slit: an extracellular protein necessary for development of midline glia and commissural axon pathways contains both EGF and LRR domains

The Drosophila slit locus encodes a protein with four regions containing tandem arrays of a 24-amino-acid leucine-rich repeat (LRR) with conserved flanking sequences (flank-LRR-flank surrounding these arrays), followed by two regions with epidermal growth factor (EGF)-like repeats. Each of these motifs has been implicated in protein-protein interactions as part of an extracellular domain in a variety of other proteins. Analysis of slit cDNA clones reveals that as a consequence of alternative splicing, the locus can code for two distinct protein species differing by 11 amino acids at the carboxyl terminus of the last EGF repeat. The existence of a putative signal sequence and the absence of a transmembrane domain suggest that slit is secreted, an observation supported by an analysis of its expression in tissue culture. Examining the expression pattern of slit in the embryo by antibody staining, enhancer trap detection, and in situ hybridization, we demonstrate that the protein is expressed by a subset of glial cells along the midline of the developing central nervous system. Through immunoelectron microscopy, slit can be seen on the commissural axons traversing the glial cells although it is absent from the cell bodies of these neurons, implying that slit is exported by the glia and distributed along the axons. Finally, we demonstrate that a reduction in slit expression results in a disruption of the developing midline cells and the commissural axon pathways. The embryonic localization, mutant phenotype, and homology of slit to both receptor-binding EGF-like ligands and adhesive glycoproteins suggest that it may be involved in interactions between the midline glial cells, their extracellular environment, and the commissural axons that cross the midline.

Pharmacokinetic model-driven infusion of fentanyl: assessment of accuracy

Computer-assisted continuous infusion (CACI) is a pharmacokinetic model-driven infusion device that enables physicians to administer intravenous (iv) drugs in a quantitative fashion, specifying a theoretical blood or plasma concentration. This study evaluated the accuracy of CACI administration of fentanyl using a newly developed CACI device programmed with a well-known set of pharmacokinetic parameters for fentanyl. Patients received diazepam 1 or 2 h before surgery. Anesthesia was induced by a combination of 70% N2O and fentanyl administered by CACI to a predicted concentration of 15-25 ng.ml-1. After neuromuscular blockade and tracheal intubation, the desired plasma fentanyl concentration (setpoint) entered into CACI was 3-6 ng.ml-1, and then the setpoint fentanyl concentration was titrated according to strict criteria of adequate or inadequate anesthesia. Plasma samples for subsequent assay of fentanyl concentration then were taken: at predefined stimuli, when inadequate anesthesia occurred, or 5 min before an anticipated decrease in the fentanyl setpoint. The predictive accuracy of CACI was assessed by calculating for each patient the tenth, 50th, and 90th percentile of the performance error and absolute performance error from each measured and predicted plasma sample pair. Cumulative probability functions for each of these were then plotted. Precision was defined as the dispersion of the tenth to 90th percentile of the median percent performance error for the population and was found to be -31-26%. The median population performance error was -4%, and the median population absolute performance error was 21%.(ABSTRACT TRUNCATED AT 250 WORDS)

Duplex imaging and incidence of carotid radiation injury after high-dose radiotherapy for tumors of the head and neck

Radiation-induced carotid artery disease following high-dose (greater than 50-Gy) radiotherapy for head and neck cancer may become more common as improved treatment results in longer survival. Duplex ultrasound scans were obtained in 91 consecutive patients to determine whether increased incidence and severity of extracranial carotid disease correlate with prior radiotherapy. Fifty-three patients who underwent radiotherapy an average of 28 months previously and 38 patients who received no radiotherapy were studied. Thirty percent of the irradiated group had lesions of the carotid arteries that were either moderate or severe vs only 6% of the control patients. Five patients were symptomatic; all had undergone radiotherapy. Long-term follow-up with sequential duplex ultrasound examinations is indicated in patients receiving high-dose radiotherapy for head and neck tumors, to detect radiation-induced carotid artery disease and prevent late sequelae.

