Intravenous anesthesia

Anticholinergics, tranquilizers, and sedative-hypnotics are the usual agents used for preanesthetic sedation of the horse. Of these drugs, the anticholinergics are of little importance in the horse. Acepromazine is the most useful and widely used tranquilizer, whereas xylazine is a safe and popular sedative. A newer sedative recently made available to the veterinarian for clinical use in horses is detomidine. Thiobarbiturates are seldom used alone any longer but are still useful when combined with guaifenesin for induction and maintenance of anesthesia. Other, more contemporary drug combinations that have largely replaced thiobarbiturates and chloral hydrate include xylazine with ketamine, xylazine with Telazol, detomidine with Telazol, and guaifenesin with ketamine and xylazine.     

Partial pressures of oxygen and carbon dioxide, pH, and concentrations of bicarbonate, lactate, and glucose in pleural fluid from horses

Samples of pleural fluid from 20 horses with effusive pleural diseases of various causes were evaluated; samples from 19 horses were used for the study. There were differences for pH (P = 0.001) and partial pressure of oxygen (PO2) between arterial blood and nonseptic pleural fluid (P = 0.0491), but there were no differences for pH, PO2, partial pressure of carbon dioxide (PCO2), and concentrations of bicarbonate (HCO3-), lactate, and glucose between venous blood and nonseptic pleural fluid. Paired comparisons of venous blood and nonseptic pleural fluid from the same horse indicated no differences. There were differences (P = 0.0001, each) for pH, PO2, PCO2, and concentrations of HCO3- between arterial blood and septic pleural fluid. Differences also existed for pH (P = 0.0001), PCO2 (P = 0.0003), and concentrations of HCO3- (P = 0.0001), lactate (P = 0.0051), and glucose (P = 0.0001) between venous blood and septic pleural fluid. Difference was not found for values of PO2 between venous blood and septic pleural fluid, although 4 samples of septic pleural fluid contained virtually no oxygen. Paired comparisons of venous blood and septic pleural fluid from the same horse revealed differences (P less than 0.05) for all values, except those for PO2. These alterations suggested functional and physical compartmentalization that separated septic and healthy tissue. Compartmentalization and microenvironmental factors at the site of infection should be considered when developing therapeutic strategies for horses with septic pleural disease.     

Molecular and neuronal substrate for the selective attenuation of anxiety

Benzodiazepine tranquilizers are used in the treatment of anxiety disorders. To identify the molecular and neuronal target mediating the anxiolytic action of benzodiazepines, we generated and analyzed two mouse lines in which the alpha2 or alpha3 GABAA (gamma-aminobutyric acid type A) receptors, respectively, were rendered insensitive to diazepam by a knock-in point mutation. The anxiolytic action of diazepam was absent in mice with the alpha2(H101R) point mutation but present in mice with the alpha3(H126R) point mutation. These findings indicate that the anxiolytic effect of benzodiazepine drugs is mediated by alpha2 GABAA receptors, which are largely expressed in the limbic system, but not by alpha3 GABAA receptors, which predominate in the reticular activating system.     

Phylogenetic history of Phytophthora cryptogea and P. drechsleri isolates from floriculture crops in North Carolina greenhouses

The evolutionary history of Phytophthora cryptogea and P. drechsleri isolates previously collected from floriculture crops in North Carolina commercial greenhouses was explored with coalescent- and parsimony-based analyses. Initially, 68 isolates representing 13 location-host groups were sequenced at multiple loci. Sequences of all isolates within a group were identical. A subset of isolates were selected, cloned to resolve heterozygous sites, and analyzed with SNAP Workbench. The internal transcribed spacer (ITS) region of the ribosomal DNA and cytochrome oxidase II gene genealogies were congruent and indicated that P. cryptogea and P. drechsleri are sister species diverged from a common ancestor with no evidence of gene flow. In contrast, genealogies inferred from β-tubulin (β-tub) and translation elongation factor 1α (EF-1α) genes were in conflict with these loci. Coalescent analysis based on a nonrecombining partition in β-tub and EF-1α showed an initial (older) split between P. cryptogea and P. drechsleri, with a later (recent) event separating the remaining P. cryptogea haplotypes from P. drechsleri. A parsimony-based minimal ancestral recombination graph inferred recombination between P. cryptogea and P. drechsleri isolates in the ITS region and β-tub, suggesting genetic exchange between species. Also, putative recombination between A1 and A2 mating types of P. cryptogea suggests that sexual reproduction has occurred in the history of these P. cryptogea isolates.     

