Imaging of small-scale features on 433 Eros from NEAR: evidence for a complex regolith.

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

NEAR at eros: imaging and spectral results

Eros is a very elongated (34 kilometers by 11 kilometers by 11 kilometers) asteroid, most of the surface of which is saturated with craters smaller than 1 kilometer in diameter. The largest crater is 5.5 kilometers across, but there is a 10-kilometer saddle-like depression with attributes of a large degraded crater. Surface lineations, both grooves and ridges, are prominent on Eros; some probably exploit planes of weakness produced by collisions on Eros and/or its parent body. Ejecta blocks (30 to 100 meters across) are abundant but not uniformly distributed over the surface. Albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith. On scales of 200 meters to 1 kilometer, Eros is more bland in terms of color variations than Gaspra or Ida. Spectra (800 to 2500 nanometers) are consistent with an ordinary chondrite composition for which the measured mean density of 2.67 +/- 0.1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent.

Imaging of asteroid 433 eros during NEAR's flyby reconnaissance

During the 23 December 1998 flyby of asteroid 433 Eros, the Near-Earth Asteroid Rendezvous (NEAR) spacecraft obtained 222 images of Eros, as well as supporting spectral observations. The images cover slightly more than two-thirds of Eros (best resolution is approximately 400 meters per pixel) and reveal an elongated, cratered body with a linear feature extending for at least 20 kilometers. Our observations show that Eros has dimensions of 33 x 13 x 13 kilometers. The volume, combined with the mass determined by the NEAR radio science experiment, leads to a density of 2.5 +/- 0.8 grams per cubic centimeter. This relatively high density, and the presence of an extensive linear feature, suggest that Eros may be a structurally coherent body.

Quantitative analysis of yeast gene function using competition experiments in continuous culture.

One possible route to the evaluation of gene function is a quantitative approach based on the concepts of metabolic control analysis (MCA). An important first step in such an analysis is to determine the effect of deleting individual genes on the growth rate (or fitness) of S. cerevisiae. Since the specific growth-rate effects of most genes are likely to be small, we employed competition experiments in chemostat culture to measure the proportion of deletion mutants relative to that of a standard strain by using a quantitative PCR method. In this paper, we show that both densitometry and GeneScan analysis can be used with similar accuracy and reproducibility to determine the proportions of (at least) two strains simultaneously, in the range 10-90% of the total cell population. Furthermore, we report on a model competition experiment between two diploid nuclear petite mutants, homozygous for deletions in the cox5a or pet191 genes, and the standard strain (ho::kanMX4/ho::kanMX4) in chemostat cultures under six different physiological conditions. The results indicate that competition experiments is continuous culture are a suitable method to distinguish quantitatively between deletion mutants that qualitatively exhibit the same phenotype.

NEAR's flyby of 253 mathilde: images of a C asteroid

On 27 June 1997, the Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 1212 kilometers of asteroid 253 Mathilde. Mathilde is an irregular, heavily cratered body measuring 66 kilometers by 48 kilometers by 46 kilometers. The asteroid's surface is dark (estimated albedo between 0.035 and 0.050) and similar in color to some CM carbonaceous chondrites. No albedo or color variations were detected. The volume derived from the images and the mass from Doppler tracking of the spacecraft yield a mean density of 1.3 +/- 0.2 grams per cubic centimeter, about half that of CM chondrites, indicating a porous interior structure.

Depression and multiple sclerosis.

The objective of the present study were (1) to ascertain the lifetime risk of a depression in a representative group of multiple sclerosis (MS) patients, (2) to assess the morbidity risks for depression among first-degree relatives of these MS patients, and (3) to compare these familial risks for first-degree relatives of MS patients with those for first-degree relatives of a primary depression population, i.e., depression but no MS. We psychiatrically evaluated 221 MS patients (index cases) using a structured clinical interview for the DSM-III-R and calculated the rate and lifetime risk of depression for these index cases using the product limit estimate of survival function. We obtained psychiatric histories for all first-degree relatives of index cases, and we calculated morbidity risks for depression for these relatives using the maximum likelihood approach and compared the risks using the likelihood ratio tests. Index cases had a 50.3% lifetime risk of depression. Morbidity risks for depression among first-degree relatives of index cases were decidedly lower when compared with morbidity risks among first-degree relatives of the reference population. Although there appears to be a very high rate of depression among MS patients, the data for their first-degree relatives do not support a clear genetic basis for this depression, or at least the same genetic basis that probably operates within families when depression occurs in the absence of MS.

