Kinase-independent requirement of EphB2 receptors in hippocampal synaptic plasticity.

During development, Eph receptors mediate the repulsive axon guidance function of ephrins, a family of membrane attached ligands with their own receptor-like signaling potential. In cultured glutamatergic neurons, EphB2 receptors were recently shown to associate with NMDA receptors at synaptic sites and were suggested to play a role in synaptogenesis. Here we show that Eph receptor stimulation in cultured neurons modulates signaling pathways implicated in synaptic plasticity, suggesting cross-talk with NMDA receptor-activated pathways. Mice lacking EphB2 have normal hippocampal synapse morphology, but display defects in synaptic plasticity. In EphB2(-/-) hippocampal slices, protein synthesis-dependent long-term potentiation (LTP) was impaired, and two forms of synaptic depression were completely extinguished. Interestingly, targeted expression of a carboxy-terminally truncated form of EphB2 rescued the EphB2 null phenotype, indicating that EphB2 kinase signaling is not required for these EphB2-mediated functions.

Saphenous neuralgia after coronary artery bypass grafting.

OBJECTIVE: To determine the incidence, extent and site of saphenous neuralgia (anaesthesia, hyperaesthesia and pain) in the lower limb after harvesting of great saphenous vein (GSV) for coronary artery bypass grafting (CABG). METHODS: Thirty-two consecutive patients (39 lower limbs) aged 58+/-16 years undergoing CABG were prospectively reviewed. All patients were assessed pre-operatively to establish the presence of normal sensation, then at 3 days, 6 weeks and 20+/-4 months post-operatively for symptoms or signs of saphenous neuralgia. The data were recorded on serial diagrammatic representations, and the area of sensory loss for each site was recorded at each review. The decrease in areas of sensory loss over time was investigated with statistical analysis. RESULTS: Thirty-five (90%) of the lower limbs examined showed some degree of anaesthesia at 3 days with 23 (72%) still symptomatic at a mean follow up of 20 months. Hyperaesthesia and pain were infrequently noted. Anaesthesia was generally confined to three main areas, which were denoted sites A, B and C for descriptive purposes. The mean area of sensory loss in the lower limb at 3 days post-surgery was 53.4 cm2, for an incision of mean length 42+/-22 cm from the medial malleolus. This area reduced to 31.7 cm2 by 20 months, and the decrease in area over time for each site was found to be statistically significant using analysis of variance for repeated measures and the Freidman-Rubin test. CONCLUSIONS: This study demonstrates that saphenous neuralgia after harvest of GSV for CABG is common. The main symptom is anaesthesia and certain areas may persist for some considerable time post-operatively.

Neurotrophins: peripherally and centrally acting modulators of tactile stimulus-induced inflammatory pain hypersensitivity.

Brain-derived neurotrophic factor (BDNF) is expressed in nociceptive sensory neurons and transported anterogradely to the dorsal horn of the spinal cord where it is located in dense core vesicles in C-fiber terminals. Peripheral inflammation substantially up-regulates BDNF mRNA and protein in the dorsal root ganglion (DRG) in a nerve growth factor-dependent fashion and results in novel expression of BDNF by DRG neurons with myelinated axons. C-fiber electrical activity also increases BDNF expression in the DRG, and both inflammation and activity increase full-length TrkB receptor levels in the dorsal horn. Sequestration of endogenous BDNF/neurotrophin 4 by intraspinal TrkB-Fc fusion protein administration does not, in noninflamed animals, change basal pain sensitivity nor the mechanical hypersensitivity induced by peripheral capsaicin administration, a measure of C fiber-mediated central sensitization. TrkB-Fc administration also does not modify basal inflammatory pain hypersensitivity, but does block the progressive hypersensitivity elicited by low-intensity tactile stimulation of inflamed tissue. BDNF, by virtue of its nerve growth factor regulation in sensory neurons including novel expression in A fibers, has a role as a central modulator of tactile stimulus-induced inflammatory pain hypersensitivity.

Expression of Trk receptors in the developing mouse trigeminal ganglion: in vivo evidence for NT-3 activation of TrkA and TrkB in addition to TrkC.

