Simon Stapleton

Clinical and microbiologic features guiding treatment recommendations for brain abscesses in children.

Background: There are no guidelines for the management of brain abscesses in children, and there is a paucity of recent data describing clinical and microbiologic features. We aimed to identify factors affecting outcome to inform antibiotic recommendations. Methods: From 1999 to 2009, 118 children presented with brain abscesses to 4 neurosurgical centers in the United Kingdom. Clinical, microbiologic and treatment data were collected. Results: The commonest preceding infection was sinusitis, with 59% of all children receiving antibiotics before diagnosis. Nonspecific symptoms were common, with only 13% having the triad of fever, headache and focal neurological deficit. Time between symptom onset and diagnosis varied widely (median, 10 days; range, 0–44). Magnetic resonance imaging was more frequently diagnostic than computed tomography. The most frequent organisms were Streptococcus milleri (38%), except after penetrating head injury or neurosurgery, for which Staphylococcus aureus was most common. The commonest empiric antibiotics were ceftriaxone/cefotaxime and metronidazole, which offered effective antimicrobial therapy in up to 83% of cases. Metronidazole added benefit in a maximum of 7% of cases, with ceftriaxone/cefotaxime alone sufficient in at least 76% and in all cases with cyanotic congenital heart disease or meningitis. A carbapenem would have been effective in 90%. The case fatality rate was 6% (33% in the immunocompromised). Long-term neurological sequelae affected 35%. Age younger than 5 years and a Glasgow Coma Scale score ⩽8 were associated with poor outcome at 6 months. Conclusions: We recommend ceftriaxone/cefotaxime and metronidazole as empiric treatment, although metronidazole may be unnecessary in many cases, with antistaphylococcal cover in cases of head trauma. Meropenem potentially would be a better choice in the immunocompromised. A prospective study of intravenous and oral treatment guided by clinical improvement is required beause 1–2 weeks of intravenous antibiotics during a total of 6 weeks may be sufficient in children.

Effects of metabolic blockers on Ca2+‐dependent currents in cultured sensory neurones from neonatal rats

1 The whole cell variant of the patch clamp technique was used to record high voltage‐activated Ca2+ currents and Ca2+‐activated Cl− tail currents from cultured neonatal rat dorsal root ganglion neurones. The aim of the project was to use these currents as physiological indices of intracellular Ca2+ regulation under control conditions and in the presence of metabolic inhibitors. 2 Carbonyl cyanide p‐trifluoromethoxyphenylhydrazone (5 μm) and sodium cyanide (1 μm) inhibited Ca2+ currents within 20 s, even when ATP was present in the patch pipette solution, suggesting a direct action on Ca2+ channels. These metabolic inhibitors did not affect Ca2+ current ‘run down’ or inactivation kinetics. 3 Cultured neonatal dorsal root ganglion neurones of the rat were relatively insensitive to the removal of glucose and ATP from the recording solutions for up to 3 h. These data suggest that the Ca2+ homeostatic mechanisms in these cells are highly resistant to metabolic insult. 4 However 2‐deoxy‐d‐glucose (5 mM) in the extracellular recording medium with no ATP or glucose present did prolong the deactivation time of Ca2+‐activated Cl− tail currents and increase the total charge flow following activation of a 500 ms voltage‐activated Ca2+ current. This effect was prevented by inclusion of d‐fructose 1,6‐diphosphate (500 μm) in the patch pipette solution. 5 We conclude that some agents used to induce chemical hypoxia, such as carbonyl cyanide p‐trifluoromethoxyphenylhydrazone and sodium cyanide, may interact directly with voltage‐activated Ca2+ channels and are therefore not appropriate for use in studying disturbed neuronal Ca2+ homeostasis. However, the use of 2‐deoxy‐d‐glucose in the absence of glucose and ATP does represent a model of disturbed Ca2+ homeostasis in cultured dorsal root ganglion neurones. In this study we have combined the whole cell recording technique with cultured neurones under conditions which produce a degree of metabolic stress as reflected by prolonged Ca2+‐activated Cl− tail currents. The reduced efficiency of handling of intracellular Ca2+ loads may be an important factor contributing to the onset of neuronal damage during hypoxia and ischaemia.

