Development of Ice-Shelf Estuaries Promotes Fractures and Calving.

As the global climate warms, increased surface meltwater production on ice shelves may trigger ice-shelf collapse and enhance global sea-level rise. The formation of surface rivers could help prevent ice-shelf collapse if they can efficiently evacuate meltwater. Here, we present observations of the evolution of a surface river into an ice-shelf estuary atop the Petermann Ice Shelf in northwest Greenland, and identify a second estuary at the nearby Ryder Ice Shelf. This surface hydrology process can foster fracturing and enhance calving. At the Petermann estuary, sea ice was observed converging at the river mouth upstream, indicating a flow reversal. Seawater persists in the estuary, after the surrounding icescape is frozen. Along the base of Petermann estuary, linear fractures were initiated at the calving front and propagated upstream along the channel. Similar fractures along estuary channels shaped past large rectilinear calving events at the Petermann and Ryder Ice Shelves. Increased surface melting in a warming world will enhance fluvial incision, promoting estuary development, longitudinal fracturing orthogonal to ice-shelf fronts, and increase rectilinear calving. Estuaries could develop in Antarctica within the next half-century, resulting in increased calving and accelerating both ice loss and global sea-level rise.

Metabolic syndrome and psoriatic arthritis among patients with psoriasis vulgaris: Quality of life and prevalence.

Interest has increased in comorbidities associated with psoriasis and their effects on health-related quality of life (HRQoL). This study aimed to evaluate the prevalence of metabolic syndrome (MetS) and psoriatic arthritis (PsA) and to investigate HRQoL and the prevalence of hypertension, type 2 diabetes mellitus (T2DM), obesity and dyslipidemia. In a cross-sectional design, patients diagnosed with plaque psoriasis answered an interview and standardized questionnaires (Dermatology Life Quality Index questionnaire [DLQI], 36-Item Short Form Health Survey [SF-36] and EuroQol Five-Dimension Questionnaire Three-Level version [EQ-5D-3L]). Physical examination and several tests to assess desired outcomes were performed by a dermatologist and a rheumatologist during three visits. The prevalence of MetS and PsA was 50.0% and 41.8%, respectively. Dyslipidemia was the most prevalent (74.5%) secondary comorbidity, followed by hypertension (61.8%), obesity (52.5%) and T2DM (30.9%). The mean (standard deviation) DLQI score was 6.5 (6.9), and mean physical and mental SF-36 measures were 45.2 (10.4) and 45.5 (12.3), respectively, and for EQ-5D-3L, mean utility index and EQ-VAS scores were 0.68 (0.27) and 72.7 (19.7), respectively. PsA and MetS are important comorbidities; a reduced HRQoL is noted among plaque psoriasis patients with these comorbidities, emphasizing the relevance of diagnosis and treatment beyond the care of skin lesions.

Direct measurements of meltwater runoff on the Greenland ice sheet surface.

Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream fluvial catchment area. A first 72-h trial for a 63.1-km2 moulin-terminating internally drained catchment (IDC) on Greenland's midelevation (1,207-1,381 m above sea level) ablation zone is compared with melt and runoff simulations from HIRHAM5, MAR3.6, RACMO2.3, MERRA-2, and SEB climate/SMB models. Current models cannot reproduce peak discharges or timing of runoff entering moulins but are improved using synthetic unit hydrograph (SUH) theory. Retroactive SUH applications to two older field studies reproduce their findings, signifying that remotely sensed IDC area, shape, and supraglacial river length are useful for predicting delays in peak runoff delivery to moulins. Applying SUH to HIRHAM5, MAR3.6, and RACMO2.3 gridded melt products for 799 surrounding IDCs suggests their terminal moulins receive lower peak discharges, less diurnal variability, and asynchronous runoff timing relative to climate/SMB model output alone. Conversely, large IDCs produce high moulin discharges, even at high elevations where melt rates are low. During this particular field experiment, models overestimated runoff by +21 to +58%, linked to overestimated surface ablation and possible meltwater retention in bare, porous, low-density ice. Direct measurements of ice surface runoff will improve climate/SMB models, and incorporating remotely sensed IDCs will aid coupling of SMB with ice dynamics and subglacial systems.