Esmolol for treatment of intraoperative tachycardia and/or hypertension in patients having cardiac operations. Bolus loading technique

Esmolol, administered as a bolus followed by continuous infusion, was used to treat the occurrence of transient tachycardia and hypertension or tachycardia alone before cardiopulmonary bypass in 45 patients. The study was conducted in two phases. Phase I (15 patients) was a dose-finding study and phase II (30 patients) was a randomized, double-blind, placebo-controlled efficacy study. All patients received the last dose of their usual beta-adrenergic blocker the night before the operation and were anesthetized with midazolam, vecuronium, and enflurane in oxygen. Treatment criteria were either a systolic blood pressure greater than 140 mm Hg and a heart rate greater than 70 or a heart rate greater than 80 beats/min. In phase I, graduated doses of esmolol were given to successive patients. A dose of 80 mg followed by a 12 mg/min infusion was declared effective. Phase II patients were randomized to receive esmolol (n = 16) or placebo (n = 14). Hemodynamic data were collected at baseline and 1, 3, 5, and 10 minutes after the administration of esmolol. Plasma norepinephrine was measured at baseline, 1, and 10 minutes. Esmolol significantly (p less than 0.05) reduced heart rate at 1, 3, 5, and 10 minutes but did not change blood pressure, pulmonary artery diastolic pressure, right atrial pressure, cardiac output, or systemic vascular resistance. Our results show that a bolus loading dose of esmolol is safe and effective in the treatment of tachycardia in patients with ischemic heart disease and that esmolol rapidly blocks the beta-adrenergic effects of norepinephrine associated with surgical stress.

Two equally valid interpretations of the linear multicompartment mammillary pharmacokinetic model

In pharmacokinetic modeling it is common to use compartmental structures to describe the disposition of a drug in the blood or plasma. Typically, a linear multicompartment mammillary model is equated with the multiexponential equation derived from observing the decay of the plasma drug concentration following an intravascular injection. Classically, the mammillary models are constructed so that the concentrations in each of the compartments are equal at steady state, the apparent volume of distribution at steady state is equal to the sum of the individual compartment volumes, and the apparent volume of each peripheral compartment is equal to the ratio of its intercompartmental rate constants times the central compartment volume. On the basis of what can be measured in the plasma, however, it is equally valid to assume that the sizes of the peripheral compartment volumes are equal to the central compartment volume and that the steady-state concentration in each peripheral compartment is equal to the ratio of its intercompartmental rate constants times the concentration in the central compartment. In fact, these are but two of an infinite number of interpretations of the peripheral compartment volumes.

Nerve sheath tumors of the paranasal sinuses: electron microscopy and histopathologic diagnosis

Tumors of the nerve sheaths are very unusual. They occur with the highest frequency in the head and neck region, yet only 4% have been found to occur within the paranasal sinuses. Only 40 cases of nerve sheath tumors with direct involvement of the paranasal sinuses have been reported in the world's literature to date. Three new cases of neurofibroma not associated with Recklinghausen's disease and one case of a schwannoma of the frontoethmoid and maxillary sinuses are presented. The clinical, radiographic, and histopathologic features of these lesions will be discussed with emphasis on electron microscopy and immunohistochemical differentiation of these rare and often confusing lesions.

Algorithm for optimal linear model-based control with application to pharmacokinetic model-driven drug delivery

Computerized pharmacokinetic model-driven administration of intravenous anesthetic agents has been implemented using a variety of algorithms to control the drug infusion regimen. All such algorithms are similar to the extent that they use a linear pharmacokinetic model of the drug being administered to determine drug infusion rates to theoretically achieve and maintain plasma drug concentrations (setpoints) specified by the physician. Since the behavior of the pharmacokinetic model can be computed for any input, it should be possible to achieve regulation of the drug infusion rates that is flexible (i.e., the physician can interactively adjust the setpoint), practical, and analytically optimized; these objectives are realized by the algorithm described in this communication.

