Continuous renewal of the axonal pathway sensor apparatus by insertion of new sensor molecules into the growth cone membrane

BACKGROUND

Growth cones at the tips of growing axons move along predetermined pathways to establish synaptic connections between neurons and their distant targets. To establish their orientation, growth cones continuously sample for, and respond to, guidance information provided by cell surfaces and the extracellular matrix. To identify specific guidance cues, growth cones have sensor molecules on their surface, which are expressed differentially during the temporospatial progress of axon outgrowth, at levels that depend on the pattern of neural activity. However, it has not been elucidated whether a change in gene expression can indeed change the molecular composition and, hence, the function of the sensor apparatus of growth cones.

RESULTS

We have constructed adenoviral gene transfer vectors of the chicken growth cone sensor molecules axonin-1 and Ng-CAM. Using these vectors, we initiated the expression of axonin-1 and Ng-CAM in rat dorsal root ganglia explants during ongoing neurite outgrowth. Using specific surface immunodetection at varying time points after infection, we found that axonin-1 and Ng-CAM are transported directly to the growth cone and inserted exclusively in the growth cone membrane and not in the axolemma of the axon shaft. Furthermore, we found that axonin-1 and Ng-CAM do not diffuse retrogradely, suggesting that the sensor molecules are integrated into multimolecular complexes in the growth cone.

CONCLUSIONS

During axon outgrowth, the pathway sensor apparatus of the growth cone is continuously updated by newly synthesized sensor molecules that originate directly from the transcription/translation machinery. Changes in the expression of sensor molecules may have a direct impact, therefore, on the exploratory function of the growth cone.

Clustering and functional cooperation of Ng-CAM and axonin-1 in the substratum-contact area of growth cones

Growth cones and neurites of chicken dorsal root ganglia neurons cultured on laminin, Ng-CAM, or axonin-1 exhibit substratum-dependent morphology and growth patterns which are accompanied by distinctive distributions of axonin-1 and Ng-CAM in the growth cone membrane. On either Ng-CAM or axonin-1 substratum, both Ng-CAM and axonin-1 were depleted from some areas of the apical growth cone membrane. In contrast, on laminin, both axonin-1 and Ng-CAM remained randomly distributed. Removal of axonin-1 from growth cones resulted in a blockage of neurite outgrowth on both Ng-CAM and axonin-1 substrata, indicating that in these neurons axonin-1 cooperates with Ng-CAM in the activation of axon growth. Based on these results possible molecular models for cooperation between axonin-1 and Ng-CAM on the growth cone are discussed.

Effects of L-serine on neurons in vitro

We have examined the influence of amino acids on chicken embryonic dorsal root ganglion (DRG) neurons in vitro and have found that serine has a marked impact on the morphology of the developing neurites. In cultures supplemented with L-serine (but not D-serine) at micromolar concentrations (10-200 microM), the length of the neurites was increased by up to 100% and they were seen to develop a more complex branching pattern. These effects of L-serine were found to be concentration-dependent and stereospecific and were observed on several different substrata such as laminin, Ng-CAM and axonin-1. Similar observations were also made in the case of embryonic retinal explants, while the addition of non-essential amino acids other than L-serine to DRG neurons was found to have no effect. We conclude that, although belonging to the group of non-essential amino acids and not a recognized neurotransmitter, L-serine is an important factor for the morphological differentiation of neurons in vitro.

[Isokinetic muscle training with high motion speeds in the rehabilitation following surgical treatment of fresh anterior cruciate rupture]

In the course of a prospective investigation 17 patients with operatively treated acute anterior cruciate ligament ruptures received an isokinetic muscle training with high motion velocities in addition to the common physiotherapy from the 7th to the 19th week after operation. The comparative group consisted of 17 patients with operatively treated acute anterior cruciate ligament ruptures who were receiving the common physiotherapy only. The aim of the study was to improve both the postoperative dysbalance between agonists and antagonists and the active muscular stabilisation of the knee. The isokinetic muscle training was done with 150 degrees/s and a motion limit for flexion/extension of 0-20-90 degrees. The postoperative muscular dysbalance was improved significantly in the isokinetic group after 6 weeks of training compared to the control group. The flexion/extension ratio of the operated leg at 60 degrees/s came to 100% in the training group compared to 135% in the control group. This difference was even more apparent at 180 degrees/s with 100% in the isokinetic group compared to 160% in the control group and at 240 degrees/s with 110% compared to 200% respectively. The average maximum torque was 10 to 15% better with the training group as with the control group though there was no training of maximum force done explicitly. There was no effect on the postoperative anterior stability of the knee.

How successful is OKT3 rescue therapy for steroid-resistant acute rejection episodes after heart transplantation?