Defining thresholds of sustainable impact on benthic communities in relation to fishing disturbance.

While the direct physical impact on seabed biota is well understood, no studies have defined thresholds to inform an ecosystem-based approach to managing fishing impacts. We addressed this knowledge gap using a large-scale experiment that created a controlled gradient of fishing intensity and assessed the immediate impacts and short-term recovery. We observed a mosaic of taxon-specific responses at various thresholds. The lowest threshold of significant lasting impact occurred between 1 and 3 times fished and elicited a decrease in abundance of 39 to 70% for some sessile epifaunal organisms (cnidarians, bryozoans). This contrasted with significant increases in abundance and/or biomass of scavenging species (epifaunal echinoderms, infaunal crustaceans) by two to four-fold in areas fished twice and more. In spite of these significant specific responses, the benthic community structure, biomass and abundance at the population level appeared resilient to fishing. Overall, natural temporal variation in community metrics exceeded the effects of fishing in this highly dynamic study site, suggesting that an acute level of disturbance (fished over six times) would match the level of natural variation. We discuss the implications of our findings for natural resources management with respect to context-specific human disturbance and provide guidance for best fishing practices.

Welfare Reform and Labor Force Exit by Young, Low-Skilled Single Males.

While the labor market woes of low-skilled male workers in the United States over the past several decades have been well documented, the academic literature identifying causal factors leading to declines in labor force participation (LFP) by young, low-skilled males remains scant. To address this gap, I use the timing and characteristics of welfare-reform policies implemented during the 1990s and fixed-effects, instrumental variable regression modeling to show that policies seeking to increase LFP rates for low-skilled single mothers inadvertently led to labor force exit by young, low-skilled single males. Using data from the Current Population Survey and a bundle of work inducements enacted by states throughout the 1990s as exogenous variation in a quasi-experimental design, I find that the roughly 10 percentage point increase in LFP for low-skilled single mothers facilitated by welfare reform resulted in a statistically significant 2.8 percentage point decline in LFP for young, low-skilled single males. After conducting a series of robustness checks, I conclude that this result is driven entirely by white males, who responded to welfare-reform policies with a 3.7 percentage point decline in labor supply. Young black males, as well as other groups of potentially affected workers, appear to be uninfluenced by the labor supply response of less-educated single mothers to welfare reform. Impacts on young, single white males are large and economically significant, suggesting that nearly 150,000 males departed the formal labor market in response to directed welfare-reform policies.

Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet.

Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km(2) of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54-2.81 cm⋅d(-1)) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41-98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056-0.112 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅d(-1)), and when integrated over the melt season, totaled just 37-75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.

S100A8 and S100A9-oxidant scavengers in inflammation.

S100A8 and S100A9 are generally considered proinflammatory. Hypohalous acids generated by activated phagocytes promote novel modifications in murine S100A8 but modifications to human S100A8 are undefined and there is no evidence that these proteins scavenge oxidants in human disease. Recombinant S100A8 was exquisitely sensitive to equimolar ratios of HOCl, which generated sulfinic and sulfonic acid intermediates and novel oxathiazolidine oxide/dioxide forms (mass additions, m/z +30 and +46) on the single Cys42 residue. Met78(O) and Trp54(+16) were also present. HOBr generated sulfonic acid intermediates and oxidized Trp54(+16). Evidence for oxidation of the single Cys3 residue in recS100A9 HOCl was weak; Met63, Met81, Met83, and Met94 were converted to Met(O) in vitro. Oxidized S100A8 was prominent in lungs from patients with asthma and significantly elevated in sputum compared to controls, whereas S100A8 and S100A9 were not significantly increased. Oxidized monomeric S100A8 was the major component in asthmatic sputum, and modifications, including the oxathiazolidine adducts, were similar to those generated by HOCl in vitro. Oxidized Met63, Met81, and Met94 were variously present in S100A9 from asthmatic sputum. Results have broad implications for conditions under which hypohalous acid oxidants are generated by activated phagocytes. Identification in human disease of the novel S100A8 Cys derivatives typical of those generated in vitro strongly supports the notion that S100A8 contributes to antioxidant defense during oxidative stress.

