Androgen directs sexual differentiation of laryngeal innervation in developing Xenopus laevis

In adult Xenopus laevis, innervation of the vocal organ is more robust in males than in females. This sex difference originates during tadpole development; at stage 56, when the gonads first differentiate, the number of axons entering the larynx is the same in the sexes, but by stage 62, innervation is greater in males. To determine if androgen secretion establishes sex differences in axon number, we treated tadpoles with antiandrogen or androgen beginning at stage 48 or 54 and counted laryngeal nerve axons at stage 62 using electron microscopy. When male tadpoles were treated with the antiandrogen hydroxyflutamide, axon numbers were reduced to female-typical values; axon numbers in females were unaffected by antiandrogen treatment. When female tadpoles were treated with the androgen DHT (dihydrotestosterone), axon numbers were increased to male-like values. These findings suggest that endogenous androgen secretion during late tadpole stages in males is required for the sexual differentiation of laryngeal innervation observed from stage 62 on. Because androgen treatment and laryngeal innervation affect myogenesis in postmetamorphic frogs, numbers of laryngeal dilator muscle fibers were determined for hormonally manipulated tadpoles. At stage 62, vehicle-treated males had more laryngeal axons than females; laryngeal muscle fiber numbers did not, however, differ in the sexes. Both male and female tadpoles, treated from stage 54 with DHT, had more muscle fibers at stage 62 than vehicle-treated controls. Thus, while endogenous androgen secretion during late tadpole stages is subthreshold for the establishment of masculinized muscle fiber numbers, laryngeal myogenesis is androgen sensitive at this time and can be increased by suprathreshold provision of exogenous DHT. A subgroup of tadpoles, DHT treated from stage 54 to 62, was allowed to survive, untreated, until postmetamorphic stage 2 (PM2: 5 months after metamorphosis is complete). Androgen treatment between tadpole stages 54 and 62 does not prevent the ontogenetic decrease in axon numbers characteristic of laryngeal development. In addition, the elevation in stage 62 axon numbers produced by DHT-treatment at late tadpole stages was not associated with elevated numbers of laryngeal muscle fibers at PM2. Juvenile males normally maintain elevated axon numbers (relative to final adult values) through PM2 and the presence of these additional axons may result from--rather than contribute directly to--laryngeal muscle fiber addition.

High-energy fractures of the tibial plateau

High-energy tibial plateau fractures are often the result of blunt trauma. In addition to extensive bony injuries, soft-tissue problems are very common. Preoperative planning for surgical repair of these injuries is invaluable. Contemporary internal fixation techniques using ligamentotaxis, percutaneous fixation, and antiglide techniques provide the basis for internal fixation of these injuries. When extensive comminution and damaged soft tissues prohibit their use, the circular external fixator provides an excellent option for management of these complex injuries. Whether internal or external fixation techniques are used, appropriate management of the soft tissues is also a factor in the successful management of these severe injuries to the knee.

The role of distraction in improving the space available in the lumbar stenotic canal and foramen

STUDY DESIGN

The terminal event in disc space narrowing and facet subluxation of the lumbar spine can produce clinical symptoms of spinal stenosis. Reversal of this process via distraction was performed on ten cadaveric motion segments with documented stenosis.

METHODS

Computerized tomography and caliperic methods for the measurement of canal and foraminal areas were calculated in each segment after 5 and 10 mm of symmetrical distraction. Measurements were done in a blinded manner verified with orthographic software and statistical analysis.

RESULTS

Decompression of foraminal space was statistically significant in 7 of 10 cadaveric specimens after 5 mm of distraction and 9 of 10 specimens after 10 mm of distraction. Minimal yet insignificant improvement in stenotic canal area was evident with distraction.

CONCLUSION

The presence of posterior vertebral osteophytes was associated uniformly with poor improvement of space available in both stenotic canal and foramen.

