Biomedical subjects

S M Bailey

Publications and source records attributed to S M Bailey.

At least 19 recordsLinked to original sources

PubMed1992

Organizational and morphological features of cat sacrocaudal motoneurons.

We have investigated the organizational and morphological features of motoneurons from cat sacrocaudal spinal cord, the portion of the neuraxis that innervates the tail. This information is pertinent for development of a new model of spinal cord injury. An understanding of sacrocaudal circuitry is essential for physiological and behavioral assessment of the effects of sacrocaudal lesions. Observations from Nissl-stained sections corroborated Rexed's cytoarchitectural scheme. Putative motoneurons were located within two regions of the ventral horn: the ventromedial nucleus (lamina IX) and the nucleus commissuralis. To map motoneuron pools, cholera toxin-horseradish peroxidase conjugate was injected into each dorsal tail muscle. The dorsomedial muscle was innervated by ipsilateral nucleus commissuralis motoneurons. The dorsolateral and intertransversarius muscles were innervated by ipsilateral lamina IX and nucleus commissuralis motoneurons. Cell bodies of retrogradely labeled sacrocaudal motoneurons ranged from 22 to 82 microns in diameter; the unimodal distributions peaked between 45 and 50 microns. Dendritic trees of motoneurons, revealed by retrograde labeling or by intracellular injection with horseradish peroxidase, were extensive. Five to eight primary dendrites originated from the cell body. Dendritic branches extended throughout the ipsilateral ventral gray matter, with processes spreading into the surrounding white matter and the base of the dorsal horn. Dendrites from motoneurons with their soma in the lateral portion of lamina IX formed a longitudinal plexus at the gray/white border. Medial dendrites from motoneurons in the nucleus commissuralis formed bundles in the ventral gray commissure and spread throughout the contralateral ventral horn. It is speculated that contralateral dendrites subserve synchronized co-contraction of medial muscles from both sides of the tail.

Animals↗

PubMed1992

Structure-activity relationships for DT-diaphorase reduction of hypoxic cell directed agents: indoloquinones and diaziridinyl benzoquinones.

The flavoenzyme DT-diaphorase has the potential either to bioactivate or to detoxify different bioreductive cytotoxins. Elucidation of structural features governing the ability to act as a substrate for DT-diaphorase should facilitate rational optimization or elimination of this reductive pathway for a particular class of bioreductive drug. We have examined structure-activity relationships governing both the cytotoxicity and the DT-diaphorase mediated reduction of two groups of bioreductive alkylating agents: (1) Indoloquinones related to EO9 [3-hydroxy-methyl-5-aziridinyl-1-methyl-2-(1H-indole-4,7-dione)prop-beta - en-alpha-ol]; and (2) derivatives of diaziridinyl benzoquinone or diaziquone [2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone]. The rat U.K. 256 Walker tumor cell line and the human HT29 colon carcinoma line were studied because of their high DT-diaphorase content. Enzyme activity was measured spectrophotometrically by dicoumarol inhibitable cytochrome c reduction in the presence of drug, and aerobic cytotoxicity was assessed by the MTT assay. EO9 acted as a good substrate for both enzyme preparations and was highly potent in each cell line, especially in Walker tumor cells (ID50 0.039 nM). AZQ was also reduced efficiently and gave an ID50 of 6 nM in the Walker tumor line. Slight modifications in structure resulted in large variations in both DT-diaphorase metabolism and toxicity for both types of agent. There was a clear tendency for the most efficiently reduced analogues to exhibit greater cytotoxic potency. Inclusion of an aziridine moiety in the structure appears to be desirable, but not essential, for both rapid reduction and cytotoxicity. There was no evidence of active site-directed enzyme inhibition.

Animals↗

PubMed1992

Gastric emptying after minor gynaecological surgery. The effect of anaesthetic technique.

Gastric emptying was measured using the paracetamol absorption method in 30 patients immediately after a general anaesthetic for minor gynaecological surgery and in 10 female controls. Anaesthesia was induced with either propofol alone, propofol and alfentanil (4.5 micrograms.kg-1) or propofol and fentanyl (1.4 micrograms.kg-1) and maintained with intermittent propofol and 66% nitrous oxide in oxygen. Gastric emptying was delayed significantly in all patient groups when compared with volunteers. However, the delay in gastric emptying was similar in the three patient groups.

Acetaminophen↗

PubMed1991

Crossed and uncrossed projections to cat sacrocaudal spinal cord: II. Axons from muscle spindle primary endings.