Regional heterogeneity of benzodiazepine binding sites in rat brain

Displacement of [3H]propyl-beta-carboline-3-carboxylate ([3H]PrCC) and [3H]flunitrazepam ([3H]FNM) was studied in rat hippocampus and cerebellum. Diazepam displaced both ligands with equal potency in both regions. Ethyl-beta-carboline-3-carboxylate (beta CCE) and CL 218,872 displaced [3H]PrCC more potently than [3H]FNM and were more potent in the cerebellum than the hippocampus. Beta CCE and CL 218,872 interact more potently with BZ1 than BZ2 sites, while diazepam is equipotent. GABA and chloride ions enhance the potency of diazepam and CL 218,872 but not beta CCE.

Palmitoyl‐dl‐carnitine has calcium‐dependent effects on cultured neurones from rat dorsal root ganglia

1 The effects of palmitoyl‐dl‐carnitine (0.01 to 1 mm) on whole cell voltage‐activated calcium channel currents carried by calcium or barium and Ca2+‐activated chloride currents were studied in cultured neurones from rat dorsal root ganglia. 2 Palmitoyl‐dl‐carnitine applied to the extracellular environment or intracellularly via the patch solution reduced Ca2+ currents activated over a wide voltage range from a holding potential of −90 mV. Inhibition of high voltage activated Ca2+ channel currents was dependent on intracellular Ca2+ buffering and was reduced by increasing the EGTA concentration from 2 to 10 mm in the patch solution. Barium currents were significantly less sensitive to palmitoyl‐dl‐carnitine than Ca2+ currents. 3 The amplitude of Ca2+‐activated Cl− tail currents was reduced by palmitoyl‐dl‐carnitine. However, the duration of these Cl− currents was greatly prolonged by palmitoyl‐dl‐carnitine, suggesting slower removal of free Ca2+ from the cytoplasm following Ca2+ entry through voltage‐activated channels. 4 Palmitoyl‐dl‐carnitine evoked Ca2+‐dependent inward currents which could be promoted by activation of the residual voltage‐activated Ca2+ currents and attenuated by intracellular application of EGTA. 5 We conclude that palmitoyl‐dl‐carnitine reduced the efficiency of intracellular Ca2+ handling in cultured dorsal root ganglion neurones and resulted in enhancement of Ca2+‐dependent events including inactivation of voltage‐activated Ca2+ currents. The activation of inward currents by palmitoyl‐dl‐carnitine may involve Ca2+‐induced Ca2+ release from intracellular stores, or direct interaction of palmitoyl‐dl‐carnitine with Ca2+ stores.

Inhibitory actions of synthesised polyamine spider toxins and their analogues on Ca2+-activated Cl− currents recorded from cultured DRG neurones from neonatal rats

The whole cell variant of the patch clamp technique was used to investigate the actions of polyamine spider toxins and their analogues on high voltage-activated Ca2+ currents and Ca2+-activated Cl- currents (I(Cl(Ca))). The actions of synthesised FTX (putative natural toxin from the American funnel web spider), sFTX-3.3, Orn-FTX-3.3, Lys-FTX-3.3, and argiotoxin-636 on cultured dorsal root ganglion neurones from neonatal rats were investigated. Synthesised FTX (1 microM) inhibited I(Cl(Ca)) but did not inhibit high voltage-activated Ca2+ currents. In contrast, sFTX-3.3 (10 microM) inhibited both high voltage-activated Ca2+ currents and the associated I(Cl(Ca)) in near equal proportions. Argiotoxin-636 (1-10 microM) inhibited I(Cl(Ca)) evoked by Ca2+ entry through voltage-activated channels and by intracellular photorelease of Ca2+ from a caged precursor DM-nitrophen. This data indicates that synthesised FTX and argiotoxin-636 directly inhibit Ca2+-activated Cl- channels. In conclusion, the potency of polyamines as non-selective inhibitors of Ca2+ channels and Ca2+-activated Cl- channels is in part determined by the presence of a terminal arginine and this may involve an interaction between terminal guanidino groups and Ca2+ binding sites.