Singing by male and female Kloss gibbons (Hylobates klossii) in the Peleonan Forest, Siberut Island, Indonesia.

Kloss gibbons (Hylobates klossii) are endemic to the Mentawai Islands in Indonesia and are one of only two gibbon species in which mated pairs do not sing duets. This is the first long-term study of the factors influencing the singing activity of Kloss gibbons within a northern Siberut Island population and follows two previous studies in central Siberut nearly 30 years ago. We collected data on the presence/absence of male and female singing within the study area on 198 days and within a focal group on 47 days. Rainfall during the time period in which they normally sing inhibits singing in both males and females. Our study supports the hypothesis that male and female songs function in intrasexual resource defence, as singing is associated with singing by same-sex neighbours, and same-sex choruses are more likely to occur after one or more days of silence (from that sex), suggesting there is pressure for individuals to communicate with same-sex neighbours regularly. Singing was not coordinated within a mated pair, suggesting that vocal coordination of the pair has been lost with the loss of the duet and that Kloss gibbon songs do not convey information to neighbours about the strength of the pair bond. On days when males sang predawn, females were more likely to sing after dawn and earlier in the morning. Additionally, the number of groups singing in female choruses was positively associated with the number of males that had sung in the predawn male chorus. We suggest that female songs have an intersexual territory defence as well as an intrasexual function.

Child size and household characteristics in rural Timor-Leste.

OBJECTIVES: The main objective was to determine those characteristics of the family and household that affects child health (as measured by child size for age) in the rural Ossu area of Timor-Leste. METHODS: Interviews of parents in 102 households assessed reproductive histories, the amount and type of resources available and family composition (number, sex, and age of members). Height, weight, and mid-upper arm circumference were measured for all children in the household. To standardize for age and sex, raw measures were transformed into WHO Z scores and compared across households. RESULTS: Children were low in both height and weight relative to international standards and older children compared with international standards more poorly than under-fives. There was no evidence of sex difference in relative growth. The number of children in a household was negatively associated with height but not weight and positively with BMI. Children living in the villages more distant from Ossu town center had significantly lower Z scores for height than children in town. No crop or livestock indices were related to growth. Fostered children did not show growth different from biological children, but biological children in households with fostered children were slightly larger for age. CONCLUSIONS: Short stature inflates BMI and harvest season measures may have captured short-term increases in children's energy balance. Social networks may increase child well-being by moving children toward resource richer households. Social and cultural factors influence resource allocations among children and their health in rural Timor-Leste.

Comments on shielding for dual energy accelerators.

Determination of shielding requirements for medical linear accelerators has been greatly facilitated by the publication of the National Council on Radiation Protection and Measurements (NCRP) latest guidelines on this subject in NCRP Report No. 151. In the present report the authors review their own recent experience with patient treatments on conventional dual energy linear accelerators to examine the various input parameters needed to follow the NCRP guidelines. Some discussion is included of workloads, occupancy, use factors, and field size, with the effects of intensity modulated radiotherapy (IMRT) treatments included. Studies of collimator settings showed average values of 13.1 x 16.2 cm2 for 6 MV and 14.1 x 16.8 cm2 for 18 MV conventional ports, and corresponding average unblocked areas of 228 and 254 cm2, respectively. With an average of 77% of the field area unblocked, this gives a mean irradiated area of 196 cm2 for the 18 MV beam, which dominates shielding considerations for most dual energy machines. Assuming conservatively small room dimensions, a gantry bin angle of 18 degrees was found to represent a reasonable unit for tabulation of use factors. For conventional 18 MV treatments it was found that the usual treatment angles of 0, 90, 180, and 270 degrees were still favored, and use factors of 0.25 represent reasonable estimates for these beams. As expected, the IMRT fields (all at 6 MV) showed a high degree of gantry angle randomization, with no bin having a use factor in excess of 0.10. It is concluded that unless a significant number of patients are treated with high energy IMRT, the traditional use factors of 0.25 are appropriate for the dominant high energy beam.

Fast-track surgery may reduce complications following major colonic surgery.