The terminal fields of primary afferent fibers from tail muscle spindle primary endings were mapped within cat sacrocaudal spinal cord (S3-Ca7), using intra-axonal recording and horseradish peroxidase staining techniques. We sought to determine the ipsilateral and contralateral projection patterns and to relate these to the fibers' muscles of origin. Fifty-three group Ia fibers were successfully stained. Segmental collaterals originated from either the ascending or descending branch within the dorsal columns. Collaterals coursed rostromedially within the dorsal columns and traversed the medial aspect of the dorsal horn. Ipsilateral terminations were similar for all fibers. Within the ventral horn, boutons were consistently observed in the medial or central portions of lamina VII. In lamina VIII, a variable number of boutons was seen on fine branches emerging from larger fibers coursing ventrally. Clusters of terminals were plentiful in the regions of motoneurons, i.e., lamina IX and the nucleus commissuralis. Terminals were found in the adjacent white matter. In addition to ipsilateral terminations, some group Ia fibers (20 of 53) had collateral branches that crossed ventrally to the central canal, terminating within the midline ventral gray commissure and/or the contralateral ventral horn. Crossed projections always originated in medial (dorsal or ventral), but not lateral, muscles of the tail. These data suggest that ipsilateral projections of group Ia fibers make connections on sacrocaudal motoneurons, on neurons mediating segmental reflex functions and on neurons conveying ascending information. It is speculated that crossed and uncrossed connections between group Ia fibers from medial muscles and bilateral dendritic trees of motoneurons subserve synchronized co-contraction of synergistic muscles located on the two sides of the body, such as with dorsal or ventral flexion of the tail. Group Ia projections from lateral muscles, that are entirely ipsilateral, would be involved with lateral movements of the tail.

Afferent Pathways↗

PubMed1991

Design and operation of a simple environmental chamber for rapid freezing fixation.

Rapid freezing is the most important step in sample preparation for freeze-fracture and other cryotechniques for electron microscopy. We present the design and operation of a simple environmental chamber coupled to a plunger-driven freezing device that has provided simple and reliable freezing from temperatures and humidities other than ambient. The chamber can be constructed and operated with equipment and techniques common to most electron microscopy labs. Temperature control of +/- 0.1 degree C and relative humidities of greater than 90% were provided over the range -5-60 degrees C. Typical electron micrographs showing well preserved structures comparable to jet-freezing are presented.

Atmosphere Exposure Chambers↗

PubMed1991

Validation of convection-limited cooling of samples for freeze-fracture electron microscopy.

Rapid freezing is the most important step in sample preparation for freeze-fracture and other cryotechniques for electron microscopy. A simple heat transfer model is experimentally validated to show that convection from the cryogen to the specimen is the limiting step in rapid freezing of small samples [Biot modulus, (hd/k) less than 1] by measuring cooling rates in a variety of samples, materials, and cryogens. In comparison to the commonly accepted conduction-limited model, the convection-limited model predicts, and our experiments show, that cooling rates are proportional to the surface area to volume ratio, independent of the sample thermal conductivity, and inversely proportional to the product of sample density and heat capacity. We show that almost any material can be frozen at similar rates if the sample thickness, the cryogen, and the method and velocity of contact with cryogen are similar. Liquid ethane or propane cooled to liquid nitrogen temperature are shown to give the best results.

Ethane↗

PubMed1989

Crossed and uncrossed projections to cat sacrocaudal spinal cord: I. Axons from cutaneous receptors.

Intra-axonal recording and horseradish peroxidase staining techniques were used to map terminal fields of primary afferent fibers from cutaneous receptors within the cat sacrocaudal spinal cord. It was hypothesized that projection patterns of cutaneous afferent fibers mirror the known somatotopic organization of sacrocaudal dorsal horn cells. Forty-three primary afferent fibers, innervating either slowly adapting type I receptors, hair follicles, or slowly adapting type II receptors, all on the tail, were recovered. All collaterals (N = 372) branched from parent axons in the dorsal columns. Most collaterals coursed rostromedially to the ipsilateral gray matter, penetrated the medial dorsal horn, and arborized within laminae III, IV, and to a lesser extent, V. Ipsilateral projections to dorsal horn were as follows: axons with dorsal or dorsolateral receptive fields (RFs; n = 20) to the lateral portion, axons with lateral RFs (n = 4) to the central portion, and axons with ventral or ventro-lateral RFs (n = 19) to the medial portion. Most axons (16 of 20) with dorsal or dorsolateral RFs also had contralateral projections to lateral dorsal horn and most axons (15 of 19) with ventral or ventrolateral RFs also had contralateral projections to medial dorsal horn. No axons with lateral RFs had crossed projections. These data represent the first complete mapping of the somatotopic organization of primary afferent fiber projection patterns to a spinal cord level. The findings demonstrate that ipsilateral projection patterns of sacrocaudal primary afferent fibers are in register with the somatotopic organization of the dorsal horn. Our earlier suggestion that crossed projections of primary afferent fibers give rise to crossed components of dorsal horn RFs spanning the midline is supported by these results.

