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S M Sykes

Publications and source records attributed to S M Sykes.

11 recordsLinked to original sources
PubMed1999

Medullary lateral tegmental field: an important synaptic relay in the baroreceptor reflex pathway of the cat.

This study was designed to test the hypothesis that the medullary lateral tegmental field (LTF) is an important synaptic relay in the baroreceptor reflex pathway controlling sympathetic nerve discharge (SND) of urethan-anesthetized cats. We determined the effects of blockade of excitatory amino acid-mediated neurotransmission in the LTF on three indexes of baroreceptor reflex function: cardiac-related power in SND, strength of linear correlation (coherence value) of SND to the arterial pulse (AP), and inhibition of SND during increased arterial pressure produced by abrupt obstruction of the abdominal aorta. Bilateral microinjection of D-(-)-2-amino-5-phosphonopentanoic acid, an N-methyl-D-aspartate (NMDA) receptor antagonist, abolished cardiac-related power and coherence of SND to the AP, and it prevented inhibition of SND during aortic obstruction. These data support the view that NMDA receptor-mediated neurotransmission in the LTF is critical for baroreceptor reflex control of SND. Bilateral microinjection of 1,2, 3,4-tetrahydro-6-nitro-2,3-dioxobenzo-[f]-quinoxaline-7-sulfonamid e, a non-NMDA receptor antagonist, decreased cardiac-related power and total power in the 0- to 6-Hz band of SND; however, the AP-SND coherence value remained high, and inhibition of SND during aortic obstruction was preserved. These data imply that non-NMDA receptor-mediated neurotransmission in the LTF is involved in setting the level of excitatory drive to sympathetic nerves.

2-Amino-5-phosphonovalerate↗
PubMed1997

The complete genome sequence of the hyperthermophilic, sulphate-reducing archaeon Archaeoglobus fulgidus.

Archaeoglobus fulgidus is the first sulphur-metabolizing organism to have its genome sequence determined. Its genome of 2,178,400 base pairs contains 2,436 open reading frames (ORFs). The information processing systems and the biosynthetic pathways for essential components (nucleotides, amino acids and cofactors) have extensive correlation with their counterparts in the archaeon Methanococcus jannaschii. The genomes of these two Archaea indicate dramatic differences in the way these organisms sense their environment, perform regulatory and transport functions, and gain energy. In contrast to M. jannaschii, A. fulgidus has fewer restriction-modification systems, and none of its genes appears to contain inteins. A quarter (651 ORFs) of the A. fulgidus genome encodes functionally uncharacterized yet conserved proteins, two-thirds of which are shared with M. jannaschii (428 ORFs). Another quarter of the genome encodes new proteins indicating substantial archaeal gene diversity.

Archaeoglobus fulgidus↗
PubMed1992

Photoaging effects on spectral transmittance of plastic filters.

We examined the effects of ultraviolet (UV) radiation in combination with high levels of infrared (IR) radiation on the spectral transmittance of plastic filters. The biological action spectrum for damage to the human eye and skin changes dramatically in the 300-400 nm wavelength range. Cut-off filters used in this region to shape the spectrum of exposure sources are thus critical to the design of experiments which use broadband light sources. The changes in transmittance of three types of plastic filters were observed over an exposure period of 1000 h. One set of three filters was exposed mainly to UV radiation, while the other set was exposed to UV radiation plus IR radiation. Filters exposed to both UV and IR radiation showed spectral changes in their transmittance, while the filters exposed to UV only showed no measurable changes.

Eye↗
PubMed1984

Recovery of absolute threshold with UVA-induced retinal damage.

A within-trial psychophysical procedure tracked the initial loss and subsequent recovery of visual thresholds in albino rats exposed to ultraviolet light at 350 nanometers and 0.4 milliwatts per square centimeter. Absolute thresholds increased up to 5 log units immediately following the 15 hour ultraviolet exposure, with a daily recovery of 1-2 log to asymptotic thresholds over a 7-day post-exposure period. The corresponding retinal damage on Day 1 included extensive vesiculation of the photoreceptor outer segments, vacuolation of the inner segments, and pyknosis of cell nuclei. The total number of photoreceptor nuclei and outer segments was unchanged relative to control eyes through post-exposure Day 3. Both nuclei and outer segment counts then consistently decreased 15-20 percent between Days 3-7. The two-stage loss of photoreceptors but daily recovery of absolute thresholds again suggests a significant dissociation of retinal structure and psychophysical function in light-induced ocular pathology.

Animals↗
PubMed1983

Changes in absolute threshold with light-induced retinal damage.

Albino rats were trained on a mixed signalled reinforcement procedure designed to yield repeated absolute visual thresholds within each session. After threshold stability animals were exposed 12 hours per night to 1000 lux of light froma cool-white fluorescent source. Log threshold rose as an approximate linear function of exposure time to a maximum of 2.0 log units above baseline after 36 cumulative hours of exposure. Light and electron microscopic analysis of the irradiated retinas revealed vesiculated photoreceptor outer segments, with varying degrees of vacuolation of the inner segments and pyknosis of photoreceptor nuclei depending on exposure time. The various combinations of retinal pathology suggests that damage to photoreceptor outer segments and inner segments interact to jointly affect psychophysical thresholds in light-induced retinal damage.

Animals↗
PubMed1982

Control of wheel running by near-ultraviolet light.

Wheel running by mice was compared during incandescent and incandescent plus near-ultraviolet (UV) illumination in three experiments. During the daily 12-hour light period, running rates decreased with supplemental UV compared to previous incandescent only baselines. The decrements were systematically replicated in a second experiment using alternating UV exposure and recovery phases programmed across blocks of sessions. Again, running rates consistently decreased with supplemental UV irradiation of phases two and four compared to preceding baselines of phases one and three. In comparison, running rates were inconsistently affected during the 12-hour dark period in both experiments. A third experiment compared the relative decremental effects of UV, blue and red illumination. Baseline running rates monotonically decreased as an inverse function of wavelength for all subjects. The data suggest that the spectral composition of ambient illumination may affect behavior.

Animals↗
PubMed1981

Damage to the monkey retina by broad-spectrum fluorescent light.

Adult rhesus and pigtail monkeys were exposed to a uniform field of light from daylight fluorescent lamps to determine the initial site and characteristics of structural retinal damage induced by continuous exposure and the threshold intensity required to produce the effects. Electron microscopic examination revealed that the initial site of damage is the photoreceptor outer segments. Damage remained restricted to the outer segments at intensities as high as 24,700 lux and with 12 hr exposure periods repeated for up to 4 days. Rods were swollen at the distal tip and showed disc membrane separation. Come outer segments were affected at the proximal end with vesiculation and membrane rearrangement. The threshold intensity for morphological changes to comes in the macula for a single 12 hr exposure was between 195 and 361 mu W/cm2 at the retina (400 to 700 mm; uncorrected for ocular transmittance), whereas the threshold for changes in rods was higher, at between 361 and 615 mu W/cm2. These levels correspond to between 5900 and 10,800 lux (550 to 1000 ft-cd) for comes and 10,800 to 19,400 lux (1000 to 1800 ft-cd) for rods of monkeys with fully dilated pupils. The paramacular areas of the retina were less sensitive to damage than macular areas of the same animal. No paramacular changes were observed in animals exposed to 10,800 lux or less. The patched (control) eyes of each monkey remained structurally normal in both the macula and paramacula at all exposure levels. These results demonstrate the sensitivity of the adult primate retina to damage by relatively moderate levels of light.

Animals↗