Development of the murine pulmonary vein and its relationship to the embryonic venous sinus

BACKGROUND

Arguments concerning the development of the pulmonary vein, and its relationship to the embryonic venous sinus (sinus venosus) have continued for well over a century. Recently, attention has again been focused on the origin of the pulmonary vein. It has been suggested that, whereas the pulmonary vein originates from the left atrium in humans, in all other vertebrates it originates from the venous sinus, with subsequent transfer to the left atrium. The nature of this transfer has not, however, been elucidated, although there is speculation that the pulmonary vein is "pinched off" from the left side of the embryonic venous sinus.

METHODS

We studied closely staged hearts of normal mouse embryos from a C57BL/6 x CBAcross days 10 and 11 of gestation (plug day = day 1). Two series of embryos were collected and fixed in 2% glutaraldehyde, 1% formaldehyde, buffered with 0.05 M sodium cacodylate pH 7.4 (adjusted to 330 mOsm with NaCl). One series was wax embedded, serially sectioned, and stained with Masson's trichrome. The second series was subject to microdissection and scanning electron microscopy.

RESULTS

The atrial component of the heart tube is attached to the body of the embryo by reflections of the atrial myocardial wall. The attachment can be considered, from the outset, as the heart stalk, with the myocardial-mesodermal connections forming a horseshoe of tissue that projects ventrally into the lumen of the atrium, surrounding a single evagination in the midline of the embryo. This heart stalk is cranial to the connections of the tributaries of the embryonic venous sinus and ventral to the foregut. When traced through its developmental stages, the evagination in the centre of the stalk, which we describe as the pulmonary pit, is seen to become the portal of entry for the developing pulmonary vein.

CONCLUSIONS

The heart stalk, representing the area used by the pulmonary vein to gain access to the heart, and analogous to the dorsal mesocardium, is, from the outset, discrete from the area occupied by the orifices of the horns of the embryonic venous sinus. The pulmonary vein does not, in the mouse, develop from the tissues that form the walls of the tributaries of the systemic venous sinus. Comparisons with other studies suggest that early events in the development of the pulmonary vein are likely to be the same in all mammals, including humans.

Specification of left-right asymmetry in mammals: embryo culture studies of stage of determination and relationships with morphogenesis and growth

The internal mammalian body plan is laterally asymmetric with a consistent handedness such that some organs are placed on one side (stomach on the left, for example) and paired organs are not symmetric (for example, there are more lung lobes on the right). Some chemical teratogens can affect the development of asymmetry, and some can cause asymmetric defects in overtly symmetric structures, but the mechanisms are unknown. We have used chemical treatment of rat embryos in culture to examine the stage at which the left-right axis is determined and show that all effective treatments can affect left-right axis development up to the early headfold stage, but not from late headfold onwards. This suggests that the left-right axis is determined by the late headfold stage, even though the embryo is overtly symmetric at this stage. It appears to be much easier to induce an abnormal left-right axis from late allantoic bud and early headfold stages than the early allantoic bud stage, but we have not established the earliest stage at which a response can be induced. Complete situs inversus was the most common chemically induced abnormality, although heart looping and body turning could be inverted separately, suggesting that the two phenomena are linked but not wholly interdependent. The treatments appeared to cause a loss of handedness, rather than inducing inversion, since the incidence of an abnormal left-right axis never exceeded 50%. All treatments except methoxamine, an alpha1 adrenergic agonist, induced an abnormal left-right axis in association with other morphologic defects and growth retardation. However, there was no relationship between the severity or incidence of dysmorphology, nor growth retardation, and left-right abnormality, suggesting that although the process that specifies lateral asymmetry is labile, it is independent of general growth and morphogenesis.

Left-right development: mammalian phenotypes and conceptual models

Consistent left-right asymmetry in a population requires a special kind of developmental specification. Models of this process must account for the complex phenotypes seen when left-right is abnormal. In some human and mouse mutations, there appears to be a randomisation of global situs to either solitus or inversus, whereas in the inv/inv mouse essentially all are inversus. However, in these and all additional examples there are frequently other anomalies, including symmetry (isomerism) and discordance between organs (heterotaxia). Current models invoke a molecular chiral referent as the source of the primary handed information. We describe a new two-gradient model which accommodates all defects of situs whilst leaving the primary asymmetry unaltered.

The Telemedicine Information Exchange (TIE)

An on-line information service, the Telemedicine Information Exchange (TIE), was established to provide a comprehensive source of telemedicine information. The TIE comprised a number of frequently updated, searchable, linked databases, each dealing with an important aspect of telemedicine. These included an extensive bibliography on telemedicine consisting of more than 2000 citations, many with abstracts. There was also a series of topical sections describing current telemedicine projects, products and services, legislation, funding, research activities, and news in the field. The TIE was designed to exploit the features of electronic information storage: hypertext linking between related pieces of information; specialized views (technical, legal, and business) of the bibliographic database; and usage monitoring to determine which data were most frequently accessed and therefore where any enhancement should be done. The TIE was made available via the World Wide Web, by remote telnet access over the Internet, and via modern. The rapid increase in the usage of the TIE since its introduction in April 1995 indicated that the TIE satisfied a need in the telemedicine community.

