Basolateral amygdala hyperexcitability is associated with precocious developmental emergence of fear-learning in Fragile X Syndrome.

Fragile X Syndrome (FXS) is a neurodevelopmental disorder and the most common monogenic cause of intellectual disability, autism spectrum disorders (ASDs) and anxiety disorders. Loss of fragile x mental retardation protein (FMRP) results in disruptions of synaptic development during a critical period (CP) of circuit formation in the basolateral amygdala (BLA). However, it is unknown how these alterations impact microcircuit development and function. Using a combination of electrophysiologic and behavioral approaches in both male (Fmr1-/y) and female (Fmr1-/-) mice, we demonstrate that principal neurons (PNs) in the Fmr1KO BLA exhibit hyperexcitability during a sensitive period in amygdala development. This hyperexcitability contributes to increased excitatory gain in fear-learning circuits. Further, synaptic plasticity is enhanced in the BLA of Fmr1KO mice. Behavioral correlation demonstrates that fear-learning emerges precociously in the Fmr1KO mouse. Early life THIP intervention ameliorates fear-learning in Fmr1KO mice. These results suggest that CP plasticity in the amygdala of the Fmr1KO mouse may be shifted to earlier developmental timepoints.SIGNIFICANCE STATEMENTIn these studies we identify early developmental alterations in principal neurons in the FXS BLA. We show that as early as P14, excitability and feed-forward excitation, and synaptic plasticity is enhanced in Fmr1KO lateral amygdala. This correlates with precocious emergence of fear-learning in the Fmr1KO mouse. Early life THIP intervention restores CP plasticity in WT mice and ameliorates fear-learning in the Fmr1KO mouse.

Disrupted inhibitory plasticity and homeostasis in Fragile X syndrome.

Fragile X Syndrome (FXS) is a neurodevelopmental disorder instigated by the absence of a key translation regulating protein, Fragile X Mental Retardation Protein (FMRP). The loss of FMRP in the CNS leads to abnormal synaptic development, disruption of critical periods of plasticity, and an overall deficiency in proper sensory circuit coding leading to hyperexcitable sensory networks. However, little is known about how this hyperexcitable environment affects inhibitory synaptic plasticity. Here, we show that in vivo layer 2/3 of the primary somatosensory cortex of the Fmr1 KO mouse exhibits basal hyperexcitability and an increase in neuronal firing rate suppression during whisker activation. This aligns with our in vitro data that indicate an increase in GABAergic spontaneous activity, a faulty mGluR-mediated inhibitory input and impaired inhibitory plasticity processes. Specifically, we find that mGluR activation sensitivity is overall diminished in the Fmr1 KO mouse leading to both a decreased spontaneous inhibitory postsynaptic input to principal cells and a disrupted form of inhibitory long-term depression (I-LTD). These data suggest an adaptive mechanism that acts to homeostatically counterbalance the cortical hyperexcitability observed in FXS.

DPD epitope-specific glutamic acid decarboxylase (GAD)65 autoantibodies in children with Type 1 diabetes.

AIM: To study whether DPD epitope-specific glutamate decarboxylase autoantibodies are found more frequently in children with milder forms of Type 1 diabetes. METHODS: We prospectively evaluated 75 children with new-onset autoimmune Type 1 diabetes, in whom we collected demographic, anthropometric and clinical data and measured islet autoantibodies. Glutamate decarboxylase 65 autoantibody-positive samples were analysed for epitope specificities using recombinant Fab against the DPD-defined epitope of glutamate decarboxylase 65. RESULTS: After adjustment for age, positive DPD epitope recognition was significantly associated with higher C-peptide levels at onset (P = 0.02, r2 =0.21, n = 35), and high DPD recognition in the highest quartile tended to be associated with HbA1c ≤ 53 mmol/mol (7%) at the last follow-up [mean (sd) follow-up 1.3 (0.4) years; P = 0.07; for the model, P = 0.044, n = 30)]. Age- and sex-adjusted BMI percentile was significantly correlated with recognition of the DPD-defined epitope (P < 0.03, r2 =0.14, n = 34), but this correlation was driven by the older age group (age ≥ 10 years; P = 0.016, r2 =0.27, n = 21) and was not significant in younger children (P = 0.93, n = 13). There were no independent associations with sex, race/ethnicity, diabetic ketoacidosis, HbA1c , HLA DR3-DQ2/DR4-DQ8 or autoantibody number. CONCLUSIONS: Our findings suggest that recognition of the DPD-defined glutamate decarboxylase 65 autoantibody epitope at Type 1 diabetes onset is directly associated with ß-cell function, BMI and age, which supports the hypothesis that immunological factors contribute to the clinical heterogeneity of Type 1 diabetes. Larger studies relating epitope-specific glutamate decarboxylase 65 autoantibody to clinical phenotype in children with Type 1 diabetes are warranted.

