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Biomedical subjects

L J Rogers

Publications and source records attributed to L J Rogers.

At least 19 recordsLinked to original sources
PubMed1992

Testosterone: a role in the development of brain asymmetry in the chick.

The visual projections from the thalamus to the Wulst of the chick forebrain are asymmetrically organized. The development of this asymmetry is dependent on light stimulation just prior to hatching, and it is present to a greater extent in males than in females. We have shown that administration of testosterone to the developing embryo alters the development of the asymmetry of the projections in both sexes. Following testosterone treatment, the asymmetry normally present in male chicks after hatching was marginally reversed in direction, and that normally present in females was no longer present. Thus the development of these visual projections depends on the interaction of light stimulation and the level of circulating testosterone.

Aging↗
PubMed1992

Metabolic activity in the hyperstriatum of 2-day-old chicks during optomotor and contrasting visual stimulation.

Our earlier report of differences in metabolic activity within the visual regions of the hyperstriatum and ectostriatum, in 2-day-old chicks compared with 23-day-old chicks, suggested that two visual pathways within the visual system develop at different rates. Here we have investigated whether the demands of varying visual environments will increase the activity of the hyperstriatum accessorium (HA) in 2-day-olds. Metabolic activity in the HA was monitored in 2-day-old chicks by the radioactive 2-deoxyglucose technique during monocular stimulation with three different visual environments: moving stripes in a rotating drum, which induced eye and head movements, a featureless white environment, and the complex visual environment of the home cage with other chicks. Although a small but significant level of activity was found in HA in the hemisphere opposite the open eye, the activity did not vary with the visual treatment. On the other hand, a raised level of activity in the hyperstriatum dorsale (HD) appeared in chicks viewing the rotating stripes, indicating that at this age the thalamo-hyperstriatal pathway may be involved in processing whole-field visual movement. The optomoter environment also produced high activity in the medial hyperstriatum ventrale (MHV), a region that has been implicated in memory formation of imprinting. We suggest that during the sensitive period for imprinting, HA may either have not developed its fully functional capacity, or that following or during imprinting it is actively shut down to protect itself and associated regions from interfering visual input. In contrast to the 2-day-olds, 17-day-old chicks in a visually rich cage environment, had high levels of activity in HA, demonstrating that the functional maturation of the HA, related to performance in the cage environment, is complete at least 6 days earlier than previously observed.

Aging↗
PubMed1992

Structural asymmetry in the thalamofugal visual projections in 2-day-old chick is correlated with a hemispheric difference in synaptic density in the hyperstriatum accessorium.

Differences in visual discrimination ability between the left and right eyes of chicks, which are most prominent in young males, may result from a structural asymmetry in the organization of the visual projections from the thalamus to the visual Wulst. This asymmetry in projections is no longer present by 21 days in males when the contralateral projections from the right thalamus to the left hyperstriatum have developed. Since the asymmetry of the thalamo-hyperstriatal system results in a differential input of fibres to regions of the hyperstriatum which in turn project to the hyperstriatum accessorium (HA), one of the major differences expected within this region would be an asymmetry in the numerical density of synapses (Nv.syn/microns3). When this was examined in the hyperstriatum accessorium of 2-day-old male chicks, the density of synapses in the right HA was found to be significantly higher (22%, P less than 0.05) than in the left HA. The consequences of this asymmetry in synaptic density in the HA could be widespread and influential within the chick visual system.

Animals↗
PubMed1992

Crystal structure of oxidized flavodoxin from a red alga Chondrus crispus refined at 1.8 A resolution. Description of the flavin mononucleotide binding site.

In order to describe the detailed conformation of the oxidized flavodoxin from a eukaryotic red alga, Chondrus crispus, the crystal structure has been refined by a restrained least-squares method. The crystallographic R factor is 0.168 for 13,899 reflections with F greater than 2 sigma F between 6.0 and 1.8 A resolution. The refined model includes 173 amino acid residues, flavin mononucleotide (FMN) and 110 water molecules. The root-mean-square deviation in bond lengths from ideal values is 0.015 A, and the mean co-ordinate error is estimated to be 0.2 A. The FMN is located at the periphery of the molecule. The orientation of the isoalloxazine ring is such that the C-7 and C-8 methyl groups are exposed to solvent and the pyrimidine moiety is buried in the protein. Three peptide segments, T8-T13, T55-T58 and D94-C103, are involved in FMN binding. The first segment of T8-T13 enfolds the phosphate group of the FMN. The three oxygen atoms in the phosphate group form extensive hydrogen bonds with amide groups of the main chain and the O gamma atoms of the side-chains in this segment. T55 O and W56 N epsilon 1 in the second segment form hydrogen bonds with O-2 in the ribityl moiety and one of the oxygen atoms in the phosphate group, respectively. The O gamma H of T58 forms a hydrogen bond with the N-5 atom in the isoalloxazine ring, which is expected to be protonated in the semiquinone form. The third segment is in contact with the isoalloxazine ring. It appears that the hydrogen bond acceptor of the NH of Asp94 in the third segment is O-2 rather than N-1 in the isoalloxazine ring. The isoalloxazine ring is flanked by the side-chains of Trp56 and Tyr98; it forms an angle of 38 degrees with the indole ring of Trp56 and is almost parallel to the benzene ring of Tyr98. The environment of the phosphate group is conserved as in other flavodoxins whereas that of the isoalloxazine ring differs. The relationship between the hydrogen bond to the N-5 in the ring and the redox potential for the oxidized/semiquinone couple is discussed.

Amino Acid Sequence↗
PubMed1992

Hemispheric specialization for the control of copulation in the young chick and effects of 5 alpha-dihydrotestosterone and 17 beta-oestradiol.