Regulation of serotonin re-uptake transporter mRNA expression by ovarian steroids in rhesus macaques

It has been widely hypothesized that the ovarian steroids, estrogen (E) and progesterone (P), act on serotonin neurons to modulate mood and increase prolactin secretion in women. However, information is needed on the molecular consequences of ovarian hormone action in serotonin neurons. This study examined the effect of E and P on the expression of mRNA for the serotonin re-uptake transporter (SERT) in monkeys using in situ hybridization and a 253 bp human SERT cRNA probe. Monkeys (n=5 animals/group) were ovariectomized and hysterectomized (spayed) and then untreated (control), or treated, with E for 28 days (E treated) or treated with E for 28 days and supplemented with P for the last 14 days of the E regimen (E+P treated). Densitometric analysis of autoradiographs with gray-level thresholding was performed at five levels of the dorsal and median raphe. The number of pixels exceeding background in defined areas was obtained (pixel number). The average pixel number for spayed, E- and E+P-treated groups was 22 280+/-3517, 15 227+/-1714, and 14 827+/-2042, respectively, in the combined dorsal and median raphe. In the E- and E+P-treated groups compared to the control group, there was a 32% and 33% decrease in SERT mRNA signal represented by pixel number (ANOVA, P<0.05). Hence, E- and E+P-treated groups were significantly less than the control group, but they were not different from one another. Also, there were significantly fewer SERT mRNA-positive cells in the dorsal raphe of E- and E+P-treated groups (ANOVA, P<0.001). Therefore E, with or without P, reduces SERT mRNA expression. These results suggest that the ability of P to increase prolactin secretion in E-primed monkeys does not involve an action at the level of SERT gene transcription. Hence, the mechanism by which the CNS transduces the action of P on prolactin secretion remains to be elucidated. However, these data suggest that one action of E replacement therapy in postmenopausal women may be to decrease expression of the SERT gene.

Cardiac morphology at late fetal stages in the mouse with trisomy 16: consequences for different formation of the atrioventricular junction when compared to humans with trisomy 21

OBJECTIVE

The mouse with trisomy 16 (Ts16) is held to be a genetic model for humans with Down's syndrome (Ts21). Both trisomies are associated with atrioventricular septal defects, but the precise morphology in the mouse remains unclear. We have therefore characterised cardiac morphology in the mouse with Ts16.

METHODS

Ts16 fetuses, from a Rb(11.16)2H/Rb(16.17)7Bnr x C57BL/6J cross, were collected on gestational days 17 or 18 (full term = 19 days) and studied using scanning electron microscopy and serial sections.

RESULTS

The hearts showed a spectrum of deficient atrioventricular septation which we categorised into two types. In one, a common atrioventricular junction was separated into right and left orifices by a tongue of tissue joining two valvar leaflets that bridged the ventricular septum to varying extent. In the other, a common atrioventricular junction was connected exclusively to the left ventricle. All hearts had ostium primum atrial and ventricular septal defects, together with abnormal ventriculo-arterial connections. No heart had the typical morphology seen in the human with Down's syndrome, namely a balanced common atrioventricular junction, guarded by a common valve, with the aorta connected exclusively to the left ventricle.

CONCLUSIONS

The cardiac defects seen in Ts16 mice show marked differences from the typical anatomy in human Ts21, suggesting more complex mechanisms of cardiac dysmorphogenesis in Ts16. The mouse model will prove valuable in elucidating the mechanism of normal expansion of the atrioventricular junctions, and help in charting the precise steps involved in atrial and ventricular septation.

Gene expression domains as markers in developmental toxicity studies using mammalian embryo culture

We are examining the hypothesis that expression domains of developmental control genes may be informative markers in mammalian embryo culture studies of developmental toxicity. Expression domains might be altered directly by chemical exposure, or might reflect developmental abnormality prior to any overt morphological defect. Whole-mount in situ hybridization using digoxygenin-labeled RNA probes was used to monitor the regions of expression of Hoxb-4, Pax-3 and Emx-2. These genes were selected because of their different restrictions within the developing CNS; Hoxb-4 for its anterior margin in the hindbrain, Pax-3 for its dorso-ventral pattern in the spinal cord, and Emx-2 for being restricted to a portion of the forebrain. Valproic acid was used as a prototype developmental toxicant because of its known actions on neural tube closure and on segmentation. For patterns of expression, we made three comparisons, between: rat in vivo developed embryos and published descriptions for mouse; rat cultured and in vivo; control and valproate exposed. For these genes, there were no differences between domains of expression in rat and mouse, nor between rat cultured and in vivo embryos. In valproate-exposed embryos, some domains were spatially abnormal, for example Pax-3 in the neural crest, but this was coincident with structural defects induced by the treatment. There was no indication, for these three genes, and this teratogen, that treatment caused any shifts in boundaries of expression, nor induced any ectopic domains, even though exposures induced overt malformation.

Embryonic asymmetry: left TGFbeta at the right time?

Vertebrates have consistent differences between their left and right sides. In all species, nodal, a transforming growth factor beta superfamily signalling protein, is involved in a late step in the pathways that specify such asymmetry in the embryo. Earlier components seem not so well conserved.

Decentration of 5.1 mm intraocular lenses after continuous curvilinear capsulorhexis and in-the-bag fixation

PURPOSE

To determine the incidence of decentration in eyes with 5.1 mm optic intraocular lenses (IOLs) and to assess the effect on vision.

SETTING

Clinical Cataract Research Unit, Oxford Eye Hospital, Oxford, England.

METHODS

Patients having phacoemulsification and small IOL implantation over 12 months were identified and invited for assessment. Intraocular lens decentration was measured geometrically using a modified, digital, retroillumination camera. The expected incidence of symptoms caused by decentration was estimated by determining the presence of an IOL edge within an artificial pupil overlaid on the digital image.

RESULTS

In 13 eyes (20%), IOL decentration was more than 0.5 mm. Symptoms were expected in 38 patients (59%) but occurred in only 14 (22%).

CONCLUSION

Decentration of the 5.1 mm optic IOL caused fewer clinical problems than anticipated, although the results raise concerns that such IOLs may be inappropriate in patients who need excellent vision in scotopic illumination.

Hepatitis-B-virus resistance to lamivudine given for recurrent infection after orthotopic liver transplantation

BACKGROUND

Orthotopic liver transplantation for end-stage hepatitis-B-virus (HBV) infection is commonly complicated by recurrence of HBV. Lamivudine, a cytosine nucleoside analogue, has been shown to suppress HBV infection. We report the development of resistance to lamivudine in three patients who underwent transplantation for end-stage liver disease secondary to hepatitis B.