Drosophila neuroglian: a member of the immunoglobulin superfamily with extensive homology to the vertebrate neural adhesion molecule L1

Drosophila neuroglian is an integral membrane glycoprotein that is expressed on a variety of cell types in the Drosophila embryo, including expression on a large subset of glial and neuronal cell bodies in the central and peripheral nervous systems and on the fasciculating axons that extend along them. Neuroglian cDNA clones were isolated by expression cloning. cDNA sequence analysis reveals that neuroglian is a member of the immunoglobulin superfamily. The extracellular portion of the protein consists of six immunoglobulin C2-type domains followed by five fibronectin type III domains. Neuroglian is closely related to the immunoglobulin-like vertebrate neural adhesion molecules and, among them, shows most extensive homology to mouse L1. Its homology to L1 and its embryonic localization suggest that neuroglian may play a role in neural and glial cell adhesion in the developing Drosophila embryo. We report here on the identification of a lethal mutation in the neuroglian gene.

Embryonic development of axon pathways in the Drosophila CNS. II. Behavior of pioneer growth cones

We have identified the neurons that pioneer the major CNS axon tracts in the Drosophila embryo and determined their trajectory and fasciculation choices using serial section electron microscopy. Although Drosophila pioneer neurons make choices similar to those of their grasshopper homologs, there are interesting differences that reflect the much smaller nervous system size and the much faster rate of development characteristic of Drosophila. For example, where 2 longitudinal tracts are pioneered independently in grasshopper, only one is formed in Drosophila. This change is due to a change in fasciculation affinity of the pCC growth cone. Additionally, the intersegmental (IS) nerve is pioneered by a different neuron in Drosophila (aCC) than in the grasshopper (U1) because the smaller Drosophila CNS places the IS nerve within filopodial reach of the aCC soma, while in the grasshopper it is not. Drosophila growth cones explore a much more confined neuropil volume than do grasshopper growth cones but can also sample a larger fraction of the CNS as well. For this reason, some cell-cell recognition events critical to pathfinding in the grasshopper embryo may not be as essential in Drosophila. Nevertheless, many specific cellular affinities have been retained through the evolutionary divergence of these 2 species.

Embryonic development of axon pathways in the Drosophila CNS. I. A glial scaffold appears before the first growth cones

Three classes of glial cells are present early in embryogenesis and appear to play a major role in axon pathway formation in the Drosophila CNS. Six longitudinal glial (LG) cells are present over the longitudinal connective on each side of each segment. Six midline glia (MG) cells surround the anterior and posterior commissures of each segment. Finally, the intersegmental nerve root is covered by a glial cell: the segment boundary cell (SBC). All 3 classes of glial cells are present in their final position before axon outgrowth and their pattern prefigures the first axon pathways. The pioneer growth cones that establish the first axon pathways in the longitudinal connective and intersegmental nerve extend along the elongate surface of the LG and SBC glial cells; the pioneer growth cones for the anterior and posterior commissures extend toward and make close contact with the end feet of the MG glial cells. Later, all 3 classes of glial cells enwrap the axon tracts in much the same way as vertebrate oligodendrocytes. The results suggest that these early glial cells provide guidance cues for the first growth cones in the Drosophila CNS. More than simply providing a permissive substrate, the differential extension of specific early growth cones towards either the MG cells or along the LG cells suggests an active role for these glia in growth cone guidance.

Effects of combined modality therapy of head and neck carcinoma on shoulder and head mobility

One hundred twenty-six patients were evaluated prospectively for head and shoulder mobility following combined treatment of their advanced head and neck carcinoma. In the absence of a pectoral myocutaneous flap reconstruction, the sacrifice of the spinal accessory nerve does not appear to be deleterious to overall head and shoulder mobility with the exception of shoulder elevation. The addition of the pectoral myocutaneous flap reconstruction negated the shoulder elevation difference between the modified neck dissection and the classical neck dissection. The administration of postoperative radiation therapy appears to decrease the range of motion of both the head and the shoulder by up to 20%. We conclude that head and shoulder mobility following combined modality treatment for patients with head and neck carcinoma appears to be a multifaceted problem involving more than the presence or absence of the accessory nerve and psychosocial considerations. The multifaceted etiology of this problem should be taken into consideration when developing physical and occupational programs directed specifically at this problem.

