Neurochemical analysis of focal ischemia in rats

BACKGROUND AND PURPOSE

Increases in uric acid follow experimental stroke, which may be related to free radical formation by xanthine oxidase. The present study examined the time course of changes in xanthine and uric acid and their relationship to changes in the free radical scavengers glutathione, cysteine, and ascorbic acid.

METHODS

Focal ischemia was induced by occluding the middle cerebral artery, followed by transient occlusion of the common carotid arteries for 60 minutes. At varying time points, animals were sacrificed, and ischemic cortex was dissected. Neurochemical measurements were made by high-performance liquid chromatography with 16-sensor electrochemical detection.

RESULTS

Marked increases in uric acid were seen at all time points, with a maximal increase at 1 day and a persistent increase lasting up to 21 days. There were smaller reciprocal decreases in xanthine. Glutathione, cysteine, and ascorbic acid showed significant decreases, consistent with the generation of free radicals. Reductions in levels of cysteine and glutathione were significantly correlated with increases in uric acid levels.

CONCLUSIONS

These findings confirm marked alterations in purine metabolism following focal ischemia and suggest that xanthine oxidase contributes to the generation of free radicals.

The effect of noise exposure on the aging ear

The effect of noise exposure on auditory sensitivity and inner ear morphology was compared in aged and young mature mice. Hearing thresholds were obtained by auditory evoked brain stem responses (ABR) before and after noise exposure, and hair cell loss was quantified. The study was done in two parts: first to assess the effect of noise exposure on subjects with presbycusis, and second to assess its effect on aged subjects without measurable presbycusis. In the first experiment C57BL/6 mice, with an age-related hearing loss, were used as a model for presbycusis. C57BL/6 mice exhibiting presbycusis were more susceptible to noise injury than age-matched CBA/Ca mice. In the second experiment CBA/Ca mice were used. These mice retain normal hearing even with advancing age. The aged CBA/Ca mice had the same susceptibility to noise injury as young CBA/Ca mice.

The effects of Carbogen, carbon dioxide, and oxygen on noise-induced hearing loss

An investigation into the effect of Carbogen (95% O2/5% CO2), 5% CO2/air, and 100% oxygen on cochlear threshold shifts caused by noise was undertaken. Five groups of eight pigmented guinea pigs were exposed to 105 dB broad band noise for 6 h per day for five consecutive days with each group receiving the various gaseous mixtures either during noise exposure or for 1 h immediately after noise exposure. A control group received the same noise exposure but respired air. Auditory threshold shifts, as measured by the auditory evoked brainstem response, were measured at 2,4,8,12,16, 20 and 24 kHz. Recordings were taken pre-exposure and at Day 1, 3, 5, and Weeks 2 and 3 after noise exposure. Carbogen, given during noise exposure, resulted in a trend toward less post noise exposure threshold shift (as compared to controls) which reached statistical significance by Week 3 at all frequencies except 2 and 20 kHz. Subjects given Carbogen after exposure also showed a general trend toward decreased noise induced threshold shifts, as compared to controls, but this was not statistically significant. The mixture of 5% CO2/air given during noise exposure yielded no difference in threshold shifts as compared to controls. When 100% oxygen was administered during noise exposure, a marked decrease in noise induced threshold shifts could be seen as compared to controls, with differences reaching statistical significance by day 5 at most frequencies. These results indicate that oxygen (i.e. cochlear-oxygenation) is a more important factor than CO2 (i.e., as a vasodilator) in protection of the cochlea from noise induced damage.