Animals lacking neurotrophin-3 (NT-3) are born with deficits in almost all sensory ganglia. Among these, the trigeminal ganglion is missing 70% of the normal number of neurons, a deficit which develops during the major period of neurogenesis between embryonic stages (E) 10.5 and E13.5. In order to identify the mechanisms for this deficit, we used antisera specific for TrkA, TrkB, and TrkC to characterize and compare the expression patterns of each Trk receptor in trigeminal ganglia of wild type and NT-3 mutants between E10.5 and E15.5. Strikingly, TrkA, TrkB, and TrkC proteins appear to be exclusively associated with neurons, not precursors. While some neurons show limited co-expression of Trk receptors at E11.5, by E13. 5 each neuron expresses only one Trk receptor. Neuronal birth dating and cell counts show that in wild-type animals all TrkB- and TrkC-expressing neurons are generated before E11.5, while the majority of TrkA-expressing neurons are generated between E11.5 and E13.5. In mice lacking NT-3, the initial formation of the ganglion, as assessed at E10.5, is similar to that in wild-type animals. At E11.5, however, the number of TrkC-expressing neurons is dramatically reduced and the number of TrkC-immunopositive apoptotic profiles is markedly elevated. By E13.5, TrkC-expressing neurons are virtually eliminated. At E11.5, compared to wild type, the number of TrkB-expressing neurons is also reduced and the number of TrkB immunoreactive apoptotic profiles is increased. TrkA neurons are also reduced in the NT-3 mutants, but the major deficit develops between E12.5 and E13.5 when elevated numbers of TrkA-immunoreactive apoptotic profiles are detected. Normal numbers of TrkA- and TrkB-expressing neurons are seen in a TrkC-deficient mutant. Therefore, our data provide evidence that NT-3 supports the survival of TrkA-, TrkB- and TrkC-expressing neurons in the trigeminal ganglion by activating directly each of these receptors in vivo.

Roles of ephrinB ligands and EphB receptors in cardiovascular development: demarcation of arterial/venous domains, vascular morphogenesis, and sprouting angiogenesis.

Eph receptor tyrosine kinases and their cell-surface-bound ligands, the ephrins, regulate axon guidance and bundling in the developing brain, control cell migration and adhesion, and help patterning the embryo. Here we report that two ephrinB ligands and three EphB receptors are expressed in and regulate the formation of the vascular network. Mice lacking ephrinB2 and a proportion of double mutants deficient in EphB2 and EphB3 receptor signaling die in utero before embryonic day 11.5 (E11.5) because of defects in the remodeling of the embryonic vascular system. Our phenotypic analysis suggests complex interactions and multiple functions of Eph receptors and ephrins in the embryonic vasculature. Interaction between ephrinB2 on arteries and its EphB receptors on veins suggests a role in defining boundaries between arterial and venous domains. Expression of ephrinB1 by arterial and venous endothelial cells and EphB3 by veins and some arteries indicates that endothelial cell-to-cell interactions between ephrins and Eph receptors are not restricted to the border between arteries and veins. Furthermore, expression of ephrinB2 and EphB2 in mesenchyme adjacent to vessels and vascular defects in ephB2/ephB3 double mutants indicate a requirement for ephrin-Eph signaling between endothelial cells and surrounding mesenchymal cells. Finally, ephrinB ligands induce capillary sprouting in vitro with a similar efficiency as angiopoietin-1 (Ang1) and vascular endothelial growth factor (VEGF), demonstrating a stimulatory role of ephrins in the remodeling of the developing vascular system.

Depolarization and cAMP elevation rapidly recruit TrkB to the plasma membrane of CNS neurons.

Here, we describe a novel mechanism for the rapid regulation of surface levels of the neurotrophin receptor TrkB. Unlike nodose ganglion neurons, both retinal ganglion cells (RGCs) and spinal motor neurons (SMNs) in culture display only low levels of surface TrkB, though high levels are present intracellularly. Within minutes of depolarization or cAMP elevation, surface TrkB levels increase by nearly 4-fold, and this increase is not blocked by cycloheximide. These findings suggest that activity and cAMP elevation rapidly recruit TrkB to the plasma membrane by translocation from intracellular stores. We propose that a fundamental difference between peripheral nervous system (PNS) and central nervous system (CNS) neurons is the activity dependence of CNS neurons for responsiveness to their peptide trophic factors and that differences in membrane compartmentalization of the receptors underlie this difference.

Characterization of neurotrophin and Trk receptor functions in developing sensory ganglia: direct NT-3 activation of TrkB neurons in vivo.

