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L M Davis

Publications and source records attributed to L M Davis.

At least 19 recordsLinked to original sources
PubMed2001

Multiple paternity and mating patterns in the American alligator, Alligator mississippiensis.

Eggs were sampled from 22 wild American alligator nests from the Rockefeller Wildlife Refuge in south-west Louisiana, along with the females guarding the nests. Three nests were sampled in 1995 and 19 were sampled in 1997. Females and offspring from all clutches were genotyped using five polymorphic microsatellite loci and the three nests from 1995 were also genotyped using one allozyme locus. Genotypes of the hatchlings were consistent with the guarding females being the mothers of their respective clutches. Multiple paternity was found in seven of the 22 clutches with one being fathered by three males, and the remaining six clutches having genotypes consistent with two males per clutch. Paternal contributions of multiply sired clutches were skewed. Some males sired hatchlings of more than one of the 22 clutches either as one of two sires of a multiple paternity clutch, as the sole sire of two different clutches, or as the sole sire of one clutch and one of two sires of a multiply sired clutch. There was no significant difference between females that had multiple paternity clutches and those that had singly sired clutches with respect to female total length (P = 0.844) and clutch size (P = 0.861). Also, there was no significant correlation between genetic relatedness of nesting females and pairwise nest distances (r2 = 0.003, F1,208 = 0.623, P = 0.431), indicating that females in this sample that nested close to one another were no more related than any two nesting females chosen at random. Eleven mutations were detected among hatchlings at the five loci over the 22 clutches. Most of these mutations (eight of 11) occurred at Ami(mu)-17, the only compound microsatellite locus of the five used in this study, corresponding to a mutation rate of 1.7 x 10-3. Finally, most of the mutations (82%) were homoplasious, i.e., mutating to an allelic state already present in this Louisiana population.

Alleles↗
PubMed1999

Mus and Peromyscus chromosome homology established by FISH with three mouse paint probes.

Fluorescence-labeled DNA probes constructed from three whole house mouse (Mus domesticus) chromosomes were hybridized to metaphase spreads from deer mouse (Peromyscus maniculatus) to identify homologies between the species. Mus Chr 7 probe hybridized strongly to the ad-centromeric two-thirds of Peromyscus Chr 1q. Most of Mus 3 probe hybridized principally to two disjunct segments of Peromyscus Chr 3. Mus Chr 9 probe hybridized entirely to the whole Peromyscus Chr 7. Three Peromyscus linkage groups were assigned to chromosomes, based on linkage homology with Mus. The data also are useful in interpretation of chromosomal evolutionary history in myomorphic rodents.

Animals↗
PubMed1999

MR imaging of implanted depth and subdural electrodes: is it safe?

This study evaluates the safety of imaging chronic epilepsy patients with intracranial depth and subdural electrodes by magnetic resonance (MR). To identify an epileptogenic focus, the precise location of the electrode contacts is necessary, and MR can provide this information. However, many neurosurgeons and neuroradiologists are hesitant to scan patients by MR with these implanted, metallic electrodes for fear of electrode displacement, current induction or heating secondary to the strong magnetic field. In the present study, the subdural electrodes were made of stainless steel with either stainless steel or platinum contacts. The depth electrodes were made of either platinum or a nickel-chromium alloy (nichrome). We reviewed 98 cases in which patients with implanted depth electrodes, subdural electrodes, or both underwent MR scanning. A total of 143 depth electrodes, 688 subdural strips, and 38 subdural grids were implanted in the 98 procedures. MR scanning was performed on a 1.5-T unit and consisted of T1, T2, and/or spoiled gradient echo pulse sequences. There were no documented complications related to the MR scans. Based on this study and a review of the literature, we feel that MR imaging can safely localize intracranial electrodes.

Dura Mater↗
PubMed1999

Hybridization-based karyotyping of mouse chromosomes: hybridization-bands.

We have developed a method, which we have named hybridization-banding, to identify simultaneously all chromosomes in a mouse metaphase spread. The method uses a combination of hybridization probes labeled with a single fluor to yield a simple, unique, readily identifiable hybridization pattern on each chromosome. The method is superior to Giemsa- or fluorescence-based banding methods for chromosome identification because the hybridization patterns are simpler and easier to identify, and unique patterns can be designed at will for each chromosome. Analysis can be performed with a standard fluorescence microscope, and images can be recorded on film with an ordinary 35-mm camera, making the method useful to many investigators. The method can also be applied to any species for which chromosomes and probes can be prepared.

