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Biomedical subjects

R J Adams

Publications and source records attributed to R J Adams.

At least 73 records · Page 4Linked to original sources
PubMed1996

Metaphase spindles rotate in the neuroepithelium of rat cerebral cortex.

Time-lapse confocal microscopy has been used to image cells in mitosis at the apical surface of neuroepithelium from the rat cerebral cortex during the period of neurogenesis. Staining with vital chromatin dyes reveals that mitotic spindles that are aligned parallel to the surface of the tissue are highly motile, rotating within the plane of the epithelium throughout metaphase, and come to rest only as anaphase begins. Spindles may make several complete turns, parallel to the epithelium, but only rarely tumble into an orientation perpendicular to the epithelial sheet. Analysis shows that spindles do not rotate randomly; rather, they spend most of their time aligned parallel or antiparallel to the direction in which they will later enter anaphase and undergo cell division. This conclusion is strongly supported by statistical analyses of the data. Stereotyped movements of this kind show that the direction of division is determined early in mitosis. This suggests the existence of intracellular and perhaps intercellular signals that define the polarity of the cell both in the apico-basal direction and within the plane of the epithelium. Such mechanisms may be important for maintaining the structure of the epithelium and cell-cell communication during development and may also provide a mechanism for the precise distribution of cytoplasmic determinants that might influence the fate of the daughter cells at a time when neuronal fate is being determined.

Animals↗
PubMed1996

Infant peripheral vision: the development of monocular visual acuity in the first 3 months of postnatal life.

Quantitative data on the early morphological development of the human retina show that the peripheral region is relatively more mature than the central region. These results have stimulated researchers to compare the development of visual functions in the central and peripheral regions of the visual field. Here, we used preferential looking to evaluate 1-, 2- and 3-month-old infants' central and peripheral (10 degrees and 30 degrees) monocular visual acuity. There were three findings: (i) both central and peripheral acuities were poor at 1 month, improved over the age range tested, but were still about 3 octaves worse than adults' acuity; (ii) at all ages monocular acuity decreased with increasing eccentricity; (iii) 2- and 3-month-olds showed higher acuity for gratings in the temporal than in the nasal visual field at 30 degrees. The implications of these results for issues in visual development are discussed.

Adult↗
PubMed1996

Monocular contrast sensitivity in 3- to 36-month-old human infants.

A recently developed psychophysical "card" technique was used to evaluate monocular contrast sensitivity in ninety 3-, 6-, 12-, 24-, and 36-month-old human infants. Results showed that for 3-, 6-, 24-, and 36-month-olds, monocular contrast sensitivity functions were very similar to binocular contrast sensitivity functions estimated in a previous experiment. However, at 12-months, monocular contrast sensitivity functions were significantly lower (about 1 octave) than binocular contrast sensitivity functions, a trend also observed in developmental studies of visual acuity. This asymmetry suggests that the neural substrate underlying the development of monocular and binocular spatial vision undergoes different rates of development, at least during the months surrounding the end of the first postnatal year.

Aging↗
PubMed1996

Stroke in children and young adults.

This selective review of stroke in children and young adults addresses: (1) stroke in sickle cell disease, particularly the prognostic use of transcranial Doppler, (2) oral contraceptives as a stroke risk factor, (3) stroke in pregnancy, and (4) the prognosis of ischemic stroke in young adults. Factors relevant to the primary prevention and outcome of stroke are emphasized.

Adolescent↗
PubMed1995

Further exploration of human neonatal chromatic-achromatic discrimination.

Newborn (n = 140) and 1-month-old (n = 120) human infants were habituated to achromatic ("white") squares of varying luminance (.35 to 1.16 log cd/m2) and then tested for recovery of habituation with chromatic stimuli from particular spectral locations. Results showed that newborns appear to discriminate 32 degrees yellow-green (dominant lambda = 565 nm) from white, but not 16 degrees or 32 degrees blue (450 nm), 16 degrees blue-green (493 nm), 16 degrees or 32 degrees yellow-green (572 nm), or 16 degrees purple from white. Performance of 1-month-olds was marginally better than that of newborns. Combined with our previous results with the habituation method, these data imply that newborns show little ability to make any chromatic-achromatic discriminations when stimulus size is smaller than 8 degrees, and that even with very large stimuli (e.g. 32 degrees) performance is relatively poor in the blue and yellow-green spectral regions. Although several models were considered, these limitations in the short- and mid-wavelength regions may best be accounted for by the argument that young infants possess general rather than selective immaturities or inefficiencies within their chromatic mechanisms.

Child Development↗
PubMed1995

Development of chromatic discrimination in early infancy.

