Rebound Period Research Articles

Volcanic and tectonic processes coinciding with glaciation and crustal rebound: an early Holocene rhyolitic eruption in the Dyngjufjöll volcanic centre and the formation of the Askja caldera, north Iceland

A pronounced volcanic production maximum on the rift zones through Iceland coincided with rapid crustal rebound during and after glacier melting at the Pleistocene/Holocene boundary. At peak glaciation, ice thickness over central Iceland may have reached 1,500–2,000 m, causing 400–500-m depression of the crust. Rapid climatic improvement caused glacier melting and removal of the ice load within about 1,000 years. Low mantle viscosity resulted in rapid crustal rebound which was completed in about 1,000 years, with an average rate of uplift on the order of nearly half a metre per year over central Iceland. High volcanic production rate is documented by tephrachronological dating and volume estimates of several large-volume monogenetic lava shields and polygenetic volcanic centres along the plate boundary. A Plinian rhyolitic eruption, dated at about 10 ka within the Askja caldera in the Dyngjufjoll volcanic centre, left a pumice deposit which serves as a marker horizon during this remarkable, high-intensity period in the history of the volcano. At the time of the eruption, glaciers had retreated from the coastal areas of the country but the central, elevated parts were covered with a thinning glacier. The Plinian eruption (1–2 km3 dense rock equivalent) was triggered by pressure release caused by glacier melting and volatile supersaturation. Distal deposits of rhyolitic pumice are found in soil sections in coastal areas of eastern and northern Iceland where the pumice occurs between tephra layers from other sources which have been dated by independent methods. A few proximal deposits are preserved within the Dyngjufjoll centre. These provide age constraints on major tectonic and volcanic events during the period of crustal rebound, before and after complete glacier removal. The rhyolitic pumice is sandwiched between thick layers of phreatomagmatic basaltic tephra formed in an open melt-water lake. Sharp contacts between the deposits suggest quick succession of events, but lack of mixing between magmas indicates separate vent locations. The vent location for the 10-ka Plinian eruption has been obliterated by later events but available evidence, supported by a gravity survey, suggests its location in the central part of the Dyngjufjoll volcano. The eruption formed a subsidence structure, presently seen as an embayment in the hyaloclastite mountain block in the southern part of the Askja caldera where a second Plinian eruption occurred in 1875 A.D. The Plinian 10-ka eruption occurred while thinning glaciers were still present over central Iceland, but the Askja caldera formed after lavas started to flow over ice-free surfaces. The morphology of the caldera faults suggests non-simultaneous movement, and the tectonics are not easily compatible with conventional caldera models. A model is proposed involving uplift of tectonically well-defined crustal blocks to the north and west of the Askja caldera, combined with downsagging caused by voluminous outpouring of basaltic lava. The southern and eastern borders of the caldera are remnants of a subsidence following the 10-ka Plinian eruption, partly reactivated by the 1875 A.D. Plinian eruption. The model provides a satisfactory explanation for the enigmatic Oskjuop pass, and it is in agreement with a gravity survey of the Dyngjufjoll centre. The uplift coincided with rapid crustal rebound which was amplified by crustal deformation (doming) of the volcanic centre caused by high magmatic pressure in the plumbing system of the volcano. This is supported by emission of very large lava flows produced in the first millennia of the Holocene.

Is the increase in bronchial responsiveness or FEV1 shortly after cessation ofβ2 -agonists reflecting a real deterioration of the disease in allergic asthmatic patients? A comparison between short-acting and long-acting β2-agonists

