UNT Libraries - Browse


Biogeographic Relationships of Pocket Gophers (Geomys breviceps and Geomys bursarius) in the Southeastern Portion of Their Ranges

Description: This research utilized population genetic analyses (protein starch-gel electrophoresis and DNA sequencing of the cytochrome b mtDNA gene), host-parasite specificity (lice coevolution), remote sensing of satellite data, and geographic information systems (GIS) to characterize newly discovered populations of pocket gophers (genus: Geomys) in Arkansas. These populations are isolated and occur in seemingly unsuitable habitat in the Ozark Mountains of Arkansas. Analyses of electrophoretic and ectoparasite data suggested the populations in the Ozark Mountains represented isolates allied to Geomys bursarius, a species not known to occur in Arkansas. Comparison of mitochondrial DNA sequence data of the cytochrome b gene with that of other taxa and morphometric analyses confirmed that these populations are most closely allied to G. bursarius occurring to the north in Missouri. Moreover, these mtDNA sequence analyses indicated a degree of differentiation typical of that between other subspecies of pocket gophers. Therefore, these populations represent a distinct genetic entity in an intermediate stage of speciation and should be designated as a new subspecies, Geomys bursarius ozarkensis. Molecular clock analysis revealed a time of lineage divergence for this new subspecies as approximately 511,000 YBP. Due to the isolated nature and limited distribution of this subspecies, an evaluation of critical habitat needs was initiated. Remote sensing and GIS technologies were used to identify and describe suitable habitat Computerized classification of satellite imagery of suitable vegetation, integrated with ancillary digital information on soil associations, roads, and water systems, revealed that human activity had played a positive role in the establishment and dispersal of pocket gophers in this area. This research represents an initial combination of classical systematic tools with remote sensing and GIS to investigate biogeographic patterns and evolution. This project establishes a framework for using an interdisciplinary approach to studying organisms with limited distributions, determining evolutionary status, and providing recommendations for ...
Date: August 1998
Creator: Elrod, Douglas Allen

Dalbergia and Albizia: Plantlet Production via Tissue Culture, Karyological Evaluation, and Seed Anatomy with Scanning Electron Microscopy

Description: A publication by the National Academy of Sciences, USA (1979) outlined some of the research need for a great variety of economically important woody species whose remaining genetic resources need urgently to be collected and conserved. A viable regeneration system was established via tissue and cell suspension culture for Albizia falcataria and A. lebbeck, two important wood yielding leguminous tree species. The culture medium was standardized after several trials to obtain callus from the leaflet explants of these two tree species. The optimum use of casein hydrolysate (w/v) and coconut milk (v/v) in addition to 6-Benzylaminopurine and Indole-3-butyric acid could induce morphogenesis and somatic embryogenesis in the cultured tissue. This reports the first observation on somatic embryogenesis ofA. lebbeck using leaflets as the explants. Scanning Electron Microscopy and histological studies were done on the different stages plant development following standard techniques. Embryogenesis in suspension culture followed regeneration of plantlets in A. lebbeck. In A.falcaaria the regenerative process followed via organogenesis from the shoot buds developed on the leaf explants. After hardening the regenerated plants were transferred to the greenhouse. Some of the trees grew more than 25 feet tall within a few months outside the greenhouse. Karyotype of the three leguminous trees Albizia lebbeck, A. falcataria, and Dalbergia sissoo was analyzed. In D. sissoo, various chromosomal anomalies were observed in the cultured tissue. The abnormality indices and ploidy level varied with the age and the frequency of the subculture. In the aged culture the regenerative potential declined but was reinstated to some extent with the addition of two complex growth factors, coconut milk and casein hydrolysate. Seed anatomy of 26 species of 4 leguminous genera was studied with SEM. The main distinguishing anatomical features observed in the seed sections were uniseriate or multiseriate epidermis, epidermal projections, and number of rows ...
Date: December 1998
Creator: Ghosh, Nabarun

