Joseph J. Quinlan

Anesthesia Sensitivity in Mice that Lack the β3 Subunit of the γ-Aminobutyric Acid Type A Receptor

BackgroundThe mammalian gamma-aminobutyric acid type A (GABAA) receptor, a likely target of anesthetic action, exhibits remarkable subunit heterogeneity. In vitro expression studies suggest that there is subunit specificity to anesthetic responses at the GABAA receptor. The authors tested whether ge

Pharmacologic and behavioral responses of inbred C57BL/6J and strain 129/SvJ mouse lines.

Gene-targeting technology is creating an explosion in the number of animals available with single gene mutations that affect the function of the central nervous system. Most gene-targeted mice are produced on a mixed genetic background of C57BL/6J and substrains of Strain 129. Understanding the behavioral characteristics and responses to various drugs of these parental strains is vital to interpreting data from gene-targeted mice. We directly compared C57BL/6J and Strain 129/SvJ mouse lines on several behavioral paradigms and in response to several hypnotic and anesthetic drugs. Compared to Strain 129/SvJ mice, C57BL/6J animals are more sensitive to the hypnotic effects of midazolam, zolpidem, and propofol, less sensitive to etomidate and ethanol, and do not differ in sensitivity to Ro15-4513 or pentobarbital. These strains do not differ in their sensitivity to the motor ataxic effects of the volatile anesthetics enflurane or halothane. However, Strain 129/SvJs are more sensitive to the immobilizing effects of halothane but not enflurane. Motor coordination differs initially, but with repeated testing strain differences are no longer apparent. Strain 129/SvJ mice are more anxious on the elevated plus maze and open-field activity assays. Thus, these mouse strains harbor polymorphisms that influence some, but not all, traits of interest to behavioral neuroscientists.

Normal electrophysiological and behavioral responses to ethanol in mice lacking the long splice variant of the γ2 subunit of the γ-aminobutyrate type A receptor

The γ subunit of the γ-aminobutyric acid type A receptor (GABAA-R) is essential for bestowing both normal single channel conductance and sensitivity to benzodiazepines on native GABAA-Rs. The long splice variant of the γ2 subunit (γ2L) has been postulated to be essential in mediating the modulatory actions of ethanol at the GABAA-R. In order to evaluate this hypothesis, gene targeting was used to delete the 24bp exon which distinguishes γ2L from the short splice variant (γ2S). Mice homozygous for this exon deletion (γ2L−/−) are viable and indistinguishable from wild-type (γ2L+/+) mice. No γ2L mRNA was detected in these mice, nor could γ2L-containing GABAA-R protein be detected by specific antibodies. Radioligand binding studies showed the total amount of γ2 subunit protein to be not significantly changed, suggesting that γ2S replaces γ2L in the brains of the knockout animals. Electrophysiological recordings from dorsal root ganglion neurons revealed a normal complement of functional receptors. There was no difference in the potentiation of GABA currents by ethanol (20–200 mM) observed in neurons from γ2L+/+or γ2L−/− mice. Several behavioral effects of ethanol, such as sleep time, anxiolysis, acute functional tolerance, chronic withdrawal hyperexcitability and hyperlocomotor activity were also unaffected by genotype. It is concluded that γ2L is not required for ethanol’s modulatory action at the GABAA-R or whole animal behavioral effects.

The incidence and outcome of perioperative pulmonary aspiration in a university hospital: a 4-year retrospective analysis.

We evaluated the current incidence and outcome of perioperative pulmonary aspiration (PPA) in the nonobstetric adult population at a tertiary university medical center. A 4-yr retrospective analysis (January 2001–December 2004) was conducted using both quality improvement data and the hospital-wide medical archive recording system. PPA was defined as either detection of nonrespiratory secretions from the tracheobronchial tree or development of new pulmonary symptoms and/or new abnormalities in chest radiographs within 24 hr postoperatively. Of 99,441 anesthetics, 14 cases had confirmed PPA. Seven of them (50%) occurred in connection with gastroesophageal procedures. All patients had one or more predisposing risk factors for PPA. PPA occurred under general anesthesia in 10 patients and under monitored anesthesia care in 4 patients. In general anesthesia cases, the aspiration was recognized immediately after induction in 5 patients and occurred during changing of the endotracheal tubes in 5. The PPA was detected during the surgical procedures in all the monitored anesthesia care cases. Six patients with confirmed PPA developed pulmonary complications, of which, one died. Ten of 14 (70%) cases of PPA were the result of improper anesthesia technique. The current incidence of PPA is 1 of 7103, with morbidity 1 of 16,573 and mortality 1 of 99,441.

