Ozone uptake (flux) as it relates to ozone-induced foliar symptoms of Prunus serotina and Populus maximowiziixtrichocarpa.

Field studies were conducted during 2003 and 2004 from early June to the end of August, at 20 sites of lower or higher elevation within north-central Pennsylvania, using seedlings of black cherry (Prunus serotina, Ehrh.) and ramets of hybrid poplar (Populus maximowiziixtrichocarpa). A linear model was developed to estimate the influence of local environmental conditions on stomatal conductance. The most significant factors explaining stomatal variance were tree species, air temperature, leaf vapor pressure deficit, elevation, and time of day. Overall, environmental factors explained less than 35% of the variation in stomatal conductance. Ozone did not affect gas exchange rates in either poplar or cherry. Ozone-induced foliar injury was positively correlated with cumulative ozone exposures, expressed as SUM40. Overall, the amount of foliar injury was better correlated to a flux-based approach rather than to an exposure-based approach. More severe foliar injuries were observed on plants growing at higher elevations.

Physiological and foliar symptom response in the crowns of Prunus serotina, Fraxinus americana and Acer rubrum canopy trees to ambient ozone under forest conditions.

The crowns of five canopy dominant black cherry (Prunus serotina Ehrh.), five white ash (Fraxinus americana L.), and six red maple (Acer rubrum L.) trees on naturally differing environmental conditions were accessed with scaffold towers within a mixed hardwood forest stand in central Pennsylvania. Ambient ozone concentrations, meteorological parameters, leaf gas exchange and leaf water potential were measured at the sites during the growing seasons of 1998 and 1999. Visible ozone-induced foliar injury was assessed on leaves within the upper and lower crown branches of each tree. Ambient ozone exposures were sufficient to induce typical symptoms on cherry (0-5% total affected leaf area, LAA), whereas foliar injury was not observed on ash or maple. There was a positive correlation between increasing cumulative ozone uptake (U) and increasing percent of LAA for cherry grown under drier site conditions. The lower crown leaves of cherry showed more severe foliar injury than the upper crown leaves. No significant differences in predawn leaf water potential (psi(L)) were detected for all three species indicating no differing soil moisture conditions across the sites. Significant variation in stomatal conductance for water vapor (g(wv)) was found among species, soil moisture, time of day and sample date. When comparing cumulative ozone uptake and decreased photosynthetic activity (P(n)), red maple was the only species to show higher gas exchange under mesic vs. drier soil conditions (P < 0.05). The inconsistent differences in gas exchange response within the same crowns of ash and the uncoupling relationship between g(wv) and P(n) demonstrate the strong influence of heterogeneous environmental conditions within forest canopies.

Responses of hybrid poplar clones and red maple seedlings to ambient O(3) under differing light within a mixed hardwood forest.

The responses of ramets of hybrid poplar (Populus spp.) (HP) clones NE388 and NE359, and seedlings of red maple (Acer rubrum, L.) to ambient ozone (O(3)) were studied during May-September of 2000 and 2001 under natural forest conditions and differing natural sunlight exposures (sun, partial shade and full shade). Ambient O(3) concentrations at the study site reached hourly peaks of 109 and 98 ppb in 2000 and 2001, respectively. Monthly 12-h average O(3) concentrations ranged from 32.3 to 52.9 ppb. Weekly 12-h average photosynthetically active radiation (PAR) within the sun, partial shade and full shade plots ranged from 200 to 750, 50 to 180, and 25 to 75 micromol m(-2) s(-1), respectively. Ambient O(3) exposure induced visible foliar symptoms on HP NE388 and NE359 in both growing seasons, with more severe injury observed on NE388 than on NE359. Slight foliar symptoms were observed on red maple seedlings during the 2001 growing season. Percentage of total leaf area affected (%LAA) was positively correlated with cumulative O(3) exposures. More severe foliar injury was observed on plants grown within the full shade and partial shade plots than those observed on plants grown within the sun plot. Lower light availability within the partial shade and full shade plots significantly decreased net photosynthetic rate (Pn) and stomatal conductance (g(wv)). The reductions in Pn were greater than reductions in g(wv), which resulted in greater O(3) uptake per unit Pn in plants grown within the partial shade and full shade plots. Greater O(3) uptake per unit Pn was consistently associated with more severe visible foliar injury in all species and/or clones regardless of differences in shade tolerance. These studies suggest that plant physiological responses to O(3) exposure are likely complicated due to multiple factors under natural forest conditions.

Influence of light fleck and low light on foliar injury and physiological responses of two hybrid poplar clones to ozone.