METHODS

Two of the patients received lamivudine for recurrent HBV infection after transplantation, whereas the third patient began treatment 1 month before transplantation in an attempt to prevent HBV recurrence after transplantation. The three patients initially responded well to treatment, but viral recurrence occurred after 9-10 months of treatment in all patients. HBV DNA was amplified from serum and sequenced through a conserved polymerase domain-the tyrosine, methionine, aspartate, aspartate (YMDD) locus. We assessed the susceptibility of HBV to lamivudine by infecting primary human hepatocytes with serum taken before the start of treatment and after recurrence in varying concentrations of lamivudine.

FINDINGS

DNA sequencing showed a common mutation within the YMDD locus of the HBV polymerase gene in all patients during lamivudine treatment. In hepatocyte cultures infected with pretreatment serum, HBV DNA concentrations were reduced to less than 6% of those in control cultures by addition of lamivudine in concentrations as low as 0.03 mumol/L. By contrast, in cultures treated with serum taken after recurrence, HBV DNA concentrations did not fall below 20% of control values, even with lamivudine at 30 mumol/L.

INTERPRETATION

Resistance to lamivudine has been reported in HIV patients with mutations in the YMDD locus of the polymerase gene. Our findings indicate a common mechanism of lamivudine resistance for HIV and HBV that involves similar point mutations in homologous domains of the viral polymerases.

Ovarian steroid regulation of tryptophan hydroxylase mRNA expression in rhesus macaques

Progesterone (P) stimulates prolactin secretion through an unknown neural mechanism in estrogen (E)-primed female monkeys. Serotonin is a stimulatory neurotransmitter in prolactin regulation, and this laboratory has shown previously that E induces progestin receptors (PR) in serotonin neurons. Therefore, we questioned whether E and/or E+P increased serotonin neural function. The expression of mRNA for tryptophan hydroxylase (TPH) was examined in ovariectomized (spayed) control, E-treated (28 d), and E+P-treated monkeys (14 d E and 14 d E+P) using in situ hybridization and a 249 bp TPH cRNA probe generated with RT-PCR (n = 5 animals/group). Densitometric analysis of film autoradiographs revealed a ninefold increase in TPH mRNA in E-treated macaques compared to spayed animals (p < 0.05). With supplemental P treatment, TPH mRNA signal was increased fivefold over spayed animals (p < 0.05), but was not significantly different compared to E-treated animals. These results were verified by grain counts from photographic emulsion-coated slides. There were significantly higher single-cell levels of TPH mRNA in serotonergic neurons of the dorsal raphe in E- and E+P-treated groups (p < 0.05). These data indicate that E induces TPH gene expression in nonhuman primates and that the addition of P has little additive effect on TPH gene expression. Thus, the action of P on prolactin secretion is probably not mediated at the level of TPH gene transcription. However, because P increases raphe serotonin content in E-primed rodents, the possibility remains that P may have other actions on post-translational processing or enzyme activity.

Steroid regulation of estrogen and progestin receptor messenger ribonucleic acid in monkey hypothalamus and pituitary

The regulation of estrogen and progestin receptor (ER and PR, respectively) messenger RNA (mRNA) and protein by their cognate hormones was examined in the hypothalamus and pituitary of steroid-treated monkeys. Rhesus macaques (Macaca mulatta) were ovariectomized, hysterectomized (spayed), and implanted with SILASTIC brand capsules containing 17 beta-estradiol (E) or progesterone (P). The spayed control group received empty capsules. The E-treated group received E-filled capsules for 28 days. The E + P-treated animals received an E-filled capsule for 28 days and then a P-filled capsule for the last 14 of the 28 days. Steroid regulation of ER and PR mRNA levels in the hypothalamus and pituitary was examined with in situ hybridization. In the hypothalamus, ER and PR immunodetectable proteins were also examined in nearby sections. In the pituitary, mRNA levels were compared to previous ER and PR protein analysis of identically treated animals. E treatment induced PR mRNA in the medial basal hypothalamus and pituitary. Supplemental P treatment had no effect on PR mRNA levels in the hypothalamus, but markedly reduced PR mRNA in the pituitary. There was excellent agreement with PR protein detection by immunocytochemistry. E treatment had no effect on ER mRNA in the hypothalamus or pituitary. Supplemental P treatment decreased ER mRNA in the ventromedial nucleus, but not in the arcuate nucleus or pituitary. There was agreement between ER mRNA and ER protein in these areas. In summary, there is cell-specific regulation of PR by P in the hypothalamus and pituitary, where P down-regulates PR in the pituitary without affecting ER. However, P has no significant effect on PR expression in the hypothalamus even though P decreases ER in the ventromedial nucleus. Although these observations suggest diverse cell-specific regulatory mechanisms, they are consistent with ER- and PR-mediated physiological events, such as PRL secretion and sexual behavior.

The anatomy of the heart revisited

BACKGROUND

There is a marked conservative tendency to be found in anatomic descriptions, with a seeming reluctance on the part of acknowledged experts to test new theories by returning to direct studies of gross anatomy. This tendency has become manifest to us during recent attempts to review the structure and function of the heart.

METHODS

We have reviewed our recent experience in trying to describe the structure and development of the atrial septum and arterial roots, attempting at the same time to establish the place of semantic as opposed to morphologic factors in disagreements on these topics.

RESULTS

Dissection of the structures separating the right atrium from the left atrium shows a fundamental difference between the infolded superior rim of the oval foramen, made up of the atrial walls, versus the make up of the sinus and atrioventricular septums, which are true septal structures. Analysis of the arterial roots shows that the major feature is the semilunar attachment of the valvar leaflets, an arrangement not ideally described in terms of an annulus.

CONCLUSIONS

Understanding of details of cardiac anatomy, as set out in standard textbooks, is hindered by a reluctance on the part of some to accept material presented on the basis of straightforward gross dissection. Instead, there is a seeming desire to depend on conventional wisdom, often unsupported by anatomic fact. Such controversies can be ameliorated by appropriate recognition to contributions of gross morphology and by using simple words to describe the observed anatomic features.