Transgastric continuous-wave Doppler to determine cardiac output

A new method to measure cardiac output using transgastric continuous-wave Doppler was evaluated in 31 consecutive patients undergoing cardiac surgery with simultaneous measurement of cardiac output by the thermodilution technique. A 5 MHz single-plane imaging/5 MHz continuous-wave Doppler transesophageal transducer was used to image the left ventricular outflow tract, aortic valve and ascending aorta from a modified transgastric short-axis plane. The continuous-wave Doppler cursor was aligned parallel with blood flow across the aortic valve to obtain the maximal Doppler velocity spectra. Stroke volume was obtained by multiplying the mean Doppler flow velocity integral by the aortic annulus area, which was calculated from its diameter measured from the esophageal 5-chamber view. The stroke volume was multiplied by heart rate to yield cardiac output. A total of 57 simultaneous thermodilution and Doppler studies were attempted. Doppler data were technically limited for 2 patients both before and after cardiopulmonary bypass and for 3 patients before cardiopulmonary bypass with a result of 50 adequate studies of 57 (88%) attempted. The Doppler-derived cardiac outputs were correlated with the simultaneous measurements of cardiac output by the thermodilution technique. Linear regression analysis revealed a close correlation with R = 0.91, SEE = 0.8 liter/min, and y = 1.01x + 0.2 (p < 0.001). In conclusion, transgastric continuous-wave Doppler across the aortic valve is a promising new technique that may be used in selected patients for accurate measurement of cardiac output.

Immediate effects of lung transplantation on right ventricular morphology and function in patients with variable degrees of pulmonary hypertension

OBJECTIVES This study sought to determine the immediate effects of lung transplantation on right ventricular morphology and function in patients with variable degrees of pulmonary hypertension and to evaluate these features as potential markers of immediate outcome. BACKGROUND Selected lung transplant recipients with severe preoperative pulmonary hypertension have previously been shown to have a reduction in right ventricular size and improved function at follow-up evaluation. METHODS Thirty-two consecutive patients (mean [+/- SD] age 44 +/- 11 years) were prospectively classified into three groups according to their pretransplantation pulmonary artery systolic pressure: severe pulmonary hypertensive group > or = 75 mm Hg, intermediate pulmonary hypertensive group 40 to 74 mm Hg and non-pulmonary hypertensive group < 40 mm Hg. Hemodynamic and transesophageal echocardiographic variables were measured immediately before and after lung transplantation. RESULTS Pulmonary artery systolic and mean pressures markedly decreased after transplantation in the severe pulmonary hypertensive group (from 115 +/- 26 to 45 +/- 19 mm Hg and from 76 +/- 14 to 31 +/- 11 mm Hg, respectively, both p < 0.05). Mean pulmonary artery pressure decreased in the intermediate group (from 34 +/- 7 to 26 +/- 7 mm Hg, p < 0.05). Right ventricular end-diastolic area, end-systolic area and eccentricity index decreased in the severe pulmonary hypertensive group after transplantation. End-diastolic area also decreased in the intermediate pulmonary hypertensive group. Right ventricular fractional area change was not significantly different between groups and did not change consistently after transplantation. Three patients with severe pulmonary hypertension who had continued depression of right ventricular function after transplantation died in the immediate postoperative period. CONCLUSIONS Lung transplantation is associated with an immediate decrease in pulmonary artery pressures and right ventricular size and normalization of septal geometry but variable changes in right ventricular function. Continued depression of right ventricular fractional area change may be a potential marker of poor outcome.

Isoflurane's Enhancement of Chloride Flux through Rat Brain γ-Aminobutyric Acid Type A Receptors Is Stereoselective

Background Recent evidence is consistent with the view that volatile anesthetics interact directly with excitable membrane-bound channel proteins. If these agents interact directly with chiral centers in the neuronal cell membrane, then their effects should be stereoselective. Using rat brain membranes enriched in gamma-aminobutyric acid type A (GABA sub A) receptors, we investigated the hypothesis that the permeability response of this well-characterized central nervous system channel protein to stereoisomers of isoflurane is stereoselective.