Effects of aging on quinolinic acid lesions in rat striatum

Several neurologic illnesses in which excitotoxic mechanisms may play a role increase in prevalence with age. In the present study we examined the susceptibility of rats to quinolinic acid striatal lesions at 1, 4 and 20 months of age, and susceptibility to N-methyl-D-aspartate (NMDA) at 1 and 4 months of age. The extent of the lesions was quantitated with measurements of substance P-like immunoreactivity (SPLI) and gamma-aminobutyric acid (GABA). The lesions in the 4- and 20-month-old age groups showed significantly smaller depletions of SPLI and GABA than those in 1-month-old animals. Neuropeptide Y-like immunoreactivity (NPYLI) and somatostatin-like immunoreactivity (SLI) were unchanged in the lesioned striata. NMDA lesions were also attenuated in 4-month- and 12-month-old animals as compared with 1-month-old animals. Uric acid concentrations showed marked dose-dependent increases in the lesioned striatum, and to a lesser extent in the overlying cerebral cortex, in all 3 age groups. There were no changes of SLI, NPYLI or SPLI with aging in the cerebral cortex or hippocampus. Kynurenine and kynurenic acid concentrations showed significant increases with aging in frontal cortex. The present results show a reduced susceptibility of animals to striatal quinolinic acid and NMDA lesions with normal aging. The delayed onset of several neurodegenerative illnesses is therefore unlikely to be due to an increasing susceptibility to excitotoxin lesions with aging.

Usefulness of the delta HA interval to accurately distinguish atrioventricular nodal reentry from orthodromic septal bypass tract tachycardias

Surface electrocardiographic criteria may be inadequate to distinguish some cases of atrioventricular (AV) nodal reentrant supraventricular tachycardia (SVT) from those with orthodromic SVT incorporating a posterior septal bypass tract (orthodromic SVT) because of similarities in P-wave morphology and timing during SVT. Invasive electrophysiologic studies may occasionally leave uncertainty in the correct diagnosis, using currently accepted criteria. A new criterion for distinguishing these 2 forms of SVT was therefore devised and tested based on differences in the sequence of activation of the His bundle and atrium during SVT and ventricular pacing. Eighty-four patients underwent invasive electrophysiologic studies (60 with proved AV nodal SVT, 24 with proved orthodromic SVT), during which His to atrial (HA) intervals were measured during SVT as well as ventricular pacing at the same rate. The newly devised criterion, the delta HA interval (HApace-HAsvt) was found to accurately distinguish AV nodal SVT (delta HA greater than 0 ms) from orthodromic SVT (delta HA less than -27 ms). An intermediate value of delta HA = -10 ms was chosen which had a 100% sensitivity, specificity and predictive accuracy in differentiating the 2 forms of SVT. A clear retrograde His potential during ventricular pacing, which is essential for application of this criterion, was present in 78 of 84 (93%) cases. In summary, patients with delta HA intervals greater than -10 ms separate AV nodal reentry from orthodromic SVT incorporating a septal bypass tract, and no overlap exists between the 2 groups. This criterion may be useful in differentiating the mechanism of SVT in cases in which distinction is not possible by other methods.

The effect of CO2- and O2-gas mixtures on laser Doppler measured cochlear and skin blood flow in guinea pigs

The effects of carbogen (5% CO2: 95% O2) 10% CO2-in-air and 100% O2 on cochlear blood flow (CBF), skin blood flow (SBP), blood pressure (BP) and arterial blood gases were investigated in the anesthetized, respired or self-respiring guinea pig. In respired animals, CBF and SBF were increased with carbogen and 10% CO2-in-air and decreased with O2. BP was elevated with each gas. In freely breathing animals, only 10% CO2-in-air caused a small increase in CBF; both carbogen and O2 caused CBF to decrease. SPF changes were similar in form, but larger than those seen in respirated subjects. No consistent change in BP was seen during breathing of these mixtures. Arterial PO2 was increased by carbogen and 10% CO2-in-air for both groups. PCO2 increased for both CO2 gas mixtures during forced respiration; but in free-breathing animals PCO2 only increased for 10% CO2-in-air (normal PCO2 values were maintained with carbogen thorough increased breathing rate). The observed changes in CBF were consistent with a balance between a combined vasoconstrictive effect of PO2 and vasodilation effect of PCO2 on cochlear vessels. Analysis of cochlear vascular conductivity (CBF/BP) indicated that vasodilation was significant only with 10% CO2-in-air in respirated animals. In all other conditions the increased CBF apparently reflects the increase profusion pressure associated with respiration of each gas. For clinical purposes, while carbogen does not appear to directly cause vasodilation of cochlear vessels it does lead to an increased oxygenation of the cochlea blood and would appear to avoid the cochlear vasoconstriction caused by 100% O2.