Modulation of Ca2+-dependent currents in metabolically stressed cultured sensory neurones by intracellular photorelease of ATP

1 The whole cell recording technique was used to study high voltage‐activated Ca2+ currents and Ca2+‐activated Cl− tail currents from cultured neonatal dorsal root ganglion neurones of the rat which were metabolically stressed. The neurones were metabolically stressed with 2‐deoxy‐d‐glucose (5 mm) for 30 min to 3 h. The aim of the project was to examine the actions of intracellular photorelease of ATP on the properties of Ca2+‐dependent currents and determine if the effects of metabolic stress could be reversed. 2 The mean duration of Ca2+‐activated Cl− tail currents was significantly increased by metabolic stress and this effect was reversed by intracellular photorelease of approximately 300 μm ATP. Intracellular photolysis of ‘caged’ photolabile compounds was achieved with a xenon flash lamp. 3 Intracellular photorelease of ATP and adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) (about 40 μm) also accelerated the inactivation of high voltage‐activated Ca2+ currents evoked by 500 ms depolarizing step commands from −90 mV to 0 mV. This effect was prevented by intracellular application of the calcineurin (protein phosphatase‐2B) inhibitor cyclosporin A (14 nm) and cyclophihn A (50 nm) either applied together or individually. In contrast the protein phosphatase 1 and 2A inhibitor, calyculin A, increased voltage‐activated Ca2+ currents, but failed to prevent enhanced inactivation induced by intracellular photorelease of ATP. Intracellular photorelease of ATP had no effect on Ca2+ currents recorded from control neurones which were not metabolically stressed and supplied with glucose and ATP in the extracellular and patch pipette solutions respectively. 4 In conclusion, intracellular photorelease of ATP increases the decay of Ca2+‐activated Cl− tail currents in metabolically stressed neurones suggesting that the efficiency of intracellular Ca2+ buffering was improved. Additionally, an ATP/cyclic AMP‐dependent component of high voltage‐activated Ca2+ current inactivation which is mediated by calcineurin is revealed following photolysis of ‘caged’ ATP or cyclic AMP in metabolically stressed neurones.

INHIBITORY ACTIONS OF SYNTHESISED POLYAMINE SPIDER TOXINS AND THEIR ANALOGUES ON NEURONAL VOLTAGE-ACTIVATED CALCIUM CURRENTS

Abstract The whole cell variant of the patch-clamp technique was used to investigate the actions of polyamine spider toxins and their analogues on high voltage-activated Ca 2+ currents. The actions of synthesised FTX (putative natural toxin from the American funnel web spider), sFTX-3.3, Orn-FTX-3.3 and Lys-FTX-3.3 (synthetic analogues of FTX) were studied using cultured dorsal root ganglion neurones from neonatal rats, C2D7 cells (HEK293 cells stably coexpressing recombinant human N-type voltage-activated Ca 2+ channel, α 1B-1 - α 2b δβ 1b subunits) and freshly isolated cerebellar Purkinje neurones. In dorsal root ganglion neurones, sFTX-3.3 (10 μ M) inhibited high voltage-activated Ca 2+ currents evoked by depolarisations to 0 mV from a holding potential of −90 mV. Partial overlap in Ca 2+ current sensitivity to the polyamine sFTX-3.3 and the peptide spider toxin ω -Aga IVA was observed. However, evidence also suggests sFTX-3.3 and ω -Aga IVA do not show complete pharmacological overlap and that distinct parts of the Ca 2+ current are sensitive to one of two inhibitors. The arginine group on sFTX-3.3 appears to be important for its inhibitory action on Ca 2+ currents, because analogues where this amino acid was replaced with either ornithine (Orn-FTX-3.3) or lysine (Lys-FTX-3.3) were relatively inactive at concentrations below 1 mM. Synthesised FTX (100 μ M) was inactive as an inhibitor of Ca 2+ currents recorded from dorsal root ganglion and only produced modest effects in Purkinje neurones and C2D7 cells. At a concentration of 1 mM, nonselective actions were observed that indicated that synthesised FTX and sFTX-3.3 could reversibly inhibit both N- and P-type Ca 2+ channels equally well. In conclusion, the potency of polyamines as nonselective inhibitors of Ca 2+ channels is in part determined by the presence of a terminal arginine, and this may involve an interaction between terminal guanidino groups with Ca 2+ binding sites.

Yawning as a presenting symptom of Chiari malformation Type I: report of 2 cases

Yawning is thought to be a behavior regulated by the brainstem. Although excessive yawning has been reported in brainstem strokes, demyelination, and tumors, the cases presented here are the first reports of excessive yawning in patients with Chiari malformation Type I (CM-I). The authors believe that brainstem compression at the craniocervical junction and ensuing edema were implicated in this curious symptomatology. They describe excessive yawning as a presenting feature of CM-I in 2 adolescent females. The presentation was acute in the first case and more chronic in the second. Both patients underwent foramen magnum decompression, which resulted in complete cessation of the excessive yawning.