Chemotherapy following surgery for head and neck cancer. A Radiation Therapy Oncology Group Study

The feasibility of chemotherapy of three courses of cis-platin and 120-h 5-fluorouracil (5-FU) infusion after definitive surgery, followed by standard radiotherapy, in patients with resectable locally advanced head and neck cancer was carried out in Radiation Therapy Oncology Group (RTOG). Seventy-nine percent of the patients had stage IV cancer, 65% of the tumors were moderately differentiated, and primary sites were 38% oropharynx and 28% larynx. Toxicity to chemotherapy was acceptable, with no life-threatening side effects. Nausea and vomiting were the most common side effects (78%) and were severe in 26%; 30% of patients experienced had leukopenia, 22% had anemia, 13% had thrombocytopenia, and 9% had renal impairment--all of which were mild and reversible. In six patients, chemotherapy was not given for medical conditions or because of patient refusal. Of 23 patients started on cis-platin and 5-FU postsurgery, 18 (78%) completed all three courses. Ninety-six percent of the patients finished adequate radiotherapy according to the protocol. With minimum follow-up of 24 months, 62% of the patients were alive. Of the expired patients, 5 died from other causes, without evidence of recurrence at the time of their death. It is our conclusion that chemotherapy with cis-platin and 5-FU infusion following definitive surgery is feasible on the group level, and a Phase III trial comparing this combined modality therapy to standard treatment of surgery and post-operative radiotherapy is underway by the Head and Neck Cancer Intergroup.

Lineage, migration, and morphogenesis of longitudinal glia in the Drosophila CNS as revealed by a molecular lineage marker

Previous studies described three different classes of glial cells in the developing CNS of the early Drosophila embryo that prefigure and ensheath the major CNS axon tracts. Among these are 6 longitudinal glial cells on each side of each segment that overlie the longitudinal axon tracts. Here we use transformant lines carrying a P element containing a 130 bp sequence from the fushi tarazu gene in front of the lacZ reporter gene to direct beta-galactosidase expression in the longitudinal glia. Using this molecular lineage marker, we show that 1 of the "neuroblasts" in each hemisegment is actually a glioblast, which divides once symmetrically, in contrast to the typical asymmetric neuroblast divisions, producing 2 glial cells, which migrate medially and divide to generate the 6 longitudinal glial cells. As with neuroblasts, mutations in Notch and other neurogenic genes lead to supernumerary glioblasts. The results indicate that the glioblast is similar to other neuroblasts; however, the positionally specified fate of this blast cell is to generate a specific lineage of glia rather than a specific family of neurons.

Cellular DNA content parameters in untreated and recurrent squamous cell cancers of the head and neck

The presence and degree of DNA aneuploidy as measured by the DNA index (DI) and the S phase fraction (SPF) were determined by flow cytometry in 294 specimens from 237 patients with untreated and recurrent squamous cell carcinomas of the head and neck (SCCHN). A descriptive analysis was performed in which the specimen DNA parameters were correlated with stage, size of primary, degree of lymph node involvement, morphological grade, and treatment status of the corresponding patients. Approximately 70% of the previously untreated specimens contained DNA aneuploid populations (DI greater than 1.10) and three quarters had SPF that were above 15%. There was a strong, direct association between DI and SPF (P less than 0.001). There was no correlation of the presence or degree of DNA aneuploidy with the stage of the tumor or the size of the primary or conventional morphological grade of the tumor. Specimens from patients with recurrent tumors and untreated patients with N3 lymph nodes had significantly lower rates of DNA aneuploidy and mean DI. Serial determinations of DNA aneuploidy in patients with SCCHN undergoing cytotoxic therapy are ongoing and may prove useful in the identification and understanding of resistance and response in this tumor.