Endocardial cushion development and heart loop architecture in the trisomy 16 mouse

Murine trisomy 16 (Ts16) is a model for Down's syndrome and has close to a 100% incidence of atrioventricular septal defects (AVSDs). These have been proposed to result from abnormal development of the endocardial cushions, but the mechanisms are unknown. We aim to identify the initial defects in Ts16 hearts, both to characterise the pathogenesis of AVSDs and as a first step in the search for molecular mechanisms. In 38 litters from an Rb(11.16)2H/Rb(16.17)7Bnr x C57BL/6J cross, which was examined on days 10 and 11 of gestation, 28.4% of embryos were trisomic. Trisomic embryos were uniformly retarded compared to their normal litter mates, having on average 3.3 fewer somite pairs. All further comparisons were made between embryos of the same somitic stage. Twenty-one trisomic and 21 normal embryos of between 15 and 43 somites were serially sectioned, and stereomorphometric methods were used to reconstruct the volumes of the endocardial cushions and to count their number of mesenchymal cells. There were fewer cells in Ts16 superior and inferior cushions. In contrast, the volumes of trisomic cushions were significantly greater than normal. Thus, cell density was markedly lower in trisomic cushions. Importantly, the volumes of the cushions in trisomic embryos were already greater than normal at the 18 somite stage, prior to the invasion of cushions by mesenchymal cells. The architecture of Ts16 heart tubes in 15-25 somite embryos was subtly abnormal. This was reflected in the angle between the axis of the atrioventricular canal and the first pharyngeal cleft, which was significantly larger in trisomic hearts and showed a different relationship to somite stage when compared to normal embryos. These observations suggest that the primary cardiac defect in Ts16 mice may be localised to the myocardium, thus influencing the shape of the heart tube, with changes in the mesenchymal population of the endocardial cushions being later events. Whether AVSDs arise from one or both of these abnormalities remains to be established.

The structure of the mouse heart in late fetal stages

Because of the opportunities for genetic manipulation, the mouse has become the major species for models of human disease. Recently, targeted and insertional mutations have induced many novel models of developmental abnormality, including several of congenital heart defects. Interpretation and use of such models requires a precise understanding of the similarities and differences between mouse and human in terms of cardiac development and structure. To this end, we have characterised the late fetal mouse heart using scanning electron microscopy and serial histological sections. Right atrial anatomy is dominated by the venous valves, which separate the orifices of the caval veins from the musculature of the primary atrium. Their structure and location suggest that the pulmonary vein is unlikely to develop from the venous sinus. The pectinated wall of the appendage serves to distinguish the morphologically right atrium, in that it runs around the atrioventricular junction, from the left atrium in which this vestibular region is smooth-walled. The persistence of the left superior caval vein draining to the right atrium, along with a solitary opening for the pulmonary vein in the left atrium, distinguishes the atrial anatomy of the mouse from that of the human. The flap valve of the oval foramen is extensive and represents the embryonic primary atrial septum. The superior rim of the foramen is an infolding of the atrial roof, as has been described in the human, showing that, contrary to orthodox opinion, there is no extensive formation of a secondary atrial septum. The region of the membranous septum seen in the human heart is a relatively thick structure in the late fetal mouse, and is located exclusively in an atrioventricular position. Unlike the human, there is little distinction between the apical trabeculations of the left and right ventricles of the mouse heart.

Cell proliferation in mammalian gastrulation: the ventral node and notochord are relatively quiescent

During gastrulation, the node of the mammalian embryo appears to be an organising centre, homologous to Hensen's node in the chick and the dorsal lip of the amphibian blastopore. In addition, the node serves as a precursor population for the head process, notochord and foregut endoderm. We have studied node architecture and cell morphology by electron microscopy, and cell proliferation using bromodeoxyuridine incorporation and mitotic counts. The dorsal (ectodermal) and ventral (endodermal) components of the node are two distinct populations, separated by a basement membrane. The ventral node, contiguous with the head process, is characterised by a relatively low proliferation rate, with only approximately 10% of cells incorporating BrdU over 4 hr, compared to > 95% in surrounding mesodermal and ectodermal tissues. This is the case from the beginning of node formation, at the no-allantoic-bud stage, until the 7 somite stage, and is not compatible with the idea that the ventral node is a stem cell population. The dorsal node is highly proliferative, its rate of division being indistinguishable from the neurectoderm, with which it is contiguous. In the ventral node, two regions can be recognised: cells in the "pit" are columnar and all monociliated; around them lies a "crown" of cells arranged radially in a horseshoe shape and less often ciliated. Node derivatives share common features with the ventral node; the head process and the notochord are relatively quiescent; and some head process cells are also monociliated. Node and head process monocilia are immotile and appear to be associated with non-proliferation. We suggest that the ventral node contains all the properties of the organiser, while the dorsal node is indistinct from the surrounding epiblast. The cranial end of the foregut pouch, the thyroid diverticulum, and the promyocardium of early somite stage embryos are also areas of low cell division. All the described regions of relative quiescence are sites of expression of members of the TGF beta family, which may be involved in maintaining non-proliferation.

Involvement of G-protein alpha il subunits in activation of G-protein gated inward rectifying K+ channels (GIRK1) by human NPY1 receptors

This study investigated the type of G-protein alpha subunit(s) that human neuropeptide Y (NPY)1 receptors preferentially utilize when activating G-protein gated K+ currents. Two electrode voltage-clamp recordings were made from Xenopus oocytes that had been injected with cDNAs encoding either human NPY1 or D2(short) dopamine receptors, and GIRK1 a cloned rat brain K+ channel. These receptors were also co-injected with G-protein alpha i1, alpha i2, alpha i3 and alpha o1 subunits to determine which subunit(s) modulate the efficiency of signal transduction. In NPY1 receptor injected cells neuropeptide Y (100 nM) caused a 53 +/- 10 nA inward current (n = 14; EC50 = 3 nM) and this effect was blocked by pertussis toxin (500 ng ml-1 24 h). Activation of GIRK1 currents by neuropeptide Y was selectively potentiated by alpha i1 subunit cDNA whereas coupling dopamine of D2 receptors to this channel was not.