Direct electrical stimulation of the cochlear nucleus: surface vs. penetrating stimulation

Prosthetic stimulation of the cochlear nucleus (CN) has been used for rehabilitation of profoundly deaf patients who are not suitable candidates for cochlear implants. The goal of this article was to assess the relative effectiveness of surface vs. penetrating stimulation of the CN. Electrophysiologic and autoradiographic measures were used to study central auditory system activation elicited by direct stimulation of the CN. Eighteen pigmented guinea pigs, divided into three groups, underwent acute implantation of bipolar electrodes in the CN. One group was not stimulated and acted as a control (n = 7). Electrodes were placed on the surface of the CN in one test group (n = 4) and within the CN in a second test group (n = 7). Thresholds for electrically evoked middle latency responses (EMLR) were determined and input/output (I/O) functions were obtained. The two test groups were then pulsed with [14C]-2-Deoxyglucose (2-DG) intramuscularly and stimulated for 1 hour with biphasic; charge-balanced pulses having a total duration of 400 microseconds, a repetition rate of 100/sec, and an amplitude of 200 microA. After stimulation, animals were killed and brains were harvested and prepared for autoradiography using standard techniques. Threshold current for EMLRs in the surface-stimulated group had a mean of 67.5 +/- 23.9 microA (range, 40 to 100 microA). Thresholds for in-depth stimulated group had a mean of 11.4 +/- 3.5 microA (range, 10 to 20 microA). The saturation level of the I/O function for the surface-stimulated group had a mean of 287.5 +/- 41.5 microA (range, 250 to 350 microA). The saturation level for the in-depth stimulated group had a mean of 192.9 +/- 49.5 mciroA (range, 100 to 250 microA). The dynamic range for the surface electrodes had a mean of 13.1 +/- 2.7 dB (range, 9.9 to 15.9 dB), whereas the dynamic range for the penetrating electrodes had a mean of 24.5 +/- 2.6 dB (range, 20 to 28.0 dB). Autoradiographs generated by CNS tissue from stimulated animals demonstrated no significant difference in metabolic activity of the CN between surface and in-depth stimulated groups. However, there were highly significant differences in 2-DG uptake in the contralateral superior olivary complex, contralateral inferior colliculus, and ipsilateral and contralateral lateral lemniscus, with greater uptake in in-depth stimulated preparations. Electrophysiologic and autoradiographic data suggest that a penetrating CN prosthesis is capable of activating the auditory tract at a lower threshold, with a relatively wider dynamic range than a surface prosthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Isoenzyme analysis of Pseudomonas cepacia as an epidemiologic tool

Multilocus enzyme electrophoresis has successfully been used to establish basic marker systems for the epidemiologic analysis of a variety of bacterial pathogens. This study was done to determine the efficacy of this technique for characterizing Pseudomonas cepacia, using 31 known-related strains isolated during an outbreak of infections involving intrinsically contaminated povidone-iodine solution, and five outbreak-unrelated strains used in serotyping of P. cepacia. Crude cell extracts were analyzed by starch gel electrophoresis for electrophoretic variants using 13 enzyme substrates; esterase bands were detected using an additional four substrates. The 31 outbreak strains had identical isoenzyme patterns for all enzymes examined. Five electrophoretic types were obtained for the serotyping strains; electrophoretic mobilities of one of the five strains corresponded to the patterns obtained for the outbreak strains. These results suggest that enzyme electrophoretic typing may be a useful adjunct to other typing methods used in epidemiologic analyses of P. cepacia infections.

Hybrid kinoform fanout holograms in dichromated gelatin

The technique for fabricating hybrid holograms, introduced by Bartelt and Case [Appl. Opt. 21, 2886 (1982)], is applied here to record extremely high-efficiency (>90%) space-invariant fanout holograms in dichromated gelatin. The object wave front corresponding to that produced by a kinoform with a continuous-phase profile is derived by appropriate spatial filtering from a binary computer-generated hologram fabricated using electron-beam lithography.

