Background-The eVect of histamine H 2 receptor antagonists on gastric emptying is controversial. Aims-To determine the eVects of ranitidine, famotidine, and omeprazole on gastric motility and emptying. Patients and methods-Fifteen normal subjects underwent simultaneous antroduodenal manometry, electrogastrography (EGG), and gastric emptying with dynamic antral scintigraphy (DAS). After 30 minutes of fasting manometry and EGG recording, subjects received either intravenous saline, ranitidine, or famotidine, followed by another 30 minutes recording and then three hours of postprandial recording after ingestion of a radiolabelled meal. Images were obtained every 10-15 minutes for three hours to measure gastric emptying and assess antral contractility. Similar testing was performed after omeprazole 20 mg daily for one week. Results-Fasting antral phase III migrating motor complexes (MMCs) were more common after ranitidine (9/15 subjects, 60%), famotidine (12/15, 80%), and omeprazole (8/12, 67%) compared with placebo (4/14, 29%; p<0.05). Postprandially, ranitidine, famotidine, and omeprazole slowed gastric emptying, increased the amplitude of DAS contractions, increased the EGG power, and increased the antral manometric motility index. Conclusions-Suppression of gastric acid secretion with therapeutic doses of gastric acid suppressants is associated with delayed gastric emptying but increased antral motility. (Gut 1998;42:243-250)

SummaryCrystal structure analyses of five crystalline enamines tog,ether with recently published structural data for two other enamines reveal varying degree of pyramidality at the emamine nitrogen atom. The pyramidality appears to be most pronounced in (mamines from piperidine and morpholine, less so in enamines derived from prolinoid amines. A pyrrolidine enamine obtained from a derivative of cyclohexane-1,4-dione seems to have a virtually planar enamine group. The implications of these findings for current stereochemical problems in enamine chemistry are discussed.Introduction. -When one considers the importance of enamines [l] as intermediates in present-day synthetic and enzymatic chemistry, it seems astonishing that so very little is known about the fine details of the structure of the enamine grouping [ 2 ] . Indeed, until quite recently it seems to have been taken for granted that the enamine group is more or less planar. This presumption seems not to have been seriously questioned, probably because it appeared to be so nicely consistent with, or even indicated by, the most characteristic and useful feature of enamine chemistry, namely, nucleophilic reactivity at the carbon atom.Our interest in this problem arose out of attempts to understand the mechanism of enantioselection in intramolecular aldol condensations of type 1 + 2 [3] [4]; these transformations involve the important synthetic principle of introducing chirality by conversion of a prochiral center to a chiral one by means of enantioselective catalysis4). In the absence of evidence to the contrary, it seems likely that enamine intermediates are formed during these ring-closure reactions and are implicated in the stereoselection step. Enantioselection involving an enamine intermediate of type 3 would require a mechanism for distinguishing between opposite diastereotopic facer; of the enamine grouping. If the enamine nitrogen atom were not

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Abstract:The geochemistry and vertical stratification of shallow meltwater ponds at 78°S near Bratina Island (McMurdo Ice Shelf) have been determined for late winter (October) and summer (January) conditions as part of the Latitudinal Gradient Project. Of the five frozen ponds investigated in October, all were stratified with respect to conductivity, and three had highly saline basal brines beneath the ice at temperatures of -16 to -20°C. In the ice column, inclusions of saline fluid were observed in channels between ice crystals; the abundance increasing with depth and decreasing ice crystal size. In January, seven of the ten ponds investigated (including ponds sampled in October) retained conductivity stratification, whereas significant thermal stratification was observed in only three ponds (maximum ΔT = 5.5°C). Basal brines, ice and meltwaters were Na-Cl or Na-SO 4 dominated. FREZCHEM52 modelling, supported by changes in ion ratios, indicated that the precipitation of mirabilite (Na 2 SO 4 .10H 2 O) and gypsum (CaSO 4 .2H 2 O) during progressive freezing is an important determinant in chemical evolution of the basal brine. High pH (8.8-11.2) and over-saturation with respect to dissolved oxygen (> 20 mg L -1 ) in summer, and the presence of sulphide ions in basal brines in winter, occurred in those ponds which experienced high biological productivity during the summer months.