Role of α-Keto Acids In Cyanide Detoxification and Assimilation by Pseudomonas Bacteria

Description: Cyanide was rapidly removed when added to culture supernatants of seven different Pseudomonas. The ability to remove cyanide was correlated with the accumulation of α-keto acids (pyruvate and α-ketoglutarate). These compounds react with cyanide forming less toxic cyanohydrins, thus conferring a mechanism for bacterial cyanide tolerance. When added to growth media the α-keto acids were shown also to serve as effective cyanide antagonists. While all bacteria tested accumulated α-keto acids, only those capable of utilizing cyanide as a nutritional nitrogen source were able to metabolize cyanohydrins. In P. fluorescens NCIMB 11764, the same enzyme (cyanide oxygenase) shown previously to be involved in cyanide metabolism appears responsible for cyanohydrin transformation. Keto acid excretion is believed to represent a new mechanism of bacterial cyanide detoxification with further enzymatic metabolism of the cyanohydrins helping to explain how cyanide can satisfy the nitrogen requirement in cyanide-utilizing bacteria.
Date: December 1998
Creator: Pan, Guangliang

Regulation of an S6/H4 Kinase in Crude Lymphosarcoma P1798 Preparations

Description: Purified S6/H4 kinase (Mr 60,000) requires autophosphorylation for activation. A rabbit anti-S6/H4 kinase peptide (SVIDPVPAPVGDSHVDGAAK) antibody recognized both the S6/H4 kinase holoenzyme and catalytic domain. Immunoreactivity with p60 kinase protein, and S6/H4 kinase activity were precisely correlated in fractions obtained from ion exchange chromatography of P1798 lymphosarcoma extracts. An enzyme which catalyzed the MgATP-dependent phosphorylation and activation of S6/H4 kinase coeluted with immunoreactivity from Mono 5, but not Mono Q chromatography. Since S6/H4 kinase is homologous with rac-activated PAK65, the observation that phosphorylation is also required for activation suggests a complex mechanism for in vivo activation of the S6/H4 kinase.
Date: December 1998
Creator: Taylor, Allison Antoinette

Biodiversity of Dragonflies and Damselflies (Odonata) of the South-Central Nearctic and Adjacent Neotropical Biotic Provinces

Description: The south-central United States serves as an important biogeographical link and dispersal corridor between Nearctic and Neotropical elements of western hemisphere odonate faunas. Its species are reasonably well known because of substantial collections, but there has been no concerted effort to document the extent of biodiversity and possible geographic affinities of dragonflies and damselflies of this region. The recent discoveries of Argia leonorae Garrison, Gomphus gonzalezi Dunkle and Erpetogomphus heterodon Garrison from southern and western Texas and northern Mexico suggest that Odonata species remain to be discovered in this area, particularly from far south Texas and northern Mexico. I have documented a total of 12,515 records of Odonata found in 408 counties within the south-central U.S. A total of 73 species of damselflies and 160 species of dragonflies was revealed in the region. The 233 (197 in Texas) Odonata species are distributed among 10 families and 66 genera. Illustrated family, generic, and species-level keys are provided. Since the beginning of this work in the Fall of 1993, one species has been added each to the Louisiana and Oklahoma faunas, and 12 species have been added, previously unreported from Texas, including four new to the U.S. The area of highest Odonata biodiversity overall (161 spp.) is in the Austroriparian biotic province. The greatest degree of faunal similarity between the south-central U.S. and other intra-continental regions was observed for the eastern (64%) United States. Diversity is a function of area, and as expected, the numbers of breeding birds and Odonata, in each contiguous U.S. state are positively correlated (r=0.376, n=33, p=0.031). There is, however, no strong correlation between land area and species diversity within the region, but those natural biotic provinces (Austroriparian, Texan, Balconian) where aquatic systems and topographic heterogeneity are the greatest provide a broader spectrum of potential Odonata habitats and ...
Date: May 1999
Creator: Abbott, John C.

