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Biomedical subjects

C N Stewart

Publications and source records attributed to C N Stewart.

35 records · Page 2Linked to original sources
PubMed1996

Insect Control and Dosage Effects in Transgenic Canola Containing a Synthetic Bacillus thuringiensis cryIAc Gene.

Zygotic hypocotyls of canola (Brassica napus L.) cv Oscar, cv Westar, and the breeding line UGA188-20B were transformed with a truncated synthetic Bacillus thuringiensis insecticidal crystal protein gene (Bt cryIAc) under the control of the cauliflower mosaic virus 35S promoter using Agrobacterium tumefaciens-mediated transformation. Fifty-seven independently transformed lines were produced, containing 1 to 12 copies of the transgenes. A range of cry expressors was produced from 0 to 0.4% Cry as a percentage of total extractable protein. The Brassica specialists, the diamondback month (Plutella xylostella L.) and the cabbage looper (Trichoplusia ni Hubner), were completely controlled by low-, medium-, and high-expressing lines. Whereas control of the generalist lepidopteran, the corn earworm (Helicoverpa zea Boddie), was nearly complete, the other generalist caterpillar tested, the beet armyworm (Spodoptera exigua Hubner), showed a dose response that had a negative association between defoliation and cry expression. These plants were produced as models for an ecological research assessment of the risk involved in the field release of naturalized transgenic plants harboring a gene (Bt) that confers higher relative fitness under herbivore-feeding pressure.

Journal Article↗
PubMed1996

Genetic transformation, recovery, and characterization of fertile soybean transgenic for a synthetic Bacillus thuringiensis cryIAc gene.

Somatic embryos of jack, a Glycine max (L.) Merrill cultivar, were transformed using microprojectile bombardment with a synthetic Bacillus thuringiensis insecticidal crystal protein gene (Bt cryIAc) driven by the 35S promoter and linked to the HPH gene. Approximately 10 g of tissue was bombarded, and three transgenic lines were selected on hygromycin-containing media and converted into plants. The recovered lines contained the HPH gene, but the Bt gene was lost in one line. The plasmid was rearranged in the second line, and the third line had two copies, one of which was rear-ranged. The CryIAc protein accumulated up to 46 ng mg-1 extractable protein. In detached-leaf bioassays, plants with an intact copy of the Bt gene, and to a lesser extent those with the rearranged copy, were protected from damage from corn earworm (Helicoverpa zea), soybean looper (Pseudoplusia includens), tobacco budworm (Heliothis virescens), and velvetbean caterpillar (Anticarsia gemmatalis). Corn earworm produced less than 3% defoliation on transgenic plants, compared with 20% on the lepidopteran-resistant breeding line GatIR81-296, and more than 40% on susceptible cultivars. Unlike previous reports of soybean transformation using this technique, all plants were fertile. To our knowledge, this is the first report of a soybean transgenic for a highly expressed insecticidal gene.

Animals↗
PubMed1988

Elevated shock threshold in sexually receptive female rats.

Previous studies have found cyclic differences in wheel running, extinction of conditioned avoidance responses, and open field behavior as a function of the estrous cycle in rodents. The purpose of this study was to investigate possible sensory changes associated with estrus in rodents. Female rats were monitored for behavioral and physiological changes related to the estrous cycle. Using the method of constant stimuli and foot shock, jump thresholds were determined during the estrous cycle stages of sexual receptivity (proestrus) and non-receptivity (metestrus). A significantly higher jump threshold was demonstrated by animals during proestrus as compared to metestrus. Possible explanations for the failure of previous investigators to find attenuated sensitivity as a function of the estrous cycle are discussed.

Animals↗
PubMed1985

Profiling, mimicking and masking the flavor of a selected rodenticide.

In Experiment 1, rats drank strychnine solution followed by an injection of LiCl. Generalization of learned strychnine avoidance to 4 non-toxic flavors was then assessed. Additional conditioning and generalization trials followed until 24 flavors had been presented. In Experiment 2, rats were conditioned to avoid individual flavors, or flavor mixtures concocted on the basis of avoidance generalization observed in Experiment 1. Tests followed for generalization of learned avoidance from the simple flavors to the mixtures, from the mixtures to the simple flavors, and from either to strychnine. In Experiment 3, two concentrations of NaCl were mixed with strychnine or one of the flavors (SOA) used in the previous experiments. These stimuli, as well as SOA alone, strychnine alone, and each of the NaCl concentrations, were presented to rats during conditioning. Generalization followed, as in the previous experiments. In Experiment 1, strychnine avoidance generalized to 'bitter' flavors (ps less than 0.01). In Experiment 2, avoidance of flavor mixtures generalized more strongly to strychnine than did learned avoidance of simple flavors (ps less than 0.01). In Experiment 3, NaCl masked or otherwise suppressed the 'bitter' flavor of strychnine or SOA insofar as no groups conditioned with a 'bitter'-salt mixture generalized avoidance to 'bitter' alone (ps less than 0.01). Rats are therefore capable of recognizing the flavor components of strychnine. Moreover, when these components are mixed in proportion to the degree of generalized avoidance, a mimic (either in terms of flavor characteristics or perceived intensity) of strychnine is obtained. Avoidance learning appears useful in the development of rodenticide baits and pre-bait formulations.

Animals↗
PubMed1984

Disparity between formation of conditioned flavor aversions and neophobia during grooming in rats and mice.

Mice (Mus musculus) allowed to groom a paste containing saccharin from their fur before injection with lithium chloride displayed a saccharin aversion in subsequent drinking preference tests. No attenuation of neophobia was observed in mice grooming saccharin because the animals failed to display a neophobia towards saccharin in drinking tests. Rattus norvegicus displayed neophobia towards saccharin in two- and single-bottle drinking tests but this neophobia was not attenuated by grooming experience with the saccharin paste. Rats apparently learn that if a taste is hazardous in the grooming context it is also likely hazardous in an appetitive context. Learned safety in grooming, however, does not generalize into the appetitive context. The results support the view that neophobia and learned taste aversion depend upon different mechanisms.

Animals↗
PubMed1979

Effects of fetal and early postnatal thiamin deficiency on avoidance learning in rats.

Thiamin deficiency was induced in two groups of young rats during two stages of growth: deficiency 1, from 8 days prepartum to 10 days postpartum or deficiency 2, from 1 to 18 days postpartum. The deficiency was reversed by thiamin injections for 5 days and return to a normal diet following which animals were tested at 35 days of age. Body weights at 21 and 36 days of age were not significantly reduced by the deficiency nor was brain weight affected. Activity levels were not significantly reduced by deficiency 1 but were reduced in deficiency 2. Both active and passive avoidance learning were significantly impaired in both deficiency 1 and 2, a finding which could not be attributed to alterations in pain sensitivity, motor ability or reduced activity levels. The results indicate that the developing brain is vulnerable to reduced thiamin intake and that the period of vulnerability may be different for activity and avoidance learning.

Aging↗
PubMed1975

Avoidance behavior in vitamin B-6 deficient rats.

Pyridoxine deficiency was induced during the postweaning period in infant and young adult male rats and the effects on active avoidance and escape learning were studied. Five weeks of pyridoxine deficiency was sufficient to produce a deficit in active avoidance learning in the postweanling animals, whereas up to 10 weeks of deficient diet ingestion produced no effect on young adult animals. Mild motor impairment was produced in the young pyridoxine-deficient rats but the avoidance learning deficit could not be explained away on this basis, because a deficit in passive avoidance was also produced by the deficiency. Reversal of the deficiency by pyridoxine injection restored the active avoidance learning to normal within 1 week.

Age Factors↗