Presynaptic inhibition of soleus Ia afferent terminals in Parkinson's disease.

The possible role of changes in presynaptic inhibition of muscle spindle primary afferent terminals in Parkinson's disease was investigated. The pathway from tibialis anterior Ia afferents to soleus Ia terminals was assessed in 20 patients with Parkinson's disease and in 17 age matched controls, both at rest and during maintenance of tonic plantar flexing torques about the ankle. At all torques less presynaptic inhibition was present in the patients with Parkinson's disease than in the controls. The difference was significant at rest (p < 0.03) and at 2 Nm (p < 0.05) but not at 5 Nm and 7 Nm torque. The amount of presynaptic inhibition did not change with torque in either group. The observed alteration in presynaptic inhibition in Parkinson's disease is likely to make only a small contribution to the rigidity and impaired movement control.

Pregnancy and multiple sclerosis. A prospective study.

OBJECTIVE: To conduct a prospective assessment of pregnancy on women with multiple sclerosis (MS), focusing on pregnancy outcome and relapses during gestation and up to 6 months after delivery. DESIGN: Expected numbers of relapses were based on data for (1) "self-controls": the mothers ("cases") themselves prior to becoming pregnant and (2) "matched controls": female patients with MS "matched" to the mothers for year of birth, age of MS onset, MS type, MS course, and initial MS symptom(s). SETTING: Cases and controls were identified from an ambulatory care MS clinic that serves the province of British Columbia, Canada. PATIENTS OR OTHER PARTICIPANTS: Women with a diagnosis of MS who attended the MS clinic during 1982 through 1986 and subsequently became pregnant during 1982 through 1989 inclusive were included in this study as cases. Matched controls were women with MS who attended the MS clinic during the same period but did not become pregnant. RESULTS: No significant increase in relapse rate was found for cases during the first two trimesters of gestation. The number of relapses was significantly less than expected during the third trimester compared with matched controls (chi 2 = 6.80, df = 1, P < .02), but not compared with self-controls (chi 2 = 3.39, df = 1, P > .05). The observed number of relapses for the 6 months after delivery did not differ significantly from expected (self-controls: chi 2 = 2.84, df = 2, P > .05; matched controls: chi 2 = 1.76, df = 2, P > .05). CONCLUSION: These data suggest that neither pregnancy nor the 6-month period after delivery is a risk factor for relapse in MS. They are consistent with previous observations that, in the long term, pregnancy does not influence subsequent MS disability.

Responses to preferred intensities of exertion in men differing in activity levels.

We compared ratings of perceived exertion (RPE), state anxiety, percentage of peak oxygen uptake (% VO2peak), percentage of ventilatory threshold (% Tvent), and blood lactate concentration [HLa] in 11 high-active and 12 low-active men (23 +/- 3 yr) at self-selected power outputs during 20 min of cycling. The high-active group selected higher power outputs than did the low-active group, but % VO2peak and % Tvent were lower for the high-active subjects during the initial 5-10 min of cycling. Both groups reported increased RPE across time, but contrary to past studies of load-incremented cycling, RPE was identical for the groups despite their differences in relative intensity. No differences were found for [HLa] or state anxiety during cycling. The groups did not differ on exertional symptoms, but the high-active subjects reported a significant reduction in state anxiety immediately after cycling. A preferred exertion protocol provides an alternative approach to identifying influences on perceived exertion during prolonged exercise. The influence of physical activity history/status on the association between the concomitant pattern of self-selected power outputs and postexercise anxiety reduction merits study.

The impact of blinding on the results of a randomized, placebo-controlled multiple sclerosis clinical trial.