Absence of effect of simvastatin on the progression of lens opacities in a randomised placebo controlled study. Oxford Cholesterol Study Group

AIMS

A detailed assessment of ophthalmic effects of an HMG CoA reductase inhibitor, simvastatin, was performed.

METHODS

Six hundred and twenty one individuals considered to be at increased risk of coronary heart disease were randomised, following an 8 week placebo 'run in' period, to receive 40 mg daily simvastatin, 20 mg daily simvastatin, or matching placebo. Patients with a baseline corrected visual acuity better than 6/24 and without a history of cataract were eligible for detailed ophthalmic assessment at 6 months (539 patients assessed) and at 18 months (474 patients assessed).

RESULTS

No significant differences between the treatment groups were detected at the 6 month or 18 month visit in the refractive condition of the eye or in the mean intraocular pressure. Nor were there clear differences in the Oxford grading system scores for various measures of the major types of cataract (cortical spokes, posterior subcapsular cataract, nuclear brunescence, white scatter) or for other morphological features visible within the lens (fibre folds or focal dots). Scheimpflug slit image photographs and retroillumination analysis of the percentage of cataract within a defined region of the lens were also performed at each visit, with no clear differences observed between the treatment groups.

CONCLUSION

This single centre double blind study found no good evidence of any adverse effects of 18 months of simvastatin treatment on lens opacity formation, using a variety of validated techniques to assess cataract development. Routine clinic follow up of visual symptoms and admission to hospital for ophthalmic procedures over 5 years of treatment was also reassuring, with no excess adverse outcomes observed with simvastatin.

Morphology of the sinus node in human and mouse hearts with isomerism of the atrial appendages

BACKGROUND

The location of the sinus node is known to be at best abnormal, or at worst unknown, in patients with isomerism of the morphologically left atrial appendage. In contrast, the sinus node is known to be an excellent histological marker of the morphologically right appendage, being duplicated in those with right isomerism. The aim of the study was to investigate this condition further in fetal human and mouse hearts.

METHODS

Serial histological sections of the area anticipated to contain the sinus node were studied in hearts with isomerism of the atrial appendages taken from 14 human fetuses and 13 iv/iv mice, using 12 mouse hearts with normally arranged or mirror imaged atrial chambers for controls.

RESULTS

All hearts with isomerism of the right appendages (two human and four mouse) had bilateral sinus nodes. The cases with isomerism of the left appendages (12 human and nine mouse) showed absence of a recognisable sinus node except in four cases (19%) in which a small remnant of the node was found. In three of these cases, it was related postero-inferiorly to the superior cavoatrial junction.

CONCLUSIONS

The concept of isomerism of the atrial appendages is endorsed by findings on the morphology of the sinus node, this being the most reliable histological criterion for existence of a morphologically right atrium. A small proportion of hearts with left isomerism had a structure resembling the sinus node, but it was hypoplastic and displaced postero-inferiorly, distant from its expected position had the hearts possessed an incompletely formed morphologically right appendage.

Phosphorylation- and voltage-dependent inhibition of neuronal calcium currents by activation of human D2(short) dopamine receptors

1. Activation of human D2(s) dopamine receptors with quinpirole (10 nM) inhibits omega-conotoxin GVIa-sensitive, high-threshold calcium currents when expressed in differentiated NG108-15 cells (55% inhibition at +10 mV). This inhibition was made irreversible following intracellular dialysis with the non-hydrolysable guanosine triphosphate analogue GTP-gamma-S (100 microM), and was prevented by pretreatment with pertussis toxin (1 microgram ml-1 for 24 h). 2. Stimulation of protein kinase C with the diacylglycerol analogue, 1-oleoyl-2-acetyl-sn-glycerol (100 microM), also attenuated the inhibition of the sustained calcium current but did not affect the receptor-mediated decrease in rate of current activation. Similarly, okadaic acid (100 nM), a protein phosphatase 1/2A inhibitor, selectively occluded the inhibition of the sustained current. 3. The depression of calcium currents by quinpirole (10 nM) was enhanced following intracellular dialysis with 100 microM cyclic adenosine monophosphate (cyclic AMP, 72.8 +/- 9.8% depression), but was not mimicked by the membrane permeant cyclic GMP analogue, Sp-8-bromoguanosine-3',5':cyclic monophosphorothioate (100 microM). 4. Inhibition of calcium currents was only partly attenuated by 100 ms depolarizing prepulses to +100 mV immediately preceding the test pulse. However, following occlusion of the sustained depression with okadaic acid (100 nM) the residual kinetic slowing was reversed in a voltage-dependent manner (P < 0.05). 5. Thus pertussis toxin-sensitive G-proteins liberated upon activation of human D2(short) dopamine receptors inhibited high-threshold calcium currents in two distinct ways. The decrease in rate of calcium current activation involved a voltage-dependent pathway, whereas the sustained inhibition of calcium current involved, in part, the voltage-resistant phosphorylation by cyclic AMP-dependent protein kinases and subsequent dephosphorylation by protein phosphatases 1/2A.

Section directed cryosectioning of specimens for scanning electron microscopy: a new method to study cardiac development

A new method to study the developing heart was developed. Using this "section directed" cryosectioning method, appropriate fixed embryos can be trimmed optimally to obtain sectional planes that, if necessary, can be matched with histologically treated sections. As a result, the morphological information obtained with the scanning electron microscope can be compared in detail with the information on the molecular phenotypes of the subpopulations of cells as deducted from staining patterns of the sections. This method allows combination of the specific advantages of sophisticated histological techniques, such as immunohistochemistry and in situ hybridisation, with those of the scanning electron microscope.

