Deletion of choline acetyltransferase in enteric neurons results in postnatal intestinal dysmotility and dysbiosis

Acetylcholine (ACh)-synthesizing neurons are major components of the enteric nervous system (ENS). They release ACh and peptidergic neurotransmitters onto enteric neurons and muscle. However, pharmacological interrogation has proven inadequate to demonstrate an essential role for ACh. Our objective was to determine whether elimination of ACh synthesis during embryogenesis alters prenatal viability, intestinal function, the neurotransmitter complement, and the microbiome. Conditional deletion of choline acetyltransferase ( ChAT), the ACh synthetic enzyme, in neural crest-derived neurons ( ChAT-Null) was performed. Survival, ChAT activity, gut motility, and the microbiome were studied. ChAT was conditionally deleted in ENS neural crest-derived cells. Despite ChAT absence, mice were born live and survived the first 2 wk. They failed to gain significant weight in the third postnatal week, dying between postnatal d 18 and 30. Small intestinal transit of carmine red was 50% slower in ChAT-Nulls vs. WT and ChAT- Het. The colons of many neonatal ChAT-Null mice contained compacted feces, suggesting dysmotility. Microbiome analysis revealed dysbiosis in ChAT-Null mice. Developmental deletion of ChAT activity in enteric neurons results in proximal gastrointestinal tract dysmotility, critically diminished colonic transit, failure to thrive, intestinal dysbiosis, and death. ACh is necessary for sustained gut motility and survival of neonatal mice after weaning.-Johnson, C. D., Barlow-Anacker, A. J., Pierre, J. F., Touw, K., Erickson, C. S., Furness, J. B., Epstein, M. L., Gosain, A. Deletion of choline acetyltransferase in enteric neurons results in postnatal intestinal dysmotility and dysbiosis.

APEX2-enhanced electron microscopy distinguishes sigma-1 receptor localization in the nucleoplasmic reticulum

The sigma-1 receptor (Sig1R) is an endoplasmic reticulum chaperonin that is attracting tremendous interest as a potential anti-neurodegenerative target. While this membrane protein is known to reside in the inner nuclear envelope (NE) and influences transcription, apparent Sig1R presence in the nucleoplasm is often observed, seemingly contradicting its NE localization. We addressed this confounding issue by applying an antibody-free approach of electron microscopy (EM) to define Sig1R nuclear localization. We expressed APEX2 peroxidase fused to Sig1R-GFP in a Sig1R-null NSC34 neuronal cell line generated with CRISPR-Cas9. APEX2-catalyzed gold/silver precipitation markedly improved EM clarity and confirmed an apparent intra-nuclear presence of Sig1R. However, serial sectioning combined with APEX2-enhanced EM revealed that Sig1R actually resided in the nucleoplasmic reticulum (NR), a specialized nuclear compartment formed via NE invagination into the nucleoplasm. NR cross-sections also indicated Sig1R in ring-shaped NR membranes. Thus, this study distinguishes Sig1R in the NR which could otherwise appear localized in the nucleoplasm if detected with low-resolution methods. Our finding is important for uncovering potential Sig1R regulations in the nucleus.

The Sigma-1 Receptor-A Therapeutic Target for the Treatment of ALS?

The membrane bound 223 amino acid Sigma-1 Receptor (S1R) serves as a molecular chaperone and functional regulator of many signaling proteins. Spinal cord motor neuron activation occurs, in part, via large ventral horn cholinergic synapses called C-boutons/C-terminals. Chronic excitation of motor neurons and alterations in C-terminals has been associated with Amyotrophic Lateral Sclerosis (ALS ). The S1R has an important role in regulating motor neuron function. High levels of the S1R are localized in postsynaptic endoplasmic reticulum (ER) subsurface cisternae within 10-20 nm of the plasma membrane that contain muscarinic type 2 acetylcholine receptors (M2AChR), calcium activated potassium channels (Kv2.1) and slow potassium (SK) channels. An increase in action potentials in the S1R KO mouse motor neurons indicates a critical role for the S1R as a "brake" on motor neuron function possibly via calcium dependent hyperpolarization mechanisms involving the aforementioned potassium channels. The longevity of SOD-1/S1R KO ALS mice is significantly reduced compared to SOD-1/WT ALS controls. The S1R colocalizes in C-terminals with Indole(ethyl)amine-N-methyl transferase (INMT ), the enzyme that produces the S1R agonist , N,N'- dimethyltryptamine (DMT). INMT methylation can additionally neutralize endogenous toxic sulfur and selenium derivatives thus providing functional synergism with DMT to reduce oxidative stress in motor neurons . Small molecule activation of the S1R and INMT thus provides a possible therapeutic strategy to treat ALS .

Sigma-1 receptor expression in the dorsal root ganglion: Reexamination using a highly specific antibody

Sigma-1 receptor (S1R) is a unique pluripotent modulator of living systems and has been reported to be associated with a number of neurological diseases including pathological pain. Intrathecal administration of S1R antagonists attenuates the pain behavior of rodents in both inflammatory and neuropathic pain models. However, the S1R localization in the spinal cord shows a selective ventral horn motor neuron distribution, suggesting the high likelihood of S1R in the dorsal root ganglion (DRG) mediating the pain relief by intrathecally administered drugs. Since primary afferents are the major component in the pain pathway, we examined the mouse and rat DRGs for the presence of the S1R. At both mRNA and protein levels, quantitative RT-PCR (qRT-PCR) and Western confirmed that the DRG contains greater S1R expression in comparison to spinal cord, cortex, or lung but less than liver. Using a custom-made highly specific antibody, we demonstrated the presence of a strong S1R immuno-fluorescence in all rat and mouse DRG neurons co-localizing with the Neuron-Specific Enolase (NSE) marker, but not in neural processes or GFAP-positive glial satellite cells. In addition, S1R was absent in afferent terminals in the skin and in the dorsal horn of the spinal cord. Using immuno-electron microscopy, we showed that S1R is detected in the nuclear envelope and endoplasmic reticulum (ER) of DRG cells. In contrast to other cells, S1R is also located directly at the plasma membrane of the DRG neurons. The presence of S1R in the nuclear envelope of all DRG neurons suggests an exciting potential role of S1R as a regulator of neuronal nuclear activities and/or gene expression, which may provide insight toward new molecular targets for modulating nociception at the level of primary afferent neurons.

Immunostaining to visualize murine enteric nervous system development

The enteric nervous system is formed by neural crest cells that proliferate, migrate and colonize the gut. Following colonization, neural crest cells must then differentiate into neurons with markers specific for their neurotransmitter phenotype. Cholinergic neurons, a major neurotransmitter phenotype in the enteric nervous system, are identified by staining for choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine. Historical efforts to visualize cholinergic neurons have been hampered by antibodies with differing specificities to central nervous system versus peripheral nervous system ChAT. We and others have overcome this limitation by using an antibody against placental ChAT, which recognizes both central and peripheral ChAT, to successfully visualize embryonic enteric cholinergic neurons. Additionally, we have compared this antibody to genetic reporters for ChAT and shown that the antibody is more reliable during embryogenesis. This protocol describes a technique for dissecting, fixing and immunostaining of the murine embryonic gastrointestinal tract to visualize enteric nervous system neurotransmitter expression.