PURPOSE: Fast-track (enhanced recovery) care pathways for colonic surgery are becoming increasingly popular; however, there have been concerns regarding protocol compliance, high readmission rates, and also the true impact on morbidity rates with these protocols. This study was conducted to assess the impact of a fast-track program for colonic surgery on hospital stay, complications, and readmission rates. METHODS: From December 2005 to March 2007, consecutive patients undergoing colonic surgery were prospectively studied. The comparison group consisted of a comorbidity-matched group of patients who had undergone similar surgery before establishment of the fast-track program. RESULTS: Fifty patients were included in each group. Groups were comparable at baseline. The fast-track group received significantly smaller amounts of intraoperative and postoperative intravenous fluids, were fed earlier, mobilized earlier, passed flatus earlier, and were discharged earlier than the comparison group (4 vs. 6.5 days, P < 0.001). The numbers of patients with urinary infections (2 vs. 12, P = 0.008), ileus (5 vs. 18, P = 0.005), and cardiopulmonary complications (11 vs. 21, P = 0.032) were significantly lower in the fast-track group. There was no difference in the rate of readmission. CONCLUSION: Fast-track is a safe and effective approach for reducing hospital stay and morbidity following major colonic surgery.

Potential value of changes in cell markers in organotypic hippocampal cultures associated with chronic EtOH exposure and withdrawal: comparison with NMDA-induced changes.

BACKGROUND: Previous studies have shown that withdrawal from ethanol (EtOH) exposure induces neuronal damage, as indicated by propidium iodide (PI) uptake, in organotypic hippocampal slice cultures. This is prevented by MK801, suggesting that damage is "excitotoxic," resulting from activation of N-methyl-d-aspartate (NMDA) receptors by endogenous glutamate. To avoid reliance on a single indicator, and to enable assessment of recovery from the EtOH withdrawal (EWD) insult, we assessed changes in cell markers for neurons and glia, as well as cell division, following either EWD or NMDA challenge (as a positive control). METHODS: Organotypic cultures from postnatal day (PND) 8 rats were cultured for 5 days before exposure to EtOH (mean concentration approximately 65 mM) for 10 days before EWD. Cultures of the same "days in vitro" age (DIV16) were exposed to NMDA (200 microM) for 1 hour. Neuronal injury was visualized using PI and indices of neurons, glia, or cell division were measured at intervals up to 10 days following the neurotoxic insults. Each time point and measurement used separate slice cultures, and these were treated as separate experiments with paired controls. Regional neuronal content was assessed by neuronal nuclear protein (NeuN) and calbindin D28k (Calb), glial content by glial fibrillary acidic protein (GFAP), and cell division by bromodeoxyuridine (BrdU) incorporation, all measured immunohistochemically. RESULTS: Chronic exposure to EtOH was associated with a dramatic reduction in BrdU incorporation in all regions of cultures. Propidium iodide fluorescence in the CA1 region was elevated significantly after EWD and more so after NMDA challenge. Reduced immunoreactivity (IR) of NeuN and Calb suggested that loss of neurons resulted from the EWD insult. Bromodeoxyuridine incorporation was initially depressed even further by EWD, but had returned to control levels after 3 days. In contrast, following NMDA insult, BrdU incorporation was significantly and persistently elevated above control levels after 3 days. Glial fibrillary acidic protein was reduced immediately after both EWD and NMDA challenge. Several days after EWD, expression of neuronal and glial markers, although variable, had generally returned to control levels. In contrast, NeuN IR remained significantly reduced after NMDA challenge. CONCLUSIONS: In general, the use of additional markers supports data obtained with PI uptake alone and suggests that neurons (and glia) are lost from the culture following EWD or NMDA challenge. These cell markers recover several days after EWD, but it is unclear whether functional recovery accompanies these changes. If the dramatic effect of EtOH exposure and EWD on BrdU incorporation reflects reduced neuro- and gliogenesis, it is likely that this adversely affects long-term recovery from EWD. Finally, some markers showed significant and consistent changes after EWD, whereas others did not. This information may facilitate the use of this model in evaluation of potential medications that protect against and/or promote recovery from neurotoxicity.

N-n-alkylnicotinium analogs, a novel class of antagonists at alpha 4 beta 2* nicotinic acetylcholine receptors: inhibition of S(-)-nicotine-evoked 86Rb+ efflux from rat thalamic synaptosomes.