Teledermatology: one application of telemedicine

Telemedicine can be defined as the use of telecommunications technologies to provide medical information and services. This field has recently begun a period of explosive growth. Oregon's teledermatology program within the National Library of Medicine's high-performance computing and communications initiative is designed to generate much-needed basic and clinical research information about one specific telemedicine application. The background of this program is discussed, and the research objectives are described.

Block of human voltage-sensitive Na+ currents in differentiated SH-SY5Y cells by lifarizine

1. The ability of lifarizine (RS-87476) to block human voltage-sensitive Na+ channel currents was studied by use of whole cell patch clamp recording from differentiated neuroblastoma cells (SH-SY5Y). 2. The Na+ conductance in differentiated SH-SY5Y cells (24.0 +/- 2.4 nS, n = 11) was half-maximally activated by 10 ms depolarizations to -37 +/- 2 mV and was half-maximally inactivated by predepolarizing pulses of 200 ms duration to -86 +/- 3 mV (n = 11). 3. At low stimulus frequencies (0.1 to 0.33 Hz) voltage-dependent sodium currents were completely blocked, in a concentration-dependent manner, by extracellular application of either tetrodotoxin (EC50 = 4 +/- 1 nM, n = 12) or by lifarizine (EC50 = 783 +/- 67 nM, n = 9). The onset of block by lifarizine (tau = 91 +/- 14 s at 10 microM) was considerably slower than that of tetrodotoxin (tau = 16 +/- 3 s at 100 nM). 4. Lifarizine (1 microM) reduced the peak sodium conductance in each cell (from 26.4 +/- 2.0 nS to 15.1 +/- 2.7 nS, n = 4) without changing the macroscopic kinetics of sodium current activation or inactivation (V1/2 = -35 1 mV and -87 +/- 4 mV respectively, n = 4). Similarly, lifarizine (1 microM) did not affect the reversal potential of the macroscopic sodium current (+14 +/- 5 mV in control and +16 +/- 2 mV in 1 microM lifarizine; n = 4) or reactivation time-constant (tau = 14.0 +/- 4.4 ms). 5. Block of the sodium channel open state by tetrodotoxin (30 nM) did not prevent the inhibition caused by a subsequent application of lifarizine (3 micro M). In contrast the depression caused by lifarizinewas readily reversible after pretreatment of cells with the local anaesthetic, lignocaine (1O mM).6. These data demonstrate that lifarizine is a use- and voltage-dependent antagonist of human voltage sensitive sodium currents. The slow kinetics and pharmacology of the block by lifarizine indicate that access of this drug to the channel is more restricted than that of tetrodotoxin and may involve an allosteric site or state of the channel that is also regulated by local anaesthetics.

Inhibition of yolk sac function in late gastrulation rat conceptuses as a cause of teratogenesis: an in vivo/in vitro study

A rabbit anti-rat yolk sac antiserum, administered by intraperitoneal injection at 0.25 mL/100 g bodyweight into 8.5-day pregnant rats, resulted in a resorption incidence of 20%, and growth retardation and malformation of all surviving fetuses at term. In all subsequent experiments, pregnant rats either received this same dose of antiserum at 8.5 days or were untreated. When 9.5-day rat conceptuses were cultured for 48 h in a medium containing serum from a 9.5-day pregnant rat that had been treated with antiserum, development was severely abnormal, regardless of whether conceptuses were explanted from antiserum-treated or untreated dams. In contrast, culture for 48 h in serum from untreated 9.5-day pregnant rats resulted in normal growth and development of conceptuses explanted from untreated dams, and in slight growth retardation and dysmorphogenesis in 9.5-day conceptuses explanted from antiserum-treated dams. In the former, development was similar to that attained by 11.5-day conceptuses from untreated dams; in the latter, development was appreciably better than in 11.5-day conceptuses from antiserum-treated dams. These results indicate that the critical period of exposure of embryos in utero to teratogenic antiserum after administration to the 8.5-day pregnant rat is longer than 24 h and that a significant insult is delivered to the conceptus before 9.5 days ea. Using 9.4-day ea conceptuses in culture, pinocytosis (uptake of 125I-labelled polyvinylpyrrolidone) by the yolk sac, and its inhibition by antiserum, was demonstrated. No pinocytic activity was evident in the embryo itself. These data support the hypothesis that anti-yolk sac antiserum exerts its teratogenic action by inhibiting the nutritional function of the yolk sac during early organogenesis.

Cloning of decidual prolactin from rhesus macaque

Rhesus monkey (Macaca mulatta) decidual prolactin cDNA was cloned and sequenced. The first 210 bp of the monkey sequence is not contiguous to the human pituitary prolactin transcription initiation site. Reverse transcription-polymerase chain reaction (RT-PCR) and Southern analysis confirmed that this 5'-extended prolactin transcript is present in monkey decidua but not in pituitary. Isolation and sequencing of a partial genomic monkey prolactin clone verified the nucleotide changes found in the rhesus cDNA. Comparison of the rhesus decidual prolactin cDNA to the human pituitary cDNA revealed more than 97% homology between the two. These data indicate that monkey prolactin mRNA from the decidualized endometrium of pregnancy contains unique 5' sequence not present in pituitary prolactin mRNA, suggesting the use of an alternative start site. Thus it is likely that the decidua uses promoter and regulatory regions different from those reported for pituitary prolactin.

Central corneal light scatter in long-term diabetics

Changes in corneal thickness have been correlated with severity of diabetic retinopathy. Measuring light scatter at the central cornea may reflect the changes in corneal thickness and hence the retinopathy. This study compared the peak central corneal light scatter between 22 insulin-dependent diabetic patients with disease of at least 10 years' duration and 29 controls. No significant difference was found in the light-scattering properties of the central cornea between the two groups. This technique does not offer an alternative method of screening for diabetic retinopathy.