Regular use of β2-agonists might result in increased bronchial hyper-responsiveness (BHR) and decreased forced expiratory volume in 1 sec (FEV1). It has been suggested that these possible detrimental effects are not a real deterioration of the disease but that it might be only a transient (rebound) effect shortly after discontinuing this regular use. Moreover these effects are thought to occur especially during short-acting and not during long-acting β2-agonists use. The aim of this study was to investigate whether a rebound effect (a pharmacological deterioration effect diminishing after several hours) in FEV1 and PC20 (concentration of histamine causing a 20% fall in FEV1 with regard to baseline) occurred after cessation of regular use ofβ2 -agonists and whether this occurred both after short-acting and long-actingβ2 -agonists. Allergic asthmatic patients (n=134) were randomly allocated to the use of a short-acting (salbutamol) a long-acting β2-agonist (formoterol) or placebo for 12 weeks (double-blind double-dummy). No other asthma medication was allowed including inhaled corticosteroids. At the start and every 4 weeks later FEV1 and PC20 were measured each time at least 12 h after the last doses of study medication which is in the possible rebound period. To investigate whether a (transient) rebound effect occurred parameters were additionally measured at least 72 h later after discontinuation of the study medication. After 12 weeks of short-acting β2-agonist use a drop was seen in FEV1 from 85·6(±2·21)% predicted to 78·8 (±2·9)% predicted measured 15 h (median) after the last doses of medication. This was significantly different compared to placebo. When measured 168 h (median) later FEV1 recovered to 85·5 (±2·4)% predicted comparable to baseline. PC20 decreased with −1·17 (±0·44) doubling dose after 12 weeks of short-acting β2-agonist use measured 15 h after the last doses of medication which was significantly different compared to placebo. However 168 h later PC20 recovered slightly with +0·55 (±0·34) doubling dose but this value was still lower compared to placebo. In contrast during long-actingβ2 -agonist and placebo use no significant changes were seen. In conclusion the use of short-actingβ2 -agonists resulted in a transient (rebound) effect in FEV1 while the effects on PC20 may point to a real deterioration of the disease. Long-acting β2-agonist and placebo use showed no changes. We conclude that a mono-therapy of short-acting and not of long-acting β2-agonists might have deleterious effects in asthma.

Probability of adult overweight and risk change during the BMI rebound period.

To develop a probability chart of adult overweight based on childhood body mass index (BMI) values and to evaluate the BMI change during the BMI rebound period during childhood, in different populations, with the use of risk function curves. A longitudinal growth study of 3650 full-term healthy Swedish children followed from birth to 18 years of age. Weight and height values of our subjects were obtained. A probability chart for reaching a BMI > 23 kg/m(2) at 18 years of age was constructed for boys and girls. For example, a BMI of 18 kg/m(2) at 4 years of age is associated with 0.70 probability of attaining a BMI > 23 kg/m(2) at 18 years of age in boys; a BMI of 16 kg/m(2) at 4 years of age leads to 0.40 probability of having a BMI > 23 kg/m(2) at 18 years of age in girls. Children with an obvious BMI rebound before 8 years of age have a high risk of being overweight at 18 years of age. There is a clear trend of BMI increase from the 1970s to the 1990s in U.S. children from a parallel dataset, and Hispanic children are at the highest risk of adult overweight. The probability chart for adult overweight developed here provides a functional method of defining childhood obesity that is based on the risk of long-term ill health rather than on a certain statistical cut-off point. It will help pediatricians or healthcare workers identify those children who are at a high risk of becoming overweight in adulthood, which will allow clinical intervention at younger ages.

Long-lasting rebound cue effects following single doses of nicotine and amphetamine: implications for understanding tolerance.

Previous drug-discrimination studies have, with the exception of nicotine (NIC), demonstrated tolerance to the cue effects of a broad range of drugs of abuse. Barrett et al. have shown that tolerance to a drug's cue properties reflects drug-induced rebound shifts in the discrimination baseline and not a weakened or less salient cue. The objective of the present study was to use a discrimination task sensitive to bidirectional cue changes to characterize the interoceptive cues associated with both the primary and rebound cues produced by nicotine in an attempt to understand why a recent study by Shoaib et al. failed to observe tolerance to the nicotine cue. Since dopamine (DA) has been implicated in mediating the NIC cue, rats were trained to discriminate between 0.25 mg/kg amphetamine (AMPH), an indirect DA agonist, and 0.033 mg/kg haloperidol (HAL), a DA antagonist at the D2 receptor site. Training doses were chosen so that rats responded about equally on both levers when tested on saline (SAL) following acquisition. This procedure provided a behavioral baseline to assess NIC-related changes along a presumed continuum of DA-mediated cues. Following acquisition of the discrimination: (i) NIC substitution tests were conducted, (ii) rats were tested for lever choice at intervals from 2 h to 48 h following treatment with single doses of 0.25 mg/kg and 0.50 mg/kg NIC, and (iii) rats were challenged with test doses of NIC during a period of NIC rebound. (i) NIC substituted for AMPH in a dose- dependent manner. (ii) At short intervals after treatment with 0.25 mg/kg and 0.50 mg/kg NIC, rats responded primarily on the AMPH lever followed by a shift to predominant responding on the HAL lever 16-24 h post-treatment, before returning to predrug levels. (iii) No evidence was observed for acute tolerance to NIC. The robust and long-lasting rebound cues associated with training level doses of NIC suggest that maximal tolerance would likely develop to the NIC cue during the acquisition phase of the conventional NIC-saline discrimination study.