Spinal sensory ganglia have been shown to contain neuronal subpopulations with different functions and neurotrophin dependencies. Neurotrophins act, in large part, through Trk receptor tyrosine kinases: nerve growth factor (NGF) via TrkA, brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) via TrkB, and neurotrophin-3 (NT-3) via TrkC. In the present paper, we use antibodies to TrkA, TrkB, and TrkC to characterize their expression patterns and to determine which subpopulations of cells are lost in mice lacking individual neurotrophins or Trk receptors. Despite previous reports of Trk receptor mRNAs in neural crest cells, we detect Trk receptor proteins only in neurons and not in neural crest cells or neuronal precursors. Comparisons of neonatal mice deficient in NT-3 or its cognate receptor TrkC have shown that there is a much greater deficiency in spinal sensory neurons in the former, suggesting that NT-3 may activate receptors in addition to TrkC. Using the same antibodies, we show that, during the major period of neurogenesis, NT-3 is required to maintain neurons that express TrkB in addition to those that express TrkC but is not essential for neurons expressing TrkA. Results also indicate that survival of cells expressing both receptors can be maintained by activation of either one alone. NT-3 can thus activate more than one Trk receptor in vivo, which when coexpressed are functionally redundant.

Differential dependency of unmyelinated and A delta epidermal and upper dermal innervation on neurotrophins, trk receptors, and p75LNGFR.

The impact of the nerve growth factor (NGF) family of neurotrophins and their receptors was examined on the cutaneous innervation in the mystacial pads of mice. Ten sets of unmyelinated and thinly myelinated sensory and autonomic innervation were evaluated that terminated in the epidermis, upper dermis, and upper part of the intervibrissal hair follicles. Mystacial pads were analyzed from newborn to 4-week-old mice that had homozygous functional deletions of the genes for NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), tyrosine kinase (trk) A, trkB, trkC, or p75. Mystacial pads were also analyzed in adult transgenic mice that had overproduction of NGF, BDNF, or NT-3 driven by a keratin promoter gene. The innervation was revealed by using immunofluorescence and immunocytochemistry with antibodies for protein gene product (PGP) 9.5, calcitonin gene-related product (CGRP), substance P (SP), galanin (GAL), neuropeptide Y (NPY), tyrosine hydroxylase (TH), and a neurofilament protein. The cumulative results indicated that NGF/trkA signaling plays a major role in the outgrowth and proliferation of sensory axons, whereas NT-3/ trkA signaling plays a major role in the formation of sensory endings. TrkC is also essential for the development of three sets of trkA-dependent sensory innervation that coexpress CGRP, SP, and GAL. Another set of sensory innervation that only coexpressed CGRP and SP was solely dependent upon NGF and trkA. Surprisingly, most sets of trkA-dependent sensory innervation are suppressed by trkB perhaps interacting with p75. BDNF and NT-4 appear to mediate this suppressing effect in the upper dermis and NT-4 in the epidermis. In contrast to sensory innervation, sympathetic innervation to the necks of intervibrissal hair follicles depends upon NGF/trkA signaling interacting with p75 for both the axon outgrowth and ending formation. Although NT-3/trkA signaling is essential for the full complement of sympathetic neurons, NT-3 is detrimental to the formation of sympathetic terminations to the necks of hair follicles. TrkB signaling mediated by BDNF but not NT-4 also suppresses these sympathetic terminations. One sparse set of innervation, perhaps parasympathetic, terminating at the necks of hair follicles is dependent solely upon NT-3 and trkC. Taken together, our results indicate that the innervation of the epidermis, upper dermis, and the upper portion of hair follicles is regulated by a competitive balance between promoting and suppressing effects of the various neurotrophins.

Neurotrophin-3 is a survival factor in vivo for early mouse trigeminal neurons.

Mice lacking neurotrophin-3 (NT-3) have been shown previously to be born with severe sensory deficits. This study characterizes the developmental course of this deficit in the trigeminal sensory ganglion, which in NT-3 homozygous mutants contains only 35% of the normal number of neurons at birth. At embryonic day 10.5 (E10.5), normal numbers of neurons, as assessed by expression of neurofilament protein and of total cells, are present in the ganglia of mutant homozygotes. During the next 3 d (E10.5-E13.5), virtually all of the deficit develops, after which mutant animals retain only approximately 30% the normal number of neurons. Quantification of neuronal and neuronal precursor numbers in normal and mutant animals reveals that neurons are specifically depleted in the absence of NT-3. A deficiency in precursor proliferation is only seen after most of the neuronal deficit has developed. Numbers of apoptotic cells in the ganglia of mutant animals are elevated during this same interval, indicating that the neuronal deficit is caused, in large part, by increased cell death of embryonic neurons. To determine sources of NT-3 in the trigeminal system, we examined the expression pattern of beta-galactosidase in mice, in which lacZ has replaced the NT-3 coding exon. E10.5-E11.5 embryos exhibit intense reporter expression throughout the mesenchyme and epithelia of the first branchial arch. Beta-galactosidase expression in E13.5 embryos is largely confined to the oral epithelium and the mesenchyme underlying the skin. Throughout the E10.5-E13.5 interval, the trigeminal ganglion and its targets in the CNS do not express reporter activity. We conclude that NT-3 acts principally as a peripherally derived survival factor for early trigeminal neurons.