Comparative Biochemistry and Evolution of Aspartate Transcarbamoylase from Diverse Bacteria

Description: Aspartate transcarbamoylase (ATCase) catalyzes the first committed step in pyrimidine biosynthesis. Bacterial ATCases are divided into three classes, A, B and C. Class A ATCases are largest at 450-500, are. dodecamers and represented by Pseudomonas ATCase. The overlapping pyrBC' genes encode the Pseudomonases ATCase, which is active only as a 480 kDa dodecamer and requires an inactive pyrC'-encoded DHOase for ATCase activity. ATCase has been studied in two non-pathogenic members of Mycobacterium, M. smegmatis and M. phlei. Their ATCases are dodecamers of molecular weight 480 kDa, composed of six PyrB and six PyrC polypeptides. Unlike the Pseudomonas ATCase, the PyrC polypeptide in these mycobacteria encodes an active DHOase. Moreover, the ATCase: DHOase complex in M. smegmatis is active both as the native 480 kDa and as a 390 kDa complex. The latter lacks two PyrC polypeptides yet retains ATCase activity. The ATCase from M. phlei is similar, except that it is active as the native 480 kDa form but also as 450,410 and 380 kDa forms. These complexes lack one, two, and three PyrC polypeptides, respectively. By contrast,.ATCases from pathogenic mycobacteria are active only at 480 kDa. Mycobacterial ATCases contain active DHOases and accordingly. are placed in class A1 . The class A1 ATCases contain active DHOases while class A2 ATCases contain inactive DHOases. ATCase has also been purified from Burkholderia cepacia and from an E. coli strain in which the cloned pyrB of B. cepacia was expressed. The B. cepacia ATCase has a molecular mass of 550 kDa, with two different polypeptides, PyrB (52 kDa) and PyrC of (39 kDa). The enzyme is active both as the native enzyme at 550 kDa and as smaller molecular forms including 240 kDa and 165 kDa. The ATCase synthesized by the cloned pyrB gene has a molecular weight of 165 kDa composed ...
Date: May 1999
Creator: Hooshdaran, Massoumeh Ziba

Mutagenized HLA DNA Constructs: Tools for Validating Molecular HLA Typing Methodologies

Description: This study describes the development and validation of mutagenized cloned DNA constructs, which correspond to the polymorphic regions of the class II region of the HLA complex. The constructs were used to verify the allelic specificity of primers and probes in polymerase chain reaction (PCR)-based HLA typing assays such as Sequence Specific Primers (SSP) and Sequence Specific Oligonucleotide Probes (SSOP). The constructs consisted of the entire polymorphic region of exon 2 of class II HLA allele sequences that included primer annealing sites or probe hybridization sites. An HLA allele sequence was inserted into a plasmid, cloned, then mutagenized to match a specific HLA allele, and finally, the correct clone was verified by bidirectional sequencing of the insert. Thus, the construct created a cloned reference DNA sample for any specific allele, and can be used to validate the accuracy of various molecular methodologies.
Date: May 1999
Creator: Schulte, Kathleen Q.

Isolation and Characterization of a New Capsule-Forming Bacterium

Description: A unique, previously undescribed Gram-negative bacterium was isolated from several soils in Texas and extensively characterized in this study. The cells measured 1-2 by 4-6 μm. The distinguishing characteristic of the bacterium is the extraordinary capsular material which surrounds the cells. The new isolates are aerobic, mesophilic, non motile and have the ability to utilize a variety of organic compounds as the sole source of carbon and energy. The organism grows optimally at 30° C and the optimal pH lies between 7.0-8.0. The isolates produce catalase but oxidase is not produced. They do not produce indole or hydrogen sulfide. The organism can hydrolyze gelatin and Tween 80 but not starch, esculin and casein. The major cellular fatty acid is anteiso 15:0. The guanine and cytosine content is 58-62 mole%. The organism's taxonomic position was further established by specific gene probes, 16S rRNA homology, DNA homology and "ribotyping." These data showed that it was most closely related to members of the genus Paenibacillus, although somewhat divergent from other species classified in this genus. After careful evaluation of the results obtained during this study, it is proposed that this unique bacterium be named Paenibacillus velasolus sp. nov.
Date: May 1999
Creator: Thongmee, Acharawan