Role of the Sigma-1 receptor in Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease affecting spinal cord motoneurons (MN) with an associative connection to Frontotemporal Lobar Dementia (FTLD). The endoplasmic reticulum (ER) bound Sigma-1 Receptor (S1R) chaperone protein localizes to specialized ER cisternae within 10 nm of the plasma membrane in spinal cord ventral horn cholinergic post synaptic C-terminals. Removal of the S1R gene in the Superoxide Dismutase-1 (SOD-1) mouse model of ALS exacerbated the neurodegenerative condition and resulted in a significantly reduced longevity when compared to the SOD-1/S1R wild type (WT) mouse. The proposed amelioration of the ALS phenotype by the S1R is likely due to a "brake" on excitation of the MN as evidenced by a reduction in action potential generation in the MN of the WT when compared to the S1R KO mouse MN. Although the precise signal transduction pathway(s) regulated by the S1R in the MN has/have not been elucidated at present, it is likely that direct or indirect functional interactions occur between the S1R in the ER cisternae with voltage gated potassium channels and/or with muscarinic M2 receptor signaling in the post synaptic plasma membrane. Possible mechanisms for regulation of MN excitability by S1R are discussed.

Dopamine transporter gene susceptibility to methylation is associated with impulsivity in nonhuman primates

Impulsivity, the predisposition to act without regard for negative consequences, is a characteristic of several psychiatric disorders and is thought to result in part from genetic variation in the untranslated region of the dopamine transporter (DAT) gene. As the exact link between genetic mutations and impulsivity has not been established, we used oculomotor behavior to characterize rhesus monkeys as impulsive or calm and genetic/epigenetic analysis and positron emission tomography (PET) to correlate phenotype to DAT genotype, DAT gene methylation, and DAT availability. We found three single nucleotide polymorphisms (SNPs) in the 3'-UTR of the DAT gene, one of which provided a potential site for methylation in the impulsive group. Bisulfite analysis showed that the DNA of the impulsive but not the calm subjects was methylated at one SNP. Because genetic/epigenetic modifications could lead to differences in protein expression, we measured DAT availability using [(18)F]2β-carbomethoxy-3β-(4-chlorophenyl)-8-(2-fluoroethyl)-nortropane ([(18)F]FECNT) PET and found higher DAT availability in the internal globus pallidus, an output nucleus of the basal ganglia, of the impulsive group. Higher DAT availability lowers dopamine levels, potentially altering neuronal circuits involved in the initiation of action, thus contributing to the impulsive phenotype. The association between increased methylation in the DAT gene and greater DAT availability suggests that mutations to the regulatory portion of the DAT gene lead to a susceptibility to epigenetic modification resulting in a discrete behavioral phenotype.

Intestinal dysbiosis and bacterial enteroinvasion in a murine model of Hirschsprung's disease

BACKGROUND/PURPOSE

Hirschsprung's disease (HSCR), characterized by the absence of ganglia in the distal colon, results in functional obstruction. Despite surgical resection of the aganglionic segment, around 40% of patients suffer recurrent life threatening Hirschsprung's-associated enterocolitis (HAEC). The aim of this study was to investigate whether gut microbiota and intestinal immunity changes contribute to the HAEC risk in an HSCR model.

METHODS

Mice with neural crest conditional deletion of Endothelin receptor B (EdnrB) and their littermate controls were used (EdnrB-null and EdnrB-het). Bacterial DNA was prepared from cecal contents of P16-18 and P21-24 animals and pyrosequencing employed for microbiome analysis. Ileal tissue was isolated and secretory phospholipase A2 (sPLA2) expression and activity determined. Enteroinvasion of Escherichia coli into ileal explants was measured using an ex vivo organ culture system.

RESULTS

EdnrB-het and EdnrB-nulls displayed similar flora, sPLA2 expression and activity at P16-18. However, by P21-24, EdnrB-hets demonstrated increased Lactobacillus and decreased Bacteroides and Clostridium, while EdnrB-nulls exhibited reciprocal changes. EdnrB-nulls also showed reduced sPLA2 expression and luminal activity at this stage. Functionally, EdnrB-nulls were more susceptible to enteroinvasion with E. coli ex vivo and released less sPLA2 than EdnrB-hets.

CONCLUSIONS

Initially, EdnrB-het and EdnrB-nulls contain similar cecal flora but then undergo reciprocal changes. EdnrB-nulls display dysbiosis, demonstrate impaired mucosal defense, decreased luminal sPLA2 and increased enteroinvasion of E. coli just prior to robust colonic inflammation and death. These findings suggest a role for the intestinal microbiome in the development of HAEC.

Appearance of cholinergic myenteric neurons during enteric nervous system development: comparison of different ChAT fluorescent mouse reporter lines

BACKGROUND

Cholinergic neurons have been identified with the acetylcholine synthetic enzyme choline acetyltransferase (ChAT). However, ChAT is difficult to localize in newly differentiated peripheral neurons making the study of cholinergic neuronal development problematic. Consequently, researchers have used mouse reporter lines to indicate the presence of ChAT.

METHODS

Our objective was to determine which ChAT reporter line was the most sensitive indicator of ChAT expression. We utilized two different fluorescent ChAT reporter lines (ChAT-GFP and ChAT-Cre;R26R:floxSTOP:tdTomato) together with immunolocalization of ChAT protein (ChAT-IR) to characterize the spatial and temporal expression of ChAT in myenteric neurons throughout enteric nervous system (ENS) development.

KEY RESULTS

ChAT-IR cells were first seen in the intestine at E10.5, even within the migration wavefront of neural precursors. Myenteric neurons within the distal small intestine (dSI) and proximal colon were first labeled by ChAT-IR, then ChAT-GFP, and finally ChAT-Cre tdTomato. The percentage of ChAT-IR neurons is equivalent to adult levels in the dSI by E13.5 and proximal colon by P0. After these stages, the percentages remained relatively constant throughout development despite dramatic changes in neuronal density.

CONCLUSIONS & INFERENCES

These observations indicate that neurotransmitter expression occurs early and there is only a brief gap between neurogenesis and neurotransmitter expression. Our finding that the proportion of ChAT myenteric neurons reached adult levels during embryonic development suggests that the fate of cholinergic neurons is tightly regulated and that their differentiation might influence further neuronal development. ChAT-GFP is a more accurate indicator of early ENS cholinergic neuronal differentiation than the ChAT-Cre;R26R:floxSTOP:tdTomato reporter mouse.

Lack of sigma-1 receptor exacerbates ALS progression in mice

The function of the sigma-1 receptor (S1R) has been implicated in modulating the activity of various ion channels. In the CNS S1R is enriched in cholinergic postsynaptic densities in spinal cord motoneurons (MNs). Mutations in S1R have been found in familial cases of amyotrophic lateral sclerosis (ALS). In this study we show that a knockout of S1R in the SOD1*G93A mouse model of ALS significantly reduces longevity (end stage). Electrophysiological experiments demonstrate that MN of mice lacking S1R exhibit increased excitability. Taken together the data suggest the S1R acts as a brake on excitability, an effect that might enhance longevity in an ALS mouse model.

Colonic enteric nervous system analysis during parenteral nutrition

INTRODUCTION

Parenteral nutrition (PN) is a necessary therapy used to feed patients with gastrointestinal dysfunction. Unfortunately, PN results in intestinal atrophy and changes to host immune function. PN may also induce additional effects on gut motility that we hypothesized would result from changes in the enteric nervous system.

METHODS

Mice received an intravenous (i.v.) catheter and were randomized to chow (n = 5), i.v. PN (n = 6), or i.v. PN + bombesin (BBS, 15 μg/kg, 3×/d) (n = 6) for 5 d. Colons were removed and dissected to measure the length and circumference. Enteric neuronal density and neurotransmitter expression were determined by co-immunostaining whole-mount tissue with Hu and neuronal nitric oxide synthase (nNOS).