Analysis and expansion of the eosinophilic esophagitis transcriptome by RNA sequencing.

Eosinophilic esophagitis (EoE) is an allergic inflammatory disorder of the esophagus that is compounded by genetic predisposition and hypersensitivity to environmental antigens. Using high-density oligonucleotide expression chips, a disease-specific esophageal transcript signature was identified and was shown to be largely reversible with therapy. In an effort to expand the molecular signature of EoE, we performed RNA sequencing on esophageal biopsies from healthy controls and patients with active EoE and identified a total of 1607 significantly dysregulated transcripts (1096 upregulated, 511 downregulated). When clustered by raw expression levels, an abundance of immune cell-specific transcripts are highly induced in EoE but expressed at low (or undetectable) levels in healthy controls. Moreover, 66% of the gene signature identified by RNA sequencing was previously unrecognized in the EoE transcript signature by microarray-based expression profiling and included several long non-coding RNAs (lncRNA), an emerging class of transcriptional regulators. The lncRNA BRAF-activated non-protein coding RNA (BANCR) was upregulated in EoE and induced in interleukin-13 (IL-13)-treated primary esophageal epithelial cells. Repression of BANCR significantly altered the expression of IL-13-induced proinflammatory genes. Together, these data comprise new potential biomarkers of EoE and demonstrate a novel role for lncRNAs in EoE and IL-13-associated responses.

Two-photon microendoscope for label-free imaging in stereotactic neurosurgery.

We demonstrate a gradient refractive index (GRIN) microendoscope with an outer diameter of ∼1.2 mm and a length of ∼186 mm that can fit into a stereotactic surgical cannula. Two photon imaging at an excitation wavelength of 900 nm showed a field of view of ∼180 microns and a lateral and axial resolution of 0.86 microns and 9.6 microns respectively. The microendoscope was tested by imaging autofluorescence and second harmonic generation (SHG) in label-free human brain tissue. Furthermore, preliminary image analysis indicates that image classification models can predict if an image is from the subthalamic nucleus or the surrounding tissue using conventional, bench-top two-photon autofluorescence.

Hyperexcitability and Loss of Feedforward Inhibition Contribute to Aberrant Plasticity in the Fmr1KO Amygdala.

Fragile X syndrome (FXS) is a neurodevelopmental disorder (NDD) characterized by intellectual disability, autism spectrum disorders (ASDs), and anxiety disorders. The disruption in the function of the FMR1 gene results in a range of alterations in cellular and synaptic function. Previous studies have identified dynamic alterations in inhibitory neurotransmission in early postnatal development in the amygdala of the mouse model of FXS. However, little is known about how these changes alter microcircuit development and plasticity in the lateral amygdala (LA). Using whole-cell patch clamp electrophysiology, we demonstrate that principal neurons (PNs) in the LA exhibit hyperexcitability with a concomitant increase in the synaptic strength of excitatory synapses in the BLA. Further, reduced feed-forward inhibition appears to enhance synaptic plasticity in the FXS amygdala. These results demonstrate that plasticity is enhanced in the amygdala of the juvenile Fmr1 knock-out (KO) mouse and that E/I imbalance may underpin anxiety disorders commonly seen in FXS and ASDs.

Cellular origins of beta-cell regeneration: a legacy view of historical controversies.