Intramedullary nailing of the tibia without a fracture table: the transfixion pin distractor technique

A series of 44 fractures of the tibia requiring operative stabilization were treated using an intraoperative external transfixion pin frame to correct angular deformity and maintain length in preparation for intramedullary (IM) nailing, eliminating the need for a fracture table. The technique requires a radiolucent operating room table; the injured extremity is draped free. A transfixion pin is inserted in the os calcis. Rotational deformity is manually corrected. Using fluoroscopic control, a second transfixion pin is inserted at a location just distal and parallel to the proximal tibial articular surface, paralleling the horizontal plane of the first pin. The transfixion pins are connected with carbon fiber rods, creating a rectangular frame. Manual fracture reduction is followed by "fine tuning" with compressor/distractor clamps as needed. Alternatively, for added reduction force, the carbon fiber rod on the concave side of the angular deformity may be replaced with the AO/ASIF universal distractor. IM nailing is then performed in the usual fashion. In this series, an acceptable reduction was obtained in all cases. This technique shortens setup time, provides complete access to the distal part of the tibia, and allows free manipulation of the limb, thereby facilitating nail insertion and placement of distal locking screws. Use of medial and lateral bars prevents the angular deformity often created or exacerbated with the use of the universal distractor alone. This technique is recommended for IM nailing of all fractures of the tibia that would otherwise require use of the fracture table or universal distractor.

Quantitative assessment of cysteine and cystine in peptides and proteins following organomercurial derivatization and analysis by matrix-assisted laser desorption ionization mass spectrometry

Protocols for the analysis of the sulfhydryl content in peptides and proteins using chemical derivatization by organomercurial reagents and analysis by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) have been developed. The number of reactive cysteine residues in peptides and proteins can be determined by exploiting the affinity and selectivity of organomercurial reagents for macromolecular thiols. Mass shifts observed in MALDI mass spectra obtained before and after cysteine derivatization with p-hydroxy-mercuribenzoate (pHMB) permit the number of free sulfhydryl groups to be determined. The pHMB derivative of each free cysteine residue provides a mass shift of 321 u, overcoming limitations in the mass resolution of MALDI time-of-flight mass spectrometry. Reactive cysteine residues in a macromolecule can be selectively derivatized by using a fivefold molar excess of pHMB reagent. Total sulfhydryl content (i.e., cysteine and cystine) can be determined after disulfide reduction. However, analyses for total cysteine content are more complex, requiring protein denaturation, cystine reduction, and sample purification before derivatization and analysis by MALDI-MS. Conditions for sample denaturation, alkyl-phosphine reduction, pHMB derivatization, and sample purification by analyte adsorption and desalting on protein transfer membranes, are described for cysteine/cystine analysis performed on microgram (10-200 pmol) quantities of somatostatin, insulin, hemoglobin, and β-lactoglobulin.

Food and drug administration guidance sections. A new paradigm for medical devices. Committee for Clinical Review. FDA

The data submitted for Food and Drug Administration (FDA) review of medical devices are often not approved because of poor study design. This article proposes a new approach for developing FDA study design guidance through panels of colleagues from the academic, federal, and private sectors. This piece focuses discussion and thought on Guidance Sections, similar to Study Sections of the National Institutes of Health, to serve as common ground for the continual upgrading of guidance documents through peer review and leading edge scientific and clinical judgement.

Analysis of amino acids by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry: simultaneous derivatization of functional groups by an aqueous-phase chloroformate-mediated reaction

The one-step ethyl chloroformate derivatization of amino acids in an aqueous medium is extended with the use of a variety of alkyl chloroformate reagents. This provides a new and convenient procedure for preparing esters with different alkoxy groups. A new mechanism for esterification during chloroformate derivatization is proposed based on the formation of an intermediate mixed carboxylic-carbonic acid anhydride followed by the exchange with an alcohol. Among the different reagents investigated, isobutyl chloroformate derivatized amino acids were found to provide more sensitivity for analyses by GC-flame ionization detection and GC-MS relative to derivatives prepared by other alkyl chloroformates.