In the randomized, placebo-controlled, physician-blinded Canadian cooperative trial of cyclophosphamide and plasma exchange, neither active treatment regimens (group I: i.v. cyclophosphamide and prednisone; group II: weekly plasma exchange, oral cyclophosphamide, and prednisone) were superior to placebo (group III: sham plasma exchange and placebo medications) using the blinded, evaluating neurologists' assessments of disease course (primary analysis). All patients were examined by both a blinded and an unblinded neurologist at each assessment in this trial. We compared the blinded and unblinded neurologists' judgment of treatment response and analyzed the clinical behavior of patients who correctly guessed their treatment. The unblinded (but not the blinded) neurologists' scores demonstrated an apparent treatment benefit at 6, 12, and 24 months for the group II patients (not group I or placebo; p < 0.05, two-tailed). There were no significant differences in the time to treatment failure or in the proportions of patients improved, stable, or worse between the group II and group III patients who correctly guessed their treatment assignments and those who did not. Physician blinding prevented an erroneous conclusion about treatment efficacy (false positive, type 1 error).

The effect of age and voluntary contraction on presynaptic inhibition of soleus muscle Ia afferent terminals in man.

Transmission in a pathway mediating presynaptic inhibition of soleus Ia afferent terminals was assessed from the reduction of soleus muscle H reflex amplitude brought about by a short conditioning vibration pulse applied to the anterior tibialis muscle. In a group of young subjects (aged between 21 and 37 years) the mean reduction in reflex size with the limb relaxed was to 29.2% of control, whereas in a group of older subjects (aged between 59 and 74 years) the reduction was significantly less, to 55.0% of control (P < 0.001, Student's t test). In the younger group the amount of presynaptic inhibition elicited was inversely related to the plantar-flexor torque produced by tonic contraction of gastrocnemius-soleus; often at higher torques no reduction in reflex size was seen. In contrast the older group showed only a slight reduction in presynaptic inhibition with increasing torque, so that at torques of 5 and 7 N m the amount of presynaptic inhibition elicited was similar in the younger and older groups. The older subjects were not able to sustain the higher torques produced by the younger subjects. These results suggest that the control of transmission in this spinal pathway changes with increasing age.

Protein disulfide isomerase is essential for viability in Saccharomyces cerevisiae.

Protein disulfide isomerase (PDI) is an enzyme involved in the catalysis of disulfide bond formation in secretory and cell-surface proteins. Using an oligodeoxyribonucleotide designed to detect the conserved 'thioredoxin-like' active site of vertebrate PDIs, we have isolated a gene encoding PDI from the lower eukaryote, Saccharomyces cerevisiae. The nucleotide sequence and deduced open reading frame of the cloned gene predict a 530-amino-acid (aa) protein of Mr 59,082 and a pI of 4.1, physical properties characteristic of mammalian PDIs. Furthermore, the aa sequence shows 30-32% identity with mammalian and avian PDI sequences and has a very similar overall organisation, namely the presence of two approx. 100-aa segments, each of which is repeated, with the most significant homologies to mammalian and avian PDIs being in the regions (a, a') that contain the conserved 'thioredoxin-like' active site. The N-terminal region has the characteristics of a cleavable secretory signal sequence and the C-terminal four aa (-His-Asp-Glu-Leu) are consistent with the protein being a component of the S. cerevisiae endoplasmic reticulum. Transformants carrying multiple copies of this gene (designated PDI1) have tenfold higher levels of PDI activity and overproduce a protein of the predicted Mr. The PDI1 gene is unique in the yeast genome and encodes a single 1.8-kb transcript that is not found in stationary phase cells. Disruption of the PDI1 gene is haplo-lethal indicating that the product of this gene is essential for viability.

The effect of dantrolene sodium on the discharge of alpha and gamma motoneurones to the soleus muscle in the decerebrate rat.

1. The effects of intravenous infusion of the direct acting muscle relaxant, dantrolene sodium (5 mg kg-1), on tension, integrated EMG, soleus muscle motor unit discharge frequency and gamma nerve fibre discharge were measured in the decerebrate rat. 2. Dantrolene sodium did not have any detectable direct effect upon the discharge of the gamma nerve fibres. 3. The soleus muscle of the decerebrate preparations exhibited spontaneous tension and reflex responses. 4. With the muscle held at constant length, dantrolene sodium caused an increase in the integrated EMG in 15 out of 18 experiments and a decrease in muscle tension in 15 out of 17. The results from these experiments showed great variability. 5. Dantrolene sodium caused a slight reduction in the tension response to tonic stretch; this was accompanied by an increase in the integrated EMG. 6. Dantrolene sodium also caused a shift in the relationship between tension and integrated EMG during the phasic component of the stretch reflex, with a greater integrated EMG being associated with a reduced tension. 7. Motor unit discharge frequencies were found to increase but not sufficiently to overcome the action of dantrolene sodium. It is concluded that motor unit recruitment must play an important role in the compensation for the muscle weakening action of dantrolene sodium.