Beta-cell regeneration represents a major goal of therapy for diabetes. Unravelling the origin of beta cells during pancreatic regeneration could help restore a functional beta-cell mass in diabetes patients. This scientific question has represented a longstanding interest still intensively investigated today. This review focuses on pioneering observations and subsequent theories made 100 years ago and describes how technical innovation helped resolve some, but not all, of the controversies generated by these early investigators. At the end of the 19th century, complete pancreatectomy demonstrated the crucial physiological role of the pancreas and its link with diabetes. Pancreatic injury models, including pancreatectomy and ductal ligation, allowed investigators to describe islet function and to assess the regenerative capacity of the pancreas. Three main theories were proposed to explain the origins of newly formed islets: (i) transdifferentiation of acinar cells into islets, (ii) islet neogenesis, a process reminiscent of islet formation during embryonic development, and (iii) replication of preexisting islet cells. Despite considerable technical innovation in the last 50 years, the origin of new adult beta cells remains highly controversial and the same three theories are still debated today.

Structural and kinetic characterization of mutant human uroporphyrinogen decarboxylases.

Porphyria cutanea tarda (PCT) is caused by inhibition of uroporphyrinogen decarboxylase (URO-D) activity in hepatocytes. Subnormal URO-D activity results in accumulation and urinary excretion of uroporphyrin and heptacarboxyl porphyrin. Heterozygosity for mutations in the URO-D gene is found in the familial form of PCT (F-PCT). Over 70 mutations of URO-D have been described but very few have been characterized structurally. Here we characterize 3 mutations in the URO-D gene found in patients with F-PCT, G318R, K297N, and D306Y. Expression of the D306Y mutation results in an insoluble recombinant protein. G318R and K297N have little effect on the structure or activity of recombinant URO-D, but the proteins display reduced stability in vitro.

Longitudinal study of a mouse model of familial porphyria cutanea tarda.

Most rodent models of porphyria cutanea tarda (PCT) share in common the administration of iron and agents that induce transcription of cytochrome P450s. Dissection of changes related to porphyrin accumulation required generation of a genetic model free from exogenous precipitants. Mice heterozygous for a null Urod mutation and homozygous for null Hfe alleles spontaneously develop major increases in hepatic and urinary porphyrins several months after weaning but the high % uroporphyrin signature of PCT is established earlier, before total hepatic and urinary porphyrins rise. Total porphyrin levels eventually plateau at higher levels in females than in males. Porphyrinogens were the dominant tetrapyrroles accumulating in hepatocytes. Hepatic Urod activity is markedly reduced but total hepatic heme content does not diminish. Microsomal heme, however, is reduced and in vitro metabolism of prototype substrates showed that some but not all cytochrome P450 activities are reduced. High hepatic levels of uroporphyrinogen are also associated with increased glutathione S-transferase activity and elevated mRNA of 2 transporters, Abcc1 and Abcc4. This murine model of familial PCT affords the opportunity to study changes in porphyrinogen and porphyrin accumulation and transport in the absence of exogenous factors that alter P450 activity and transmembrane transporters.

The role of iron in the pathogenesis of porphyria cutanea tarda. II. Inhibition of uroporphyrinogen decarboxylase.

Porphria cutanea tarda is characterized biochemically by excessive hepatic synthesis and urinary excretion of uroporphyrin I and 7-carboxylporphyrins. This pattern of excretion suggest an impaired ability to decarboxylate uroporphyrinogen to the paired ability to decarboxylate uroporphyringen to the 4-carboxyl porphyrinogen, coproporphyrinogen, a reaction catalyzed by the enzyme uroporphyringen decarboxylase. Because clinical evidence has implicated iron in the pathogenesis of porphyria cutanea tarda, these experiments were designed to study the effect of iron on uroporphyrinogen decarboxylase in procine crude liver extracts. Mitochondria-free crude liver extracts were preincubated with ferrous ion and aliquots were assayed for uroporphyrinogen decarboxylase activity. Uroporphyrinogens I and III, the substrates for the decarboxylase assay, were prepared enzymatically from (3H)porphobilinogen. The products of the decarboxylase reaction were identified and quantitated by three methods: (a) extraction into 1.5 N HCl and spectrophotometric quantitation; (b) adsorption onto talc, esterification, paper chromatographic identification, and quantitation by liquid scintillation counting; and (c) adsorption onto talc, esterification, thin-layer chromatographic identification on silica gel, and quantitation by liquid scintillation counting. The thin-layer scinllation method proved most sensitive as it was the only method which accurately identified and quantitated the 7-carboxyl porphyrin reaction product. Uroporphyrinogens I and III were decarboxylated at the same rate by porcine hepatic uroporphyrinogen decarboxylase, and the addition of iron induced marked inhibition of the decarboxylase activity. Ortholpehanthroline blocked the inhibitory effect of iron. The inhibition of uroporphyrinogen decarboxylase by ferrous ion, coupled with its previously reported inhibitory effect on uroporphyrinogen III cosynthetase, provides a possible biochemical explanation for the pattern of urinary porphyrin excretion observed in patients with porphyria cutanea tarda and the clinical association with disordered iron metabolism.