Cellulase activity as a mechanism for suppression of phytophthora root rot in mulches

Wood-based mulches are used in avocado production and are being tested on Fraser fir for reduction of Phytophthora root rot, caused by Phytophthora cinnamomi. Research with avocado has suggested a role of microbial cellulase enzymes in pathogen suppression through effects on the cellulosic cell walls of Phytophthora. This work was conducted to determine whether cellulase activity could account for disease suppression in mulch systems. A standard curve was developed to correlate cellulase activity in mulches with concentrations of a cellulase product. Based on this curve, cellulase activity in mulch samples was equivalent to a cellulase enzyme concentration of 25 U ml(-1) or greater of product. Sustained exposure of P. cinnamomi to cellulase at 10 to 50 U ml(-1) significantly reduced sporangia production, but biomass was only reduced with concentrations over 100 U ml(-1). In a lupine bioassay, cellulase was applied to infested soil at 100 or 1,000 U ml(-1) with three timings. Cellulase activity diminished by 47% between 1 and 15 days after application. Cellulase applied at 100 U ml(-1) 2 weeks before planting yielded activity of 20.08 μmol glucose equivalents per gram of soil water (GE g(-1) aq) at planting, a level equivalent to mulch samples. Cellulase activity at planting ranged from 3.35 to 48.67 μmol GE g(-1) aq, but no treatment significantly affected disease progress. Based on in vitro assays, cellulase activity in mulch was sufficient to impair sporangia production of P. cinnamomi, but not always sufficient to impact vegetative biomass.     

A practical technique for preparation of antiserum to canine factor VIII-related antigen

Identification and measurement of canine factor VIII-related antigen (VIIIR:Ag) has many clinical and research applications, including differential diagnosis of hemophilia A and von Willebrand's disease, use as a marker for specific cell types, and elucidation of the structure of this factor VIII component. We have developed a practical method for producing antibodies to canine VIIIR:Ag that uses 2% agarose filtration for purification and identifies the antigen by correlation with the elution of the peak A280 fraction in the void volume. Antisera for electroimmunoassay (EIA) can be produced in less than four weeks from simple starting materials and with commonly available laboratory equipment. This technique would be useful for either clinical veterinary or comparative research laboratories.     

Efficacies of trimethoprim-sulfadiazine and gentamicin sulfate in the treatment of fibrinous peritonitis in rats

Trimethoprim-sulfadiazine and gentamicin sulfate decreased early mortality in an established model of fibrinous peritonitis in the rat. Both drugs failed to prevent abscess formation, indicating that there was poor penetration of fibrin; however, they significantly decreased (P less than 0.01) bacterial numbers in residual abscesses. The colony count per abscess in the gentamicin sulfate-treated group was significantly lower (P less than 0.01) than that in the trimethoprim-sulfadiazine-treated group.     

Anesthetic management of ruminants and swine with selected pathophysiologic alterations

Surgical diseases induce pathophysiologic alterations in ruminants and swine that are often of critical importance in the perioperative period. Circulation and ventilation may be severely compromised. Alterations in acid-base balance, fluids, and electrolytes should be anticipated, identified, and corrected. Also discussed is the selection of appropriate anesthetic techniques and supportive therapy based upon the patient's physiologic status and surgical requirements.     

Alterations in the arrhythmogenic dose of epinephrine after adrenergic receptor blockade with prazosin, metoprolol, or yohimbine in halothane-xylazine-anesthetized dogs

Recent evidence has linked alpha-receptor and beta-receptor activations with ventricular arrhythmia genesis. In order to assess the relative contribution of specific adrenoceptors (alpha 1, alpha 2, beta 1) on ventricular arrhythmogenic activity during xylazine (1.1 mg X kg-1 X hr-1)-halothane (1.35%) anesthesia, the arrhythmogenic dose of epinephrine (ADE) was repeatedly determined before and after prazosin (alpha 1 antagonist; 0.1 mg X kg-1), metoprolol (beta 1 antagonist; 0.5 mg X kg-1), and yohimbine (alpha 2 antagonist; 0.125 mg X kg-1) administration in 6 dogs. The ADE was expressed as infusion rate and total dose. The ADE was defined as the dose which produced 4 or more intermittent premature ventricular contractions within 15 s during a 3-minute infusion period or within 1 minute from end of infusion. Control ADE was 2.69 +/- 0.372 (micrograms X kg-1 X min-1) and 4.17 +/- 0.544 (micrograms X kg X -1) for infusion rate and total dose, respectively. The ADE significantly increased after prazosin (P less than 0.005), metoprolol (P less than 0.005), and yohimbine (P less than 0.05) administration. The ADE values increased to 5.42 +/- 1.22 (rate) and 8.10 +/- 1.95 (dose) after alpha 2 blockade, but were significantly less than the alpha 1 and beta 1 blockade ADE values. In conclusion, although both alpha- and beta-adrenoceptor blockade depressed ventricular arrhythmia genesis in xylazine-halothane-anesthetized dogs, alpha 2 blockade, which was achieved with the recommended dose of yohimbine for reversal of anesthetic-induced CNS depression, was not as protective as alpha 1 (prazosin) or beta 1 (metoprolol) blockade.