Preventing obesity in children and adolescents.

In this review, we address the natural history of obesity in children, the most promising family- and school-based approaches to the prevention of obesity, and the barriers and opportunities associated with secondary prevention. In childhood, the most important periods of risk appear to be the periods of adiposity rebound and adolescence. Caution regarding the period of adiposity rebound is still warranted, because it is not yet clear that early rebound is attributable to changes in body fat. Families and schools represent the most important foci for preventive efforts in children and adolescents. One productive approach is to proceed from an examination of factors that affect energy balance to the identification of more proximal influences on those factors. This approach may help to narrow the strategies necessary to prevent or treat childhood obesity. For example, television viewing affects both energy intake and energy expenditure, and therefore represents a logical target for interventions. Anticipatory guidance by pediatricians may offer an effective mechanism by which to change parental attitudes and practices regarding television viewing. A similar process is used to emphasize the potential influence of school-based interventions directed at changes in food choices and sedentary behavior.

Nutritional and other influences in childhood as predictors of adult obesity.

It has been proposed that there are critical periods during childhood that influence the development of obesity, including gestation and early infancy, the period of adiposity rebound that occurs between ages 5 and 7 years, and adolescence. Despite an extensive literature, there is to date only modest evidence for most of the factors such as nutrition, physical activity and other behavioural factors that are suspected as playing a role in the development of obesity. A recent review of this evidence (Parsons et al. 1999) showed, however, a consistent relationship between socio-economic status (SES) of origin and adult obesity, whereby those from lower SES backgrounds were fatter subsequently in adulthood. This association appeared to apply to both men and women, a finding that contrasts with the trends observed in cross-sectional studies, of an association with SES for women only. There are several potential explanations for the SES of origin-adult obesity relationship. SES of origin may be confounded by parental body size; studies to date provide insufficient evidence of an independent association with SES after allowing for parental body size. Alternatively, environment in early life (for which SES of origin is a proxy measure) may have a long-term impact on obesity later in adulthood, through one or more of several processes. Three major potential explanations can be identified: (1) nutrition in infancy and childhood, either over- or undenutrition, followed subsequently by overnutrition; (2) psychological factors, possibly involving emotional deprivation in childhood; (3) cultural or social norms regarding dietary restraint and attitudes to fatness that may be acquired during childhood.

Strong rebound of wakefulness follows prostaglandin D2- or adenosine A2a receptor agonist-induced sleep.

We studied the effect of sleep excess on the sleep-wakefulness pattern of rats. Subarachnoid infusion of prostaglandin D2 or the adenosine A2a receptor agonist CGS21680 effectively induced slow wave sleep (SWS) for the first 12 h of the night-time period, whereas they did not induce sleep during the following 24 h of infusion. An increase in the amount of wakefulness was seen during the last 12 h of prostaglandin D2 infusion. The amounts of wakefulness strongly increased during the following 36-h recovery period. Rebound wakefulness was extraordinarily strong after the cessation of CGS21680 infusion, reaching almost complete insomnia during the night-time. Treatment of animals with prostaglandin D2 overnight, following by treatment with CGS21680 on the next night, resulted in the strongest induction of wakefulness rebound. During the rebound period, the amount of wakefulness reached up to 50 min per hour in the daytime. Rebound of wakefulness depended on the amounts of preceding SWS induced by infusion of prostaglandin D2 for 6 or 12 h and of CGS21680 for 12 h. The larger the amount of SWS, the larger the amount of the following rebound of wakefulness. Rebounds of wakefulness occurred as a result of decrease in SWS amounts, whereas paradoxical sleep amounts did not change. Desensitization of adenosine A2a receptors and accumulation of prostaglandin E2 may be involved in the production of strong wakefulness rebound following relatively long treatments (more than 12 h) with prostaglandin D2 or CGS21680.