An inherited enzymatic defect in porphyria cutanea tarda: decreased uroporphyrinogen decarboxylase activity.

Uroporphyrinogen decarboxylase activity was measured in liver and erythrocytes of normal subjects and in patients with porphyria cutanea tarda and their relatives. In patients with porphyria cutanea tarda, hepatic uroporphyrinogen decarboxylase activity was significantly reduced (mean 0.43 U/mg protein; range 0.25-0.99) as compared to normal subjects (mean 1.61 U/mg protein; range 1.27-2.42). Erythrocyte uroporphyrinogen decarboxylase was also decreased in patients with porphyria cutanea tarda. The mean erythrocyte enzymatic activity in male patients was 0.23 U/mg Hb (range 0.16-0.30) and in female patients was 0.17 U/mg Hb (range 0.15-0.18) as compared with mean values in normal subjects of 0.38 U/mg Hb (range 0.33-0.45) in men and 0.26 U/mg Hb (range 0.18-0.36) in women. With the erythrocyte assay, multiple examples of decreased uroporphyrinogen decarboxylase activity were detected in members of three families of patients with porphyria cutanea tarda. In two of these families subclinical porphyria was also recognized. The inheritance pattern was consistant with an autosomal dominant trait. The difference in erythrocyte enzymatic activity between men and women was not explained but could have been due to estrogens. This possibility was supported by the observation that men under therapy with estrogens for carcinoma of the prostate had values in the normal female range. It is proposed that porphyria cutanea tarda results from the combination of an inherited defect in uroporphyrinogen decarboxylase and an acquired factor, usually siderosis associated with alcoholic liver disease.

The role of iron in the pathogenesis of porphyria cutanea tarda. An in vitro model.

Porphyria cutanea tarda (PCT) is characterized biochemically by excessive hepatic synthesis and urinary excretion of uroporphyrin I. Clinical evidence has implicated iron in the pathogenesis of PCT. The synthesis of the normally occurring isomer of uroporphyrin, namely uroporphyrin III, from porphobilinogen (PBG) requires two enzymes; uroporphyrinogen I synthetase and uroporphyrinogen III cosynthetase (COSYN). In the absence of COSYN only uroporphyrinogen I is formed. These experiments were designed to study the effect of iron on porphyrin biosynthesis in porcine and human crude liver extracts and to measure COSYN activity in the presence of iron.Mitochondria-free crude liver extracts were prepared in 0.25 m sucrose at pH 7.4 by centrifugation at 37,000 g. Preparations were incubated with either 0.2 mm amino-levulinic acid (ALA) or 0.1 mm PBG. The addition of ferrous ion (either from ferritin iron [4 mug/ml] and cysteine [6.7 mm] or ferrous ammonium sulfate [0.3 mm Fe] and cysteine) significantly increased the rate of uroporphyrin synthesis from either ALA or PBG. The predominant porphyrin synthesized in the presence of ferrous ion was uroporphyrin I whereas coproporphyrin III predominated in its absence. Orthophenanthroline blocked these effects of ferrous ion.To investigate the effect of ferrous ion on COSYN, crude liver extracts were incubated with ferrous ammonium sulfate (0.3 mm Fe) and cysteine (6.7 mm) and the COSYN activity of the incubates was assayed directly. In both porcine and human extracts ferrous ion caused marked inhibition of COSYN activity. Orthophenanthroline blocked the inhibitory effect.Inactivation of COSYN by heating resulted in marked enhancement of porphyrin synthesis from PBG. The sole product was uroporphyrin I.Thus, inactivation of COSYN results in accelerated synthesis of uroporphyrin I. This effect of ferrous ion provides a possible biochemical explanation for the excess production and excretion of uroporphyrin I in patients with PCT and the reversal of this defect by phlebotomy.