Laryngeal muscle and motor neuron plasticity in Xenopus laevis: testicular masculinization of a developing neuromuscular system

In Xenopus laevis, the sexual differentiation of the neuromuscular system responsible for courtship song is controlled by testicular androgen secretion. To explore the sensitivity of this system to androgenic stimulation, male and female frogs were gonadectomized and given testis transplants at seven different developmental stages between the end of metamorphosis and adulthood, grown to sexual maturity, and the laryngeal muscle fibers and motor axons were counted. Muscle fiber and axon numbers in males were not affected by the testicular transplant at any stage. In females, testicular transplants at all developmental stages increased muscle fiber numbers in adulthood. Values attained were, however, significantly less than those of adult intact or testis-transplanted males. Testis transplantation increased laryngeal axon numbers in females to levels equivalent to those of intact males; this effect was obtained at every stage of postmetamorphic development including adulthood. To further explore androgen regulation in adults, males and females were gonadectomized and implanted with silicone tubes containing testosterone propionate for 1.5-3 years and laryngeal muscle fibers and axon numbers compared to those of gonadectomized or sham-operated adult controls. Neither treatment with exogenous androgen nor gonadectomy had any effect on laryngeal muscle fiber or axon number in either males or females; values did not differ from those of sham-operated controls. We conclude that testicular secretions can induce laryngeal muscle fiber and axon addition in females throughout postmetamorphic life. This degree of plasticity, exhibited after the period when adult values are normally attained, stands in contrast to the effects of administration of synthetic androgen and suggests that the degree of plasticity in adult females may be underestimated if exogenous hormones rather than testicular transplants are provided.

Lumbar epidural anaesthesia for inguinal hernia repair in low birth weight infants

In view of the complications of general, spinal, and caudal anaesthesia for inguinal hernia repair in high-risk neonates, an evaluation of lumbar epidural anaesthesia (LEA) was undertaken to assess its technical feasibility, effectiveness and incidence of complications. In 18 consecutive cases, gestational age 26 +/- 2.6 wk, birth weight 877 +/- 310 g, 16 (89%) had bronchopulmonary dysplasia and 12 (67%) were oxygen-dependent at the time of surgery. Using a standard loss of resistance technique and a 4.0 cm 20 G epidural needle, the epidural space was positively identified on the first attempt in 16 (89%), and on the second attempt in 2 patients (11%). Reflux of 0.9% saline used to identify the epidural space was blood tinged in two cases. Epidural analgesia was achieved in all cases with bupivacaine 0.25% with and without 1:200,000 epinephrine, 0.75 ml.kg-1 for the first two cases, and subsequently 1.0 ml.kg-1. In 15 patients (83%), good operating conditions were achieved with epidural analgesia alone. Inhalational anaesthesia supplementation was necessary in three cases (17%). In the first two patients, the level of analgesia (T8) was insufficient to control the response to traction on the hernial sac. In one infant, analgesic to T4, whose surgery was inadvertently delayed for four hours, inhalation anaesthesia was needed to control restlessness rather than pain. Ten infants were analgesic to T2, four to T4, two to T6 and two to T8. Intraoperative periodic breathing was seen in seven infants (39%), four with oxyhaemoglobin desaturation to 75%, and two to 85%. All responded to increased FIO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of N-ethoxycarbonyl ethyl esters of amino acids by mass spectrometry

Derivatization of amino acids by using ethyl chloroformate-ethanol-pyridine provides volatile products, N-ethoxycarbonyl amino acid ethyl esters (ECEEs), which are easily amenable to GC or GC-MS analysis. MS behavior of these compounds under electron-impact has been studied. The fragments observed in the spectra facilitate recognition of commonly occurring protein amino acids and characterization of unknown analogues.

Charge-remote fragmentation in a disulfide-containing peptide, [Pen]-enkephalin, under fast atom bombardment collisionally activated dissociation conditions