Pyridine N-n-alkylation of S(-)-nicotine (NIC) affords N-n-alkylnicotinium analogs, previously shown to competitively inhibit [(3)H]NIC binding and interact with alpha4beta2* nicotinic receptors (nAChRs). The present study determined the ability of the analogs to inhibit NIC-evoked (86)Rb(+) efflux from rat thalamic synaptosomes to assess functional interaction with alpha4beta2* nAChRs. In a concentration-dependent manner, NIC evoked (86)Rb(+) efflux (EC(50) = 170 nmol/L). Analog-induced inhibition of NIC-evoked (86)Rb(+) efflux varied over a approximately 450-fold range. Analogs with long n-alkyl chain lengths (C(9)-C(12)) inhibited efflux in the low nmol/L range (IC(50) = 9-20 nmol/L), similar to dihydro-beta-erythroidine (IC(50) = 19 nmol/L). Compounds with shorter n-alkyl chain lengths (C(1)-C(8)) produced inhibition in the low micromol/L range (IC(50) = 3-12 micromol/L). C(10) and C(12) analogs completely inhibited NIC-evoked efflux, whereas C(1-9) analogs produced maximal inhibition of only 10% to 60%. While the C(10) analog N-n-decylnicotinium iodide (NDNI) did not produce significant inhibition of NIC-evoked dopamine release in previously reported studies, NDNI possesses high affinity for [(3)H]NIC binding sites (K(i) = 90 nmol/L) and is a potent and efficacious inhibitor of NIC-evoked (86)Rb(+) efflux as demonstrated in the current studies. Thus, NDNI is a competitive, selective antagonist at alpha4beta2* nAChRs.

Introduction of unsaturation into the N-n-alkyl chain of the nicotinic receptor antagonists, NONI and NDNI: effect on affinity and selectivity.

N-n-octylnicotinium iodide (NONI) and N-n-decylnicotinium iodide (NDNI) are selective nicotinic receptor (nAChR) antagonists mediating nicotine-evoked striatal dopamine (DA) release, and inhibiting [3H]nicotine binding, respectively. This study evaluated effects of introducing unsaturation into the N-n-alkyl chains of NONI and NDNI on inhibition of [3H]nicotine and [3H]methyllycaconitine binding (alpha4beta2* and alpha7* nAChRs, respectively), (86)Rb+ efflux and [3H]DA release (agonist or antagonist effects at alpha4beta2* and alpha6beta2*-containing nAChRs, respectively). In the NONI series, introduction of a C3-cis- (NONB3c), C3-trans- (NONB3t), C7-double-bond (NONB7e), or C3-triple-bond (NONB3y) afforded a 4-fold to 250-fold increased affinity for [3H]nicotine binding sites compared with NONI. NONB7e and NONB3y inhibited nicotine-evoked 86Rb+ efflux, indicating alpha4beta2* antagonism. NONI analogs exhibited a 3-fold to 8-fold greater potency inhibiting nicotine-evoked [3H]DA overflow compared with NONI (IC50 = 0.62 microM; Imax = 89%), with no change in Imax, except for NONB3y (Imax = 50%). In the NDNI series, introduction of a C4-cis- (NDNB4c), C4-trans-double-bond (NDNB4t), or C3-triple-bond (NDNB3y) afforded a 4-fold to 80-fold decreased affinity for [3H]nicotine binding sites compared with NDNI, whereas introduction of a C9 double-bond (NDNB9e) did not alter affinity. NDNB3y and NDNB4t inhibited nicotine-evoked 86Rb+ efflux, indicating antagonism at alpha4beta2* nAChRs. Although NDNI had no effect, NDNB4t and NDNB9e potently inhibited nicotine-evoked [3H]DA overflow (IC50 = 0.02-0.14 microM, Imax = 90%), as did NDNB4c (IC50 = 0.08 microM; Imax = 50%), whereas NDNB3y showed no inhibition. None of the analogs had significant affinity for alpha7* nAChRs. Thus, unsaturated NONI analogs had enhanced affinity at alpha4beta2*- and alpha6beta2*-containing nAChRs, however a general reduction of affinity at alpha4beta2* and an uncovering of antagonist effects at alpha6beta2*-containing nAChRs were observed with unsaturated NDNI analogs.