OKT3 is recommended as rescue therapy for cases of steroid-resistant, clinically persistant acute rejection episodes after heart transplantation. In this study we determined the efficacy of such treatment. One hundred thirty-two patients were included in this study. The postoperative immunosuppressive regimen consisted of triple-drug therapy and perioperative antithymocyte globulin. During a follow-up of 10 to 108 weeks (mean, 51 +/- 20 weeks) 281 treatment-requiring acute rejection episodes (International Society for Heart and Lung Transplantation > or = II) were observed. In 29 cases (10.3%) the grade of the acute rejection episodes was either unchanged after two series of intravenous steroid pulse therapy, was worsened after the first steroid course, or the patient experienced clinical deterioration as a result of the acute rejection episodes. These patients were considered to have steroid-resistant acute rejection episodes and received a 10-day rescue therapy with OKT3, followed by control endomyocardial biopsy. In 17 cases, control endomyocardial biopsy revealed normal myocardium (group I). In 10 cases acute rejection episodes remained unchanged (group II); twice a deterioration was found (group III). However, 12 of the 17 patients from group I experienced a rebound of the acute rejection episodes (International Society for Heart and Lung Transplantation > or = II) 1 to 3 weeks later. Side effects of OKT3 treatment were fever, chills, intestinal complications, hemodynamic response, convulsions, and viral infections.(ABSTRACT TRUNCATED AT 250 WORDS)

Heart transplantation after Senning operation for transposition of the great arteries

In a 17.5-year-old boy and a 21-month-old girl orthotopic heart transplantation was performed after intractable right-heart failure had developed 14.5 years and 15 months respectively after Senning operation for TGA. Before the atrial repair, combined with closure of the VSD in each case, initial operation had involved a banding of the pulmonary artery in the boy and a modified Blalock-Taussig shunt in the girl. A coarctation of the first patient remained untreated. After resection of the diseased organ a new intraatrial septum of glutaraldehyde-fixed bovine pericardium was created. 15 and 3 months respectively after orthotopic heart transplantation both patients belong to NYHA classification I.

Cell-cell adhesion by homophilic interaction of the neuronal recognition molecule axonin-1

The axonal surface glycoprotein axonin-1, which occurs both as a glycosyl-phosphatidylinositol-anchored membrane-bound form and a secreted form, promotes neurite outgrowth and is thought to be involved in axon-guidance mechanisms in the developing nervous system. Recently, we have demonstrated that the neurite-outgrowth-promoting activity of axonin-1, presented as a substratum for cultured neurons, is mediated by a heterophilic interaction with the axonal glycoprotein neuronglia cell-adhesion molecule (Ng-CAM). Here we present evidence for homophilic (like-like) binding among axonin-1 molecules. Axonin-1 was heterologously expressed in myeloma cells. Clonal cell lines, with exposed membrane-bound axonin-1 at their surface, formed large multicellular aggregates. Incubations of transfected and parental myeloma cells, under a series of different conditions, revealed homophilic axonin-1/axonin-1 interactions across the intermembrane space as the molecular mechanism promoting stable cell-cell contacts. Using structural and functional characterisation, recombinant axonin-1 was very similar to native axonin-1, suggesting that homophilic axonin-1 interactions are also established in neurons. The capability of axonin-1 to interact with both Ng-CAM and other axonin-1 molecules might contribute to the formation of macromolecular networks at contact sites of growth cones and axons, comprising molecules of both membranes, and thus represent a mechanism for regulating neurite outgrowth and pathfinding.

Long-term myocardial function after heart transplantation

With an increasing number of heart transplantations and an improved survival rate a characterization of the long-term hemodynamic profile of the transplanted heart is necessary. 222 cardiac catheterizations were performed in 71 heart recipients under cyclosporine A immunosuppression during a 7-year follow-up after transplantation. Hemodynamic evaluation revealed a non-progressive arterial hypertension due to an increased systemic vascular resistance, leading to a mild increase of left-ventricular chamber stiffness. Parameters of systolic myocardial function were found to be normal and did not deteriorate during the 7 year period. The prevalence of allograft coronary angiopathy increased from 13% one year to 54% five years after transplantation. Myocardial function was neither adversely influenced by the presence of coronary angiopathy nor by the number or severity of former rejection episodes. Unchanged annual pressure-volume loops excluded the development of a dilated or restrictive posttransplantation cardiomyopathy. Thus, not the myocardial function, but the coronary angiopathy represents the most critical cardiac long-term problem after transplantation.

The attachment of nematocytes from the primitive invertebrate Hydra to fibronectin is specific and RGD-dependent

The transient attachment of cells to components of the extracellular matrix is an important step in the complex molecular mechanisms involved in amoeboid cell locomotion. We have analyzed the attachment of nematocytes from the freshwater cnidarian Hydra to fibronectin which is a constituent of the mesoglea, the extracellular matrix, of the polyps. The percentage of attaching cells increased gradually in a concentration-dependent manner and reached a plateau value at a fibronectin concentration of 50 micrograms/ml. Attachment was inhibited by exposure of the fibronectin-coated surfaces to antibodies against the cell binding domain of fibronectin or by incubating the cells with peptides containing the recognition sequence Arg-Gly-Asp (RGD) known from vertebrate cells. This, together with data obtained by affinity chromatography, indicates that RGD-dependent binding to fibronectin, mediated by a receptor which possibly belongs to the integrin family, already occurs in Hydra, a member of an evolutionary low invertebrate phylum.