Fast atom bombardment collisionally activated dissociation tandem mass spectrometry (FAB CAD MS/MS) of a disulfide-containing peptide, [2-D-penicillamine, 5-D-penicillamine]- enkephalin ([Pen]-enkephalin), is described. Unlike those of most other disulfide-containing peptides investigated, CAD of the native, unreduced protonated molecule of [Pen]-enkephalin yields a relatively large number of fragment ions. Most of the peaks in the CAD spectrum represent fragmentations of the peptide backbone with 'unsymmetric' cleavage of the disulfide bond with charge retention on the N-terminus; the fragment ions generally do not contain a sulfur atom or a disulfide group. The CAD spectrum of the N-terminal ethyl-triphenylphosphonium derivative, on the other hand, shows few fragment ions and is dominated by the single peak at m/z 523. This dominant ion also results from 'unsymmetric' cleavage and corresponds to the analogous protonated species (m/z 235) in the spectrum of the underivatized peptide. The chemical method of charge localization by triphenylphosphonium derivative formation at one end of the peptide is shown to be useful for investigating fragmentation mechanisms in FAB CAD MS/MS. Comparison of the CAD spectra of derivatized and underivatized [Pen]-enkephalin suggests that charge-remote fragmentation plays a significant role in the high-energy dissociation of this disulfide-bonded peptide.

Preliminary studies of 6 beta-hydroxydexamethasone and its importance in the DST

The role of the metabolites of dexamethasone (DEX) in the dexamethasone suppression test (DST) has never been fully elucidated. We report here our preliminary studies of 6 beta-hydroxydexamethasone (6 OH-Dex), a known metabolite of DEX, on the hypothalamic-pituitary-adrenal (HPA) axis of the rat; its activity in the most commonly used radioimmunoassay for plasma DEX; and its plasma concentrations in a normal human subject during the standard 1.0 mg DST. Six OH-Dex administered subcutaneously to rats at a dose of 1 mg/kg was able to completely suppress corticosterone production for at least 3 hr. In the IgG Corp. radioimmunoassay for plasma DEX, 6 OH-Dex was moderately cross-reactive yielding a 50% cross-reactivity of 10%. Gas chromatographic coupled mass spectroscopic analysis of human plasma samples, obtained 12 to 20 hr after the oral ingestion of 1.0 mg DEX, demonstrated similar plasma concentrations for both the parent compound and the 6-hydroxyl metabolite. The relevance of these findings, particularly to pharmacokinetic studies of the DST, is discussed.

Testicular masculinization of vocal behavior in juvenile female Xenopus laevis reveals sensitive periods for song duration, rate, and frequency spectra

In Xenopus laevis, adult males but not females produce courtship songs comprised of rapid trills. Two experiments were conducted to determine whether male-typical singing could be induced in females. At 6 different juvenile stages, male and female frogs were gonadectomized and implanted with testes, grown to sexual maturity, and tested for vocal behavior. All frogs with functional testicular implants sang; females sang as much as males. The frequency spectra of the clicks within trills were fully masculinized in females implanted at PM0, PM1, and PM2. There were deficiencies in song quality in females implanted late in juvenile life. Females receiving testis implants at PM3, PM4, and PM5 did not produce clicks with masculine spectral qualities. In a concurrent experiment, adult males and females were gonadectomized and implanted with testes or silicone tubes containing testosterone propionate. When tested for vocal behavior 10 to 15 months after implantation, 8/10 androgen-treated males, 3/12 androgen-treated females, 5/5 testes-implanted males, and 2/4 testes-implanted females sang. The females that did sing spent much less time singing than males. The click rates of females were uniformly slower than males and no female produced clicks with a masculine frequency spectrum. Thus, testicular secretions can induce male-typical singing in females until late in juvenile development. However, females exhibit a progressive decline in vocal potential with increasing age, culminating in an almost complete loss of singing ability by adulthood.

Charge-remote fragmentation during FAB-CAD-B/E linked-scan mass spectrometry of aminoethyl-triphenylphosphonium derivatives of fatty acids

The carboxyl group of fatty acids is derivatized by aminoethyl triphenylphosphonium (AETPP) bromide. Fast atom bombardment (FAB) collision-activated dissociation (CAD) B/E linked-scan mass spectrometry of these fixed-charge derivatives shows typical charge-remote fragmentation (CRF). Locations of various structural modifications in fatty acids can be recognized easily from CAD spectra of the AETPP derivatives. Because the triphenylphosphonium group localizes positive charge in the molecule, and because a key requirement for CRF is a tightly localized charge site, these preionized molecules fragment under FAB-CAD conditions more effectively than other derivatives that involve ionic bonding with metal cations or protonation of basic sites. Thus, CAD of AETPP derivatives is likely to produce more structurally informative spectra and provide an opportunity to gain additional under-standing of the CRF process. The most profound difference between the AETPP derivatives and other cations in positive mode FAB-CAD-B/E-MS is reflected in the substantial improvement of detection limits for the AETPP derivatives over those for the metal cation adducts. For several fatty acids (C10-C22) tested, the detectability can be enhanced by one to two orders of magnitude when the analysis is performed on the AETPP derivative. In addition, for the analysis of fatty acid mixtures, the FAB mass spectrum of AETPP derivatives produces a relative intensity of the molecular ion peak for each component of the mixture that more closely represents its mole fraction than does that of metal ion adducts.