Distribution of a Novel Gram Negative, Capsule-Forming Bacterium

Description: A novel Gram negative, capsule-forming bacterium was previously isolated in Dr. G. Roland Vela's laboratory. The distribution of this bacterium in soils from various locations was investigated. Soil samples from 188 locations around the world were examined. Isolates of the bacterium were obtained from 50 of these soils, with 48 of the isolates found in soils from the southwestern United States and northern Mexico. This suggests that this region is the natural habitat of the bacterium. The other two isolates were obtained from Madrid, Spain and Taipei, Taiwan. None were found in soils from South America or Australia. A lack of variation in morphology and physiological properties in the isolates suggests that a homogeneous population exists, even from widespread geographical locations.
Date: December 1997
Creator: Hughes, Roxana Bejarano

SFE Fractionation and RP-HPLC Characterization of Aquatic Fulvic Acid

Description: The Supercritical Fluid Extraction (SFE) technique was used to fractionate Suwannee River reference fulvic acid (FA). The fractions were characterized by gas chromatography (GC) and reversed-phase high performance liquid chromatography (RP-HPLC). A SFE fractionation method was developed using stepwise gradient of supercritical CO₂ and methanol. Three FA fractions were separated. The average mass recovery was 102% with the coefficient of variation of 2.8%. The fractionation dynamics and the difference in the ratios of UV absorption to fluorescence emission indicate the real fractionation of the FA. The HPLC chromatographic peak patterns and the spectra of the corresponding peaks were almost indistinguishable. The overall results of this research support the argument that FA exhibits polymer-like molecular structure.
Date: May 1994
Creator: Shao, Peimin

Regulation of Colony-Stimulating Factor-1 Biosynthesis

Description: Recent studies suggest that synthesis of the Colony-stimulating factor (CSF) is a well regulated process. However, the molecular mechanisms of the signal transduction of the various inducers of CSF such as monokines and lymphokines are not well understood. Using Interleukin 1 (IL-1) stimulation of CSF-1 in the MIA PaCa-2 cell line as a model system, the involvement of G-protein has been studied. The IL-1 induction of CSF-1 synthesis can be inhibited by both Pertussis toxin and Cholera toxin, which are known to modify the Gᵢ and Gₛ proteins respectively, thus activating adenylate cyclase to release more cAMP. The toxin inactivation can be prevented by inhibitors of the ADP-ribosylation such as, benzamide and MBAMG. Addition of dibutyryl-cAMP inhibits the IL-1 induced CSF production. Both Theophylline and Forskolin which increase cAMP by inhibiting phosphodiesterase and stimulating adenylate cyclase respectively, also inhibit CSF-1 production. Results from these studies have shown that cAMP level inversely regulates the biosynthesis of CSF-1. Preincubation of MIA PaCa-2 cells with IL-1 and 5'- guanylylimidodiphosphate (GppNHp) prevents the inhibitory effect of pertussis toxin on CSF-1 production. These data are consistent with the hypothesis that IL-1 binds to its receptor and couples to Gᵢ∝ resulting in the inhibition of adenylate cyclase and reducing cAMP level. Lowering of the' cAMP level leads to the activation of CSF-1 gene expression. The activity of another inducer of CSF-1 production in this system, 12-0-tetradecanoylphorbol-13-acetate (TPA), can be abolished by 1- (5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), which is a specific inhibitor of protein kinase C. However, H-7 failed to inhibit IL-1 stimulated CSF-1 production. Other known activators of protein kinase C namely, Ca²⁺ and L-α-l-oleoyl-2-acetoyl-sn- 3-glycerol (OAG), also increase CSF production. On the other hand, Indomethacin which is known to inhibit prostaglandin E (PGE), stimulates CSF-1 production in MIA PaCa-2 cells. These data suggest that different mechanisms ...
Date: May 1990
Creator: Ku, Chun-Ying