Biosynthesis of 5-aminolevulinic acid and heme from 4,5-dioxovalerate in the rat.

We previously demonstrated an alternate pathway for the biosynthesis of 5-aminolevulinic acid (ALA) in bovine liver mitochondria and of tetrapyrroles in suspensions of rat hepatocytes (1980. J. Biol. Chem. 255: 3742; 1981. Proc. Natl. Acad. Sci. USA. 78: 5335). This pathway involves a transamination reaction that incorporates the intact 5-carbon skeleton of 4,5-dioxovaleric acid (DOVA) into ALA. We investigated this alternate pathway in vivo by the intraperitoneal injection of DOVA into rats. Incorporation of DOVA and [5-14C]DOVA into urinary ALA and hepatic and erythroid heme was quantified and compared with the incorporation of [4-14C]ALA and [2-14C]glycine into heme. Within 3 h of injection of 175 mumol of DOVA, urinary ALA excretion increased 2.4-fold over controls. After injection of [5-14C]DOVA, 0.11% of the radioactivity was recovered as urinary ALA, which quantitatively accounted for the 2.4-fold increase in ALA excretion. After the injection 175 mumol of [5-14C]DOVA, 0.14% of the radioactivity was recovered after 3 h as hepatic heme. The injection of 1.75 mmol of [2-14C]glycine or 175 mumol of [4-14C]ALA resulted in recovery of 0.2 and 3.4%, respectively, of the radioactivity as hepatic heme after 3 h. These doses of radiolabeled DOVA, glycine, and ALA were injected into rats with phenylhydrazine-induced anemia. Recovery of radioactivity after 3 h as splenic (erythroid) heme was 0.35% for DOVA, 0.072% for glycine, and 0.25% for ALA. These studies establish that the intact 5-carbon skeleton of DOVA can be incorporated into ALA and heme in vivo.

Uroporphyrinogen decarboxylase: a splice site mutation causes the deletion of exon 6 in multiple families with porphyria cutanea tarda.

Uroporphyrinogen decarboxylase (URO-D) is a cytosolic heme-biosynthetic enzyme that converts uroporphyrinogen to coproporphyrinogen. Defects at the uroporphyrinogen decarboxylase locus cause the human genetic disease familial porphyria cutanea tarda. A splice site mutation has been found in a pedigree with familial porphyria cutanea tarda that causes exon 6 to be deleted from the mRNA. The intron/exon junctions on either side of exon 6 fall between codons, so the resulting protein is shorter than the normal protein, missing only the amino acids coded by exon 6. The shortened protein lacks catalytic activity, is rapidly degraded when exposed to human lymphocyte lysates, and is not detectable by Western blot analysis in lymphocyte lysates derived from affected individuals. The mutation was detected in five of 22 unrelated familial porphyria cutanea tarda pedigrees tested, so it appears to be common. This is the first splice site mutation to be found at the URO-D locus, and the first mutation that causes familial porphyria cutanea tarda to be found in more than one pedigree.

Evidence for cytokine-inducible nitric oxide synthesis from L-arginine in patients receiving interleukin-2 therapy.

An interferon-gamma, tumor necrosis factor, and interleukin-1-inducible, high-output pathway synthesizing nitric oxide (NO) from L-arginine was recently identified in rodents. High-dose interleukin-2 (IL-2) therapy is known to induce the same cytokines in patients with advanced cancer. Therefore, we examined renal cell carcinoma (RCC; n = 5) and malignant melanoma (MM; n = 7) patients for evidence of cytokine-inducible NO synthesis. Activity of this pathway was evaluated by measuring serum and urine nitrate (the stable degradation product of NO) during IL-2 therapy. IL-2 administration caused a striking increase in NO generation as reflected by serum nitrate levels (10- and 8-fold increase [P less than 0.001, P less than 0.003] for RCC and MM patients, respectively) and 24-h urinary nitrate excretion (6.5- and 9-fold increase [both P less than 0.001] for RCC and MM patients, respectively). IL-2-induced renal dysfunction made only a minor contribution to increased serum nitrate levels. Metabolic tracer studies using L-[guanidino-15N2]arginine demonstrated that the increased nitrate production was derived from a terminal guanidino nitrogen atom of L-arginine. Our results showing increased endogenous nitrate synthesis in patients receiving IL-2 demonstrate for the first time that a cytokine-inducible, high-output L-arginine/NO pathway exists in humans.

