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Biomedical subjects

L E Wright

Publications and source records attributed to L E Wright.

18 recordsLinked to original sources
PubMed1998

Stable carbon and oxygen isotopes in human tooth enamel: identifying breastfeeding and weaning in prehistory.

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used delta13C to document the introduction of solid foods to infant diets and delta18O to monitor the decline of breastfeeding. We report enamel carbonate delta13C and delta18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO2 liberated by reaction of enamel with H3PO4 in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in 13C and more depleted in 18O than teeth developing at younger ages. Premolars average 0.5/1000 [corrected] higher in delta13C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the delta13C in childhood diets did not change systematically. First molars and premolars are similar in delta18O, but third molars average 0.7/1000 [corrected] lower than first molars (P = 0.0001) and 0.5/1000 [corrected] lower than premolars (P = 0.0003). First molar and premolar delta18O is heavier, because breast milk is more enriched in 18O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later.

Adult↗
PubMed1997

Intertooth patterns of hypoplasia expression: implications for childhood health in the classic Maya collapse.

Enamel hypoplasias, which record interacting stresses of nutrition and illness during the period of tooth formation, are a key tool in the study of childhood health in prehistory. But interpretation of the age of peak morbidity is complicated by differences in susceptibility to stress both between tooth positions and within a single tooth. Here, hypoplasias are used to evaluate the prevailing ecological model for the collapse of Classic Period Lowland Maya civilization, circa AD 900. Hypoplasias were recorded in the full dentition of 160 adult skeletons from six archaeological sites in the Pasion River region of Guatemala. Instead of constructing a composite scale of stress experience, teeth are considered separately by position in the analysis. No statistical differences are found in the proportion of teeth affected by hypoplasia between "Early," Late Classic, and Terminal Classic Periods for anterior teeth considered to be most susceptible to stress, indicating stability in the overall stress loads affecting children of the three chronological periods. However, hypoplasia trends in posterior teeth may imply a change in the ontogenetic-timing of more severe stress episodes during the final occupation and perhaps herald a shift in child-care practices. These results provide little support for the ecological model of collapse but do call to attention the potential of posterior teeth to reveal subtle changes in childhood morbidity when consideredindividually.

Age Determination by Teeth↗
PubMed1995

Nonlinearity in the relationship between bone Sr/Ca and diet: paleodietary implications.

Strontium in archaeological human bones is widely, almost paradigmatically, used as a measure of the relative dietary abundances of plants and meat. Quantitative modeling reveals, however, that there is not a simple proportional relationship between bone strontium and the dietary plant/meat ratio. While knowledge of specific foods and their compositions may permit accurate calculation of average bone strontium levels, knowledge of bone strontium does not inversely allow accurate calculation of specific foods. Although bone strontium quantitatively reflects the average dietary Sr/Ca ratio, it is disproportionately sensitive to high-calcium foods and can be easily affected by minor dietary constituents and culinary practices. Bone strontium, and by analogy, barium, should be seen as a reflection of the high-mineral dietary components rather than a quantitative index of trophic position.

Animals↗
PubMed1982

Neurophysiological studies on superficial medullary chemosensitive area for respiration.

In cats anesthetized with chloralose-urethane (40 mg/kg chloralose; 200 mg/kg urethane) pH sensitivity of neurons in the caudal chemosensitive area on the ventrolateral surface of the medulla oblongata was examined while monitoring phrenic nerve activity simultaneously. pH was varied by superfusion of the ventral medullary surface with mock cerebrospinal fluid (CSF) of different pH (pH 7.4 control, 7.0 and 7.8). A total of 130 units from 21 cats changed their firing rate in response to CSF-pH changes. These were subdivided into 3 groups. In Group I, 31 respiratory pH sensitive units increased their firing rate in response to decreased mock CSF-pH, noxious pinch, joint movement in contralateral forelimb, and increased inspired CO2. These responses may have originated from respiratory center neurons. Group II consisted of 59 non-respiratory pH sensitive units whose firing rate changed in an inverse manner with CSF-pH changes. Of these, 30 responded to contralateral distal forelimb movement, 15 to hair manipulation, 9 to heavy pressure and 5 to noxious pinch. Increased inspired CO2 (rebreathing) did not modify activity. The response to pH is believed to be from non-specific neurons. Group III consisted of 40 non-respiratory pH sensitive units responding to CSF-pH changes and to increased inspired CO2. The firing rate was irregular, the interval distribution approaching an exponential function. It may be postulated that the impulse frequency of chemosensitive impulses may be irregular at the site of impulse generation, the irregularity decreasing by convergence during transmission to the respiratory centers. The time course of Group III chemosensitive units was similar to phrenic nerve responses.