Altered NMDA Sensitivity and Learning Following Chronic Developmental NMDA Antagonism

We have previously shown that chronic developmental administration of N-methyl- D-aspartate (NMDA) antagonists reduces synaptic development; however, on withdrawal from NMDA antagonism, there is a rebound period during which synaptogenesis exceeds control levels. The current research was undertaken to explore this period of withdrawal, using the noncompetitive antagonist phencyclidine (PCP), examining 2 behavioral measures in which the NMDA receptor is implicated: 1. NMDA-induced seizures, and 2. learning and memory in the Morris water maze. Using a protocol identical to that previously used to examine synaptic development, male Long-Evans rats were given 1 daily SC injection of either 10 mg/kg PCP or its physiological saline vehicle for a period of 15 days, beginning on postnatal Day 5 (P5) and ending on P20. Animals were then assessed for either sensitivity to NMDA-induced seizures on P21, P26, P36, or P56, or they were assessed for their acquisition performance and initial heading in the Morris water maze on P23, P26, P30, P38, and P75. Chronic treatment with PCP resulted in greater behavioral ratings of seizure activity after NMDA administration, observed 1 (P21), 5 (P26), and 15 (P36) days after the last injection of PCP, indicating increased sensitivity of the NMDA receptor/channel complex during this period after withdrawal from developmental NMDA antagonism. PCP-treated animals also required significantly more trials to reach criterion in the Morris water maze on P23, P26, and P30, and displayed significantly less accurate initial swim headings on all test days. The results are discussed in terms of the role of the NMDA receptor-channel complex in development and learning/memory processes.

Periods of Risk in Childhood for the Development of Adult Obesity — What Do We Need to Learn?

The prenatal period, the period of adiposity rebound and adolescence appear to represent critical periods for the development of obesity that persists into adulthood. Nonetheless, relatively little is known about the extent to which incident obesity at each of these intervals contributes to the prevalence of adult obesity. Similarly, little is known about the mechanisms that operate at each of these critical periods to entrain adult obesity.

Neurophysiological mechanism of the unloading reflex as a prognostic factor in the early stages of idiopathic adolescent scoliosis.

This paper presents a new neurophysiological method of evaluating the risk of progression in idiopathic scoliosis in the early stages of the disease, by investigating the unloading reflex in paraspinal muscles. The study included 394 patients with scoliosis and 70 healthy children. Latency of the unloading reflex and repeatability of the rebound and silent period were analysed for each reflex evoked. Prolonged latency and minimal number of cycles are the most important factors in the evaluation of progressive idiopathic scoliosis. The method can be used to detect progressive idiopathic scoliosis in the early stages of the disease. The high sensitivity of the method means it can be used as a basis on which to take an early decision to perform surgery.

Geochemical and SrNd isotopic study of charnockites and related rocks in the northern Prince Charles Mountains, East Antarctica: implications for charnockite petrogenesis and proterozoic crustal evolution