Combining a habituation-recovery paradigm with procedures to minimize brightness cues, we evaluated 1-3-month-olds' ability to discriminate among broadband mid- and long-wavelength stimuli. One-month olds showed evidence of discriminating a red (dominant lambda = 650 nm) from green (dominant lambda = 545 nm) but failed to discriminate either of these from a yellow (dominant lambda = 585 nm). At 2 months, infants showed evidence of discriminating 545-nm green from 585-nm yellow, but only at 3 months do they appear to discriminate 650-nm red from the yellow. Consistent with previous work, these data imply that chromatic discrimination emerges slowly over the first three postnatal months. Moreover, the developmental pattern is consistent with the notion that early human vision is limited by general rather than selective immaturities within the requisite retinal and neural mechanisms.

Color Perception↗
PubMed1995

Risk of recurrent stroke in patients with sickle cell disease treated with erythrocyte transfusions.

OBJECTIVE: To determine the effect of a transfusion program on risk of stroke recurrence in children with sickle cell disease. DESIGN: The clinical course and experience with transfusion therapy at eight centers were reviewed for subjects whose initial stroke occurred after January 1988. RESULTS: Sixty subjects were observed for 191.7 patient-years. Eight had a single recurrent stroke (two intracranial hemorrhages and six infarctions) for a prevalence of 13.3%, or one recurrence for each 24 patient-years of observation. Thirteen subjects had 15 transient neurologic events; two of these had subsequent strokes, but the overall risk was similar for those who did and those did not have transient events. Hemoglobin S levels were greater than the desired maximum of 30% at the time of 7 of 16 transient events and five of six recurrent infarctions. The stroke recurrence rate was similar to those in previous reports of children receiving long-term transfusion therapy but significantly less than that reported for children who did not receive transfusions (p < 0.001). CONCLUSIONS: We conclude that maintenance of hemoglobin S at a level less than 30% appears to be effective in reducing the rate of recurrent infarction but does not prevent transient neurologic events. Transient neurologic events are common but do not appear to be related to recurrent stroke.

Adolescent↗
PubMed1995

Bile acid dysfunction after clam enterocystoplasty.

OBJECTIVE: To determine if the bowel dysfunction that develops in approximately 12% of patients after a clam enterocystoplasty is due to disruption of the enterohepatic circulation of bile acids. PATIENTS AND METHODS: Fourteen symptomatic patients (mean age 36 years, range 21-65) who had undergone clam enterocystoplasty were investigated by bowel frequency charts, hydrogen breath tests of expired air and the retention of radioactive 75Se-labelled homocholic acid-taurine (SeHCAT), a synthetic bile acid. Patients with abnormal results were commenced on anion-exchange resins and the symptoms evaluated 6 weeks later. RESULTS: The interruption of bile acid circulation, as estimated by SeHCAT, occurred in most of the patients studied and was due to surgical resection of the terminal ileum. All hydrogen breath tests were normal, excluding bacterial overgrowth as a cause of diarrhoea. Bowel frequency correlated well with the percentage of SeHCAT retained. Anion-exchange resins were successful in relieving the symptoms if patients complied well with the treatment. CONCLUSIONS: After clam enterocystoplasty, some patients have bowel dysfunction caused by the interruption of the enterohepatic circulation of bile acids. These patients can be identified using bowel frequency charts and treated by anion-exchange resins.

Adult↗
PubMed1995

Management issues for patients with ischemic stroke.

This review briefly summarizes the acute management of cerebral infarction and cardiac comorbidity in patients with stroke, with a focus on more general aspects of care. Important aspects of the acute management of cerebral infarction are its prompt recognition, use of appropriate emergency medical services, including 911, initial treatment, and prevention of complications. Secondary prevention begins with the diagnostic workup for the cause of the initial stroke. Although the optimal workup depends on the patient, a minimal workup consists of a history and physical examination sufficient to establish vascular risk factors and the neurologic and medical status of the patient, basic laboratory tests, ECG, chest x-ray, cranial CT, evaluation of carotid arteries, and a search for cardiac sources and the presence of atrial fibrillation. Further workup may include a search for coagulopathies, less common sources of embolism, and intracranial intravascular disease. Better education of patients at risk of vital importance. Patients with cerebral infarction share vascular risk factors with those who have coronary disease, and the presence of both coronary and cerebrovascular disease is highly likely. The likelihood of finding coronary artery disease in patients with transient ischemic attack and ischemic stroke with noninvasive testing, as well as management recommendations for these patients are reviewed.

Brain Ischemia↗
PubMed1994

Pathogenesis of SIVmac infection in Chinese and Indian rhesus macaques: effects of splenectomy on virus burden.