Toxicity of Chromium and Fluoranthene From Aqueous and Sediment Sources to Selected Freshwater Fish

Description: Research efforts in aquatic toxicology have historically centered on the chemical analyses and toxic effects of waters to aquatic organisms. More recently, sediment-source toxicity has been explored, with efforts concentrated on establishing sensitive and accurate methodologies. This study focused on the toxicity of trivalent chromium, hexavalent chromium, and fluoranthene to Pimephales promelas, Ictalurus punctatus, and Lepomis macrochirus. Test fish were exposed to both water-borne and sediment-source toxicants for 96 hours (h) and 30 days (d). A 96-h and 30-d LC50 (mg/L Cr, ug/L Fluoranthene) was determined for each fish species exposed to aqueous toxicants. In addition, 96-h and 30-d LC50s were determined for each fish species from sediment chromium concentrations (mg/kg) and sediment fluoranthene concentrations (ug/kg). Although lethality endpoints were used throughout this research, acute effects other than mortality were determined for Lepomis macrochirus exposed to hexavalent chromium. Lethal toxicity values (96-h and 30-d LC50 and their 95% confidence limits) for trivalent chromium could not be determined since trivalent chromium concentations above 6.0 mg/L could not be obtained at water pHs compatible with these fish species. Trivalent chromium addition to test waters at pHs compatible with fish survival resulted in a chromium precipitate that was not lethal to test fish. In contrast, fathead minnows, channel catfish, and bluegill sunfish exposed to hexavalent chromium in water and sediments experienced mortality. Fathead minnows exposed to fluoranthene in water for 96h demonstrated a maximum mortality of 69%, while 100% mortality was achieved with channel catfish in similar tests. Sediment tests with fluoranthene resulted in 100% mortality with both fathead minnows and channel catfish.
Date: May 1990
Creator: Gendusa, Tony C.

Opioid/Adrenergic Interaction in Regulating Canine Cardiac Function

Description: Opioid/adrenergic interactions were studied to evaluate two hypotheses: (1) naloxone potentiates the effect of epinephrine on cardiac contractility by increasing circulating epinephrine concentrations; and (2) endogenous and exogenous opioids alter left cardiac nerve stimulationinduced norepinephrine release and cardiac function. A canine isolated heart-lung preparation was used for the first study. Plasma epinephrine was determined and myocardial epinephrine uptake was calculated during intravenous epinephrine infusion. Naloxone (4 mg) was given and the epinephrine infusion was repeated. Naloxone increased cardiac contractility, coronary blood flow, and the coronary sinus epinephrine concentration. When coronary blood flow was subsequently held constant (100% above resting), naloxone increased only contractility. This result indicated that the previously observed increase in coronary sinus epinephrine was flow dependent. Corticosterone (an uptake II blocker) was employed as a positive control. Corticosterone increased the contractile response to epinephrine, but unlike naloxone, corticosterone was accompanied by a clear decrease in myocardial epinephrine uptake. The stereospecificity of the response to naloxone was investigated and (+) naloxone equaled or exceeded (-) naloxone in potentiating the inotropic effect of epinephrine. In the second study, the left cardiac nerve was isolated and electrically stimulated in intact dogs. Norepinephrine overflow gradually declined during successive control stimulations. Pretreatment with naloxone (100 Mg/kg) prevented or delayed the decline. An intracoronary dynorphin 1-9 infusion (2 nmol/min/kg for 20 minutes) reduced both norepinephrine overflow and cardiac performance, and both effects were prevented by pretreatment with naloxone (100 /xg/kg) . To summarize, naloxone potentiated the inotropic effect of infused epinephrine without altering circulating epinephrine concentrations or myocardial epinephrine uptake. This effect of naloxone was not stereospecific and probably not mediated through a traditional opiate receptor. Endogenous and exogenous opioids inhibited the left cardiac nerve stimulation-induced norepinephrine overflow, suggesting that opiate receptors may regulate cardiac excitability by modulating norepinephrine release.
Date: May 1990
Creator: Gu, Hong

