O(2-)-generating system, xanthine oxidase (0.02 U/ml) and purine (2.3 mM), also increased the inhibitory action of adenosine on ICa. Inhibition of ICa by adenosine in the presence of xanthine oxidase was not prevented by 8-Br-cGMP (300 microM) and was not influenced by pre-incubation of cells with a NO synthase inhibitor, L-NAME (0.5 mM).

CONCLUSIONS

The inhibitory effect of adenosine on ICa in rabbit AV nodal myocytes can be mediated by two mechanisms--stimulation of cGMP-stimulated phosphodiesterase by NO-induced cGMP, and a mechanism which involves interaction with .O2- production.

Ionic mechanisms mediating the differential effects of methohexital and thiopental on action potential duration in guinea pig and rabbit isolated ventricular myocytes

BACKGROUND

Commonly used barbiturate anesthetics may significantly influence cardiac electrophysiologic characteristics. The authors evaluated thiopental (a thiobarbiturate) and methohexital (an oxybarbiturate), two compounds with similar physicochemical properties but different structures, to determine whether they have distinct effects on the major ionic currents that determine action potential duration (APD) in ventricular myocytes.

METHODS

The effects of thiopental and methohexital (50 microM) on APD at 50% (APD50) and 90% (APD90) repolarization were studied in guinea pig and rabbit single ventricular myocytes using the patch-clamp technique in a whole-cell configuration. The ionic mechanisms underlying the APD changes were evaluated by measuring the anesthetics' effects on the L-type calcium inward current, the inward rectifier potassium current, and the delayed rectifier potassium current in guinea pig cells and on the transient outward potassium current in rabbit cells.

RESULTS

Thiopental and methohexital caused opposite effects on APD. Whereas thiopental prolonged APD50 and APD90 in guinea pig and rabbit ventricular myocytes, methohexital shortened them. Thiopental markedly depressed both the inward and outward components of the inward rectifier potassium current, whereas methohexital caused minimal inhibition of the inward component and no change in the outward component. The delayed rectifier potassium current was inhibited by thiopental but significantly potentiated by methohexital. Neither thiopental nor methohexital significantly affected the transient outward potassium current or the L-type calcium inward current.

CONCLUSIONS

Despite their similar lipid solubilities, molecular weights, and pKa values, thiopental increased and methohexital decreased the APD in ventricular myocytes by predominantly inhibiting the inward rectifier potassium current and the delayed rectifier potassium current and by increasing the delayed rectifier potassium current, respectively. These characteristics suggest distinct structure-specific actions of barbiturates on the function of myocardial ionic channels.

Macrophage Migration Inhibitory Factor Increases Neuronal Delayed Rectifier K+ Current

Macrophage migration inhibitory factor (MIF) has widespread actions in the immune, endocrine, and nervous systems. Previously, we reported that increases in the intracellular levels of MIF depress the firing of hypothalamus/brain stem neurons in culture, including the chronotropic actions of angiotensin II. The objective of this study was to investigate the effects of MIF on delayed rectifier K+ current ( IKv), one of the component currents whose activity contributes to neuronal firing. Intracellular perfusion of MIF (80 nM) into Sprague–Dawley rat neuronal cultures caused a significant increase in IKv, as measured by patch-clamp recordings. This effect was apparent by 3 min, and was maximal after 20–30 min. IKv current density (pA/pF) increased from 31.58 ± 2.36 in controls to 41.88 ± 3.76 in MIF-treated neurons (mean ± SE; n = 9; P < 0.01). MIF that had been inactivated by boiling did not alter IKv, and MIF-neutralizing antibodies abolished the action of recombinant MIF (rMIF). The stimulatory effect of MIF on IKv current density was mimicked by intracellular application of either P1S-MIF (80 nM) or the peptide MIF-(50–65) (0.8–8 μM), both of which harbor the thiol-protein oxidoreductase (TPOR) activity of the MIF molecule. Conversely, neither C60S-MIF (80 nM) nor the MIF homologue D-dopachrome tautomerase (80 nM), both of which lack TPOR activity, altered IKv. Finally, the increase in IKv produced by rMIF was abolished by the superoxide scavenger Tiron (1 mM). These studies indicate that the neuronal action of MIF includes a stimulatory action on IKv that may be mediated by a TPOR/superoxide-scavenging mechanism.