Dirofilaria immitis: do filarial cyclooxygenase products depress endothelium-dependent relaxation in the in vitro rat aorta?

Endothelial cells modulate the function of their underlying smooth muscle. Thus, altered endothelial behavior could be important in the pathogenesis of vascular and lymphatic diseases, including human and animal filariasis. Endothelium-dependent relaxation is depressed in both in vivo canine femoral artery of dogs infected with Dirofilaria immitis and in vitro rat aorta exposed to adult D. immitis. The experiments reported here were designed to determine if filarial cyclooxygenase products could depress endothelium-dependent relaxation in vitro. Pretreatment of the parasites, but not the vascular ring, with either indomethacin or aspirin, prevented filarial-induced depression of relaxation. Analysis of heartworm-conditioned medium by gas chromatography--mass spectrometry revealed two peaks in the biologically active medium that were not present in the control. One peak had a retention time and chromatographic profile characteristic of derivatized PGD2 standard, and the other was not identified. Incubation of the vascular ring with PGD2 mimicked filarial-induced depression of endothelium-dependent relaxation at low, but not high, concentrations of acetylcholine. Thus, filarial PGD2 may be involved in altered endothelium-dependent relaxation seen in heartworm-infected dogs.

A model for evaluating the strength of bones lengthened by distraction osteogenesis

In an effort to evaluate the strength of bones lengthened by distraction osteogenesis, a modified Ilizarov-type external fixator was applied to the right tibiae of five adult mongrel dogs. Diaphyseal corticotomies were performed, and distraction (lengthening) was carried out at a rate of approximately 1 mm per day for 20 days. After completion of the lengthening, the animals were killed, the fixators were removed, and the right and left tibiae were harvested and stripped of soft tissue. The ends of all harvested bones were fixated in polymethylmethacrylate to allow testing on a materials testing system (MTS) machine. Testing under torsional loads was performed on the MTS machine (50 degrees maximum angle of rotation at ten seconds) until failure. The right tibiae were lengthened an average of 12 mm (range, 7-15 mm). The slopes of the linear portion of the torque versus rotation curves were determined. A comparison of slopes revealed a mean change in stiffness between test and control bones of 20.32% (range, 0.64%-40.5%). All tibiae exhibiting mature regenerate bone demonstrated stiffness greater than the matched controls (range, 0.64-24.09% stiffer). Four of five dogs had problems with proximal and distal ring impingement. This study presents a reproducible model for evaluating the strength of bones lengthened by distraction osteogenesis. The lengthened bones that exhibited bony or mature regeneration were as strong as the control bones.

Complex mixture analysis based on gas chromatography-mass spectrometry with time array detection using a beam deflection time-of-flight mass spectrometer

A beam deflection time-of-flight mass spectrometer was developed in conjunction with an integrating transient recorder to provide time array detection, permitting high mass spectral scan file acquisition rates for complex mixture analysis by capillary gas chromatography-mass spectrometry (GC-MS). Results are presented for the analysis of a urinary organic acid mixture by GC-MS at a scan file acquisition rate of 10 scan files per second (sf/s), showing the advantages of such data collection in the deconvolution of partially resolved components. The reconstructed total ion current (RTIC) chromatogram available from data acquired at this scan file generation rate is shown to be comparable to the profile obtained from a flame ionization detector in representing the chromatography performed under identical experimental parameters. The RTIC chromatogram available from the database obtained at 10 sf/s is compared with that available from a database obtained at 1 sf/s, the latter representing that scan rate typically used with most GC-MS instruments. The advantages of the higher scan file acquisition rate in representing the chromatographic profile and in allowing mass spectral data to be obtained for components in the complex mixture that are unresolved chromatographically are discussed.