DNA Typing of HLA-B by PCR with Primer Mixes Utilizing Sequence-Specific Primers

Description: The aim of this study was to design a resolution typing system for the HLA-B gene. This technique involves a one-step PCR reaction utilizing genomic DNA and sequence-specific primers to determine the specificity of each allele and to produce a larger primer data base ideal for serological analysis. The application of this technique to serological analysis can improve serology detection which is currently hindered by antibody cross-reactivity and the unavailability of useful typing reagents.
Date: August 1997
Creator: Chiu, Angela Chen-Yen

Nicotinic Acetylcholine Receptor α3 mRNA in Rat Visual System After Monocular Deprivation

Description: In situ hybridization was used to examine effects of monocular enucleation on nicotinic acetylcholine receptor subunit cc3 mRNA in the rat dLGNand visual cortex. After 28 days postoperative, there were no significant differences in α3 mRNA density between the contralateral (deprived) and ipsilateral (non-deprived) sides. The lack of obvious effects of visual deprivation on α3 mRNA density suggests that other factors, possibly intrinsic to dLGNand visual cortex, govern the postnatal expression of α3 mRNA.
Date: August 1997
Creator: Taylor, James H. (James Harvey), 1970-

Nucleotide Sequence of a Bovine Arginine Transfer RNA Gene

Description: A single plaque-pure lambda clone designated λBA84 that hybridized to a ˆ32P-labeled bovine arginine tRNA was isolated from a bovine genomic library harbored in a lambda bacteriophage vector. A 2.3-kilobase segment of this clone was found to contain an arginine transfer RNAccg gene by Southern blot hybridization analysis and dideoxyribonucleotide DNA sequencing. This gene contains the characteristic RNA polymerase III split promoter sequence found in all eukaryotic tRNAs and a potential RNA polymerase III termination site, consisting of four consecutive thymine residues, in the 3'-flanking region. Several possible cis-acting promoter elements were found within the 5'-flanking region of the sequenced gene. The function of these elements, if any, is unknown.
Date: May 1996
Creator: Eubanks, Aleida C. (Aleida Christine)

Subcellular Localization of N-acylphosphatidyl-ethanolamine Synthase in Cotyledons of Cotton Seedlings

Description: N-acylation of phosphatidylethanolamine (PE) with free fatty acids catalyzed by N-acyl phosphatidylethanolamine (NAPE) synthase was reported in cotyledons of 24-h-old cotton seedlings. Here I report subcellular localization of this enzyme. Differential centrifugation, sucrose density gradient fractionation,aqueous two-phase partitioning and electron microscopy techniques were utilized to elucidate subcellular site(s) of NAPE synthase. Marker enzymes were used to locate organelles in subcellular fractions. Differential centrifugation indicated that NAPE synthase is present in more than one organelle and it is a membrane bound enzyme. Sucrose density gradient fractionations indicated that NAPE synthase is present in membranes derived from endoplasmic reticulum (ER),Golgi and possibly plasma membrane (PM) but not mitochondria, glyoxysomes or plastids. Aqueous two-phase partitioning experiments with cotton and spinach tissues supported these results but Goigi appeared to be the major site of NAPE synthesis. Electron microscopy of subcellular fractions was used to examine isolated fractions to provide visual confirmation of our biochemical results. Collectively, these results indicate that NAPE is synthesized in plant ER, Golgi and possibly PM.
Date: December 1995
Creator: Sriparameswaran, Anuja

