Justification Of Empiric Methodology to Determine Dexmedetomidine Dose for the TREX Study.

INTRODUCTION: Dexmedetomidine is the sedative agent administered in combination with remifentanil and low dose of sevoflurane in the interventional arm of the ongoing TREX trial (Trial Remifentanil DExmedetomidine). The TREX pilot study (published in Paediatr Anaesth 2019;29:59-67) established infusion rates higher than those initially proposed. This could be attributed to an inappropriate target concentration for sedation or incorrect initial pharmacokinetic parameter estimates. METHODS: The TREX study is a Phase III, randomized, active controlled, parallel group, blinded evaluator, multicentre, superiority trial comparing neurological outcome after standard sevoflurane anaesthesia with dexmedetomidine/remifentanil and low dose sevoflurane anaesthesia in children aged less than 2 years undergoing anaesthesia of 2 hours or longer. In this report, dexmedetomidine pharmacokinetics were analysed in the interventional arm of the Italian population. RESULTS: There were 162 blood samples from 32 infants (22 male and 10 female). The median (IQR) age was 12 (5.2-15.5) months, weight 9.9 (7.3-10.8) kg. Duration of anaesthesia ranged from 2-6 hours. None of the children were born premature (median postnatal age 39 weeks, IQR 38-40 weeks). A 3-compartment PK model that incorporated allometric scaling and a maturation function demonstrated plasma concentration observations from the current Italian arm of the TREX study were consistent with those predicted by a "universal" model using pooled data obtained from neonates to adults. CONCLUSIONS: This current PK analysis from the Italian arm of the TREX study confirms that plasma concentration of dexmedetomidine is predictable using known covariates such as age and size. The initial target concentration (0.6 µg.L-1 ) used to sedate children cared for in the intensive care after cardiac surgery was inadequate for infants in the current TREX study. A target concentration 1 mcg.L-1 , corresponding to a loading dose of 1 mcg.kg-1 followed by an infusion of 1 mcg.kg-1 .hour-1 , provided adequate sedation.

Effects of oxotremorine on neuronal RNA and chromatin in thalamic cholinoceptive sites.

Neuronal nucleic acid responses were examined within the rat thalamic ventrobasal nuclear complex (VBC) and nucleus reticularis (NR) following single intraperitoneal injections of the central muscarinic-cholinergic (M2) receptor agonist oxotremorine (0.1, 0.7, or 1.0 mg/kg). After stoichiometric azure B and Feulgen staining of brain sections, scanning-integrating cytophotometry was used to quantify azure B-ribonucleic acid (RNA) content, Feulgen-DNA levels, and changes in the susceptibility of chromatin to Feulgen acid hydrolysis (F-DNA yield) of neurons on an individual basis. Changes in neuronal nucleolar volume were also determined histometrically. Within the VBC, oxotremorine produced marked dose-dependent elevations in neuronal RNA content and nucleolar volume with increased F-DNA yield (chromatin activation) in a proportion of VBC neurons. In contrast, within the NR, oxotremorine elicited reductions in RNA levels, F-DNA yield and nucleolar volume. The data demonstrate that oxotremorine-induced central muscarinic receptor stimulation is associated with metabolic correlates of thalamic VBC neuroexcitation and NR neuron depression. The overall study lends further credence to the hypothesis that muscarinic-cholinergic mechanisms are operative within the mammalian thalamus.

Quantitative cytophotometric analysis of brain neuronal RNA and protein changes in acute T-2 mycotoxin poisoned rats.

Male Sprague-Dawley rats (200 g) injected intraperitoneally with T-2 toxin, a trichothecene mycotoxin protein synthesis inhibitor, at dosages of 0.75, 1.0, 1.5 and 6.0 mg/kg (1 LD50 = 0.9 mg/kg) were decapitated at 8 hr post-exposure. Data were obtained on changes in neuronal (perikaryal) RNA levels, protein contents and nucleolar volumes in cerebrocortical (layer III) and striatal (caudate-putamen) brain regions using quantitative azure B-RNA and Coomassie-protein cytophotometry and ocular filar micrometry. Correlative observations were made on changes in brain cytomorphology. Reductions in neuronal RNA/protein contents and nucleolar volume were used as indices of impaired perikaryal functioning. At 8 hr after T-2 toxin poisoning the following results were obtained in cerebrocortical and striatal brain compartments: neuronal RNA contents were generally maintained at control values in both brain regions, however, moderate RNA depletion was evidenced in the cerebral cortex with 1.5 mg/kg T-2 and in the striatum with a 6.0 mg/kg dose; neuronal protein levels were suppressed in a dose-dependent fashion within the cerebrocortex, while in the striatum there was no direct correspondence between protein loss and T-2 dosage; neuronal nucleolar volumes were typically maintained at control levels in both neuronal compartments. Microscopic observations revealed no gross evidence of T-2-induced brain cytopathology. These data indicate that T-2 toxin does not elicit direct cytopathic actions in these two brain regions, thus indicating that cerebrocortical and striatal compartments do not represent primary target sites of T-2 toxicant action.(ABSTRACT TRUNCATED AT 250 WORDS)

Mesenteric mast cell degranulation in acute T-2 toxin poisoning.

T-2 toxin-induced alterations in rat mesenteric mast cell granulation were measured by cytophotometric analyses of the metachromatic reaction of mast cell granules with azure B. Hypogranulation (diminution of metachromatic material) was observed 8 h following injections of T-2 toxin (0.5-1.5 LD50, i.p.). These data suggest that mast cell activation occurs during acute T-2 intoxication and raise the possibility that mast cell mediators may contribute to toxin-induced cardiovascular collapse.