Charnockite plutons were intruded into Meso-Neoproterozoic (∼1000 Ma) high-grade metamorphic zone in the northern Prince Charles Mountains (PCM), East Antarctica, immediately after peak granulite metamorphism in the region. Detailed geochemical and SrNd isotopic studies were carried out on these plutons and related rocks, which enables important constraints to be placed on the regional tectonic setting as well as the origin of igneous charnockites. The PCM charnockites are geochemically distinctive, characterised by having much higher TiO 2, P 2O 5, K 2O, K 2 O Na 2 O , Zr, Nb, Y, Pb, La, Ce, and Ba, and lower MgO, CaO, Mg#, Th, U, Sr Ba , and Rb Ba , than, for example, I-type granites from the Lachlan Foldbelt. The decrease in Zr, Nb, Y and Ce with increasing SiO 2, sharply contrast with those of the I-type granites. Isotopically, the PCM charnockites are relatively uniform and evolved, characterised by limited ranges of initial 87 Sr 86 Sr ratios (0.7063 to 0.7100), initial ϵ Nd values (mainly −4.0 to −5.9), and Nd depleted mantle model ages (1.60 to 1.98 Ga), implying derivation from pre-existing crustal sources. The geochemical and isotopic features are most consistent with crystal fractionation of dry hot magmas, with pyroxene, K-feldspar, plagioclase, apatite, zircon, ilmenite and magnetite as early-crystallizing phases. Although the involvement of a mantle-derived magma via AFC process cannot be ruled out, we consider that the charnockitic magmas were mainly derived from pre-existing subduction-related crustal sources, geochemically and isotopically similar to those of the I-type granites. The partial melting probably occurred under dry granulitic conditions at elevated temperatures (950–1050°C), with orthopyroxene, plagioclase and magnetite being residual phases. Under such conditions, elements including K, Rb, Ba, La, Ce, Nd, Zr, Nb and Y will be strongly incompatible and partition into the melt. The relatively low U and Th values in the charnockites are probably due to U-, Th-depletion in the sources, which may have been caused by dehydration and U-, Th-removal during amphibolite-to-granulite transition of the sources. We consider that the PCM charnockites and related regional metamorphism resulted from Meso- to Neoproterozoic continental collision between Archaean and Palaeoproterozoic cratonic blocks in East Antarctica. The Meso-Neoproterozoic collision was probably a global event, possibly related to construction of the Rodinia Supercontinent. During this collisional period or earlier orogenic events in the region (e.g. arc-continent collision in the Palaeo-Mesoproterozoic), calcareous sediments formed at plate margins or back-arc basins would have been tectonically transported to depth. Release of CO 2-rich fluids upon tectonic burial may have been responsible for amphibolite-to-granulite transition without causing dehydration melting to generate I-type granites. Instead, subsequent uplift of the dehydrated, but fertile, granulite crust during a period of crustal rebound may have facilitated decompression melting to produce high-temperature, water-deficient, charnockitic melts. Syn- to post-collision lithosphere delamination, asthenosphere upwelling and magma underplating may have also aided in heating the lower crust above its water-deficient solidus temperature.

Paradoxical sleep deprivation increases the content of glutamate and glutamine in rat cerebral cortex.

We investigated the influence of the sleep/waking cycle, the effects of paradoxical sleep deprivation (PSD) and of the vigilance-promoting drug modafinil on the amino acid contents of rat brain cortex. No significant nycthemeral variations in amino acid levels could be detected. PSD (12-24 hours), using the water tank method, significantly increased the levels of glutamate and glutamine. The increase was still observed after the sleep rebound period. gamma-Aminobutyric acid (GABA) levels did not change significantly during the instrumental sleep deprivation but increased during the rebound period. Control experiments indicate that the increase in glutamate and glutamine levels is due to PSD rather than to the stress associated with the experimental procedure. The increase in glutamate content cannot arise only from transamination reactions, because the levels of other amino acids (such as aspartate) did not decrease. Modafinil treatment did not significantly modify the brain cortex content of any of the amino acids tested.

Chronic systemic administration of 5-HT produces weight loss in mature adult male rats

Adult male rats were allowed to free-feed until their body weights had stabilised. They were next trained onto a 4 h per day feeding regimen, until further stabilisation occurred. All rats then received saline injections for 5 days, to establish baseline body weights. One group was then injected with 5.0 mg/kg 5-HT daily for 30 days while the other group continued with saline. Progressive and significant weight loss occurred in the drug-treated animals. After 30 days, the 5-HT-treated rats had lost 7.0% of their baseline body weights, whereas the control group had gained 1.3%. At this point, the 5-HT treated rats were switched back to saline injections to investigate rebound effects. Although the group that had received 5-HT treatment showed evidence of rebound weight gain, mean weights at the end of the 10 day rebound period were still 4.5% lower than baseline values. These data clearly indicate that chronic systemic administration of 5-HT can produce considerable weight loss in rats.

Surface water temperature, salinity, and density changes in the northeast Atlantic during the last 45,000 years: Heinrich events, deep water formation, and climatic rebounds