Upper and Lower Temperature Tolerances of Three Freshwater Game-Fish Species Exposed to Cycling Temperatures

Description: A total of 670 critical thermal maxima (CTMax) and minima (CTMin) were determined for three freshwater fishes acclimated to three constant temperatures and a diel regimen cycling between the lowest and highest acclimation temperatures. In all species temperature tolerance was directly related to acclimation temperature and slopes relating these variables indicate that acclimation temperature has a greater influence on tolerance of low rather than high temperatures. CTMax and CTMin values generated following exposure to 32 days of oscillating temperatures indicate that in general, fishes had temperature tolerance acclimation states consistent with the average temperature and not either the highest or lowest temperature of the diel cycle.
Date: August 1995
Creator: Currie, Rebecca J. (Rebecca Jean)

GABAᴀ Receptors in Rat Whisker Barrel Cortex: Effects of Sensory Deprivation

Description: The GABAergic system in adult sensory cortex is affected by sensory deprivation, but little is known about how this predominant inhibitory system is affected during ontogeny. The present study investigates developmental effects of whisker trimming on GABAa receptors in rat barrel cortex. Rats trimmed for 6 wk beginning at birth and adulthood showed similar decreases in [3H]muscimol binding in deprived relative to non-deprived barrels, suggesting absence of a critical period.
Date: August 1995
Creator: Salazar, Eduardo, 1962-

Subcloning and Nucleotide Sequence of the xylO/PUWCMA Region from the Pseudomonas putida TOL Plasmid pDK1

Description: The TOL plasmids of Pseudomonas putida encode enzymes required for the oxidation of toluene and other related aromatic compounds. These genes are organized into two operons, the xylUWCMABN operon (upper), and the xylXYZLTEGFJQKIH operon (lower). Here we report the nucleotide sequence of a 7107 bp segment of the TOL pDK1 plasmid encoding the region just upstream of the "upper" operon through the genes encoding xylUWCMA. Sequence analysis, comparison of base-usage patterns, codon-usage patterns, and intergenic distances between genes help support the idea that the "upper" and "lower" operons have evolved independently in different genetic backgrounds and have only more recently been brought together in TOL and related catabolic plasmids.
Date: December 1997
Creator: Guigneaux, Michelle M. (Michelle Marie)

A Two Semester Life Science Syllabus for Use in Texas Public Schools with Seventh Grade Students

Description: The problem of using a state adopted textbook written to apply to a large body of students with varying interests and needs was overcome by using a detailed syllabus that arranged course content in a meaningful sequence that appealed to student interest. The outlined syllabus prepared a two semester life science curriculum to be used by the teacher to guide lesson planning. Both semesters were divided into three units each. Materials included in the syllabus were given to actual student groups in real classroom settings. Since hands on learning was an important part of classroom instruction, two laboratory sections were included in the appendices to be used with the syllabus.
Date: May 1995
Creator: Edwards, Gail G. (Gail Graham)

Effects of External Electric Fields on Light Transmittance in Isolated Crayfish Nerves

Description: Acute effects of a pulsed external electric field (PEEF) at 20 V/cm and a d.c. EEF at 90 V/cm on light transmittance in an isolated compound crayfish nerve was measured. In a third series, the nerve was pre-treated with the Na+ channel blocker tetrodotoxin (TTX). A PEEF produced an irreversible increase in the variation of light transmittance in normal nerves but a reversible increase in TTX treated nerves. This data was statistically insignificant. The d.c. EEFs produced a reversible and statistically significant enhancement of variation in light transmittance in both untreated and TTX-treated nerves. The findings may be due to either (1) an alteration in the ion/fluid flux within the nerve or (2) a physical alteration of protein molecules in the membranes.
Date: December 1995
Creator: Northcutt, Brian S. W.