Visual performance and objectively measured grades of cataract. A correlation of methods designed for use in longitudinal trials

Objective quantification of cataract and subjective assessment of visual performance are essential features of anticataract or cataractogenic drug trials. The constrains of a longitudinal trial require a compromise in contrast sensitivity measurement between sensitivity and speed. Such a system has been developed for use in longitudinal anticataract trials. An objective cataract assessment system has also been developed for these trials. Visual performance parameters and objectively measured grades of cataract using these systems were correlated in a group of patients with early lens opacities. Overall the correlation was poor in all three morphological types of cataract. Possible reasons for this and implications for future anticataract trials are discussed.

Estimation of the thickness of the crystalline lens from on-axis and off-axis Scheimpflug photographs

Measurement of human lens biometry directly from Scheimpflug images of the anterior ocular segment may be impossible when pupil size precludes an adequate Scheimpflug view of the posterior lens surface. The authors describe a simple and accurate geometric method of overcoming this problem by estimating the true lens thickness from pairs of on-axis and off-axis Scheimpflug images. The method is validated and the variability of the estimate is quantified. This new method has utility in the study of lens biometry in subjects with large lenses whose pupils cannot be adequately dilated.

Analysis of retro-illumination photographs for use in longitudinal studies of cataract

Retro-illumination photography has potential for the monitoring of cortical and posterior subcapsular cataract formation. Variations in the individual illumination results have limited accurate quantification of opacities within such images. We present a new image analysis technique which minimises the effect of uneven and varying retro-illumination. The new technique has been tested for variation between photographers and over a short time period. We believe it is of value in lens assessment in combination with a semi-quantitative grading system.

Antibodies against highly conserved sites in the epidermal growth factor receptor tyrosine kinase domain as probes for structure and function

We generated anti-peptide antibodies against four highly conserved sequences in the kinase domain and against two nonconserved sequences surrounding autophosphorylation sites in the carboxyl-terminal domain of the epidermal growth factor receptor (EGFR). These antibodies were used to examine topology and function in catalysis of specific sequences. Two of the highly conserved sites, HRD (residues 811-818) and DFG (residues 827-838), appeared to participate in catalysis since alpha HRD and alpha DFG but not the other anti-peptide antibodies inhibited EGFR kinase activity. Examination of the topology of the six sites revealed that epitopes in all except the HRD site appeared to be exposed to antibody binding in the EGFR. The conditions that caused increased exposure of the HRD site to interaction with antibody included autophosphorylation, addition of the ionic detergent sodium dodecyl sulfate (SDS), and elevation in temperature from 4 to 34 degrees C.

The lens in diabetes

This paper reviews the changes which occur in the human lens in diabetes. They include refractive changes and cataract and age-related increases in thickness, curvatures, light scattering, autofluorescence and yellowing. The incidence of cataract is greatly increased over the age of 50 years, slightly more so in women, compared with non-diabetics. Experimental models of sugar cataract provide some evidence for the mechanism of the uncommon, but morphologically distinct, juvenile form of human diabetic cataract, where an osmotic mechanism due to sugar alcohol accumulation has been thoroughly studied in diabetic or galactose-fed rats. The discrepancy between the ready accumulation of sugar alcohol in the lens in model systems and the very slow kinetics of aldose reductase (AR) has not been satisfactorily explained and suggests that the mechanism of polyol formation is not yet fully understood in mammalian systems. The activity of AR in the human lens lies mainly in the epithelium and there appears to be a marginal expectation that sufficient sorbitol accumulates in cortical lens fibres to explain the lens swelling and cataract on an osmotic basis. This is even more so in the cataracts of adult diabetics, which resemble those of age-related non-diabetic cataracts in appearance. The very low levels of sorbitol in adult diabetic lenses make an osmotic mechanism for the increased risk of cataract even less likely. Other mechanisms, including glycation and oxidative stress, are discussed. The occurrence of cataract is a predictor for increased mortality in the diabetic.

HMG-CoA reductase mRNA in the post-implantation rat embryo studied by in situ hybridization

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (EC 1.1.1.34) is the rate limiting step in the mevalonate pathway that produces isoprenoids and cholesterol. Inhibitors of HMG-CoA reductase are teratogenic in vivo and induce neural tube defects in rat embryo culture, effects which appear unrelated to cholesterol deficiency. This study is the first to localize HMG-CoA reductase mRNA by in situ hybridization (ISH). Expression of reductase mRNA was examined in post-implantation rat embryos, and for control purposes in rat liver and UT-1 cells, using a digoxigenin-11 (dig-11) labelled cRNA probe. Eighteen-day fetal liver showed heavy but patchy hybridization, and adult rat liver showed strong hybridization only on some periportal hepatocytes, which was absent in livers of fasted animals. UT-1 cells stimulated to overexpress HMG-CoA reductase mRNA were strongly positive with the same probe. Control hybridizations with sense strand RNA probe, or with cRNA probe on pre-RNased tissue were negative. Strong hybridization signal for HMG-CoA reductase mRNA was observed in all tissues of the post-implantation rat embryo, from egg cylinder to 30 somite stages (7 to 12 days). Heavy signal was noted in primitive ectoderm and neural tube. The wide embryonic and extraembryonic distribution and abundance of HMG-CoA reductase mRNA may reflect developmental requirements for products of the mevalonate pathway, e.g., isoprenoids for post-translational farnesylation of p21ras.

The morphology of cataract and visual performance

The various effects of cataract on vision are reviewed. The morphological types of senile cataract are classified into three basic categories: cortical spoke, nuclear and posterior subcapsular (PSC). The significant basic effect of cataract on the optical system of the eye is that of light scattering. Forward light scattering (light scattered towards the retina) accounts for reduced contrast sensitivity, for glare and for reduced visual acuity. Other effects of cataract are a myopic shift, a possible astigmatism change, monocular diplopia and polyopia, colour vision shift, reduced light transmission, and field of vision reduction. The effect of the various cataract morphologies on these functions is discussed. The nature of the effect varies with the degree of the cataract and with the cataract morphology. The assessment of a patient's visual disability is therefore not a simple task and cannot be based solely on the visual acuity nor on the objective measurement of the cataract.