RESULTS

The number of myenteric neurons expressing Hu and nNOS increased per unit length in the mid-colon during PN treatment compared with chow. This increase was abrogated by the addition of BBS to the PN regimen. However, the percentage of nNOS-expressing neurons was not significantly altered by PN. Morphometric analysis revealed a decrease in the length and circumference of the colon during PN administration that was partially normalized by supplementation of PN with BBS. A significant reduction in total fecal output was observed in PN animals compared with chow and was increased by mice receiving BBS in addition to PN.

CONCLUSIONS

PN causes a constriction of the bowel wall, reducing not only the length but also the circumference of the colon. These changes cause a condensation of enteric neurons but no difference in neurotransmitter expression. BBS supplementation partially restores the constriction and increases the fecal output during PN treatment compared with PN treatment alone.

Altered neuronal density and neurotransmitter expression in the ganglionated region of Ednrb null mice: implications for Hirschsprung's disease

BACKGROUND

Hirschsprung's disease (HSCR) is a congenital condition in which enteric ganglia, formed from neural crest cells (NCC), are absent from the terminal bowel. Dysmotility and constipation are common features of HSCR that persist following surgical intervention. This persistence suggests that the portion of the colon that remains postoperatively is not able to support normal bowel function. To elucidate the defects that underlie this condition, we utilized a murine model of HSCR.

METHODS

Mice with NCC-specific deletion of Ednrb were used to measure the neuronal density and neurotransmitter expression in ganglia.

KEY RESULTS

At the site located proximal to the aganglionic region of P21 Ednrb null mice, the neuronal density is significantly decreased and the expression of neurotransmitters is altered compared with het animals. The ganglia in this colonic region are smaller and more isolated while the size of neuronal cell bodies is increased. The percentage of neurons expressing neuronal nNOS and VIP is significantly increased in Ednrb nulls. Conversely, the percentage of choline acetyltransferase (ChAT) expressing neurons is decreased, while Substance P is unchanged between the two genotypes. These changes are limited to the colon and are not detected in the ileum.

CONCLUSIONS & INFERENCES

We demonstrate changes in neuronal density and alterations in the balance of expression of neurotransmitters in the colon proximal to the aganglionic region in Ednrb null mice. The reduced neuronal density and complementary changes in nNOS and ChAT expression may account for the dysmotility seen in HSCR.

VEGF induces sensory and motor peripheral plasticity, alters bladder function, and promotes visceral sensitivity

BACKGROUND

This work tests the hypothesis that bladder instillation with vascular endothelial growth factor (VEGF) modulates sensory and motor nerve plasticity, and, consequently, bladder function and visceral sensitivity.In addition to C57BL/6J, ChAT-cre mice were used for visualization of bladder cholinergic nerves. The direct effect of VEGF on the density of sensory nerves expressing the transient receptor potential vanilloid subfamily 1 (TRPV1) and cholinergic nerves (ChAT) was studied one week after one or two intravesical instillations of the growth factor.To study the effects of VEGF on bladder function, mice were intravesically instilled with VEGF and urodynamic evaluation was assessed. VEGF-induced alteration in bladder dorsal root ganglion (DRG) neurons was performed on retrogradly labeled urinary bladder afferents by patch-clamp recording of voltage gated Na+ currents. Determination of VEGF-induced changes in sensitivity to abdominal mechanostimulation was performed by application of von Frey filaments.

RESULTS

In addition to an overwhelming increase in TRPV1 immunoreactivity, VEGF instillation resulted in an increase in ChAT-directed expression of a fluorescent protein in several layers of the urinary bladder. Intravesical VEGF caused a profound change in the function of the urinary bladder: acute VEGF (1 week post VEGF treatment) reduced micturition pressure and longer treatment (2 weeks post-VEGF instillation) caused a substantial reduction in inter-micturition interval. In addition, intravesical VEGF resulted in an up-regulation of voltage gated Na(+) channels (VGSC) in bladder DRG neurons and enhanced abdominal sensitivity to mechanical stimulation.

CONCLUSIONS

For the first time, evidence is presented indicating that VEGF instillation into the mouse bladder promotes a significant increase in peripheral nerve density together with alterations in bladder function and visceral sensitivity. The VEGF pathway is being proposed as a key modulator of neural plasticity in the pelvis and enhanced VEGF content may be associated with visceral hyperalgesia, abdominal discomfort, and/or pelvic pain.

Sacral neural crest-derived cells enter the aganglionic colon of Ednrb-/- mice along extrinsic nerve fibers

Both vagal and sacral neural crest cells contribute to the enteric nervous system in the hindgut. Because it is difficult to visualize sacral crest cells independently of vagal crest, the nature and extent of the sacral crest contribution to the enteric nervous system are not well established in rodents. To overcome this problem we generated mice in which only the fluorescent protein-labeled sacral crest are present in the terminal colon. We found that sacral crest cells were associated with extrinsic nerve fibers. We investigated the source, time of appearance, and characteristics of the extrinsic nerve fibers found in the aganglionic colon. We observed that the pelvic ganglion neurons contributed a number of extrinsic fibers that travel within the hindgut between circular and longitudinal muscles and within the submucosa and serosa. Sacral crest-derived cells along these fibers diminished in number from fetal to postnatal stages. A small number of sacral crest-derived cells were found between the muscle layers and expressed the neuronal marker Hu. We conclude that sacral crest cells enter the hindgut by advancing on extrinsic fibers and, in aganglionic preparations, they form a small number of neurons at sites normally occupied by myenteric ganglia. We also examined the colons of ganglionated preparations and found sacral crest-derived cells associated with both extrinsic nerve fibers and nascent ganglia. Extrinsic nerve fibers serve as a route of entry for both rodent and avian sacral crest into the hindgut.

Expectancy-related modulations of neural oscillations in continuous performance tasks

Analysis of neural oscillations in the electroencephalogram (EEG) during cognitive tasks provides valuable information about underlying neuronal processing not accessible by other methods such as event-related potentials (ERPs) and the BOLD signal in fMRI. We investigated neural substrates of motor preparation and expectancy by analyzing neural oscillations of healthy subjects performing the AX continuous performance task (AX-CPT), a task widely used to evaluate processes such as cognitive control, motor preparation and anticipatory and sustained attention. The task consists of letters presented sequentially on a monitor, and subjects are required to respond only when they see the letter A (cue) followed by the letter X (target). In this study, to emphasize expectation and motor preparation, three versions of AX-CPT were used in which the overall propensity to respond was differentially modulated, by changing the probability of the letter sequences. Neural activity was investigated in three time windows following presentation of the cue: sensory, evaluation and preparation. Alpha power was reduced following cue onset similarly in all versions of the task in both the sensory and evaluation periods, but in the later preparation period there were task dependent modulations. Alpha was decreased when an infrequent cue increased the chance of a response, and increased when a propensity to respond had to be overcome, possibly reflecting an anticipatory attentional mechanism to gate visuo-motor processing. Beta power was modulated by task and cue in both evaluation and preparation periods. In the latter, beta power reflected the propensity to respond and correlated both with amplitude of the contingent negative variation (CNV), an ERP that reflects response preparation, and with reaction time. Some clinical populations such as patients with schizophrenia or attention-deficit disorder show specific deficits when performing the AX-CPT. These results provide a basis for investigating the differential neural underpinnings of oscillatory cognitive control deficits observed in various patient populations.