We developed a new method to calculate sea surface salinities (SSS) and densities (SSD) from planktonic foraminiferal δ18O and sea surface temperatures (SST) as determined from planktonic foraminiferal species abundances. SST, SSS, and SSD records were calculated for the last 45,000 years for Biogeochemical Oceanic Flux Study (BOFS) cores 5K and 8K recovered from the northeast Atlantic. The strongest feature is the dramatic drop in all three parameters during the Heinrich “ice‐rafting” events. We modelled the possibility of deepwater formation in die northeast Atlantic from the SSD records, by assuming that the surface waters at our sites cooled as they flowed further north. Comparison with modelled North Atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45,000 and 30,000 14C years B.P. (interrupted by iceberg meltwater input of Heinrich event 3 and 4, at 27,000 and 38,000 14C years B.P.) and during the Holocene. No amount of cooling in the northeast Atlantic between 30,000 and 13,000 years could cause deep water to form, because of the low salinities resulting from the high meltwater inputs from icebergs. Our records indicate that after each Heinrich event there were periods of climatic rebound, with milder conditions persisting for up to 2000 years, as indicated by the presence of warmer and more saline water masses. After these warm periods conditions returned to average glacial levels. These short term cold and warm episodes in the northeast Atlantic are superimposed on the general trend towards colder conditions of the Last Glacial Maximum (LGM). Heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the Fennoscandian ice sheet. We propose that meltwater input of Heinrich event 1 significantly reduced North Atlantic Deep Water formation, reducing the heat exchange between the low and high latitudes, thus delaying deglaciation by about 1500 radiocarbon years (2000 calendar years).

Urea, Creatinine and Phosphate Kinetic Modeling during Dialysis: Application to Pediatric Hemodialysis

The kinetics of urea, creatinine and phosphate removal during dialysis were investigated in pediatric patients using a two-pool model taking into account fluid shifts and mass transfer between the two compartments. It is found that even urea must be described by a two-pool model since it presents a post dialysis rebound due to equilibration between the two compartments. Phosphate plasma concentration drops very sharply during the first hour of dialysis and rises rapidly during the rebound period. This pattern cannot be accounted for by the classical two-pool model with constant generation rate and mass transfer coefficients, but corresponds to a large time-dependent phosphate influx from the intracellular compartment in which phosphate is generated by biochemical reactions or liberated from the bones. This influx was calculated for four patients representing 8 dialysis sessions and was found to reach a plateau after 90 minutes of dialysis, dropping rapidly during the rebound period.

Analysis of donor reactive cells in ALS-treated mice bearing skin allografts after the intrathymic injection of donor specific spleen cells

The intrathymic injection of donor spleen cells into antilymphocyte serum (ALS)-treated mice induces significant prolongation of donor skin grafts. The intrathymic route of antigen presentation in this model is superior to the intravenous route in achieving unresponsiveness. To elucidate possible mechanisms involved in the induction of unresponsiveness in ALS-treated mice after intrathymic injection of donor spleen cells, we have analysed the reactivity of lymphoid cells from unresponsive mice in various ways. Deletion of donor reactive cells has been studied using the Mls antigen system. Functional inactivation was analysed by a sequential study of the frequency of donor reactive cells. Suppressor cell activity was studied using an adoptive transfer assay. Deletion of donor reactive cells was partial and occurred largely in the spleen in both early and late stages of unresponsiveness. The frequency of donor reactive cytotoxic cells was suppressed in both spleen and lymph nodes from day +13 until grafts were rejected, with the exception of a rebound period at day +22. In contrast, donor reactive cells were not deleted or inactivated in the thymus. Suppressor cell activity could only be detected in mice bearing long-term grafts. These results suggest that donor reactive cytotoxic cells are functionally inactivated in the spleen and nodes in the early and late stages of unresponsiveness after intrathymic injection of antigen. In contrast, donor reactive cells in the thymus do not appear to be affected.

Ice-proximal glaciomarine sedimentation and sea-level change in the inverness area, Scotland: A review of the deglaciation of a major ice stream of the British Late Devensian ice sheet

Evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating ‘grounded’ tidewater glacier in the Inverness Firth. These changes occurred during the latter stages of the disintegration of the Moray Firth ice-stream, one of the major ice streams that drained the British main Late Devensian ice sheet. Most of the glaciomarine deposits antedate a sequence of glacio-isostatically tilted Late Devensian marine shorelines and associated littoral and estuarine deposits. The shorelines began forming at about 13,000 BP and record a progressive fall in relative sea level. A new model for the deglaciation of the Moray Firth region is proposed after a critical appraisal of published accounts of both onshore and offshore Quaternary sequences. The disintegration of the Moray Firth ice stream involved several rapid phases of retreat to pinning points, caused by iceberg calving and triggered by rising global sea level. Each retreat was followed by minor readvances or stillstands, possibly caused by short-lived accelerated periods of glacio-isostatic rebound and concomitant temporary falls in relative sea level. Two such events occurred in the Inverness Firth: the Ardersier Oscillation and the Alturlie Stillstand. Substantial differences (lower relative sea levels, later deglaciation) are apparent between the pattern of ice-retreat in the Moray Firth region and published accounts of the deglaciation of the Irish Sea basin. These differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels. Furthermore, geological and geomorphological evidence suggesting both rising and falling sea levels in the Inverness area, prior to ca. 13,500 BP, is not fully compatible with recently published computer simulations of the dissolution of the British main Late Devensian ice sheet.