Animals↗
PubMed1999

Application of in situ PCR to yeast cells for screening YAC libraries.

We have used in situ PCR technology in yeast cells with the ultimate goal of cloning and screening genomic yeast artificial chromosome (YAC) libraries. The target sequences in YAC clones were amplified "in situ" in yeast cells by the same set of microsatellite primers used in solution-based PCR screening. The method is fast and sensitive and obviates the steps required for individual isolation of DNAs from hundreds to thousands of YAC clones and thus has an advantage over conventional solution-based PCR screening. This approach can conceivably be applied to the products of automated robotic workstations.

Animals↗
PubMed1999

CT of the brain: a comparison of transportable and fixed-platform scanners.

OBJECTIVE: The purpose of this study was to determine whether an in-hospital transportable CT scanner can provide diagnostic brain images and to compare the quality of these images with those from a conventional fixed-platform CT scanner. SUBJECTS AND METHODS: Twenty-seven patients with known or suspected intracranial pathology underwent imaging on a transportable scanner and a fixed-platform scanner within 1 hr of each other. Images from each CT examination were evaluated independently by two neuroradiologists who were unaware of patient history. Conspicuousness of intracranial pathology and normal anatomy were rated on a 5-point scale (1 point, optimal; 5 points, poor or not visualized). Statistical comparisons were made using nonparametric tests. RESULTS: Seven CT scans were interpreted as showing normal findings and 20 scans revealed intracranial pathology on both CT scanners. Image quality was higher on the fixed scanner (average rating, 2.42 points; SE = .12) than on the transportable scanner (average rating, 3.10 points; SE = .12) (p = .001). Depiction of the cerebellum, midbrain, and supratentorial gray-white matter was better on the fixed scanner (p < .05). However, we found no significant differences in detection of intracranial pathology between scanners. Both radiologists found images from both scanners to be diagnostic in all 27 patients. CONCLUSION: Images of the brain on the transportable CT scanner were less clear than those on a fixed scanner. However, images from the transportable CT scanner were diagnostic in 27 consecutive patients. The implications of this finding are important for the provision of CT services for critically ill patients who cannot be transported to the radiology department.

Adult↗
PubMed1998

Evaluation of orthodontic relapse using the cubic spline function.

A sample of 72 orthodontically treated patients was reexamined many years out of retention. They had been treated either by the extraction of four premolars or without extractions. The average number of years between the end of treatment and the taking of follow-up records was 20, with a range of 12 to 35 years. Some conventional measurements were studied such as intertooth widths, arch perimeter, and incisor irregularity. In addition, a new method for comparison of arch form at different stages of treatment, which uses the cubic spline function, was used. Cases were grouped into extraction and nonextraction, and statistics were used to test the differences between the two groups. Correlations between the spline variables and conventional variables were computed, and multiple regression analysis was carried out using the spline variables as dependent variables. Some treatment and relapse changes were independent of whether the case was treated with extractions or not, whereas other trends were unique to one treatment group. The correlation analysis revealed strong relationships between variables that measured changes during the same treatment stage. There were also moderate correlations between some of the spline variables and the traditional measurements. Multiple regression analysis was used to account for changes in some spline variables, however, the usefulness of the model as a predictor is limited.

Bicuspid↗
PubMed1998

Analysis of large and small colony L5178Y tk-/- mouse lymphoma mutants by loss of heterozygosity (LOH) and by whole chromosome 11 painting: detection of recombination.

Analysis of 122 spontaneous large and small colony mutants derived from L5178Y tk +/- mouse lymphoma cells at 28 heteromorphic microsatellite loci on chromosome 11 showed that extensive loss of heterozygosity (LOH) is common in both large colony and small colony mutants, eliminating most chromosome 11 loci as candidates for a putative growth control locus. These results, in conjunction with historical cytogenetic data, suggest that a putative growth control locus lies distal to the thymidine kinase (Tk1) gene, near the telomere. Thirty seven mutants were hybridized with a chromosome 11-specific whole chromosome painting probe for analysis of rearrangements. Generally, painting confirmed earlier observations that large colony mutants are karyotypically normal, whereas small colony mutants frequently have detectable rearrangements. A point probe distal to Tk1 revealed no evidence of chromosome breakage in small colony mutants that appeared normal on whole 11 painting and had no LOH. Therefore, the molecular difference between large and small colony mutants remains unknown. Models to explain large and small colony mutants consistent with our findings are presented, including loss of a putative growth control gene, differential mechanisms of chromosome breakage/repair and second site mutations as explanations for small colony mutants. Painting revealed translocations and aneuploidy and showed that non-disjunction was not a common explanation for complete LOH. The most common finding was that large regions of LOH do not result from deletions, demonstrating that these cells can detect recombination events as well as previously observed chromosomal rearrangements, deletions and point mutations.