Development of the sigma-1 receptor in C-terminals of motoneurons and colocalization with the N,N'-dimethyltryptamine forming enzyme, indole-N-methyl transferase

The function of the sigma-1 receptor (S1R) has been linked to modulating the activities of ion channels and G-protein-coupled receptors (GPCR). In the CNS, the S1R is expressed ubiquitously but is enriched in mouse motoneurons (MN), where it is localized to subsurface cisternae of cholinergic postsynaptic densities, also known as C-terminals. We found that S1R is enriched in mouse spinal MN at late stages of embryonic development when it is first visualized in the endoplasmic reticulum. S1Rs appear to concentrate at C-terminals of mouse MN only on the second week of postnatal development. We found that indole-N-methyl transferase (INMT), an enzyme that converts tryptamine into the sigma-1 ligand dimethyltryptamine (DMT), is also localized to postsynaptic sites of C-terminals in close proximity to the S1R. This close association of INMT and S1Rs suggest that DMT is synthesized locally to effectively activate S1R in MN.

Use of RNAlater in fluorescence-activated cell sorting (FACS) reduces the fluorescence from GFP but not from DsRed

Background

Flow cytometry utilizes signals from fluorescent markers to separate targeted cell populations for gene expression studies. However, the stress of the FACS process could change normal gene expression profiles. RNAlater could be used to stop such changes in original gene expression profiles through its ability to denature RNase and other proteins. The normal conformational structure of fluorescent proteins must be maintained in order to fluoresce. Whether or not RNAlater would affect signals from different types of intrinsic fluorescent proteins is crucial to its use in flow cytometry; this question has not been investigated in detail.

Findings

To address this question, we analyzed the effect of RNAlater on fluorescence intensity of GFP, YFP, DsRed and small fluorescent molecules attached to secondary antibodies (Cy2 and Texas-Red) when used in flow cytometry. FACS results were confirmed with fluorescence microscopy. Our results showed that exposure of YFP and GFP containing cells to RNAlater reduces the intensity of their fluorescence to such an extent that separation of such labeled cells is difficult if not impossible. In contrast, signals from DsRed2, Cy2 and Texas-Red were not affected by RNAlater treatment. In addition, the background fluorescence and clumping of dissociated cells are altered by RNAlater treatment.

Conclusions

When considering gene expression studies using cell sorting with RNAlater, DsRed is the fluorescent protein of choice while GFP/YFP have severe limitations because of their reduced fluorescence. It is necessary to examine the effects of RNAlater on signals from fluorescent markers and the physical properties (e.g., clumping) of the cells before considering its use in cell sorting.

The sigma-1 receptor is enriched in postsynaptic sites of C-terminals in mouse motoneurons. An anatomical and behavioral study

The sigma-1 receptor regulates various ion channel activity and possesses protein chaperone function. Using an antibody against the full sequence of the sigma-1 receptor we detected immunostaining in wild type but not in knockout mice. The receptor was found primarily in motoneurons localized to the brainstem and spinal cord. At the subcellular level the receptor is restricted to large cholinergic postsynaptic densities on the soma of motoneurons and is colocalized with the Kv2.1 potassium channel and the muscarinic type 2 cholinergic receptor. Ultrastructural analysis of the neurons indicates that the immunostained receptor is located close but separate from the plasma membrane, possibly in subsurface cisternae formed from the endoplasmic reticulum (ER), which are a prominent feature of cholinergic postsynaptic densities. Behavioral testing on a rotorod revealed that Sigma-1 receptor knockout mice remained on the rotorod for significantly less time (a shorter latency period) compared to the wild type mice. Together these data indicate that the sigma-1 receptor may play a role in the regulation of motor behavior.

Age-dependent changes in the gut environment restrict the invasion of the hindgut by enteric neural progenitors

The enteric nervous system (ENS) develops from neural crest cells (NCCs) that enter the foregut and hindgut to become enteric neural-crest-derived cells (ENCCs). When these cells of neural crest origin fail to colonize the terminal hindgut, this aganglionic region becomes non-functional and results in a condition in humans known as Hirschsprung's disease (HSCR). One of the genes associated with HSCR is endothelin receptor type B (Ednrb). To study the development of colonic aganglionosis we have utilized a novel knockout mouse (Ednrb(flex3/flex3)), in which the expression of a null Ednrb allele and YFP is confined to NCCs. We have identified two primary cellular defects related to defective EDNRB signaling. First, ENCC advance in Ednrb(flex3/flex3) embryos is delayed shortly after NCCs enter the gut. Apart from this early delay, Ednrb(flex3/flex3) ENCCs advance normally until reaching the proximal colon. Second, as Ednrb(flex3/flex3) ENCCs reach the colon at E14.5, they display migratory defects, including altered trajectories and reduced speed, that are not dependent on proliferation or differentiation. We constructed grafts to test the ability of donor ENCCs to invade a recipient piece of aganglionic colon. Our results indicate that the age of the recipient, and not the age or genotype of donor ENCCs, determines whether the colon is invaded. We identify changes in laminin expression that are associated with the failure of ENCCs to invade recipient tissue. Together, our data suggest that a defect in pre-enteric Ednrb(flex3/flex3) NCCs results in delayed colonic arrival, which, due to environment changes in the colon, is sufficient to cause aganglionosis.

Immunohistochemical analysis of neuron types in the mouse small intestine

The definition of the nerve cell types of the myenteric plexus of the mouse small intestine has become important, as more researchers turn to the use of mice with genetic mutations to analyze roles of specific genes and their products in enteric nervous system function and to investigate animal models of disease. We have used a suite of antibodies to define neurons by their shapes, sizes, and neurochemistry in the myenteric plexus. Anti-Hu antibodies were used to reveal all nerve cells, and the major subpopulations were defined in relation to the Hu-positive neurons. Morphological Type II neurons, revealed by anti-neurofilament and anti-calcitonin gene-related peptide antibodies, represented 26% of neurons. The axons of the Type II neurons projected through the circular muscle and submucosa to the mucosa. The cell bodies were immunoreactive for choline acetyltransferase (ChAT), and their terminals were immunoreactive for vesicular acetylcholine transporter (VAChT). Nitric oxide synthase (NOS) occurred in 29% of nerve cells. Most were also immunoreactive for vasoactive intestinal peptide, but they were not tachykinin (TK)-immunoreactive, and only 10% were ChAT-immunoreactive. Numerous NOS terminals occurred in the circular muscle. We deduced that 90% of NOS neurons were inhibitory motor neurons to the muscle (26% of all neurons) and 10% (3% of all neurons) were interneurons. Calretinin immunoreactivity was found in a high proportion of neurons (52%). Many of these had TK immunoreactivity. Small calretinin neurons were identified as excitatory neurons to the longitudinal muscle (about 20% of neurons, with ChAT/calretinin/+/- TK chemical coding). Excitatory neurons to the circular muscle (about 10% of neurons) had the same coding. Calretinin immunoreactivity also occurred in a proportion of Type II neurons. Thus, over 90% of neurons in the myenteric plexus of the mouse small intestine can be currently identified by their neurochemistry and shape.