Phenotypic and genetic characterization of mutations in the spoIVC locus of Bacillus subtilis.

The spoIVC locus of Bacillus subtilis was analysed. Fourteen spoIVC mutants isolated following nitrosoguanidine mutagenesis were used along with two previously characterized spoIVC mutants to construct a fine structure genetic map of the locus. The recombination index (RI) measured between extreme mutations was 0.26; no recombination could be detected between four of the mutations. Complementation analysis showed that all the mutations fall into two cistrons. The RI between extreme mutations in cistron A was about 0.17 and that between extreme mutations in cistron B was about 0.05. In respect of biochemical markers, the spoIVC mutations all produced similar phenotypes, irrespective of their location. However, in both cistrons oligosporogenous and asporogenous mutations mapped close together.

Direct bonding comparing a polyacrylic acid and a phosphoric acid technique.

The purpose of this study was to compare in vitro a polyacrylic acid technique (crystal bonding) with a conventional phosphoric acid-etch technique for the preparation of teeth for bonding. The potential value of the polyacrylic acid technique was evaluated for bond strength, enamel loss, cleanup, and fracture location--with and without the use of a sealant. Ninety-six premolars were evenly divided into two groups. Group A was preconditioned with polyacrylic acid and group B with phosphoric acid. Half of each group was treated with a sealant before direct bonding of orthodontic brackets. Sealant was not used on the other half of each group and brackets were bonded directly to the conditioned labial surfaces with a composite cement. Bonding and rebonding shear strength tests were carried out for both groups. Results indicated that shear bond strength values for the polyacrylic acid group were approximately one third those of the phosphoric acid group using a composite cement as the adhesive. Enamel loss was measured on the lingual surfaces of 30 of the 96 premolars. The lingual surfaces were conditioned with polyacrylic acid. Following debonding and cleanup procedures, the polyacrylic acid treated surface was left slightly pitted with no resin tags remaining. Cleanup procedures required only a rubber-cup silicate prophylaxis. The total enamel loss was minimal (4.5 micron), thus preserving most of the outermost fluoride-rich layer of enamel.

How is ventilation maintained in the presence of the muscle relaxant, dantrolene sodium? A study in the anaesthetized rat.

The effects of intravenous injection of the muscle relaxant dantrolene sodium on ventilation, integrated EMG of external intercostal muscles and motor unit discharge in these muscles were measured in anaesthetized rats. Dantrolene sodium was administered in a carrier solution at pH 10. The carrier was not responsible for the effects seen on dantrolene sodium infusion. Dantrolene sodium (5 mg kg-1 body weight) reduced inspired ventilation (VI) on average from 308 +/- 106 ml min-1 (s.d., n = 8) in the control period to 247 +/- 118 ml min-1 (n = 8) after dantrolene sodium. Expired ventilation was reduced likewise from 274 +/- 132 ml min-1 (n = 8) to 229 +/- 109 ml min-1 (n = 8). These changes are significant at P less than 0.05. The integrated EMG was increased by 40.0 +/- 29.3% (n = 9), a change significant at P less than 0.001. Dantrolene sodium not only decreased the mean interspike interval of individual motor units by 16.2 +/- 11.1% (n = 13), a change significant at P less than 0.001, but also increased the duration of the burst of activity of each individual motor unit on average by 36.2 +/- 52.4% (n = 13), a change significant at P less than 0.05. The recruitment of additional motor units was also effected by dantrolene sodium. These units did not behave in any noticeably different manner from units previously active. It is concluded that the nervous system compensates for the effect of dantrolene sodium only to a limited extent by increasing the frequency of discharge of active motor units. Recruitment ofadditional motor units and increased burst duration play at least as important a role.