Action Potentials↗
PubMed1976

Excitability and functional organization of cutaneous tactile units of the bullfrog (R. catesbeiana).

Frog skin touch receptors are discrete structures which appear as dome-shaped translucent elevations of the epidermis. These domes are particularly responsive to direct touch. Tactile stimulation of adjacent skin never caused impulse activity, except when the skin distortion disturbed the domes. On stimulation at threshold intensity, the response of all units studied always consisted of a single impulse whether the stimulus energy was electrical or mechanical. While most tactile units discharged one impulse upon application of mechanical stimulation, a few also discharged one impulse upon stimulus release (on-off response). No after discharge was seen at stimulus strengths of three or four times threshold or after repetitive stimulation at 1,000 pps. The range of distribution of active domes/receptive field was 1--14. Generally the most sensitive domes appeared to be in or near center field. Twice as many of the tactile units responded more readily to cold than to warmth. The impulse frequency of units responding to thermal stimulation ranged from 3-11/sec. The conduction velocity of tactile units measured was within a range of 9--25 m/sec, with a mean of 12 m/sec. The results suggest that the following: 1) the existence of discrete structures which respond to tactile stimuli; a phylogenetic relationship might be postulated; 2) cold/touch receptors which appear to be present in greater quantity in the frog's skin than are warm/touch receptors, 3) touch units which should be considered primarily as mechanoreceptors with a possible secondary function as thermoreceptors.

Animals↗
PubMed1976

Colonoscopy associated bacteremia.

Fifty-two patients undergoing uneventful diagnostic colonoscopy with or without polypectomy and biopsy were evaluated for evidence of bacteremia during and after the procedure. In only two instances was bacteremia noted. Positive findings were noted in patients with carcinomatosis and severe liver involvement. These data suggest that routine prophylactic antibiotic coverage is unnecessary in uncompromised patients. Further studies are warranted when patients have either severe liver involvement or impairment of normal host defense mechanisms.

Adult↗
PubMed1975

The adverse effect of chocolate on lower esophageal sphincter pressure.

Decreased lower esophageal sphincter (LES) pressure after ingestion of chocolate has been previously noted. We have further evaluated the effect of chocolate on the known ability of gastric alkalinization or bethanechol to increase LES tone. 9 normal subjects were studied using an infused open-tip recording system. Pressure was monitored for a 15-min basal period, and for 60 min after ingestion of 120 ml of chocolate syrup either alone or with the concurrent administration of commercial antacid, oral bethanechol, or subcutaneous bethanechol. After chocolate ingestion, mean basal LES pressure of 14.6 +/- 1.1 (+/-SEM) mm Hg decreased significantly (P less than 0.01) to 7.9 +/- 1.3 mm Hg. An identical LES response occurred when antacid was given with the chocolate dose. Oral bethanechol (25 mg) and chocolate together resulted in lesser decreases in LES pressure. Subcutaneous bethanechol (5 mg) and chocolate produced significant increases (P less than 0.05) in sphincter pressure, although of lesser magnitude than reported with bethanechol alone. These results indicate that the adverse effect of chocolate on the LES is not reversed by gastric alkalinization and suggest that bethanechol in sufficient dose may overcome chocolate-induced decreases in LES pressure.

Adult↗