Targeting of endothelin receptor-B to the neural crest

Endothelin receptor B (Ednrb) plays a critical role in the development of melanocytes and neurons and glia of the enteric nervous system. These distinct neural crest-derived cell types express Ednrb and share the property of intercalating into tissues, such as the intestine whose muscle precursor cells also express Ednrb. Such widespread Ednrb expression has been a significant obstacle in establishing precise roles for Ednrb in development. We describe here the production of an Ednrb allele floxed at exon 3 and its use in excising the receptor from mouse neural crest cells by use of Cre-recombinase driven by the Wnt1 promoter. Mice born with neural crest-specific excision of Ednrb possess aganglionic colon, lack trunk pigmentation, and die within 5 weeks due to megacolon. Ednrb receptor expression in these animals is absent only in the neural crest but present in surrounding smooth muscle cells. The absence of Ednrb from crest cells also results in a compensatory upregulation of Ednrb expression in other cells within the gut. We conclude that Ednrb loss only in neural crest cells is sufficient to produce the Hirschsprungs disease phenotype observed with genomic Ednrb mutations.

Behavior of enteric neural crest-derived cells varies with respect to the migratory wavefront

Neural crest-derived cells colonize the entire gastrointestinal tract. The migration of these enteric neural crest-derived cells (ENCCs) occurs by their formation of cellular strands that extend into the intestinal mesenchyme. We have studied the behavior of crest cells that underlies the formation and extension of these strands by time-lapse microscopy. ENCCs expressing fluorescent marker molecules were visualized in situ in the embryonic mouse and chick gut. The major contributor to strand extension is from cells located within a region approximately 300 microm behind (rostral to) the most caudal cells in the migratory wavefront. Cells in the region immediately behind the leading cell of the strand either move intermittently in parallel with the leading cell, or advance caudally toward the wavefront over other ENCCs. Another addition to the strands arises from isolated cells located caudal to the wavefront. These cells showed a range of behavior including attachment and separation from the strands. The extending strands converged to form nodes, and then diverged along independent paths to form new strands, a behavior suggestive of attraction and repulsion. This behavior is probably responsible for the unique reticulated arrangement of ganglia in the enteric nervous system. As cells become positioned farther behind the wavefront, they exhibit more restricted movement and varied trajectories. We conclude that ENCCs exhibit different behaviors, depending on their position with respect to the wavefront. These different behaviors suggest a critical role for cell-cell interaction in the migratory process.

The pattern of neural crest advance in the cecum and colon

Neural crest cells leave the hindbrain, enter the gut mesenchyme at the pharynx, and migrate as strands of cells to the terminal bowel to form the enteric nervous system. We generated embryos containing fluorescent enteric neural crest-derived cells (ENCCs) by mating Wnt1-Cre mice with Rosa-floxed-YFP mice and investigated ENCC behavior in the intact gut of mouse embryos using time-lapse fluorescent microscopy. With respect to the entire gut, we have found that ENCCs in the cecum and proximal colon behave uniquely. ENCCs migrating caudally through either the ileum, or caudal colon, are gradually advancing populations of strands displaying largely unpredictable local trajectories. However, in the cecum, advancing ENCCs pause for approximately 12 h, and then display an invariable pattern of migration to distinct regions of the cecum and proximal colon. In addition, while most ENCCs migrating through other regions of the gut remain interconnected as strands; ENCCs initially migrating through the cecum and proximal colon fragment from the main population and advance as isolated single cells. These cells aggregate into groups isolated from the main network, and eventually extend strands themselves to reestablish a network in the mid-colon. As the advancing network of ENCCs reaches the terminal bowel, strands of sacral crest cells extend, and intersect with vagal crest to bridge the small space between. We found a relationship between ENCC number, interaction, and migratory behavior by utilizing endogenously isolated strands and by making cuts along the ENCC wavefront. Depending on the number of cells, the ENCCs aggregated, proliferated, and extended strands to advance the wavefront. Our results show that interactions between ENCCs are important for regulating behaviors necessary for their advancement.

GDNF and insulin cooperate to enhance the proliferation and differentiation of enteric crest-derived cells

Previously we have shown that glial derived neurotrophic factor (GDNF) stimulates modest increases in the proliferation of avian enteric crest-derived cells and similar increases in the phosphorylation of the phosphoinositide 3-kinase (PI3K) downstream substrate Akt (Akt-P). In the present study we tested whether GDNF-independent increases in PI3K activation would be sufficient to support proliferation. We found that insulin induces a large increase in the phosphorylation of Akt and can initiate DNA synthesis in avian enteric crest-derived cells, but is unable to maintain proliferation over time in culture, measured by BrdU incorporation. GDNF can also initiate DNA synthesis, but it too is unable to maintain BrdU incorporation in cultured enteric crest-derived cells. Sustained incorporation of BrdU after 16-48 h in culture is shown to be dependent on a combination of GDNF and insulin. Using a phospho-specific antibody, we found Akt-P levels to be similar in the proliferating (BrdU incorporation maintained from 16-48 h in culture) and nonproliferating populations, suggesting that Akt-P levels were not solely controlling the extent of BrdU incorporation. A minimum level of PI3K activation, however, is required, as shown by the dose-dependent reduction in proliferation with the PI3K inhibitor LY-294002. We conclude that the integrity of the PI3K pathway is essential for enteric crest-derived cell proliferation, but that the absolute levels of Akt-P do not determine the extent of proliferation. The enhanced proliferation in cultures containing both GDNF and insulin suggests that other pathways are involved, including the possibility that PI3K downstream effectors other than Akt are important in the regulation of avian enteric crest-derived cell proliferation.

Appearance of neurons and glia with respect to the wavefront during colonization of the avian gut by neural crest cells

The enteric nervous system is formed by neural crest cells that migrate, proliferate, and differentiate into neurons and glia distributed in ganglia along the gastrointestinal tract. In the developing embryo some enteric crest cells cease their caudal movements, whereas others continue to migrate. Subsequently, the enteric neurons form a reticular network of ganglia interconnected by axonal projections. We studied the developing avian gut to characterize the pattern of migration of the crest cells, and the relationship between migration and differentiation. Crest cells at the leading edge of the migratory front appear as strands of cells; isolated individual crest cells are rarely seen. In the foregut and midgut, these strands are located immediately beneath the serosa. In contrast, crest cells entering the colon appear first in the deeper submucosal mesenchyme and later beneath the serosa. As the neural crest wavefront passes caudally, the crest cell cords become highly branched, forming a reticular lattice that presages the mature organization of the enteric nervous system. Neurons and glia first appear within the strands at the advancing wavefront. Later neurons are consistently located at the nodes where branches of the lattice intersect. In the most rostral foregut and in the colon, some neurons initially appear in close association with extrinsic nerve fibers from the vagus and Remak's nerve, respectively. We conclude that crest cells colonize the gut as chains of cells and that, within these chains, both neurons and glia appear close to the wavefront.

Carvedilol reverses elevated pulmonary vascular resistance in a child with dilated cardiomyopathy

There is little experience using beta-blocker therapy for the management of congestive heart failure (CHF) in children. We present the case of a child with idiopathic dilated cardiomyopathy and CHF, referred for cardiac transplantation, in whom carvedilol reversed elevated pulmonary vascular resistance.

Immediate feedback during academic testing

Performance on two multiple-choice testing procedures was examined during unit tests and a final examination. The Immediate Feedback Assessment Technique provided immediate response feedback in an answer-until-correct style of responding. The testing format which served as a point of comparison was the Scantron form. One format was completed by students in introductory psychology courses during unit tests whereas all students used the Scantron form on the final examination. Students tested with Immediate Feedback forms on the unit tests correctly answered more of the final examination questions which were repeated from earlier unit tests than did students tested with Scantron forms. Also, students tested with Immediate Feedback forms correctly answered more final examination questions previously answered incorrectly on the unit tests than did students tested previously with Scantron forms.