Heart transplantation: hemodynamics over a five-year period

Long-term hemodynamic evaluation after heart transplantation has rarely been reported. Fifty-seven heart transplant recipients (mean age, 42.1 years: range, 22 to 56 years) were investigated with annual cardiac catheterization. Mean follow-up was 2.2 years (range, 1 to 7 years). Years 1 through 5 were evaluated statistically. Hemodynamic variables did not change significantly during the 5-year period. Mean aortic pressure (105 +/- 16 to 115 +/- 17 mm Hg, minimum and maximum annual average value +/- SD of the 5-year period) and LVEDP (13 +/- 6 to 15 +/- 7 mm Hg) were slightly elevated. Borderline values were found for mean pulmonary artery pressure (18 +/- 4 to 21 +/- 5 mm Hg), systemic vascular resistance (1407 +/- 227 to 1487 +/- 409 dynes.sec.cm-5), pulmonary vascular resistance (86 +/- 42 to 118 +/- 66 dynes.sec.cm-5), and heart rate (85 +/- 17 to 95 +/- 14 beats/min). Mean right atrial pressure (5 +/- 2 to 8 +/- 4 mm Hg), cardiac index (2.8 +/- 0.6 to 3.5 +/- 1.1 L/min/m2), end-diastolic volume (111 +/- 37 to 137 +/- 35 ml) and ejection fraction (69% +/- 10% to 75% +/- 9%) were in the normal range. Pressure-volume loops for each year excluded the development of either restrictive or dilated cardiomyopathy with time. Contractility, as measured by imposing afterload stress, was normal in 12 of 14 representative patients. Prevalence of coronary abnormalities (circumscript coronary stenoses, diffuse vessel obliteration or dilated angiopathy) increased from 14.9% in the first to 66.7% in the fifth year. Of the patients, 93% received antihypertensive drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ischemia/reperfusion damage of the liver caused by free radicals--direct radical detection using electron spin resonance (ESR)]

The generation of free oxygen radicals is presumed to be a pathogenetic principle in various conditions, primarily in postischemic reperfusion injury. Their assessment is difficult. ESR is an excellent tool to assess free radicals directly. In an experimental model of rat liver ischemia and reperfusion the increased generation of free radicals during reperfusion in liver tissue could be demonstrated after 60 min of liver ischemia. Elevated production rates of radicals could be detected after 5 min of reperfusion for at least 45 min with a maximum after 15 min of reperfusion. Scavenging of these radicals has to start in the very beginning of reperfusion.

[Results of multidisciplinary assessment of patients with erectile dysfunction]

A total of 326 patients with chronic erectile dysfunction were investigated by a multidisciplinary approach. It was found that several causes combined (multifactorial genesis) in 77.1%. Organic causes alone were found quite frequently, viz. in 43.6%, while primarily psychogenic causes alone were found in only 5.5%; in contrast, combined organic and psychogenic causes were found in 46.0%. There were pathologic organic findings in 89.6%: vascular in 74.5% (arterial 64.1%, cavernous/venous 30.4%), neurogenic in 42.0%; side effects of drugs in (10.1%); endocrine (7.7%) and local penile causes (4.3%) are not so important in erectile dysfunction. Treatment suited to the pathogenesis was instituted (psychotherapy, vein ligation, self-injection of vasoactive drugs into the corpus cavernosum).

Morphological alterations in epithelial cells of the mouse gallbladder 30 hours after treatment with lithogenic diet

Mice were fed a gallstone inducing diet. Thirty hours after treatment, distinct morphological alterations in the gallbladder epithelium occurred. The most striking effect was the short-term appearance of large cisternae, which emerge as a result of coalescence of dilated cavities of the rough endoplasmic reticulum. At the same time, an increased storage of small granular material was observed. These alterations did not appear after treatment lasting for less or more than thirty hours. The development started with an enlargement of the endoplasmic cavities, whereas the Golgi apparatus did not seem to undergo transformations; therefore, a transport stop of the secretory products of the epithelial cells must be located at the connection between both organelles. The formation of the endoplasmic cisternae seemed to be caused by a reversible block of the intracellular transport pathway of the secretion products.

The intra-abdominal inspection and biopsy of lymph nodes during peritoneoscopy

The inspection and biopsy of lymph nodes during peritoneoscopy is demonstrated, particularly with reference to the supra-gastric region. The procedure involves no problems or risks and may give diagnostic hints concerning specific problems such as Hodgkin's disease, metastasis, Crohn's disease.