Papaverine injures the endothelium of the internal mammary artery.

Intraluminal injection of papaverine may be employed to dilate the internal mammary artery for use as a coronary artery bypass graft. The biochemical and morphological consequences of exposing the endothelium of the internal mammary artery to papaverine have been investigated. Biochemical injury was assessed by measuring changes in basal and vortex-stimulated prostaglandin I2 production, and morphological damage by scanning electron microscopy. Segments of internal mammary artery from 10 patients were placed in one of three solutions; papaverine (1.5 mg/ml of normal saline), normal saline acidified to the pH of the papaverine solution, and normal saline alone. Basal production of prostaglandin I2 was similar in the three groups but vortex-stimulated production was significantly lower in segments stored in papaverine (18.3 pg/mg) and acidified saline (19.1 pg/mg) compared with that of saline alone (43.6 pg/mg). No consistent morphological difference was found by scanning electron microscopy. It was concluded that the low pH of the papaverine solution injured the endothelium of the internal mammary artery.

Comparison of the use of a propofol infusion in cardiac surgical patients with normal and low cardiac output states.

OBJECTIVES: This study compared the hemodynamic effects of a propofol infusion with fentanyl analgesia in patients undergoing cardiac surgery with normal and low cardiac output states. Low cardiac output was defined as a cardiac index less than 2.5 L/min/m2 with a minimum pulmonary capillary wedge pressure of 7 mmHg. DESIGN: A prospective and open study. SETTING: A single center cardiothoracic unit within a teaching hospital. PARTICIPANTS: Patients were assigned to group P, poor cardiac output or group N, normal cardiac output, after thermodilution pulmonary artery catheter assessments. INTERVENTIONS: Both groups received a propofol infusion, 8 mg/kg/hr, until induction of anesthesia, followed by 4 mg/kg/hr until the intensive care unit. Fentanyl, 15 micrograms/kg, and pancuronium, 0.15 mg/kg, were administered after induction. The lungs were ventilated with oxygen. MEASUREMENTS AND MAIN RESULTS: Hemodynamic assessments were repeated at intervals until cardiopulmonary bypass. Changes within and between groups were compared using t tests on percentage change from baseline. Group N had significantly greater decreases in cardiac index, stroke volume, and left ventricular stroke work index than group P. There were comparable decreases in mean arterial pressure on induction of anesthesia, 14% and 8% in group N and group P, respectively. In both groups, right ventricular ejection fraction was unchanged. CONCLUSIONS: The use of a propofol infusion for induction and maintenance of anesthesia in patients with low cardiac output states undergoing cardiac surgery is not contraindicated.

Comparison of propofol and fentanyl anaesthesia in coronary artery versus valve surgery.

Total intravenous anaesthesia with propofol and fentanyl was used in 23 patients undergoing coronary artery and 16 patients undergoing valve surgery and the haemodynamic effects in the two groups were compared. Baseline values showed that the valve surgery group had a higher mean heart rate, pulmonary artery wedge pressure and pulmonary artery pressure and smaller mean stroke volume than the coronary artery surgery group. In both groups, heart rate, arterial pressure, pulmonary artery wedge pressure, pulmonary artery pressure and cardiac index decreased during surgery. In the valve surgery group there were greater percentage decreases in heart rate, mean arterial pressure and diastolic arterial pressure. Overall, propofol and moderate-dose fentanyl anaesthesia was no more detrimental to the haemodynamics in patients undergoing valve surgery when compared to those undergoing coronary artery surgery.

Omission of aspirin in patients following coronary artery bypass graft surgery.

Graft patency is a major factor contributing to the long-term results of coronary artery bypass graft (CABG) surgery. The systematic overview of the Antiplatelet Trialists' Collaboration provides unequivocal evidence that antiplatelet therapy reduces by nearly one-half the odds of coronary graft occlusion following CABG. We retrospectively reviewed patients undergoing CABG during 1993 at the Cardiothoracic Unit, Northern General Hospital, to determine the incidence of, and indications for, aspirin omission following CABG: 462 patients with isolated CABG, 75 patients with a combined CABG and a heart valve procedure and 21 patients with a combined CABG and other non-valve procedure. Thirty-six patients (7.5%) with isolated CABG and CABG combined with a non-valve procedure were not prescribed aspirin. The reasons for aspirin omission were categorized into three groups depending on whether omission was fully justified (group 1), possibly justified (group 2) or unjustified (group 3). Twenty-one patients were in groups 2 and 3, nine of whom were started on aspirin 2-6 weeks after discharge without any ill effect. Forty-two patients were discharged from hospital on a three month course of warfarin. Four months later four patients had died, 24 had changed to aspirin, 10 were still on warfarin and four were on neither drug. Aspirin was sometimes omitted without clear indications. Better provisions for supervision should be made by either the General Practitioner or Hospital Practitioner during the change-over period from oral anticoagulation to antiplatelet therapy in patients on a short course of warfarin.