Development of subtype-selective ligands as antagonists at nicotinic receptors mediating nicotine-evoked dopamine release.

N-n-Alkylation of nicotine converts it from an agonist into an antagonist at neuronal nicotinic acetylcholine receptor subtypes mediating nicotine-evoked dopamine release. Conformationally restricted analogues exhibit both high affinity and selectivity at this site, and are able to access the brain due to their ability to act as substrates for the blood-brain barrier choline transporter.

Opposing effects of ethanol and nicotine on hippocampal calbindin-D28k expression.

Long-term ethanol exposure produces multiple neuroadaptations that likely contribute to dysregulation of Ca(2+) balance and neurotoxicity during ethanol withdrawal. Conversely, nicotine exposure may reduce the neurotoxic consequences of Ca(2+) dysregulation, putatively through up-regulation of the Ca(2+)-buffering protein calbindin-D(28k). The current studies were designed to examine the extent to which 10-day ethanol exposure and withdrawal altered calbindin-D(28k) expression in rat hippocampus. Further, in these studies, we examined the ability of nicotine, through action at alpha(7)(*)-bearing nicotinic acetylcholine receptors (nAChRs), to antagonize the effects of ethanol exposure on calbindin-D(28k) expression. Organotypic cultures of rat hippocampus were exposed to ethanol (50-100 mM) for 10 days. Additional cultures were exposed to 500 nM (-)-nicotine with or without the addition of 50 mM ethanol, 100 nM methyllycaconitine (an alpha(7)*-bearing nAChR antagonist), or both. Prolonged exposure to ethanol (>/=50 mM) produced significant reductions of calbindin-D(28k) immunolabeling in all regions of the hippocampal formation, even at nontoxic concentrations of ethanol. Calbindin-D(28k) expression levels returned to near-control levels after 72 h of withdrawal from 10-day ethanol exposure. Extended (-)-nicotine exposure produced significant elevations in calbindin-D(28k) expression levels that were prevented by methyllycaconitine co-exposure. Co-exposure of cultures to (-)-nicotine with ethanol resulted in an attenuation of ethanol-induced reductions in calbindin-D(28k) expression levels. These findings support the suggestion that long-term ethanol exposure reduces the neuronal capacity to buffer accumulated Ca(2+) in a reversible manner, an effect that likely contributes to withdrawal-induced neurotoxicity. Further, long-term exposure to (-)-nicotine enhances calbindin-D(28k) expression in an alpha(7)* nAChR-dependent manner and antagonizes the effects of ethanol on calbindin-D(28k) expression.

Effects of prolonged nicotinic ligand exposure on function of heterologously expressed, human alpha4beta2- and alpha4beta4-nicotinic acetylcholine receptors.

Effects of prolonged nicotinic ligand exposure on the function of human alpha4beta2- and alpha4beta4-nicotinic acetylcholine receptor (nAChR) subtypes were studied using receptors heterologously expressed in SH-EP1 human epithelial cells. Magnitudes of acute, nAChR-mediated, specific 86Rb+ efflux responses to 1 mM carbamylcholine were reduced after pretreatment with specific nAChR ligands in effects that depended on pretreatment drug dose, duration of drug pretreatment, and duration of drug-free recovery. Fifty percent inhibition of alpha4beta2-nAChR function following 5 min of recovery occurred after 1 min of pretreatment with 1 mM nicotine but also after 1-h pretreatment at 10 nM nicotine. Seventy-five percent loss in function persisted 1 h after drug removal following 15 min or more of exposure to 1 mM nicotine. However, functional recovery was nearly complete after 1 h in drug-free medium following 1 min to 24 h pretreatment with 0.1 to 1 microM nicotine, i.e., in the range of smoker plasma nicotine levels. alpha4beta4-nAChR was similarly sensitive to persistent inactivation by prolonged nicotine exposure. Carbamylcholine exhibited slightly lower persistent inactivation potency than nicotine at both alpha4beta2- and alpha4beta4-nAChR. The nAChR antagonist, mecamylamine, exhibited persistent inactivation potency and efficacy similar to nicotine at alpha4beta2-nAChR but had a reduced effect on alpha4beta4-nAChR. These studies illustrate persistent inactivation of human alpha4beta2- or alpha4beta4-nAChR induced by prolonged exposure to nicotine and show that other ligands induce nAChR persistent inactivation in a subtype-specific manner.