Background-Cholinergic regulation of chronotropic (frequency) and inotropic (force) aspects of antral contractility and how these impact on gastric emptying are not well delineated. Aims-To determine the eVects of cholinergic stimulation and inhibition on myoelectric, contractile, and emptying parameters of gastric motility. Methods-Ten normal subjects underwent three studies each, using simultaneous electrogastrography (EGG), antroduodenal manometry, and gastric emptying with dynamic antral scintigraphy (DAS). After 30 minutes of baseline fasting manometry and EGG, subjects received saline intravenously, atropine (0.6 mg then 0.25 mg/hour intravenously), or bethanechol (5 mg subcutaneously). This was followed by another 30 minutes' recording and by three hours of postprandial recording after ingestion of a technetium-99m labelled solid meal. Results-During fasting, atropine decreased, whereas bethanechol increased, the antral manometric motility index and EGG power. Postprandially, atropine decreased the amplitude of antral contractions by DAS, decreased the postprandial antral manometric motility index, and slowed gastric emptying. Atropine caused a slight increase in postprandial frequency of antral contractions by DAS and gastric myoelectrical activity by EGG. Bethanechol slightly increased the amplitude, but slightly decreased the frequency of antral contractions by DAS and decreased the frequency of gastric myoelectrical activity by EGG, with no significant increase in the motility index or gastric emptying. Conclusions-Cholinergicantagonism with atropine reduces antral contractility and slows gastric emptying. Cholinergic stimulation with bethanechol increases antral contractility, but decreases the frequency of antral contractions, without altering the antral motility index or gastric emptying. (Gut 1999;45:346-354)

The Ladolam hydrothermal system, on Lihir Island, Papua New Guinea, hosts one of the youngest and largest gold deposits in the world. Several deep (more than 1 kilometer) geothermal wells were drilled beneath the ore bodies to extract water at >275 degrees C and to facilitate open-pit mining. Using a titanium down-hole sampler, we determined that the deep geothermal brine of magmatic origin contains approximately 15 parts per billion gold. At the current gold flux of 24 kilograms per year, this deposit could have formed within approximately 55,000 years. The combination of sustained metal flux and efficient metal precipitation led to the formation of a giant hydrothermal gold deposit in a short period.

Discrimination and reversal of the classically conditioned eyeblink response depends on cerebellar-brainstem interactions with the hippocampus. Neonatal "binge" exposure to alcohol at doses of 5 g/kg/day or more has been shown to impair single-cue eyeblink conditioning in both weanling and adult rats. The present study exposed neonatal rats to acute alcohol intubations across different developmental periods (postnatal day [PND] 4-9 or PND7-9) and tested them from PND26-31 on discriminative classical eyeblink conditioning and reversal. A high dose of alcohol (5 g/kg/day) dramatically impaired conditioning relative to controls when exposure occurred over PND4-9, but produced mild or no impairments when delivered over PND7-9. These findings support previous claims that developmental exposure period plays a critical role in determining the deleterious effects of alcohol on the developing brain. A lower dose of alcohol (4 g/kg/day) delivered from PND4-9--lower than has previously been shown to affect single-cue eyeblink conditioning--also produced deficits on the discrimination task, suggesting that discrimination learning and acquisition of responding to CS+ during reversal may be especially sensitive behavioral indicators of alcohol-induced brain damage in this rat model.

Meltwater ponds in the Victoria Valley and in the Labyrinth at the head of the Wright Valley of Victoria Land were sampled in January (summer) and October (late winter) of 2004 to establish their geochemistry and stratification, and to compare this with that of coastal meltwater ponds at a similar latitude near Bratina Island. In summer, vertical profiles were measured in 14 ponds; 10 were thermally stratified (maximum ΔT =11.5°C) and 12 demonstrated a conductivity increase (~25x) in the lowest 10-20 cm of the water column. When 11 of these ponds were resampled in October, the ice columns were stratified with respect to conductivity and five ponds had highly saline (up to 148 mS cm -1 ), oxygenated basal brines present under the ice. Basal brines and summer melt waters were Na-Cl dominated, and Victoria Valley pond meltwaters were enriched in Ca relative to the Labyrinth ponds. Early gypsum precipitation directs the chemical evolution of residual brine during freezing. These ponds were enriched in NO 3 relative to the coastal ponds at Bratina Island, due to dissolution of nitrate-bearing soil salts, and the reduced influence of marine aerosols and biological productivity on pond chemistry.