Spinal muscular atrophy is not the result of mutations at the beta-hexosaminidase or GM2-activator locus

The disease locus for the clinically heterogeneous childhood spinal muscular atrophies (SMA) maps to the chromosome 5 subregion, 5q11.2-13.3. The beta-subunit of beta-D-N-acetylhexosaminidase (hexosaminidase) (EC 3.2.1.52) (Hex B) maps to the same region, and the protein required for substrate recognition by this enzyme, GM2-activator protein, likewise maps to chromosome 5. We have investigated the possibility of allelic variation among some forms of SMA and hexosaminidase deficiency. Recombination between the Hex B and SMA loci eliminates this enzyme as a candidate site for defects causing the illness. Furthermore, we show that, despite previous evidence to the contrary, the GM2-activator locus does not map to chromosome 5, thereby eliminating it as a candidate gene for SMA.

The sonographic diagnosis of circumvallate placenta

Circumvallate placenta, a form of placenta extrachorialis, should be included in the differential diagnosis of vaginal bleeding in the second trimester with a normally implanted placenta. Heretofore, the diagnosis was made after delivery. This report presents a case of circumvallate placenta diagnosed prenatally by ultrasound. Key features included an infolding of the fetal membrane upon the fetal surface of the placenta during the middle of the second trimester. By the third trimester, only a bright border at the periphery of the placenta was noted. Antenatal diagnosis can be made and pregnancy outcome potentially altered.

Influence of topically applied adrenergic agents on cochlear blood flow

This study was designed to assess the role of adrenergic receptors in the control of cochlear blood flow. Laser Doppler flowmetry was used to determine the effects of adrenergic drugs topically applied to the round window membrane of the cochlea. The relative influence of the various receptor types (alpha 1, alpha 2, beta 1, and beta 2) was examined by a selection of agonists and antagonists. The agonists norepinephrine and epinephrine, which have mixed alpha- and beta-receptor effects, and phenylephrine, a strong alpha 1-agonist, all induced a dose-dependent reduction in cochlear blood flow. The agonists isoproterenol (beta-active), salbutamol (alpha 2-active) had no effect on cochlear blood flow. Of the antagonists, when tested alone, only the selective alpha 1-antagonist prazosin had a direct effect on cochlear blood flow, demonstrating an increase in cochlear blood flow. The selective alpha 2-antagonist idazoxan, the beta-antagonist propranolol, and the unselective alpha-antagonist phentolamine had no effect on cochlear blood flow. Interaction studies of agonists and antagonists were performed to specifically define the receptor subclasses responsible for the cochlear blood flow increases with norepinephrine and epinephrine. The results are consistent with the presence of an alpha 1-adrenergic sympathetic control of cochlear blood flow.

Differences in electrophysiological substrate in patients with coronary artery disease and cardiac arrest or ventricular tachycardia. Insights from endocardial mapping and signal-averaged electrocardiography

BACKGROUND

Many studies have combined patients with hemodynamically well-tolerated ventricular tachycardia (VT) and those with cardiac arrest (CA) as a single, homogenous group. Recent studies suggest that these two groups have different electrophysiological substrates and responses to therapy. Most of these studies, however, enrolled patients with a variety of cardiac diagnoses.

METHODS AND RESULTS

We used signal-averaged electrocardiography (SAECG) and endocardial catheter mapping to define the electrophysiological substrate in patients with coronary artery disease and VT or CA and correlate the results of the two methods. We also examined the usefulness of SAECG in CA patients to differentiate those with inducible arrhythmias from those who are noninducible. VT patients were more likely to have had a prior myocardial infarction (p = 0.0005) and to have inducible arrhythmias (p = 0.0001) than were CA patients. The induced arrhythmias in patients who presented with VT was VT in more than 90% of cases, whereas in CA patients, polymorphic ventricular tachycardia (PMVT) accounted for one third of induced arrhythmias. Mean filtered QRS duration was longer (135 versus 120 msec) and the terminal QRS voltage was smaller (20 versus 34 microV) in VT than in CA patients (p less than 0.01). Sixty-three percent of CA patients and 87% of VT patients had abnormal SAECG (p = 0.001). VT patients had more extensive endocardial abnormalities and more abnormal (53% versus 40%, p = 0.002), fractionated (8% versus 3%, p = 0.02), late (17% versus 8%, p = 0.0003), and late abnormal or fractionated (14% versus 4%, p = 0.0001) sites than CA patients. VT patients had a greater duration of the longest electrogram (129 versus 109 msec, p = 0.0006) and total endocardial activation time (68 versus 54 msec, p = 0.009). Among CA patients, those with induced VT had more extensive substrate than did those with induced PMVT and were similar to VT patients with induced VT. Among CA patients, the trend for more patients with inducible VT (77%) or PMVT (55%) than noninducible patients (47%) to have an abnormal SAECG did not reach statistical significance (p = 0.14). The positive and negative predictive values of an abnormal SAECG were 77% and 44%, respectively.