The effect of glyoxalase I on the metabolism of 4,5-dioxovaleric acid.

Biosynthesis of 5-aminolevulinic acid in mammalian cells is catalyzed by aminolevulinic acid synthase in a condensation reaction utilizing glycine and succinyl X coenzyme A. An alternate pathway in mammalian cells may involve the biosynthesis of aminolevulinic acid via a transamination reaction in which L-alanine is the amino donor and 4,5-dioxovaleric acid is the acceptor. This transamination reaction, or one very similar, is employed by plants for the biosynthesis of aminolevulinic acid which is ultimately converted to chlorophyll. The effect of glyoxalase I on the diversion of dioxovaleric acid to other products was tested using both purified glyoxalase I and crude tissue homogenates. Glyoxalase I is a metalloenzyme and glutathione is a co-substrate. Purified glyoxalase I reduced the amount of aminolevulinic acid formed in the presence of dioxovaleric acid, L-alanine, glutathione, and purified L-alanine: 4,5-dioxovaleric acid aminotransferase (dioxovalerate transaminase). The conversion of dioxovaleric acid to aminolevulinic acid was inhibited by the addition of glutathione when a dialyzed bovine liver homogenate served as the source of both glyoxalase I and dioxovalerate transaminase. Removal of metals from bovine liver homogenates produced an 85% decrease in glyoxalase I activity. These 'metal-free' homogenates still affected the conversion of dioxovaleric acid to aminolevulinic acid after preincubation with MgSO4. The effect of glyoxalase I on the metabolism of dioxovaleric acid was also studied using a fluorometric enzyme assay for the quantification of dioxovaleric acid via a coupled enzyme reaction converting it to uroporphyrin. Homogenates of both liver and barley diminished the amount of dioxovaleric acid detected by the coupled assay, but this effect could be prevented by dialysis of the homogenates. Addition of glutathione to dialyzed homogenates markedly reduced the amount of uroporphyrin generated from dioxovaleric acid. Metal-free homogenates supplemented with glutathione reduced the conversion of dioxovaleric acid to uroporphyrin in the coupled assay, but preincubation with MgSO4 greatly augmented this effect. These studies point out the difficulty in evaluating dioxovaleric acid as a heme precursor using whole cell homogenates.

Mutational analysis of human uroporphyrinogen decarboxylase.

Uroporphyrinogen decarboxylase (URO-D), a heme biosynthetic enzyme, catalyzes the multi-step decarboxylation reaction converting uroporphyrinogen I or III to coproporphyrinogen I or III. The URO-D protein has been purified from several sources and its gene has been cloned from many organisms. In spite of this, little is known about the active site(s) of the enzyme. Inhibitor studies suggest that cysteine and histidine residues are important for enzyme activity. We employed the Kunkel method of site-directed mutagenesis to convert each of the six cysteines in human URO-D to serine and each of the three conserved histidines to asparagine. Recombinant mutant URO-D's were expressed in Escherichia coli, partially purified, and their kinetic properties compared to recombinant wild-type URO-D. All cysteine mutants retained approx. 40% wild-type enzyme activity, indicating that no single cysteine is absolutely critical for the integrity of the catalytic site. The three histidine mutants also retained significant enzyme activity and one, (H339N), displayed unique properties. The H339N mutation resulted in an enzyme with high residual activity but decarboxylation of intermediate reaction products of the I isomer series was markedly abnormal. The histidine at residue 339 is likely important in imparting isomer specificity.

The treatment of localized non-Hodgkin's lymphoma in children: a report from the Children's Cancer Study Group.