The correlation of specific variables of tumor differentiation with response rate and survival in patients with advanced head and neck cancer treated with induction chemotherapy

The authors have reported previously that conventionally defined grades of tumor morphology do not correlate with tumor response or survival in advanced squamous cell cancers of the head and neck (SCCHN) treated with cisplatinum combination induction therapy. This lack of correlation may be the result of the imprecision and subjectiveness of the conventional grade determination. To examine this possibility, response and survival were correlated with individual parameters of morphologic differentiation in 136 patients with advanced, untreated SCCHN. A multi-variable analysis of degree of keratinization, number of mitotic figures per high powered field, degree of nuclear differentiation, presence of vascular invasion, intensity of inflammatory response, and invasion pattern of the cancer was performed. The grade of each variable was weighted by assigning a score from 1 to 4, with 1 representing the most differentiated and 4 the least. The cumulative score of each specimen was tallied and assigned to one of three groups, less than 12, 12 to 18, and greater than 18, analogous to the conventional grades of well, moderately, and poorly differentiated, respectively. No correlation between the grade of individual morphologic variables and response to chemotherapy was demonstrated, or between tumor response and cumulative score groups. There was no correlation of the grade of individual morphologic variables or cumulative score groups with survival. Only the survival of patients achieving a complete response to chemotherapy was correlated with the cumulative score groups: 2-year survivals of 84%, 70%, and 46% for less than 12, 12 to 18, and greater than 18, respectively. Multi-parameter analysis of individual features of tumor differentiation is not superior to conventional morphologic analysis in predicting response to chemotherapy or survival in patients with advanced SCCHN.

Continuous infusion of alfentanil for maintenance of anesthesia: comparison with halothane anesthesia

This study compares anesthetic maintenance, hemodynamic stability, and speed of recovery obtained with inhalational halothane versus intravenous alfentanil anesthesia administered continuously. In two groups of patients, anesthesia was induced with sodium thiopental, maintained with 70% nitrous oxide in 30% oxygen, and either halothane (n = 10) or a continuous infusion of alfentanil (n = 10). The administration of the allocated anesthetic was adjusted according to strict predefined criteria of inadequate anesthesia. After endotracheal intubation, hemodynamics (heart rate, systolic and diastolic pressure) changed less in the alfentanil group (P less than .01). Overall hemodynamic stability was the same in both groups. In neither group was there recall of intraoperative events. Recovery was assessed by the time from cessation of nitrous oxide administration to return of spontaneous ventilation, response to simple command, extubation, orientation, and discharge from the recovery area. The time taken to respond to simple command was significantly shorter in the alfentanil group (P less than .05), but other indices of recovery were similar.

Surgical quality control in head and neck cancer. Study 73-03 of the Radiation Therapy Oncology Group

The measurement of quality of medical care has always been a topic of concern to physicians and other health care professionals. During an age of increasing competitiveness in the health care environment, the ability to assess accurately the quality of the care delivered has become increasingly important. The head and neck surgeons within the Radiation Therapy Oncology Group have examined this problem and have developed an evaluation tool that was then applied retrospectively in an attempt to evaluate the quality of surgery performed in a randomized study. The analysis of the results suggested that the retrospective approach to surgical quality control is fraught with hazards and is unlikely to fulfill the goals set for it.

General anesthesia during percutaneous transluminary coronary angioplasty for acute myocardial infarction: results of a randomized controlled clinical trial

Acutely ill patients with myocardial infarction may require immediate cardiac catheterization and coronary angioplasty to achieve myocardial reperfusion. To determine the feasibility of using general anesthesia under these circumstances, a randomized clinical trial was performed. Of 50 patients, 25 received anesthesia and 25 receive intravenous sedation. There were transient increases in heart rate and blood pressure after tracheal intubation in the anesthetized patients, followed by significant and sustained decreases below baseline values once steady state anesthesia was attained. Arterial oxygenation was significantly improved in anesthetized patients. There were no serious complications due to anesthesia, but the small sample size limited the power of the study to detect differences in morbidity or mortality. Patients strongly preferred anesthesia. These results show that general anesthesia is feasible in patients undergoing interventional cardiac catheterization during acute myocardial infarction, when pain, anxiety or agitation do not respond adequately to conventional measures.