N-n-alkylnicotinium analogs, a novel class of nicotinic receptor antagonists: interaction with alpha4beta2* and alpha7* neuronal nicotinic receptors.

The current study demonstrates that N-n-alkylnicotinium analogs with increasing n-alkyl chain lengths from 1 to 12 carbons have varying affinity (Ki = 90 nM-20 microM) for S-(-)-[3H]nicotine binding sites in rat striatal membranes. A linear relationship was observed such that increasing n-alkyl chain length provided increased affinity for the alpha4beta2* nicotinic acetylcholine receptor (nAChR) subtype, with the exception of N-n-octylnicotinium iodide (NONI). The most potent analog was N-n-decylnicotinium iodide (NDNI; Ki = 90 nM). In contrast, none of the analogs in this series exhibited high affinity for the [3H]methyllycaconitine binding site, thus indicating low affinity for the alpha7* nAChR. The C8 analog, NONI, had low affinity for S-(-)-[3H]nicotine binding sites but was a potent inhibitor of S-(-)-nicotine-evoked [3H]dopamine (DA) overflow from superfused striatal slices (IC50 = 0.62 microM), thereby demonstrating selectivity for the nAChR subtype mediating S-(-)-nicotine-evoked [3H]DA overflow (alpha3alpha6beta2* nAChRs). Importantly, the N-n-alkylnicotinium analog with highest affinity for the alpha4beta2* subtype, NDNI, lacked the ability to inhibit S-(-)-nicotine-evoked [3H]DA overflow and, thus, appears to be selective for alpha4beta2* nAChRs. Furthermore, the present study demonstrates that the interaction of these analogs with the alpha4beta2* subtype is via a competitive mechanism. Thus, selectivity for the alpha4beta2* subtype combined with competitive interaction with the S-(-)-nicotine binding site indicates that NDNI is an excellent candidate for studying the structural topography of alpha4beta2* agonist recognition binding sites, for identifying the antagonist pharmacophore on the alpha4beta2* nAChR, and for defining the role of this subtype in physiological function and pathological disease states.

Neurotoxic effects of the human immunodeficiency virus type-1 transcription factor Tat require function of a polyamine sensitive-site on the N-methyl-D-aspartate receptor.

Human immunodeficiency virus type-I (HIV-1) infection is often associated with neuronal loss in cortical and subcortical regions that may manifest as motor dysfunction and dementia. The function of the HIV-1 transcription protein Tat and subsequent activation of N-methyl-D-aspartate receptors (NMDAr) have been implicated in this form of neurodegeneration. However, it is unclear if Tat interacts directly with the NMDAr and the role of specific NMDAr subunit composition in mediating effects of Tat is also unclear. The present studies examined the ability of HIV-1 Tat1-72 protein (10 pM-1.0 microM) to displace [3H]MK-801 binding and to attenuate spermidine-induced potentiation of this binding in rat brain homogenate comprised of cerebellum, hippocampus, and cerebral cortex. The role of NMDAr polyamine-site function in the neurotoxic effects of Tat was determined using organotypic hippocampal slice cultures. Binding of [3H]MK-801 in adult rat brain homogenate was not reduced by Tat at concentrations below 1 microM. Tat potently inhibited the potentiation of [3H]MK-801 binding produced by co-exposure of membranes to the NMDAr co-agonist spermidine (IC(50)=3.74 nM). In hippocampal explants, Tat produced neurotoxicity in the CA3 and CA1 pyramidal cell layers, as well as in the dentate gyrus, that was significantly reduced by co-exposure to MK-801 (20 microM) and the NMDAr polyamine-site antagonist arcaine (10 microM). Exposure to the HIV-1 Tat deletion mutant (Tatdelta31-61) did not produce neurotoxicity in hippocampal explants. These data suggest that the neurotoxic effects of HIV-1 Tat are mediated, in part, by direct interactions with a polyamine-sensitive site on the NMDAr that positively modulates the function of this receptor.