Investigators of the Children's Cancer Study Group entered 73 children with previously untreated localized non-Hodgkin's lymphoma on a prospective randomized trial of systemic treatment with either a four-drug program (cyclophosphamide, vincristine, methotrexate, prednisone [COMP]) or a 10-drug (LSA2-L2 modified) program of 18 months duration. All patients received central nervous system prophylaxis with intrathecal methotrexate and most received local or regional radiation treatment. The three-year relapse-free survival rate for all patients (N = 73) was 84%; for COMP (N = 42) was 85%, and for LSA2-L2 (N = 31) was 84%. Of the 12 patients who suffered adverse events eight relapsed and four died of toxicity. Histopathology was reviewed centrally. Of 32 patients with nonlymphoblastic disease treated with COMP only one relapsed. Of 26 patients treated with LSA2-L2, four relapsed. Patients with localized lymphoblastic disease were uncommon. None of three patients treated with LSA2-L2 relapsed compared with three of nine treated with COMP. COMP is an excellent treatment for patients with localized disease of nonlymphoblastic type, but the relative value of the two regimens for patients with localized lymphoblastic disease is uncertain.

Natural history of patients with unexplained syncope and a nondiagnostic electrophysiologic study.

The purpose of this study was to define the natural history of 99 patients with unexplained syncope who underwent an electrophysiologic test that either was entirely normal or demonstrated nonspecific abnormalities that were nondiagnostic (inducible polymorphic ventricular tachycardia or ventricular fibrillation, a mildly prolonged sinus node recovery time of less than 2 s, a His-ventricular interval of 55 to 99 ms or supraventricular tachycardia not associated with hypotension). The mean age (+/- SD) of the patients was 56 +/- 19 years; structural heart disease was present in 47 patients and absent in 52. Complete follow-up was available in 95 patients. During 20 +/- 11 months of follow-up, 2 patients (2%) died suddenly, 19 patients (20%) had recurrent syncope and 74 patients (78%) had no further episodes of syncope. Among the 19 patients who continued to have syncope after the electrophysiologic testing, the cause of syncope was established clinically in 4 and was found to be high degree atrioventricular (AV) block (2 patients) or sinus node dysfunction (2 patients). No clinical or laboratory findings distinguished patients who had sudden death or syncope during follow-up from patients who did not. In conclusion, in patients with unexplained syncope who undergo an electrophysiologic test that is nondiagnostic 1) the incidence of sudden death is low (2%); 2) the remission rate of syncope is high (80%); 3) the electrophysiologic test may be documented to have been falsely negative in greater than or equal to 20% of patients who continue to have syncope, syncope in these patients being caused by AV block or sinus node dysfunction; and 4) patients at risk of sudden death or recurrent syncope, or both, cannot be readily identified prospectively.

Antagonism of quinidine's electrophysiologic effects by epinephrine in patients with ventricular tachycardia.

The purpose of this study was to determine whether pharmacologically induced elevations in the plasma epinephrine concentration within reported physiologic limits alter the response to quinidine during electropharmacologic testing. Twenty-one patients with coronary artery disease and a history of unimorphic ventricular tachycardia were found to have inducible sustained unimorphic ventricular tachycardia that was suppressed by treatment with oral quinidine gluconate. Epinephrine was then infused at a rate of either 25 or 50 ng/kg per min and testing was repeated. These infusion rates of epinephrine were previously demonstrated to result in elevations of the plasma epinephrine concentration in the range of concentrations that occur during a variety of stresses. Quinidine significantly lengthened the ventricular refractory periods and the QRS duration at a ventricular pacing cycle length of 350 ms, which was used as an index of intraventricular conduction. Epinephrine partially or completely reversed the effects of quinidine on ventricular refractory periods, but had no effect on QRS duration. During electropharmacologic testing of quinidine, no ventricular tachycardia was inducible in 12 patients, and only nonsustained ventricular tachycardia, 8 to 48 beats in duration, was inducible in 9 patients. Retesting during infusion of epinephrine demonstrated inducible sustained unimorphic ventricular tachycardia in 2 of the 12 patients in whom quinidine had completely suppressed the induction of ventricular tachycardia and in 8 of the 9 patients in whom only nonsustained ventricular tachycardia had been inducible during testing of quinidine. In conclusion, physiologic elevations in the plasma epinephrine concentration may reverse quinidine-induced prolongation of ventricular refractoriness but not intraventricular conduction.(ABSTRACT TRUNCATED AT 250 WORDS)