Alfentanil and midazolam: new anesthetic drugs for continuous infusion and an automated method of administration

New drugs like alfentanil and midazolam have the primary advantage of metabolizing faster than existing compounds in their class. Because of shorter plasma half-lives, the drugs are well suited for continuous infusion. In our hands, CACI is a valuable clinical instrument and research tool. Although some anesthetic drugs can be given safely and effectively by bolus injection, whenever a titrated continuous infusion is appropriate (and physiologically closed-loop delivery is not possible), use of a CACI-type instrument should be the preferred method of administration. With the availability for continuous infusion of alfentanil and midazolam, with their highly desirable pharmacodynamic properties and relatively effervescent pharmacokinetics, we believe that computerized pharmacokinetic model-driven infusion devices will play a significant role in future anesthetic practice.

Investigations into tracheal prosthetic reconstruction

Reconstruction of circumferential tracheal defects may be necessary following trauma or oncologic surgery. For defects up to approximately 6 centimeters in an adult, an end-to-end anastomosis appears to be the method of choice. Larger defects may require utilization of a tracheal prosthesis. In dogs, a tracheal prosthesis constructed of Dacron polyurethane mesh (Osteomesh) was found to well tolerated following a two-stage implantation procedure. Normal confluent respiratory epithelium was identified in the lumen of the prosthesis. Previously reported difficulties with recurrent granulation tissue at the areas of anastomosis appear to have been successfully avoided.

Evaluation of high-dose cisplatin and 5-FU infusion as initial therapy in advanced head and neck cancer

The combination of cisplatin and 5-fluorouracil (5-FU) infusion in head and neck cancer patients produces an overall response rate of 90% for advanced disease and 70% for recurrent disease. Whether or not escalating the platinum dose in combination with other agents, as has been done with refractory ovarian and testicular patients, would improve the response rates in patients with advanced head and neck cancer has not been evaluated. We undertook a study to determine the most efficacious dose of cisplatin that could be administered with 5-FU infusion in head and neck cancer patients. Eleven patients entered the study. Initial dose of cisplatin was 40 mg/m2 (in hypertonic saline) on days 1-5 plus 5-FU 1,000 mg/m2 on days 1-5 as a continuous infusion. Subsequent cisplatin doses were adjusted for the main toxicity, which was myelosuppression. The safest tolerable dose was 30 mg/m2 for 5 days. Overall response was 90% [45% complete response (CR) (5/11) plus 45% (5/11) partial response (PR)] which is comparable to that seen with cisplatin 100 mg/m2 and 5-FU in a 120-h infusion. Although patient numbers are small, there was no appreciable difference in response rate with higher dose cisplatin and there was a significant increase in serious toxicity.

Esmolol and left ventricular function in the awake dog

Hypotension has been the most frequently reported adverse reaction associated with infusion of the beta 1-adrenergic receptor antagonist esmolol. In some patients, this hypotension has apparently occurred independent of reduction in heart rate or systemic vascular resistance, suggesting decreased stroke volume. In the present study, the preload recuitable stroke work area (PRSWA) model was used to evaluate the negative inotropic effects of esmolol in nine chronically instrumented awake dogs. Left ventricular (LV) transmural pressure and minor axis diameter were measured by micromanometers and sonomicrometry, respectively. Vena caval occlusions were performed so that an analog of stroke work (area within LV transmural pressure-diameter loop) could be measured over a range of preloading conditions during esmolol infusions of 0, 100, 300, 1000, and 3000 micrograms/kg-1.min-1 (n = 9), and at 15 and 30 min after termination of esmolol (n = 8). The linear relationship between stroke work and end-diastolic diameter was characterized for each caval occlusion by a slope and x-intercept. PRSWA was calculated for each caval occlusion as slope/two times the square of the difference between x-intercept and the largest end diastolic diameter observed in the study of a particular dog. Heart rate was different from control (91 +/- 4) only at the highest esmolol dose (127 +/- 4). LV peak positive dP/dt, minor axis ejection shortening, stroke work, and PRSWA were depressed from control at esmolol doses greater than or equal to 300 micrograms.kg-1.min-1. All parameters except dP/dt recovered within 30 min following termination of esmolol.(ABSTRACT TRUNCATED AT 250 WORDS)