Distribution of p21ras in postimplantation rat embryos

Expression of ras cellular oncogenes during the early postimplantation period in the rat was investigated using immunohistochemistry to p21ras. A broad spectrum polyclonal antibody recognizing N-, Ha- and Ki- forms of p21ras was used in an indirect avidin-biotin-peroxidase (ABC) technique. Positive staining indicating the presence of p21ras was found in embryos from 6.5 to 12 days embryonic age. In early egg cylinders (6.5 days), positive staining for p21ras was observed on the ectoplacental cone, primitive ectoderm and trophectoderm, while primitive endoderm and parietal endoderm appeared paler. In later egg cylinder stages (7.5 days), strong positive staining was observed in the primitive embryonic ectoderm and ectoplacental cone, but parietal and visceral endoderm still appeared to be devoid of positive staining. As development proceeded during primitive streak stages, the visceral and parietal endoderm became positively stained. By 10 days, all tissues appeared to be positive for p21ras, with strong staining appearing in the heart and neural elements. Therefore, p21ras does not appear to be ubiquitous in the rat conceptus prior to gastrulation, but shows differential distribution, appearing later in endodermal derivatives. Possibly p21ras is involved in determination of the ectodermal and endodermal lineages.

Comparison of staging systems for the gastrulation and early neurulation period in rodents: a proposed new system

Because there is no standard developmental staging system for the early postimplantation period of rodent embryos, investigators must now choose between a variety of systems that differ significantly. We have reviewed many of these staging systems and have summarized the ambiguities within them and the inconsistencies among them. In order to compare systems, we first obtained a consensus of the order of developmental events from the literature, and then attempted to fit existing systems into this order taking into account inconsistencies in terminology and blurred borderlines between stages. We were able to do this for most systems but not all because some were too divergent. We found that inconsistencies in definition of some terms, such as "primitive streak stage" and those used to describe the early neurulation process (neural plate, neural groove, neural folds, and head fold) cause much confusion. In order to develop an unambiguous system which can be used by all investigators, we propose to modify Theiler's system, which is one of the most commonly used systems but is not defined precisely during the early postimplantation period. We suggest making subdivisions of the original stages as follows: 1) stage 8 into 8a and 8b, by the degree of extension of the proamniotic cavity into the extraembryonic region; 2) stage 10 into 10a and 10b, by the completion of amnion formation; 3) stage 11 into 11a, 11b, and 11c, by the appearance of neural folds and foregut pocket. After Stage 12, the number of somite pairs can be used to precisely stage embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal laterality and congenital cardiac anomalies. Relations of visceral and cardiac morphologies in the iv/iv mouse

BACKGROUND

In the management of hearts with deranged laterality, it is essential that the left and right atrial chambers are correctly identified. There are two major approaches, which are based on venous connections or on the morphology of the atrial appendages, and there is no consensus as to which is the most useful. We used the iv/iv mouse mutant, which is known to be pertinent to this problem, to evaluate the relations of cardiac defects with atrial, venous, and other visceral morphologies.

METHODS AND RESULTS

The morphology of the heart and other organs was examined in 275 iv/iv mice using criteria based on abnormal laterality in humans. The arrangement of the atrial appendages was determined by morphological examination of the junction between the appendage and the venous component of the atrium. On this basis, 45.1% of cases were shown to have usual atrial arrangement, 50.2% had mirror imagery, 1.5% had right isomerism, and 3.3% had left isomerism. Every case of atrial isomerism had a cardiac lesion; the morphological types were similar to those seen in human cases. Of cases with either usual or mirror-image arrangement of the appendages, 33.2% had abnormal spleens, but only 3.1% had cardiac defects. Similarly, venous abnormalities were much more common (30.1%) than cardiac defects.

CONCLUSIONS

Study results endorse the importance of the morphology of atrial appendages in predicting cardiac abnormalities and point to the marked inconsistency of the arrangement of other organs, including the spleen and the connections of the systemic veins.

Development of left/right handedness in the chick heart

The chick heart tube develops from the fusion of the right and left areas of precardiac mesoderm and in almost all cases loops to the embryo's right-hand side. We have investigated whether any intrinsic difference exists in the right and left areas of precardiac mesoderm, that influences the direction of looping of the heart tube. Chick embryos incubated to stages 4,5 and 6 were cultured by the New method. Areas of precardiac mesoderm were exchanged between donor and host embryos of the same stage and different stages to form control, double-right and double-left sided embryos. Overall, double-right sided embryos formed many more left-hand loops than double-left sided embryos. At stages 4 and 5 a small percentage of double-right embryos formed left-hand loops (13%) whereas at stage 6 almost 50% of hearts had left-hand loops. Control embryos formed right-hand loops in 97% of cases. The stability of right-hand heart looping by double-left sided embryos, may be related to the process of ‘conversion’, whereas the direction of looping by double-right sided embryos has become randomised. There is some indication that an intrinsic change occurred in the precardiac mesoderm between stages 5 and 6 that later influenced the direction of looping of the heart tube. The direction of body turning is suggested to be linked to the direction of heart looping.

Identification of cyclophosphamide-DNA adducts in rat embryos exposed in vitro to 4-hydroperoxycyclophosphamide

Cyclophosphamide and other bifunctional alkylating agents are potent animal teratogens inducing a variety of malformations. Although cyclophosphamide-induced DNA damage is implicated as a primary mechanism underlying the teratogenesis initiated by cyclophosphamide, additional insights into the complex nature of the teratogenic process have been hampered by the inability to analyze the primary teratogenic lesions, i.e., cyclophosphamide-DNA adducts. Using tandem mass spectrometry, we show that the monofunctional adduct N-(2-chloroethyl)-N-[2-(7-guaninyl)ethyl]amine (NOR-G) and bifunctional adduct N,N-bis[2-(7-guaninyl)ethyl]amine (G-NOR-G) can be detected in the DNA of organogenesis-stage rat embryos after an in vitro exposure to an embryotoxic concentration of activated cyclophosphamide, i.e., 4-hydroperoxycyclophosphamide.