Propofol and fentanyl anaesthesia for patients with low cardiac output state undergoing cardiac surgery: comparison with high-dose fentanyl anaesthesia.

We have compared the haemodynamic effects of an infusion of propofol 8 mg kg-1 h-1 followed by 4 mg kg-1 h-1 and fentanyl 15 micrograms kg-1 (group 1) with midazolam 3-6 mg and fentanyl 60 micrograms kg-1 (group 2) in patients with a low cardiac output state undergoing cardiac surgery. Heart rate was lower in group 1 throughout the period before cardiopulmonary bypass. There were no significant differences between the groups in other measured variables. Arterial pressure decreased in both groups after induction, by 21% in group 1 and 18% in group 2. Thermodilution assessment of right ventricular ejection fraction was unchanged. Myocardial contractility was not affected adversely. Patients in group 1 who received an infusion of propofol and a smaller dose of fentanyl awakened sooner and the trachea was extubated earlier.

Overcoming perioperative spasm of the internal mammary artery: which is the best vasodilator?

After mobilization, vasospasm often reduces flow through the internal mammary artery. An established method of relaxing the artery and increasing flow is to wrap it in a papaverine-soaked swab. To our knowledge the ability of other topical vasodilators to overcome spasm of the internal mammary artery has not been studied clinically. In 50 patients in whom the left mammary artery was used for myocardial revascularization, we have investigated the effect of five agents on internal mammary artery free flow. The agents investigated were normal saline, papaverine, nifedipine, glyceryl trinitrate, and sodium nitroprusside. Under controlled hemodynamic conditions, free flow was measured before any pharmacologic intervention and a median of 18.5 minutes after the pedicle had been sprayed with one of the five agents. Normal saline produced a small increase in flow from a median of 23 ml/min (range 17 to 88) to 38 ml/min (20 to 84) (not significant), whereas a significant increase occurred with papaverine, from 25 (16 to 78) to 43 ml/min (34 to 112) (p less than 0.01). Nifedipine and glyceryl trinitrate raised free flow by almost threefold, from 23 (14 to 66) to 71 ml/min (45 to 118) and from 23 (14 to 58) to 62 ml/min (46 to 126), respectively (both p less than 0.001). Sodium nitroprusside, however, with an increase in flow from 26 (10 to 58) to 108 ml/min (46 to 196), 250% over control, proved to be more effective than nifedipine and glyceryl trinitrate (p less than 0.05). We therefore recommend the topical use of sodium nitroprusside to relieve perioperative spasm of the internal mammary artery.

Fibrinolytic treatment of acute prosthetic heart valve thrombosis. 5 cases and a review.

Acute thrombotic obstruction of prosthetic heart valves has usually needed an emergency operation and carries a high mortality. Over the past 16 years, sporadic papers have appeared reporting the successful use of fibrinolytic therapy with a low mortality. We report five consecutive cases treated in this way. The diagnosis of valve thrombosis was made on clinical, echocardiographic and cineradiographic grounds. Treatment consisted of streptokinase (SPK) in a loading dose of 250,000 units in one case and 500,000 units in the remaining four cases, followed by 100,000 units hourly. Rapid improvement in clinical state was seen in all five patients. Four patients recovered completely and have been followed up for a minimum of 3 years. One patient died of a retroperitoneal haemorrhage, a recognised complication of fibrinolytic therapy. A review of the literature is presented. Fibrinolytic therapy is recommended in the acute episode and should result in either a return to normal valve function or sufficient improvement in haemodynamics to allow semielective surgery at considerably lower risk.

Alternative operative procedure for total colonic aganglionosis.

The authors have utilized a technique recently described by Boley as the corrective procedure in two patients with complex long segment aganglionosis. The one-stage operation combines a right colon onlay patch for enhanced absorptive and reservoir purposes with an ileoendorectal pull-through. Both patients had only 3 to 4 stools per day by the end of the first postoperative month. The obligatory period of intestinal adaptation needed to achieve an acceptable stooling pattern is significantly reduced in comparison with results obtained with other commonly used procedures.