After intramuscular treatment with either oestradiol (1 mg/day for 4 days) or 5 alpha-dihydrotestosterone (0.5 mg/day for 7 days) the copulatory behaviour of young male chicks was tested monocularly using removable eye-patches. From day 11 to 14 copulation scores were significantly elevated in chicks treated with oestradiol or 5 alpha-dihydrotestosterone (5 alpha-DHT) and tested either binocularly or monocularly using the left eye. There was no elevation of copulation when the treated chicks were tested monocularly using the right eye. Thus, in the binocular condition neural circuits receiving input from the left eye, and therefore likely to be on the right side of the brain, are specialized for the activation of copulation. This result confirms previous findings using chicks treated with testosterone. On day 14 the eye-patches were changed to the other eye. For chicks treated with oestradiol, those now tested using the left eye showed significantly higher levels of copulation than those now using the right. In other words, there was very little interocular transfer from left eye to right eye. However, after transferring the eye patches, the chicks treated with 5 alpha-DHT had high copulation scores irrespective of the eye used. This suggests that there may be an interaction between prior copulatory experience and 5 alpha-DHT levels which leads to either interocular transfer of copulation behaviour or equal access of both eyes to the brain regions which control copulation.

Animals↗
PubMed1991

Light-dependent development and asymmetry of visual projections.

The projections from thalamus to visual Wulst in chicks are asymmetrical and their development is determined by exposure to light just before and after hatching. The asymmetry results from the orientation of the embryo in the egg, the left eye being occluded and not the right. We have shown that this asymmetry can be eliminated by incubating the embryos in darkness or light so that both eyes receive the same stimulation.

Animals↗
PubMed1991

Relationship of the flavodoxin isoforms from Porphyra umbilicalis.

The macroalga Porphyra umbilicalis contained two flavodoxins in approximately 5:1 ratio and differing in Mr by ca 1000. The N-terminal sequences of the isoforms were identical and there was strong immunochemical identity. Peptide mapping gave similar fragments which differed in Mr by constant amount for the two isoforms. The flavodoxins may therefore differ only at the C-terminus, possibly as a consequence of in vivo processing since inclusion of protease inhibitors during extraction had no effect on the ratio of the isoforms.

Amino Acid Sequence↗
PubMed1991

Social hierarchies in very young chicks.

1. Three behavioural tests involving social competition were used to determine rank orders in groups of 8 male chicks aged between 4 and 18 days posthatching. 2. The group structure was found to consist of one or two dominant animals which consistently held a position at the top of the rank order, with a more flexible order beneath this. 3. Compared to the top-ranking birds, the middle- and lower-ranking birds showed more variability in their ranking positions across the behavioural tests and the testing periods. 4. Treatment of the lowest ranking individual in each group with testosterone led to this individual's rise in the rank order, most often to the top rank.

Animals↗
PubMed1990

Neonatal stress and long-term modulation of GABA receptors in rat brain.

Neonatal handling, known to have long-term effects on behaviour and neuroendocrine responses to acute stress, has been found to produce a long-term change in gamma-aminobutyric acid (GABA) receptor binding (Bmax) in whole-brain membranes of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. A significant 10% increase in the binding of [3H] GABA to receptors was evident more than 100 days after handling. There were no differential effects of handling between these two strains, but there was a whole-brain deficit in GABA receptor binding in SHR as compared to WKY animals. Adult corticosterone levels did not correlate with GABA receptor binding.

Analysis of Variance↗
PubMed1979

Influence of pesticides on the growth of cyanobacteria.

Two unicellular and two filamentous cyanobacteria (blue-green algae) were exposed under conditions optimal for photoautotrophic growth to eleven pesticides. Low concentrations (0.01 to 5 ppm) of diuron, atrazine, and paraquat inhibited growth. With MCPA, MCPP, 2,4-D, milstem and ethrel, marked inhibitory effects were achieved only at concentrations above 100 ppm. Growth was inhibited by glyphosate, DDT, and thiram at intermediate concentrations. In some cases, the effective concentration of the pesticide varied considerably with the organism tested.

Cyanobacteria↗
PubMed1979

Lateralisation of function in the chicken fore-brain.

There is lateralisation of function in the chicken fore-brain. This was revealed by examining the behavioural modifications produced by administration of cycloheximide into the left or right hemisphere on Day 2 of post-hatched life. Visual discrimination learning of a task requiring a search for food was found to be performed either entirely or, at least, to a greater extent by the left hemisphere. Visual habituation learning was not found to be lateralised. The left hemisphere is more involved in auditory habituation than is the right; administration of cycloheximide to the left hemisphere slowed auditory habituation, as did bilateral administration, but treatment of the right hemisphere was ineffective. There are indications that the right hemisphere plays a more important role in response to novelty. A side-preference for response to stimuli seen by the left eye was demonstrated. These results are discussed with reference to head orientation during development in the egg.

Acoustic Stimulation↗
PubMed1979

Menstruation.

Societal attitudes to menstruation are largely negative, and so serve to reinforce the inferior social status of women. These attitudes have extended into medical practice and research on menstruation. As a result, much research on 'premenstrual syndrome' has been biased both in methodology and interpretation. Correlations between hormone levels, mood changes and other behavioural measures, which cycle together, are often incorrectly assumed to indicate causal relationships. These problems are discussed along with the report of a pilot study which used a new, and more comprehensive method of studying menstruation. This study has demonstrated numerous correlations between hormone levels, mood and psycho-physical performance. A relationship was found between task performance and early education about menstruation. Studied of the kind reported here provide a basis on which to formulate new questions about causal influences, which can only be established by entirely different methods of study.

Attitude to Health↗