Aneuploidy↗
PubMed1998

Differential destabilization of repetitive sequence hybrids in fluorescence in situ hybridization.

A method for painting a chromosome or chromosome region by fluorescence in situ hybridization (FISH) without blocking DNA is described. Both unique sequence and repetitive sequence components of a fluorescently labeled probe are hybridized under low-stringency conditions, but the chromosomes are washed in such a manner that repetitive sequences are differentially removed, while region-specific unique sequence fragments remain bound to the target chromosomes. We refer to this differential retention and removal of probe components as differential stability FISH.

Breast Neoplasms↗
PubMed1997

Slow ventricular conduction in mice heterozygous for a connexin43 null mutation.

To characterize the role of the gap junction protein connexin43 (Cx43) in ventricular conduction, we studied hearts of mice with targeted deletion of the Cx43 gene. Mice homozygous for the Cx43 null mutation (Cx43 -/-) die shortly after birth. Attempts to record electrical activity in neonatal Cx43 -/- hearts (n = 5) were unsuccessful. Ventricular epicardial conduction of paced beats, however, was 30% slower in heterozygous (Cx43 -/+) neonatal hearts (0.14+/-0.04 m/s, n = 27) than in wild-type (Cx43 +/+) hearts (0.20+/-0.07 m/s, n = 32; P < 0.001). This phenotype was even more severe in adult mice; ventricular epicardial conduction was 44% slower in 6-9 mo-old Cx43 -/+ hearts (0.18+/-0.03 m/s, n = 5) than in wild-type hearts (0.32+/-0.07 m/s, n = 7, P < 0.001). Electrocardiograms revealed significant prolongation of the QRS complex in adult Cx43 -/+ mice (13.4+/-1.8 ms, n = 13) compared with Cx43 +/+ mice (11.5+/-1.4 ms, n = 12, P < 0.01). Whole-cell recordings of action potential parameters in cultured disaggregated neonatal ventricular myocytes from Cx43 -/+ and +/+ hearts showed no differences. Thus, reduction in the abundance of a major cardiac gap junction protein through targeted deletion of a Cx43 allele directly leads to slowed ventricular conduction.

Action Potentials↗
PubMed1997

Spatially organized response zones in rat olfactory epithelium.

Electroolfactogram recordings were made with a four-electrode assembly from the olfactory epithelium overlying the endoturbinate bones facing the nasal septum. In this study we tested whether odors of different chemical structures produce maximal responses along longitudinally oriented regions following the olfactory receptor gene expression zones described in the literature. The distribution of responses along the dorsal-to-ventral direction of this epithelium (i.e., across the expression zones) was tested in two types of experiments. In one, four electrodes were fixed along the dorsal-to-ventral axis of one turbinate bone. In the other, four electrodes were placed in corresponding positions on four turbinate bones and moved together up toward the top of the bone. These experiments compared the odorants limonene and alpha-terpinene, which are simple hydrocarbons, with carvone and menthone, which differ from the hydrocarbons by the presence of ketone groups. All responses were standardized to an amyl acetate or ethyl butyrate standard. The responses to limonene and alpha-terpinene were often larger for the ventral electrodes. The responses to carvone and menthone were largest for the dorsal electrodes. Intermediate electrodes gave responses that were intermediate in amplitude for these odors. The possibility that direction of air flow caused the observed response distributions was directly tested in experiments with odor nozzles placed in two positions. The relatively larger dorsal responses to carvone and relatively larger ventral responses to limonene were present despite odor nozzle position. We conclude that the responses to this set of odors vary systematically in a fashion parallel to the four gene expression zones. The odorant property that governs this response distribution may be related to the presence of oxygen-containing functional groups. Certain odors evoked larger responses at the intermediate electrode sites than at other sites. Cineole was the best example of this effect. This observation shows that not all oxygen-containing functional groups produce the same effect. Although we cannot exclude other possible mechanisms, these three response gradients may be produced by the four receptor expression zones described for many of the putative olfactory receptor genes. Therefore many of the receptors in each zone may share common properties. It remains to be determined whether this zonal input is significant in central odor processing. However, the correlation of odor chemical properties with the structure of receptor molecules in each zone may provide significant leads to structure-function relationships in vertebrate olfaction.