Selective detection of the tolyl cation among other [C7H 7] (+) isomers by ion/molecule reaction with dimethyl ether

The ion/molecule reaction of the tolyl cation with dimethyl ether has been investigated using triple quadrupole mass spectrometry. Three isomers with [C7H7](+) composition, the 3-tolyl, benzyl, and tropylium cations, were individually selected and reacted with dimethyl ether at a pressure of 1 mtorr in the second quadrupole (Q2) collision cell. Only the tolyl ion reacted to yield a methoxylated product ion peak at m/z 122. This reaction product having m/z 122 is postulated to be identical in structure with the molecular ion of 3-methyl anisole, as supported by thermochemical data and the similarity of the collision induced dissociation (CID) daughter ion mass spectra of the product ion and the molecular ion of authentic 3-methyl anisole. The daughter ion mass spectra of the three [C7H7](+) isomers during CID, by using a triple quadrupole mass spectrometer, are nearly identical; on the other hand, the analytical approach based on the ion/molecule reaction with dimethyl ether clearly exhibits distinct gas-phase chemistry reflecting structural differences among the isomers. Sot.

Derivatization of peptides to enhance ionization efficiency and control fragmentation during analysis by fast atom bombardment tandem mass spectrometry

Novel and simple procedures for preparing ethyl-triphenylphosphonium derivatives of peptides are described. These procedures allow an ethyl-triphenylphosphonium moiety to be selectively attached to either the N- or C-terminus. The resulting derivatives contain a positive charge at a fixed position and have significant hydrophobic character. Modification of peptides by these chemical methods significantly enhances the efficiency of fast atom bombardment ionization, especially of hydrophilic peptides. Moreover, upon collisionally activated dissociation, the derivatized peptides generate a predictable series of sequence ions from either the C-terminus or the N-terminus, depending on the location of the ethyl-triphenylphosphonium moiety.

Highly resolving two-dimensional gels for protein sequencing

Two-dimensional (2D) PAGE, using carrier ampholytes for the first-dimension separation, has provided a tool for the simultaneous analysis of cellular proteins. To extend the utility of 2D PAGE to the preparative level, we have investigated the use of immobilized pH gradients (IPG) for the first-dimension separation. The results we have obtained indicate that as much as 1 mg of cellular protein can be loaded onto a single IPG gel without loss of resolution. Mutant polypeptides previously detected in carrier ampholyte-based 2D gels were equally detectable in IPG-based 2D gels. With IPG gels several hundred cellular polypeptides can be isolated, from as few as 10 gels, in sufficient amount for sequencing with current sequencing technology. We therefore conclude that IPG greatly enhances the prospects for the large-scale sequencing of cellular proteins for the development of 2D gel-related protein data bases and for the identification of new polypeptide gene products, with the attendant implications for a genome sequencing effort.

A new model to assess tibial fixation in knee arthroplasty. I. Histologic and roentgenographic results

A model to assess tibial fixation in knee arthroplasty is described. Eighteen mongrel dogs were implanted with a right tibial hemiarthroplasty. Implantation was of a press-fit, smooth implant (eight dogs) or a titanium alloy beaded device (ten dogs). Animals were studied at six, 12, 18, and 24 weeks. Roentgenographic and histologic analysis was performed for all implants. All animals were ambulatory. Roentgenographically, smooth implants showed progressive radiolucencies with increasing trabecular sclerosis under the implants. These changes were less prominent under the porous implants. Histologically, fibrous interfaces were identified focally under all implants but were thicker under smooth devices. Eighteen- and 24-week specimens showed substantial ingrowth into the porous pegs but minimal ingrowth into the porous plateau. Concurrent histologic and biochemical evaluation in dogs demonstrates the possible fate of implants in knee arthroplasty in human beings. As has been observed, histologic analyses suggest that clinically satisfactory results do not constitute evidence of stabilization by bone ingrowth.