Iodixanol pharmacokinetics in children

The objective of this report was to study the elimination pharmacokinetics of iodixanol in children. Iodixanol (Visipaque, Nycomed Inc., Wayne, PA, USA) is a new iso-osmolar iodinated radiocontrast agent. We hypothesized that elimination of this agent would be dependent on age-related differences in renal clearance. Seven centers enrolled 43 patients. Cardiac catheterization was performed in 41 patients and cranial computed tomography in 2. Patients were entered into 5 age groups: newborn to <2 months, 2 to <6 months, 6 months to <1 year, 1 to <3 years, and 3 to <or=12 years. Plasma samples were obtained before and at 4 time periods after completion of iodixanol injection: 0.75-1.25 hours, 2-4 hours, 8-12 hours, and 16-32 hours. Plasma concentrations of iodixanol were determined using high performance liquid chromatography. The primary pharmacokinetic endpoint was the terminal elimination rate constant (kel). Data were complete for 40 patients, showing mean kel significantly lower in newborn to <2-month-old patients vs older patients: (h-1, mean +/- standard deviation [SD]): newborn to <2 months 0.185 +/- 0.060, 2 to <6 months, 0.256 +/- 0.046, 6 months to <1 year 0.299 +/- 0.042, 1 to <3 years 0.322 +/- 0.058, and 3 to <or=12 years 0.307 +/- 0.071; with increasing age, excretion is more rapid, as shown by each age group's elimination half-life (t1/2 beta) (h) 4.14 +/- 1.41, 2.79 +/- 0.55, 2.36 +/- 0.37, 2.23 +/- 0.51, and 2.36 +/- 0.52, respectively. Iodixanol has elimination in children >6 months of age that is comparable to normal adults. Prolonged elimination in children <6 months of age is related to renal immaturity.

Enteric neuroblasts require the phosphatidylinositol 3-kinase pathway for GDNF-stimulated proliferation

The enteric nervous system (ENS) develops from neural crest cells that enter the gut, migrate, proliferate, and differentiate into neurons and glia. The growth factor glial-derived neurotrophic factor (GDNF) stimulates the proliferation and survival of enteric crest-derived cells. We investigated the intracellular signaling pathways activated by GDNF and their involvement in proliferation. We found that GDNF stimulates the phosphorylation of both the PI 3-kinase downstream substrate Akt and the MAP kinase substrate ERK in cultures of immunoaffinity-purified embryonic avian enteric crest-derived cells. The selective PI 3-kinase inhibitor LY-294002 blocked GDNF-stimulated Akt phosphorylation in purified crest cells, and reduced proliferation in cultures of dissociated quail gut. The ERK kinase (MEK) inhibitors PD 98059 and UO126 did not reduce GDNF-stimulated proliferation, although PD 98059 blocked GDNF-stimulated phosphorylation of ERK. We conclude that the PI 3-kinase pathway is necessary for the GDNF-stimulated proliferation of enteric neuroblasts.

P wave signal-averaged electrocardiogram as a new marker for atrial tachyarrhythmias in postoperative Fontan patients

OBJECTIVES

This study was undertaken to determine the potential role of P wave signal-averaged electrocardiogram (PSAECG) for risk assessment of atrial tachyarrhythmias (ATs) in patients after Fontan operation.

BACKGROUND

Onset of atrial flutter/fibrillation (AFF) in patients who have undergone Fontan operation for univentricular hearts constitutes an unfavorable clinical event associated with a high risk of cardiovascular complications. There is no data available on PSAECG in postoperative Fontan patients to predict potential susceptibility to ATs.

METHODS

Twenty-four post-Fontan patients and 15 age-matched healthy subjects were prospectively studied with PSAECG, and the following measurements were made: filtered P wave duration (FPWD), P wave vector integrals (PINTs), root-mean-square voltage for the initial 30 ms (RMSi30), and duration of persistent amplitude signals <4 microV from the beginning of the P wave (Di4).

RESULTS

The FPWDs were significantly longer in the study group patients with ATs when compared with the study group patients without ATs (p<0.01) and compared with the controls (p < 0.001). An FPWD cut point of 135 ms resulted in a sensitivity of 71% and a specificity of 81% in differentiating patients with ATs from patients without ATs among the postoperative Fontan patients. The PINT was significantly greater in Fontan patients with AFF and also without AFF when compared with controls (p<0.01, p<0.05, respectively). The RMSi30 and the Di4 were not significantly different between study and control groups.

CONCLUSIONS

Signal-averaged P wave duration is significantly prolonged in postoperative Fontan patients. A prolonged signal-averaged P wave duration may be an effective noninvasive marker to predict risk of development of ATs in this patient group.

Isolated right pulmonary artery discontinuity

Unilateral "absence" of the pulmonary artery is an uncommon malformation frequently associated with congenital heart disease. In fact, the pulmonary artery is typically discontinuous from the main pulmonary artery, not absent. We report a case of right pulmonary artery discontinuity not associated with congenital heart disease and review the embryogenesis and treatment of this rare congenital cardiac anomaly.

Expression of the GDNF receptors ret and GFRalpha1 in the developing avian enteric nervous system

The formation of the enteric nervous system (ENS) from neural crest-derived cell precursors requires the growth factor glial cell line-derived neurotrophic factor (GDNF) and the receptors Ret and GDNF family receptor alpha 1 (GFRalpha1). We investigated the location(s), the timing, and the extent to which these GDNF receptors appear in the population of crest-derived precursors that form the avian ENS using immunohistochemistry and in situ hybridization. Sections and whole mounts of embryonic chick gastrointestinal tract were costained with antibodies to the receptors and to HNK-1, a marker for crest-derived cells. Neural crest-derived precursors migrate through the primitive esophagus to colonize the gizzard where an extensive cellular network forms. Ret-immunoreactivity (ir) was found in a network of cells in the gizzard at embryonic day (E)3.5. As development proceeded, Ret-immunoreactive cells appeared at progressively more caudal positions and were present in the colon at E7.5. Costaining with Ret and HNK-1 was performed to determine the number of Ret-immunoreactive cells in the crest-derived population. Ret appeared in some HNK-1 cells in the esophagus and gizzard at embryonic day (E)3.5. During development, the number of crest cells with Ret increased in the ganglia of the gizzard and small intestine. GFRalpha1-ir was also found in HNK-1 cells in the esophagus at E3.5 but did not appear in the gizzard until E4.5. Surprisingly, the colonizing vanguard of crest-derived cells lacked both Ret- and GFRalpha-ir. Between E4.5 and E6.5, the fraction of HNK-1-positive cells expressing GFRalpha1 increased considerably in the foregut. Ret and GFRalpha1 were coexpressed in many cells at E6.5, and the number of such cells increased as development progressed. In the adult, GFRalpha1 and Ret were found in the neuropil of enteric ganglia. We conclude that the population of cells expressing the receptors increases during development and persists in the adult, findings that support a neurotrophic role for GDNF in the formation and maintenance of the avian ENS.