Absorption↗
PubMed1996

Identification of a heteromorphic microsatellite within the thymidine kinase gene in L5178Y mouse lymphoma cells.

The objective of this work is to identify a heteromorphism within the thymidine kinase (Tk1) gene which can be used to assay for allele loss by means of PCR. Intron F of mouse Tk1 contains two (CA)n microsatellite sequences separated by 107 bp of non-repetitive sequence. We tested this region for heteromorphism in L5178Y mouse lymphoma cells. A PCR primer pair designated Agl1 yielded products of 396 and 194 bp from L5178Y tk+/- genomic DNA. The 194-bp product resulted from a secondary binding site between the two (CA)n repeats for the forward Ag11 primer and was not produced from tk-/- mutants that had lost the functional Tk1b allele. Agl2 primers produced two PCR products of 523 and approximately 440 bp and Agl3 primers produced products of 579 and approximately 500 bp. In both these cases, the difference in product size was approximately equal, indicating that Intron F is approximately 80 bp shorter in the non-functional Tk1a allele than in Tk1b. This heteromorphism forms the basis for an assay for allele loss by means of PCR. Agl1 and Agl3 primers yielded additional products of 91 and 274 bp, respectively, consistent with sizes expected from the mouse Tk1 pseudogenes (Tk1-ps). Our conclusions drawn from an analysis of 122 mutants for Tk1b loss using Agl2 primers agreed with previous analysis of the NcoI heteromorphism. Thus, a simple PCR-based analysis can identify Tk1b loss in the L5178Y mouse lymphoma cells.

Animals↗
PubMed1996

Olfactory marker protein (OMP) gene deletion causes altered physiological activity of olfactory sensory neurons.

Olfactory marker protein (OMP) is an abundant, phylogentically conserved, cytoplasmic protein of unknown function expressed almost exclusively in mature olfactory sensory neurons. To address its function, we generated OMP-deficient mice by gene targeting in embryonic stem cells. We report that these OMP-null mice are compromised in their ability to respond to odor stimull, providing insight to OMP function. The maximal electroolfactogram response of the olfactory neuroepithelium to several odorants was 20-40% smaller in the mutants compared with controls. In addition, the onset and recovery kinetics following isoamyl acetate stimulation are prolonged in the null mice. Furthermore, the ability of the mutants to respond to the second odor pulse of a pair is impaired, over a range of concentrations, compared with controls. These results imply that neural activity directed toward the olfactory bulb is also reduced. The bulbar phenotype observed in the OMP-null mouse is consistent with this hypothesis. Bulbar activity of tyrosine hydroxylase, the rate limiting enzyme of catecholamine biosynthesis, and content of the neuropeptide cholecystokinin are reduced by 65% and 50%, respectively. This similarity to postsynaptic changes in gene expression induced by peripheral olfactory deafferentation or naris blockade confirms that functional neural activity is reduced in both the olfactory neuroepithelium and the olfactory nerve projection to the bulb in the OMP-null mouse. These observations provide strong support for the conclusion that OMP is a novel modulatory component of the odor detection/signal transduction cascade.

Animals↗
PubMed1996

Relation of chemical structure to spatial distribution of sensory responses in rat olfactory epithelium.