CONCLUSIONS

VT patients have more extensive endocardial substrate than CA patients, which translates into greater and more frequent SAECG abnormalities. Among CA patients, there are significant differences in substrate between patients with induced VT and those with induced PMVT. SAECG is not useful in differentiating CA patients who have inducible VT or PMVT from those who do not.

Determination of ability of a thymidine kinase-negative deletion mutant of bovine herpesvirus-1 to cause abortion in cattle

The Cooper isolate of bovine herpesvirus-1, which causes abortion in cattle, was used to construct a thymidine kinase-negative (TK-) deletion mutant virus. Twelve heifers were inoculated IV at 25 to 29 weeks of pregnancy with either TK- or thymidine kinase-positive (TK+) Cooper virus. All heifers developed fevers of 1 to 2 C during the first week after inoculation. Temperatures of TK+ inoculates were slightly higher and remained above normal a few days longer than in TK- inoculates. Viremia was detected in 5 of 6 TK+ inoculates and in all 6 TK- inoculates. More virus isolations were made from nasal and vaginal swab specimens of TK+ inoculates than from swab specimens of TK- inoculates. All heifers developed virus neutralizing antibody within 14 days after inoculation and antibody titers were similar between the 2 groups. None of the TK- inoculated heifers aborted and their calves did not have neutralizing antibody at birth. Abortion occurred in 5 of 6 heifers given TK+ virus. All aborted fetuses were infected with bovine herpesvirus-1, as demonstrated by virus isolation or detection of viral antigen in fetal tissues. These results indicate that inactivation of the TK gene reduces abortifacient activity of bovine herpesvirus-1.

Preliminary evaluation of Biolog, a carbon source utilization method for bacterial identification

The Biolog Identification System (Biolog, Inc., Hayward, Calif.) is a new bacterial identification method that establishes an identification based on the exchange of electrons generated during respiration, leading to a subsequent tetrazolium-based color change. This system tests the ability of a microorganism to oxidize a panel of 95 different carbon sources. We report on a preliminary investigation of the ability of the instrument to identify, using its computer-driven enzyme immunoassay reader, a diverse group of clinically relevant members of the family Enterobacteriaceae and gram-negative non-Enterobacteriaceae. The Biolog reported identifications (correct or incorrect) for 266 of 352 organisms tested (75.6%). Of the 266 identifications reported, 87.3% were correct at the genus level and 75.6% were correct at the species level at 24 h. In the total study of 352 strains, 46.6% were correct to the species level at 4 h and 57.1% were correct to the species level at 24 h. The error rate was 10.4% after 4 h and 9.6% after 24 h. The Biolog performed well with many genera, but problems were encountered with some strains of Klebsiella, Enterobacter, and Serratia. We found the system to be versatile and easy to use.

Electroconvulsive therapy revisited

Electroconvulsive therapy (ECT) remains an extremely valuable tool in the treatment of certain psychiatric disorders. Despite the sensationalism of the past decade, ECT is the treatment of choice in severe depression that is unresponsive to other therapies or in patients who are overtly suicidal. In addition, ECT is particularly valuable in the elderly population, who are at risk for serious complications from the side effects associated with drug therapy. This report describes a case of recurrent depression in which ECT was successfully used.