Aortic root dilation after the Ross procedure

This study evaluated changes in neoaortic root geometry in patients who underwent the Ross procedure. Serial postoperative echocardiographic measurements of the neoaortic root indexed to the square root of body surface area (centimeters divided by meters) were obtained from 30 patients (age range 3.1 to 31.4 years) and compared with paired preoperative and immediate postoperative values. Normal aortic root diameter Z scores were derived from root dimensions obtained from 217 healthy controls. Compared with preoperative values, an immediate stretch of the neoaortic versus pulmonary root (annulus and sinuses of valsalva) was observed at a mean follow-up period of 1 week. Additional aortic annular dilation from baseline prehospital discharge values was observed at 2 to 12 months (baseline vs follow-up annulus Z score: 1.4 vs 2.6, p <0.01, n = 16) and at 16 to 33 months follow-up (0.8 vs 2.0, p <0.05, n = 12). In a similar fashion, there was additional enlargement of the aortic sinus from its stretched state at hospital discharge at 2 to 12 months (baseline vs follow-up sinus Z score: 2.0 vs 3.3, p <0.01, n = 17) and at 16 to 33 months (1.7 vs 3.0, p <0.01, n = 13). There were no differences in root size between 2 to 12 and 16 to 33 months after surgery. There was a decrease in left ventricular size with no alteration in blood pressure or degree of aortic valve regurgitation. Thus, aortic root dilation occurs up to the first year after the Ross procedure but does not appear to progress beyond this time.

Defects in embryonic hindbrain development and fetal resorption resulting from vitamin A deficiency in the rat are prevented by feeding pharmacological levels of all-trans-retinoic acid

Vitamin A is required for reproduction and normal embryonic development. We have determined that all-trans-retinoic acid (atRA) can support development of the mammalian embryo to parturition in vitamin A-deficient (VAD) rats. At embryonic day (E) 0.5, VAD dams were fed purified diets containing either 12 micrograms of atRA per g of diet (230 micrograms per rat per day) or 250 micrograms of atRA per g of diet (4.5 mg per rat per day) or were fed the purified diet supplemented with a source of retinol (100 units of retinyl palmitate per day). An additional group was fed both 250 micrograms of atRA per g of diet in combination with retinyl palmitate. Embryonic survival to E12.5 was similar for all groups. However, embryonic development in the group fed 12 micrograms of atRA per g of diet was grossly abnormal. The most notable defects were in the region of the hindbrain, which included a loss of posterior cranial nerves (IX, X, XI, and XII) and postotic pharyngeal arches as well as the presence of ectopic otic vesicles and a swollen anterior cardinal vein. All embryonic abnormalities at E12.5 were prevented by feeding pharmacological amounts of atRA (250 micrograms/g diet) or by supplementation with retinyl palmitate. Embryos from VAD dams receiving 12 micrograms of atRA per g of diet were resorbed by E18.5, whereas those in the group fed 250 micrograms of atRA per g of diet survived to parturition but died shortly thereafter. Equivalent results were obtained by using commercial grade atRA or atRA that had been purified to eliminate any potential contamination by neutral retinoids, such as retinol. Thus, 250 micrograms of atRA per g of diet fed to VAD dams (approximately 4.5 mg per rat per day) can prevent the death of embryos at midgestation and prevents the early embryonic abnormalities that arise when VAD dams are fed insufficient amounts of atRA.

HERG channel dysfunction in human long QT syndrome. Intracellular transport and functional defects

Mutations in HERG are associated with human chromosome 7-linked congenital long QT (LQT-2) syndrome. We used electrophysiological, biochemical, and immunohistochemical methods to study the molecular mechanisms of HERG channel dysfunction caused by LQT-2 mutations. Wild type HERG and LQT-2 mutations were studied by stable and transient expression in HEK 293 cells. We found that some mutations (Y611H and V822M) caused defects in biosynthetic processing of HERG channels with the protein retained in the endoplasmic reticulum. Other mutations (I593R and G628S) were processed similarly to wild type HERG protein, but these mutations did not produce functional channels. In contrast, the T474I mutation expressed HERG current but with altered gating properties. These findings suggest that the loss of HERG channel function in LQT-2 mutations is caused by multiple mechanisms including abnormal channel processing, the generation of nonfunctional channels, and altered channel gating.

GDNF is abundant in the adult rat gut

Glial derived neurotrophic factor (GDNF) is essential for the development of the enteric nervous system (ENS). Although previous work has measured GDNF mRNA levels, little is known about the concentration of GDNF protein produced in developing or adult tissues. The aim of this study was to quantitate the concentration of GDNF protein in various tissues of the developing and adult rat and in adult human gut. A two site antibody immunoassay was used to quantitate GDNF using recombinant rat GDNF as a standard. In the adult rat gastrointestinal tract the intestine contained the highest concentration of GDNF while the stomach and esophagus have the lowest concentrations. The isolated muscular wall of the intestine has approximately four times the GDNF concentration of the intact intestine. Other tissues with smooth muscle such as the aorta and urinary bladder contain moderate GDNF concentrations. In contrast, GDNF is barely detectable in the adult kidney and liver. High concentrations of GDNF were also detected in human colon and jejunum. As development proceeds in the rat, there is a tendency for the concentration of GDNF to increase in the intestine but decrease in other tissues. Treatment of the jejunum with the cationic surfactant benzyldimethyltetradecylammonium chloride (BAC) results in an increase in the number of smooth muscle cells, a decrease in myenteric neurons, and an increase in the concentration of GDNF in homogenates of intestine. The observations that GDNF concentrations are high in the adult intestine suggest that this growth factor may be important for the maintenance of the adult ENS.

Enhanced resting left ventricular filling in patients with successful coarctation repair and exercise-induced hypertension

M-mode and Doppler echocardiographic analyses of left ventricular (LV) shortening and filling were performed in 50 patients who underwent coarctectomy (median follow-up 9.5 years) and in 16 athletes in a control group before an exercise stress test with upright bicycle ergometry was performed. Thirty-two of 50 patients and 18 of 50 patients had a normotensive and hypertensive response to exercise, respectively. Preexercise echocardiographic data were compared among the control, normotensive, and hypertensive patient groups. LV peak filling rates (dD/dt, diastole) were increased in the hypertensive group (18.3 +/- 3.5) compared with those in the normotensive group (14.4 +/- 3.2; p < 0.001) and the control group (13.6 +/- 2.8; p < 0.001). LV shortening was enhanced in the coarctectomy group compared with that in the control group. A higher aortic isthmus Doppler gradient at peak exercise was not found in the hypertensive group compared with that in the normotensive group. Therefore patients with successful coarctectomy in childhood have enhanced LV shortening and relaxation at rest. Demonstration of enhanced LV peak filling rates may help identify patients at risk for exercise-induced hypertension.

Clinical cardiotoxicity following anthracycline treatment for childhood cancer: the Pediatric Oncology Group experience

PURPOSE

To determine the incidence of clinical cardiotoxicity from anthracycline chemotherapy in children with cancer and to identify associated risk factors.

PATIENTS AND METHODS

The study population consisted of 6,493 children with cancer who had received anthracycline chemotherapy on Pediatric Oncology Group (POG) protocols from 1974 to 1990. Cardiotoxicity, defined as congestive heart failure not due to other causes, abnormal measurements of cardiac function that prompted discontinuation of therapy, or sudden death from presumed cardiac causes, was determined by a review of protocol records.

RESULTS

Cardiotoxicity was confirmed in 106 patients (1.6%): 58 had congestive heart failure, 43 had changes in measures of cardiac function that prompted the discontinuation of therapy, and five died suddenly from presumed cardiac causes. In a multivariate analysis, factors that contributed to the relative risk (RR) of toxicity were a cumulative anthracycline dose > or = 550 mg/m2 of body-surface area (RR = 5.2), maximal dose > or = 50 mg/m2 (RR = 2.8), female sex (RR = 1.9), black race (RR = 1.7), presence of trisomy 21 (RR = 3.4), and exposure to amsacrine (RR = 2.6). Cardiotoxicity within 1 year after the completion of anthracycline treatment (early cardiotoxicity) represented 89.5% of all cases.