1. Electroolfactogram (EOG) recordings were made in three configurations from the rat olfactory epithelium. Each configuration compared recordings in the dorsomedial recess of the epithelium with recordings in ventral or lateral parts of the epithelium. Most comparisons were made with simultaneous recordings. The exception was a series in which the dorsal recess and lateral space between the base of two turbinate bones were directly exposed for odor application and recording. The spatial distributions of maximal responses were largely independent of recording configuration. 2. Simultaneous recordings compared dorsomedial and lateral sites in the epithelium during stimulation with a series of 50 odorants. The odorants that evoked larger responses in the lateral sites were usually compounds that lacked oxygen containing functional groups (such as the carbonyl group). This was true for straight chain and cyclic alkanes, for terpine compounds, and for aromatic compounds. The major exception was cineole, a bicyclic compound. All compounds containing ketone groups evoked larger dorsomedial responses. The responses of aldehydes and esters depended upon whether they were attached to aliphatic or aromatic chains. 3. In the three types of preparation, the sites responding best to ketones were in the same expression zone of the epithelium according to published maps for the rat and mouse. The sites responding best to odors without functional groups were in the far lateral or ventral region and corresponded to one of the two most lateral and ventral expression zones. This fact suggests that the receptors in these regions have a preference for particular chemical properties. This level of analysis cannot determine whether all receptors in each zone have a stronger response to certain properties of these odorants or whether each zone contains different proportions of receptors with these properties.

Anesthesia, Inhalation↗
PubMed1995

Selection of hybrids by affinity capture (SHAC): a method for the generation of cDNAs enriched in sequences from a specific chromosome region.

We have established a method for preparing cDNA sublibraries enriched in sequences from specific chromosome regions, called selection of hybrids by affinity capture (SHAC). This procedure can be described in two stages. In the first stage, a particular chromosome region, in this study mouse chromosome 11, was microdissected, followed by PCR amplification with a universal degenerate primer. This material is referred to as the "target" DNA. In the second stage, a mouse liver cDNA library with unique linker-adapter ends, referred to as the "source" cDNA, was hybridized to the biotin-labeled target DNA prepared during the first stage. The resulting DNA duplexes were captured by streptavidin-coated magnetic beads. The cDNAs were released from their biotin-labeled target homologs by alkaline denaturation and recovered by PCR amplification. These cDNAs were referred to as the SHACcDNAs. Specificity of the SHACcDNA to chromosome 11 was verified by FISH analysis. To examine representation of the SHACcDNA, we confirmed the presence of seven genes or single-copy DNA segments known to be localized on mouse chromosome 11, using a dot blot assay. In addition, a second round of SHAC was performed to achieve even higher specificity for the resulting chromosome 11 SHACcDNA. The SHAC technology should facilitate construction of cytogenetically defined cDNA libraries and should assist in the fields of gene discovery and genome mapping.

Animals↗
PubMed1995

Localisation of ventricular tachycardia substrates by analysis of the surface QRS recorded during ventricular tachycardia.

BACKGROUND: Analysis of the surface ECG can predict the locations of pacing foci but is of limited value for locating arrhythmogenic substrates causing ventricular tachycardia because of the effects of myocardial infarction, ischaemia, and bundle branch block on ventricular activation. AIM: To determine whether analysis of the initial 60 ms segment of the surface QRS improves the accuracy of the ECG for predicting ventricular tachycardia origin we correlated the locations of 37 arrhythmogenic areas present in 20 patients with the 3D vectors of the ventricular tachycardias generated by each respective area. METHODS: The 3D vector of each ventricular tachycardia morphology was calculated from the integrals of the initial 60 ms of the surface vectorcardiogram and from the entire QRS recorded in each lead of the Frank orthogonal lead vectorcardiogram. Sixty eight-morphologies of ventricular tachycardia were mapped using simultaneous recordings from 60 catheter electrodes. RESULTS: Ventricular tachycardias with 3D vectors directed inferiorly and posteriorly or superiorly and anteriorly were more likely to originate from the septum, P = 0.04, whereas tachycardias directed superiorly and to the right were more likely to originate from the inferior wall and the cardiac apex, P = 0.001. However, the same arrhythmogenic area could generate multiple ventricular tachycardias with different 3D vectors. In addition, ventricular tachycardias with similar 3D vectors were generated by arrhythmogenic areas in the septal, apical and inferior walls. The variances of the mean 3D vectors of ventricular tachycardias originating from each of 12 different cardiac regions were no different when based on the initial 60 ms of the surface QRS than on the entire surface QRS. CONCLUSION: Analysis of the surface ECG provides only an approximate guide to the locations of arrhythmogenic areas generating ventricular tachycardia even when analysis is restricted to the initial forces in the surface QRS. Therefore, detailed mapping is needed to accurately determine the number and location of arrhythmogenic areas.

Bundle-Branch Block↗