Action Potentials↗

PubMed1989

Applications of freeze-fracture replication to problems in materials and colloid science.

Understanding the relationship between the molecular structure and the macroscopic properties of polymer solutions and gels, oil-water-surfactant emulsions, lyotropic and thermotropic liquid crystals, colloidal dispersions, detergents, and other such "microstructured fluids" is essential to the optimal use of these commercially important materials. Modern rapid-freezing methods followed by freeze-fracture replication techniques are ideally suited to allow the direct visualization of the three-dimensional structure of the particles or units that make up the dispersion, while simultaneously revealing their orientation and distribution with molecular resolution. This paper reviews the necessary experimental conditions required to successfully exploit the freeze-fracture technique as it applies to microstructured fluid systems. The benefits and limitations of structural studies by freeze-fracture techniques as opposed to the more commonly used light, X-ray, and neutron-scattering methods are discussed. Freeze-fracture replicas can also be imaged by scanning tunneling microscopy to reveal directly three-dimensional fracture contours with improved resolution.

Colloids↗

PubMed1989

A comparison of three methods of assessing inter-observer variation applied to ultrasonic fetal measurement in the third trimester.

The inter-observer variation of fetal biparietal diameter, head circumference, abdominal circumference, and femoral length measured in the third trimester by ultrasound was studied by three different methods--coefficient of variation, correlation coefficient, and the 95% limits of agreement. The coefficients of variation were 1.6 to 3.7%, the correlation coefficients were 0.89 to 0.98 with P values of less than 0.001, yet the limits of agreement when applied to centile charts were found to be too wide to separate reliably small fetuses from those that were not small. We conclude that the limits of agreement is the preferred method of assessing inter-observer variation, and we suggest that future research into growth retardation move away from ultrasonic measurements of the fetus.

Abdomen↗

PubMed1989

A comparison of three methods of assessing inter-observer variation applied to measurement of the symphysis-fundal height.

This study assesses the inter-observer variation of symphysis-fundal height measurements by three methods--the coefficient of variation, the correlation coefficient and the limits of agreement. The coefficient of variation was 4% and the correlation coefficient 0.959, yet the limits of agreement were very wide. Applying these limits to centile charts of symphysis-fundal height shows that the fundal height cannot be measured by different observers with sufficient agreement to separate small fundal heights from those which are not small, and this severely limits the usefulness of measurement of the symphysis-fundal height as a screening test for intrauterine growth retardation. We conclude that inter-observer variation should be assessed by the method of limits of agreement, and not by calculating the coefficient of variation or the correlation coefficient.

Female↗

PubMed1989

Telomere staining of human chromosomes and the mechanism of radiation-induced dicentric formation.

The majority of models of radiation action developed over the past half century hold that the curvilinear dose responses exhibited by eukaryotic cells to sparsely ionizing radiations result from the interaction of pairs of lesions produced in sensitive targets of the cell. Within this conceptual framework, chromosomal exchange aberrations (e.g., interchanges) are believed to occur through the interaction of damaged sites on both chromosomes participating in the exchange. In contrast, the model proposed by Chadwick and Leenhouts (as well as some other models) suggests that such exchanges arise from initial radiation damage to only one chromosome, which then becomes associated with an undamaged chromosome. A particular aspect of this theory is that asymmetrical exchanges, such as dicentrics, may be formed from the rejoining of a broken end of one chromosome to the telomere of another. By using a DNA probe that specifically hybridizes to the telomeric region of human chromosomes, we were able to test this assertion directly. After scanning more than 200 dicentrics produced in normal human fibroblasts by 6 Gy of 60Co gamma rays, virtually none were found that contained telomeres located between the centromeres of this aberration type. Therefore, since the proposed telomere-break rejoining process, per se, is not necessarily a central element of the Chadwick-Leenhouts model, we suggest the theory be modified to exclude this mechanism.

Chromosome Aberrations↗

PubMed1987