Mice Lacking the Long Splice Variant of the γ2 Subunit of the GABAA Receptor Are More Sensitive to Benzodiazepines

The gamma 2 subunit is required for benzodiazepine modulation of the GABA(A) receptor. Alternate splicing of precursor GABA(A) gamma 2 mRNA results in two splice variants, a short (gamma 2S) and a long (gamma 2L) variant. We investigated the roles of these splice variants in benzodiazepine pharmacology using mice lacking genes for the gamma 2L splice variant. Sleep time responses to midazolam and zolpidem were 20 and 18% greater, respectively, in null allele mice compared with wild-type mice, while responses to nonbenzodiazepine agents such as etomidate and pentobarbital were unchanged. Although the GABA(A) receptor number was not altered in null allele mice, there was a corresponding increase in affinity of brain membranes for benzodiazepine agonists (midazolam, diazepam, and zolpidem), while affinity for benzodiazepine inverse agonists (beta CCM and Ro15-4513) was decreased. These changes were not observed in inbred mice of the parental strains (C57BL/6J and 129/SvJ) used to create the genetically altered mice, indicating that differences between gamma 2L null allele and wild-type mice were unlikely to be simply due to cosegregation of linked alleles. Absence of the gamma 2L splice variant increases the affinity of receptors for benzodiazepine agonists, and is associated with a modest increase in behavioral sensitivity to benzodiazepine agonists. Lack of the gamma 2L subunits may shift the GABA(A) receptor from an inverse agonist-preferring toward an agonist-preferring configuration.

Why It’s Easier to Remember Seeing a Face We Already Know Than One We Don’t Preexisting Memory Representations Facilitate Memory Formation

In two experiments, we provided support for the hypothesis that stimuli with preexisting memory representations (e.g., famous faces) are easier to associate to their encoding context than are stimuli that lack long-term memory representations (e.g., unknown faces). Subjects viewed faces superimposed on different backgrounds (e.g., the Eiffel Tower). Face recognition on a surprise memory test was better when the encoding background was reinstated than when it was swapped with a different background; however, the reinstatement advantage was modulated by how many faces had been seen with a given background, and reinstatement did not improve recognition for unknown faces. The follow-up experiment added a drug intervention that inhibited the ability to form new associations. Context reinstatement did not improve recognition for famous or unknown faces under the influence of the drug. The results suggest that it is easier to associate context to faces that have a preexisting long-term memory representation than to faces that do not.

Mice with glycine receptor subunit mutations are both sensitive and resistant to volatile anesthetics.

We used two mouse lines with glycine receptor mutations to determine whether glycine receptors might play an important role in anesthetic responses in vivo. Spastic (spA) mutants were slightly more sensitive (P = 0.02) to enflurane in the loss-of-righting reflex assay (50% effective concentration [EC50] = 1.17 ± 0.06 atm for controls versus 0.97 ± 0.06 atm for spA) but were also substantially more resistant (P = 0.01) to enflurane in the tail clamp assay (EC50 = 1.96 ± 0.10 atm for controls versus 2.58 ± 0.25 atm for spA). spA mice were also more sensitive to halothane (P < 0.001) in the loss-of-righting reflex assay (EC50 = 0.81 ± 0.03 atm for controls versus 0.57 ± 0.04 atm for spA), but the responses of mutant and control mice to tail clamp in the presence of halothane were similar. Spasmodic control and mutant mice did not differ in their responses to the two drugs. Sleep time was substantially longer in both mutant mouse lines after injection of three hypnotics (midazolam, pentobarbital, and ethanol). Our results suggest a complex involvement of glycinergic pathways in mediating anesthetic responses. Greater sensitivity to the hypnotic effect of enflurane, halothane, midazolam, pentobarbital, and ethanol in mutant mice with diminished glycinergic capacity suggests that glycinergic activity is inversely related to hypnosis, whereas resistance to enflurane in the tail clamp assay suggests that glycinergic activity potentiates the minimum alveolar anesthetic concentration response. Halothane seems to share some, but not all, of enflurane’s mechanisms, indicating that not all volatile anesthetics modulate glycinergic pathways equally.