CONCLUSION

Early clinical cardiotoxicity in children treated with anthracycline is rare. A high maximal dose, or cumulative dose of anthracycline, female sex, black race, presence of trisomy 21, and treatment with amsacrine increase the risk for anthracycline-associated cardiotoxicity.

Appearance of neurons in the developing chick gut

The enteric nervous system is formed from neural crest-derived cells. These cells enter the gut, migrate, proliferate, and ultimately differentiate into neurons and glia. We have used a human anti-neuronal autoantibody (ANNA-1), which recognizes neuron-specific RNA-binding proteins of the Hu family as an early marker of neuronal phenotype, to study the appearance of enteric neurons in the developing chicken gut. Immunoreactive cells appear first in the gizzard primordium at E3.5 and are found at progressively more caudal locations in the gut as development proceeds. Nascent neurons are present at the yolk stalk at E4.5, at the ileocecal junction at E6.5, and within the rectum at E7.5-8.5. Neurons appear slightly later in the esophagus. Aggregates of cells resembling developing ganglia were first observed at E6.5 in the distal esophagus and at E8.5 in the proximal esophagus. A small number of cells appeared in the vagus nerve trunks at E4.5 and that number increased at E7.5-8.5. Immunoreactive cells were also found in the sympatho-aortic plexus between the mesonephri and in the dorsal mesentery. These cells appeared to coalesce and form the ganglionated Nerve of Remak which contained positive cells at E3.5. This Nerve extended to the yolk stalk at E4.5 and to duodenum at E6.5. We conclude that the appearance of nascent neurons occurs first in the gizzard and proceeds more rapidly in a distal than proximal direction along the gut. Furthermore, cell that appear to be nascent neurons are found in the vagus and in the dorsal mesentery.

Maturational differences in coronary flow and interstitial transudate adenosine during alteration of perfusate oxygenation in isolated rabbit hearts

This study was designed to investigate effects of perfusate oxygenation and maturation on coronary flow (CF), interstitial transudate adenosine (ITA) and coronary effluent adenosine (CEA) in isolated rabbit hearts. Hearts were paced at a fixed rate and were perfused under constant pressure at two different levels of perfusate oxygenation: baseline (B) (pO2 = 408 +/- 7 mmHg, O2 content = 1.28 +/- 0.03 ml O2/dl) and a lower level (L) (pO2 = 189 +/- 4 mmHg, O2 content = 0.59 +/- 0.02 ml O2/dl). CF was higher in immature (I, age 5 weeks) compared with mature (M, age 12 weeks) hearts at both levels of perfusate oxygenation (9.7 +/- 0.4 vs. 7.7 +/- 0.3 and 12.9 +/- 0.4 vs. 9.2 +/- 0.3 ml/min/g). I hearts had correspondingly higher values for myocardial oxygen consumption (MVO2) (53 +/- 3 vs. 49 +/- 2 and 39 +/- 3 vs. 35 +/- 2 microL O2/min/g), but similar values for venous oxygen tensions (nuO2) (240 +/- 9 vs. 219 +/- 10 and 74 +/- 4 vs. 62 +/- 3 mmHg), compared with M hearts at B and L. Although interstitial transudate adenosine (ITA) concentration was similar in I and M hearts at B (409 +/- 75 vs. 254 +/- 39 nM), it was lower in I than M hearts at L (2500 +/- 770 vs. 4210 +/- 1000 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence of a cDNA encoding chicken vasoactive intestinal peptide (VIP)

Mammalian pre-pro-vasoactive intestinal peptide (pre-proVIP) gives rise to the neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine amide (PHI). The cDNA encoding chicken VIP was cloned and sequenced. The region of chicken pre-proVIP homologous to the mammalian PHI region is not followed by an amidation signal. This unusual feature suggests that processing of the precursor may be different in the chicken.

Mapping the origin of the avian enteric nervous system with a retroviral marker

The enteric nervous system is largely formed from the vagal neural crest which arises from the neuroaxis between somites 1-7. In order to evaluate the contribution of different regions of the vagal crest to the enteric nervous system, we marked crest cells by injecting somites 1-10 with a replication-defective spleen necrosis virus vector which contains the marker gene lacZ. After incubation in X-gal, lacZ-positive blue cells were found in the wall of the gut in three locations. Most were found at the peripheral edge of the developing circular muscle and within the developing submucosa, sites characteristic of developing ganglia. LacZ-positive cells in these ganglionic sites were always surrounded by HNK-1 immunostained cells, confirming their neural crest origin. LacZ-positive cells were also seen in a third location, the circular muscle layer of the esophagus and crop, and were separated from the HNK-1 positive ganglionic elements. These cells in the circular muscle are probably muscle cells derived from labeled mesodermal cells of the somite. Injection of somites 3, 4, 5, and 6 resulted in the largest percentage of preparations with lacZ-positive crest-derived cells and in the largest number of positive cells in the gut. After injection of these somites, lacZ-positive crest-derived cells were found in all regions of the gut from the proventriculus to the rectum. Very few positive crest-derived cells were found in the esophagus.(ABSTRACT TRUNCATED AT 250 WORDS)

Large amount of (apo)ferritin in the pancreatic insulin cell and its stimulation by glucose

In screening a rat pancreatic islet cDNA library by differential hybridization for transcripts increased by glucose, the H chain of ferritin, an iron storage protein, was identified. An ELISA for rat ferritin showed that the insulin cell contains a surprisingly high amount of ferritin comparable to that of iron storage tissues. Most of the ferritin was located in the beta cell, as judged from colocalization of ferritin and insulin by immunohistochemical staining of the pancreas. Islets maintained for 24 h in culture medium containing 20 mM glucose are capable of releasing insulin in response to stimulation with glucose, but islets maintained at 1 mM glucose are incapacitated in response to glucose (see ref 1). Immunoassayable ferritin was threefold higher in 20 mM glucose islets than in 1 mM glucose islets and the glucose-stimulated increase in H ferritin mRNA was confirmed by probing Northern blots of islet RNA with authentic H and L chain cDNAs. This showed that H ferritin mRNA was four- to eightfold higher in 20 mM-glucose islets than in 1 mM glucose islets, whereas L ferritin mRNA was decreased 75-90% in 20 mM glucose islets relative to 1 mM glucose islets. The physiological reason for the abundance of (apo)ferritin in the beta cell is not readily apparent because the islet contains very little iron. Whether or not ferritin is used to handle another metal such as zinc, which is plentiful in the beta cell, is unknown. Another potential reason for ferritin in the beta cell is that ferritin has antioxidant properties and the beta cell is particularly sensitive to oxygen radicals. Regardless of its physiologic purpose, the high amount of ferritin can explain why iron is preferentially retained in the insulin cell and causes diabetes in diseases of iron overloading.

Early hypercyanotic spells unrelated to ductal constriction in tricuspid atresia with infundibular stenosis

Clinical, echocardiographic, hemodynamic, and angiographic findings were reviewed in 16 consecutive patients with tricuspid atresia (TA) and normally related great arteries, seen at the University of Florida between 1984 and 1990, to determine when and in which hypercyanotic spells (HS), unrelated to ductal constriction, occurred. Such spells developed in six patients (38%) and were life-threatening and refractory to medical management in three patients. Most HS (five of six) occurred in the first 2 months of life. Angiography done at the time of diagnosis revealed similar morphological features in all patients subsequently experiencing HS; infundibular stenosis due to anterior malalignment in the conal septum. These findings suggest a predisposition for development of early HS in TA patients with apparent infundibular stenosis due to anterior malalignment of the conal septum. Further study and a heightened clinical awareness are needed in such patients.