Isoflurane disrupts excitatory neurotransmitter dynamics via inhibition of mitochondrial complex I

BACKGROUND

The mechanisms of action of volatile anaesthetics are unclear. Volatile anaesthetics selectively inhibit complex I in the mitochondrial respiratory chain. Mice in which the mitochondrial complex I subunit NDUFS4 is knocked out [Ndufs4(KO)] either globally or in glutamatergic neurons are hypersensitive to volatile anaesthetics. The volatile anaesthetic isoflurane selectively decreases the frequency of spontaneous excitatory events in hippocampal slices from Ndufs4(KO) mice.

METHODS

Complex I inhibition by isoflurane was assessed with a Clark electrode. Synaptic function was measured by stimulating Schaffer collateral fibres and recording field potentials in the hippocampus CA1 region.

RESULTS

Isoflurane specifically inhibits complex I dependent respiration at lower concentrations in mitochondria from Ndufs4(KO) than from wild-type mice. In hippocampal slices, after high frequency stimulation to increase energetic demand, short-term synaptic potentiation is less in KO compared with wild-type mice. After high frequency stimulation, both Ndufs4(KO) and wild-type hippocampal slices exhibit striking synaptic depression in isoflurane at twice the 50% effective concentrations (EC₅₀). The pattern of synaptic depression by isoflurane indicates a failure in synaptic vesicle recycling. Application of a selective A₁ adenosine receptor antagonist partially eliminates isoflurane-induced short-term depression in both wild-type and Ndufs4(KO) slices, implicating an additional mitochondria-dependent effect on exocytosis. When mitochondria are the sole energy source, isoflurane completely eliminates synaptic output in both mutant and wild-type mice at twice the (EC₅₀) for anaesthesia.

CONCLUSIONS

Volatile anaesthetics directly inhibit mitochondrial complex I as a primary target, limiting synaptic ATP production, and excitatory vesicle endocytosis and exocytosis.

General practitioners knowledge, practice and training requirements in relation to doping in sport

This study examined General Practitioner's (GP) knowledge, practice and training requirements in relation to doping in sport in Ireland. All 2083 GPs on the Irish College of General Practitioners (ICGP) register received a postal questionnaire, yielding a 37% response rate (N=771, 63% male, average age 46.2 +/- 9SD, range 28-74 years). Results revealed that 14% (112) deemed their knowledge of doping agents to be good or very good, 12% (94) had completed specific training modules in doping or sport, and 24% (183) were connected with a specific sport as a team doctor/advisor. Over one in four (28%: 217) had been consulted for advice on doping in Sport, 33% (256) possessed the current list of prohibited substances, and 25% (190) knew of the Irish Sports Council's drug-testing procedures. The current initiatives to discourage doping in sport were felt to be ineffective, and although 92% (716) indicated that GPs had a role to play in the prevention of doping in sport, only 9% (66) felt adequately trained for such a role. There was overwhelming support for further training among GPs, although the most appropriate method of providing training is complex and requires strategic planning.

Quantitative analysis of associations between DNA hypermethylation, hypomethylation, and DNMT RNA levels in ovarian tumors

How hypermethylation and hypomethylation of different parts of the genome in cancer are related to each other and to DNA methyltransferase (DNMT) gene expression is ill defined. We used ovarian epithelial tumors of different malignant potential to look for associations between 5'-gene region or promoter hypermethylation, satellite, or global DNA hypomethylation, and RNA levels for ten DNMT isoforms. In the quantitative MethyLight assay, six of the 55 examined gene loci (LTB4R, MTHFR, CDH13, PGR, CDH1, and IGSF4) were significantly hypermethylated relative to the degree of malignancy (after adjustment for multiple comparisons; P < 0.001). Importantly, hypermethylation of these genes was associated with degree of malignancy independently of the association of satellite or global DNA hypomethylation with degree of malignancy. Cancer-related increases in methylation of only two studied genes, LTB4R and MTHFR, which were appreciably methylated even in control tissues, were associated with DNMT1 RNA levels. Cancer-linked satellite DNA hypomethylation was independent of RNA levels for all DNMT3B isoforms, despite the ICF syndrome-linked DNMT3B deficiency causing juxtacentromeric satellite DNA hypomethylation. Our results suggest that there is not a simple association of gene hypermethylation in cancer with altered DNMT RNA levels, and that this hypermethylation is neither the result nor the cause of satellite and global DNA hypomethylation.

Inherited phosphofructokinase deficiency in an American cocker spaniel

A 3-year-old female American Cocker Spaniel with a chronic hemolytic disorder and hemolytic crises was found to have M-type phosphofructokinase deficiency. This inherited erythroenzymopathy and myopathy is commonly diagnosed in English Springer Spaniels, but the family study of this Cocker Spaniel, although supporting an autosomal recessive mode of inheritance, did not reveal any English Springer Spaniel ancestors. Molecular genetic studies did, however, identify the same mutation in this dog as we previously reported in the English Springer Spaniel breed, suggesting that this mutation originated prior to the separation of these 2 breeds.

Esophageal deviation in four English Bulldogs

Regurgitation, vomiting, and aspiration pneumonia in 4 young male English Bulldogs were attributed to esophageal deviation that was demonstrated by esophageal radiography. A genetic relationship among these dogs was not determined. Exploratory thoractomy, performed in 2 dogs, demonstrated an apparent compression of the esophagus by the left subclavian artery and brachiocephalic artery at the level of the 2nd and 3rd intercostal spaces. This apparent compression correlated with the roentgen location of esophageal deviation. Surgical redirection of the left subclavian artery resulted in immediate and long-lasting remission of clinical signs.

Anomalous portosystemic anastomoses associated with chronic hepatic insufficiency in six young dogs

Chronic hepatic insufficiency due to anomalies of the portal venous system was diagnosed in 6 young dogs. The disorder was characterized by a variety of abnormal central nervous system signs or ascites, or both. Laboratory findings were characteristic of chronic, generalized hepatic dysfunction. The diagnosis was established by angiographic studies of the portal venous system. Of the 6 dogs, 3 died, 1 was euthanatized, and 2 are still alive and require medical management for ascites.