Subsequent maternal separation exacerbates neurobehavioral abnormalities in rats neonatally exposed to sevoflurane anesthesia

Several recent studies suggest that in the human population, a routine, short anesthetic in otherwise healthy infants is void of neurodevelopmental insult. On the other hand, many human retrospective epidemiological studies report evidence of cognitive abnormalities in children after testing those who had different anesthesia-requiring procedures in early childhood. We tested in a rat model whether post-anesthesia stressful environmental factors can contribute to developmental abnormalities that were initiated by a relatively short exposure to sevoflurane, the most widely used anesthetic in pediatric anesthesia, whose polyvalent actions include enhancement of gamma-aminobutyric acid type A receptor (GABA_AR) activity. Postnatal day 6 (P6) male Sprague-Dawley rats were anesthetized with sevoflurane for 60min. To simulate subsequent stress, the animals were subjected to a single maternal separation for 180min at P10. To study the role of GABA_AR-mediated depolarization, subgroups of P6 rats received a single injection of the Na⁺-K⁺-2Cl^- (NKCC1) inhibitor, bumetanide, prior to initiation of anesthesia with sevoflurane. Rats that were exposed to sevoflurane had decreased hypothalamic K⁺-2Cl^- (KCC2) mRNA level (F_(2,13)=3.839, P=0.049), increased NKCC1/KCC2 mRNA ratio (F_(2,13)=5.043, P=0.024) and increased corticotropin-releasing hormone (CRH) mRNA level (F_(2,12)=9.450, P=0.003) at P10, the age at which maternal separation was imposed. Adult rats, neonatally exposed to a combination of sevoflurane and maternal separation, exhibited increases in the escape latencies greater than animals exposed to sevoflurane only (P=0.012), and only rats in the sevoflurane plus maternal separation group spent significantly less time in the target quadrant during the Morris water maze test (F_(4,55)=4.856, P=0.002). Bumetanide ameliorated abnormalities induced by sevoflurane and a combination of sevoflurane plus maternal separation. Neonatal exposure to sevoflurane may sensitize to stressors later in life, and post-exposure stress may exacerbate neurodevelopmental abnormalities even after a relatively short exposure to sevoflurane in rodents. The NKCC1 downregulation prior to exposure to the anesthetic may be therapeutic.

Potassium outward current dependent on extracellular calcium in snail neuronal membrane

In experiments on isolated intracellularly dialysed neurons of the snail Helix pomatia a component of delayed inactivating potassium outward current depending on the presence of Ca2+ ions in the extracellular medium has been distinguished, which differs from the already known potassium current sensitive to intracellular calcium ions. This component decreases with a decrease in extracellular calcium (in the range of 10(-2) - 10(-5) M); it is not affected or even increased by intracellular introduction of ethyleneglycolbis(aminoethylether)tetra-acetate (10 mM) or fluoride ions (77 mM) and can be blocked by addition of 1.5 mM cobalt ions to the extracellular solution. Contrary to the slow rising potassium current dependent on intracellular calcium, this current has a fast rising phase (several milliseconds) and time-dependent inactivation. The inactivation depends on extracellular potassium ions: it slowed down when [K+]out is increased in the range of 1-10 mM. Extracellular application of calmodulin blockers calmidazolium (6.5 X 10(-7) M) and chlorpromazine (2.5 X 10(-6) M) selectively inhibits the potassium current dependent on intracellular calcium but does not affect that dependent on external calcium. Tetraethylammonium (10 mM) depresses the latter current on both intra- and extracellular application, the former being more effective. The existence of a special type of potassium channel sensitive to extracellular calcium ions is postulated.