The spleen and lymph nodes are the predominant sites of viral replication in SIV and HIV infections. We studied splenectomized and control unsplenectomized rhesus macaques of both the Indian and the Chinese subspecies of Macaca mulatta. All animals were inoculated with SIVmac239, a molecularly cloned strain of SIV. Our data showed: (1) splenectomized animals, particularly among the Indian subspecies, had a lower virus burden and longer survival than unsplenectomized controls, (2) the Chinese macaques controlled virus replication more effectively than did the Indian animals, and (3) that a higher infectious virus burden was present in LN/spleen than in blood in both splenectomized and control animals.

Animals↗
PubMed1994

Alpha thalassemia and stroke risk in sickle cell anemia.

In an effort to identify possible risk factors for stroke in Sickle Cell Anemia (Hb SS), we analyzed the distribution of alpha-globin gene deletions in a group of Hb SS patients with and without stroke. The group with stroke consisted of 44 patients, (27 male, 17 female) with a mean of 7.5 years at time of stroke. The control group (non-stroke) had 256 Hb SS patients (126 male, 130 female) with a mean age of 7.7 years. There were 9 patients with heterozygous alpha-thalassemia in the stroke group (20.5%). In the control group, there were 93 patients with heterozygous alpha-thalassemia and 5 with homozygous alpha-thalassemia. The incidence of alpha-thalassemia in Hb SS patients without stroke (38%) was comparable to that reported for the African-American population in general. The incidence in the stroke population (20.5%) was significantly lower (P = 0.02) These results indicate that alpha-thalassemia is associated with a lower risk of stroke in Hb SS. This observation should be confirmed in studies involving larger numbers of patients. Possible protective effects of alpha-thalassemia are unknown but may be related to decreased hemolysis and more favorable rheologic properties of red blood cells.

Adolescent↗
PubMed1994

Intracerebral infusion of TNF-alpha and IL-6 failed to activate latent SIV infection in the brains of macaques inoculated with macrophage-tropic neuroadapted SIVmac.

Lymphocyte-tropic (L-tropic) SIVmac predictably causes immunosuppression and AIDS in rhesus macaques. SIV encephalitis, on the other hand, is caused mainly by macrophage-tropic (M-tropic) SIVmac. We have previously described the derivation of M-tropic, neuroadapted SIVmac from molecularly cloned, L-tropic SIVmac239. In this report we show that inoculation of four macaques with neuroadapted virus resulted in L-tropic SIVmac-related diseases in all four but neurological disease in only two of the four animals. Because cocultivation of infected macrophages with CD4+ lymphocytes results in production of tumor necrosis factor alpha and interleukin-6, we asked whether infiltration of supernatant fluids containing these cytokines into the brains of macaques infected with neuroadapted virus would enhance the development of neurological disease. These procedures failed to promote productive virus replication in the brain. Thus, although different degrees of immunosuppression and AIDS could be induced predictably with L-tropic virus, induction of neurological disease was not predictable even when animals were inoculated with neuroadapted M-tropic virus and inflammatory cytokines were infiltrated into the brains of these animals.

Animals↗
PubMed1994

Systematic measurement of human neonatal color vision.

We used a new time-efficient method to evaluate chromatic-achromatic discrimination in newborn (n = 36) and 1-month-old (n = 34) human infants. Results showed that 74% of newborns discriminated a 10.5 x 17.5 deg broadband red patch from all relative luminances of an achromatic background, but only 14% of newborns did so with a blue, 36% with a green, and 25% with a yellow patch. Most infants who "failed" did so at relative luminances very close to the respective photopic luminance match. At 1 month, performance improved somewhat although infants still show clear evidence of discriminating only the red patch. These results, the first to be obtained from individual newborns with a method incorporating a systematic variation of luminance, imply that early color vision is very limited. Possible photoreceptoral and neural bases for these immaturities are discussed.

Child Development↗
PubMed1994

Mutations at the PAX6 locus are found in heterogeneous anterior segment malformations including Peters' anomaly.

Mutation or deletion of the PAX6 gene underlies many cases of aniridia. Three lines of evidence now converge to implicate PAX6 more widely in anterior segment malformations including Peters' anomaly. First, a child with Peters' anomaly is deleted for one copy of PAX6. Second, affected members of a family with dominantly inherited anterior segment malformations, including Peters' anomaly are heterozygous for an R26G mutation in the PAX6 paired box. Third, a proportion of Sey/+ Smalleye mice, heterozygous for a nonsense mutation in murine Pax-6, have an ocular phenotype resembling Peters' anomaly. We therefore propose that a variety of anterior segment anomalies may be associated with PAX6 mutations.

Amino Acid Sequence↗