Critical periods in childhood for the development of obesity

Critical periods of development have been well recognized for many behavioral and developmental processes. However, as others have pointed out, such periods have not been widely reported for nutritional diseases. Many observations suggest that two and possibly three critical periods exist for the development of obesity and its complications. These include gestation and early infancy, the period of adiposity rebound that occurs between 5 and 7 y of age, and adolescence. Obesity that begins at these periods appears to increase the risk of persistent obesity and its complications. The mechanisms that account for the increased risk associated with obesity at these ages remain unclear. Nonetheless, the existence of critical periods should serve to focus preventive efforts on these developmental stages.

Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the upper Judith River Group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana

The lithostratigraphic interval between the Taber and Lethbridge coal zones in the upper portion of the nonmarine Judith River Group of southeastern Alberta is divisible into two lithostratigraphic units separated by a regionally extensive and diachronous discontinuity. The lower unit, referred to here as the Oldman Formation, is characterized by very fine grained to fine-grained sandstones that contain fewer than 2% volcanic rock fragments; sandstone bodies with numerous sets of horizontally stratified sandstone, showing little or no evidence of lateral accretion; siliceous paleosols (ganisters); and a relatively high gamma-ray signal in the upper half of the formation. The Oldman Formation comprises deposits of a low-sinuosity, perhaps ephemeral fluvial system that originated in the southern Cordillera of Canada and northern Montana and flowed northeastward, perpendicular to the axis of the Alberta Basin.The upper unit is assigned to a new formation, the Dinosaur Park Formation, and is characterized by fine- to medium-grained sandstones with up to 10% volcanic rock fragments; sandstone bodies that exhibit lateral-accretion surfaces in the form of inclined heterolithic stratification; numerous articulated dinosaurs and dinosaur bone beds; and a relatively low gamma-ray signal in the lower half of the formation. The Dinosaur Park Formation comprises deposits of a high-sinuosity, fluvial-to-estuarine system that originated in the north and central Cordillera and flowed southeastward, subparallel to the axis of the Alberta Basin.40Ar/39Ar and K–Ar dating of Judith River Group bentonites shows that the contact between the Oldman and Dinosaur Park formations becomes younger toward the south and southeast. These data also demonstrate that the Dinosaur Park Formation clastics migrated southeastward at a rate of approximately 130–140 km/Ma, gradually overstepping the Oldman Formation elastics.The widely recognized north-to-south increase in intensity of overthrust loading along the western margin of the Alberta Basin during the Late Cretaceous is thought to be responsible for (i) differences in accommodation space for the proximal portions of the Oldman and Dinosaur Park formations, and (ii) the establishment of a southerly tilt in the Alberta Basin leading to the southeastward migration of the Dinosaur Park Formation elastics. In the northern portion of the basin, relatively lower rates of subsidence, combined with periods of isostatic rebound in the foredeep, resulted in the southeastward migration of Dinosaur Park Formation elastics as sediment input exceeded accommodation space. In the southern portion of the basin, relatively higher rates of subsidence and little isostatic rebound acted to trap coarse-grained Oldman Formation elastics in the foredeep and may have led to periods of sediment starvation in more distal portions of the basin. An inferred lower depositional slope associated with the Dinosaur Park Formation (relative to the Oldman Formation) is thought to have resulted from gradual loading of the basin as Dinosaur Park Formation elastics migrated southeastward or some form of tectonically induced subsidence.

Sleepwalking Precipitated by Treatment of Sleep Apnea with Nasal CPAP*

A 33-year-old man with a long history of snoring, observed apneic episodes, and excessive daytime sleepiness, underwent all-night polysomnography, which demonstrated severe obstructive sleep apnea. During the nasal CPAP trial, two episodes of sleepwalking were observed during a period of delta sleep rebound.