Usefulness of the electrophysiology laboratory for evaluation of proarrhythmic drug response in coronary artery disease

Two potential manifestations of proarrhythmic responses to type IA antiarrhythmic agents in the electrophysiology laboratory were evaluated in 122 patients with chronic coronary artery disease and previous myocardial infarction: (1) conversion of uniform nonsustained ventricular tachycardia (VT) into sustained VT after drug administration, and (2) induction of sustained VT by fewer extrastimuli after drug administration. Forty-two patients were evaluated for nonsustained VT. Eighty patients were evaluated for sustained VT: 30 of these had spontaneous sustained VT only while receiving empiric therapy with quinidine or procainamide, whereas the remaining 50 developed spontaneous VT in the absence of antiarrhythmic drugs. All patients underwent programmed stimulation in the baseline state and after procainamide. Four patients had conversion of induced uniform nonsustained VT into the same morphology, but sustained VT after procainamide administration. These responses only occurred in patients evaluated for nonsustained VT. Over 90% of patients presenting with sustained VT had uniform sustained VT induced at the baseline study and after procainamide, regardless of whether the spontaneous arrhythmia occurred only in the presence or absence of antiarrhythmic drugs. There was no significant difference in the change in mode of induction from baseline to procainamide study, regardless of whether patients had developed spontaneous VT only in the presence or absence of antiarrhythmic drugs. One patient with no inducible VT at the baseline study had inducible uniform sustained VT after procainamide administration, and 1 patient with inducible VT at baseline developed spontaneous sustained uniform VT after procainamide administration. Both patients had developed spontaneous sustained VT only while receiving therapy with type IA agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Ion-molecule reaction of alkanenitriles and transition-metal ions in the gas phase: A study on fragmentation mechanism of the adducts

Gas-phase ion-molecule reactions between transition-metal ions (Mn +, Fe+, Co+, Ni +) and propionitri1e and acetonitrile were investigated. Ion-molecule adducts were prepared in a modified fast atom bombardment source and their metastable and collision-induced fragmentations, occurring in the frrst held-free region of an E/B configuration instrument, were studied by means of B/E linked scans. The experimental data suggest a coexistence of both "end-on" and "side-on" coordination modes; the former undergoes ligand detachment alone, whereas the latter loses methyl and ethyl radicals by insertion of M+ into organic substrates and further produces ethylene via a l3-hydrogen transfer. An order for the bonding energy of RCN-M+ is also suggested: RCN-Ni+> RCN-Co+> RCN-Fe+> RCNMn+.

Inner ear damage from toy cap pistols and fire-crackers

Groups of guinea pigs comprising 7 animals in each group were exposed to 10, 50 or 100 exposures to fire-crackers or 10, 50 or 100 exposures to toy cap pistol shots. An additional group of 7 animals comprised the control material. The exposures were performed with 15-s intervals at 0.25 m distance for the toy cap pistol shots and at 0.8 m for the fire-crackers. The peak sound level at the ear was 155 dBC for both impulsive sounds. After a 3-week survival period the animals were anesthetized and decapitated. The cochleas were examined histologically in surface preparations and read double-blind. One animal in each group exposed to 10 fire-crackers and 10 toy cap pistol shots showed sensory cell loss. With 50 or 100 toy cap pistol shots or fire-cracker exposures, 24 out of 28 animals showed pronounced sensory cell loss. The present results clearly indicate the risk for noise-induced hearing loss in children playing with toy cap guns and fire-crackers.

Application of multilocus enzyme electrophoresis to epidemiologic investigations of Xanthomonas maltophilia

OBJECTIVE

To test the utility of a newly developed multilocus enzyme electrophoresis typing method for Xanthomonas maltophilia.

DESIGN

Isolates were first screened by slide agglutination, which served as the standard to characterize the outbreak strains. All isolates were then subjected to multilocus enzyme electrophoresis and the results analyzed based on epidemiological data.

SETTING

This outbreak occurred in a shock-trauma intensive care unit of a large general community hospital.

PATIENTS

Patients admitted to the shock-trauma intensive care unit who had X maltophilia isolated from any site greater than or equal to 24 hours after admission met the case definition. Specimens from patients who fit the case definition were characterized, as were specimens from other patients that were used as controls for nonoutbreak isolates. Environmental samples were also evaluated for X maltophilia.

RESULTS

Most of the 64 isolates received during this outbreak were serotype 10, and when they were subjected to multilocus enzyme electrophoresis, one electrophoretic type predominated and correlated to most outbreak isolates. Unrelated isolates of serotype 10 from other institutions all exhibited unique electrophoretic types.

CONCLUSION

Application of multilocus enzyme electrophoresis to X maltophilia outbreaks is a valuable addition to the characterization of suspected outbreak strains.