Five-month old hybrid poplar clones NE388 and NE359 were exposed to square-wave 30, 55, and 80 ppb O(3) (8 h/day, 7 day/week) under constant high light (HL) and light fleck (LF) during 28 May-29 June 1999, and exposed to 30 and 55 ppb O(3) under HL, LF, and constant low light (LL) during 22 May-28 June 2000 within Continuously Stirred Tank Reactors (CSTR) in a greenhouse. Ramets of these two hybrid clones received similar total photosynthetically active radiation (PAR) within the LF and LL treatments. Visible foliar symptoms, leaf gas exchange, and growth were measured. More severe O(3) induced foliar symptoms were observed on ramets within the LF and LL treatments than within the HL treatment for both clones. The LF treatment resulted in significantly greater foliar injury than the LL treatment for NE388. The LF and LL treatments generally resulted in lower photosynthetic rates (Pn) for both clones, but did not affect stomatal conductance (g(wv)); therefore, the ratios of g(wv)/Pn and the O(3) uptake/Pn were greatest in plants grown under the LF treatment, followed by those grown under LL treatment; plants grown under HL had the lowest ratios of g(wv)/Pn and O(3) uptake/Pn. Greater ratios of g(wv)/Pn and O(3) uptake/Pn were consistently associated with more severe visible foliar symptoms. The negative impacts of the LF treatment on growth were greater than those of the LL treatment. Results indicate that not only the integral, but also the pattern of photo flux density, may affect carbon gain in plants. Increased foliar injury may be expected under light fleck conditions due to the limited repair capacity as a result of continuity of O(3) uptake while photosynthesis decreases under LL conditions.

Response of native plants of northeastern United States and southern Spain to ozone exposures; determining exposure/response relationships.

Tropospheric ozone has been identified as the most important regional scale air pollutant across much of eastern United States of America and many areas of Mediterranean climes in southern Europe. Recent field surveys in the northeastern USA and in southeastern Spain have revealed many additional plant species that exhibit symptoms typical of ozone-induced injuries. Objectives of this study were to confirm ozone as the cause of the observed foliar symptoms, determine ozone induced exposure/response relationships, and identify possible bio-indicator species. Thirteen native species of northeastern USA and 27 native species of southeastern Spain were selected for study. Plant species were exposed to ozone within 16 CSTR chambers in a greenhouse during the summer seasons of 2000 and 2001; ozone exposures of 30, 60, 90, and 120 ppb were delivered for 7 h/day, 5 days/week. Results have confirmed that with few exceptions, symptoms observed in the field were induced by exposures to ambient ozone. Species differed significantly in terms of the exposures required for the initiation of visible symptoms and subsequent injury progression.

Use of bioindicators and passive sampling devices to evaluate ambient ozone concentrations in north central Pennsylvania.

Ambient concentrations of tropospheric ozone and ozone-induced injury to black cherry (Prunus serotina) and common milkweed (Asclepias syriaca) were determined in north central Pennsylvania from 29 May to 5 September 2000 and from 28 May to 18 September 2001. Ogawa passive ozone samplers were utilized within openings at 15 forested sites of which six were co-located with TECO model 49 continuous ozone monitors. A significant positive correlation was observed between the Ogawa passive samplers and the TECO model 49 continuous ozone monitors for the 2000 (r=0.959) and 2001 (r=0.979) seasons. In addition, a significant positive correlation existed in 2000 and 2001 between ozone concentration and elevation (r=0.720) and (r=0.802), respectively. Classic ozone-induced symptoms were observed on black cherry and common milkweed. In 2000, initial injury was observed in early June, whereas for the 2001 season, initial injury was initially observed in late June. During both seasons, injury was noted at most sites by mid- to late-July. Soil moisture potential was measured for the 2001 season and a significant positive relationship (P<0.001) showed that injury to black cherry was a function of cumulative ozone concentrations and available soil moisture.

Physiological and foliar injury responses of Prunus serotina, Fraxinus americana, and Acer rubrum seedlings to varying soil moisture and ozone.

Sixteen black cherry (Prunus serotina, Ehrh.), 10 white ash (Fraxinus americana, L.) and 10 red maple (Acer rubrum, L.) 1-year old seedlings were planted per plot in 1997 on a former nursery bed within 12 open-top chambers and six open plots. Seedlings were exposed to three different ozone scenarios (ambient air: 100% O3; non-filtered air: 98% ambient O3; charcoal-filtered air: 50% ambient O3) within each of two different water regimes (nine plots irrigated, nine plots non-irrigated) during three growing seasons. During the 1998 and 1999 growing season, leaf gas exchange, plant water relations, and foliar injury were measured. Climatic data,ambient- and chamber-ozone-concentrations were monitored. We found that seedlings grown under irrigated conditions had similar (in 1998) but significantly higher gas exchange rates (in 1999) than seedlings grown within non-irrigated plots among similar ozone exposures. Cherry and ash had similar ozone uptake but cherry developed more ozone-induced injury (< 34% affected leaf area, LAA) than ash (<5% LAA), while maple rarely showed foliar injury, indicating the species differed in ozone sensitivity. Significantly more severe injury on seedlings grown under irrigated conditions than seedlings grown under non-irrigated conditions demonstrated that soil moisture altered seedling responses to ambient ozone exposures.

A 13-week comparison of passive and continuous ozone monitors at forested sites in north-central Pennsylvania.

Ogawa passive O3 samplers were used in a 13-week study (June 1-September 1, 1999) involving 11 forested and mountaintop sites in north-central Pennsylvania. Four of the sites were collocated with TECO model 49 O3 analyzers. A significant correlation (p < 0.0001) was found for 24-hr average weekly O3 concentrations between the two methodologies at the four sites with collocated monitors. As expected, there were positive relationships between increasing elevation of the sites and increasing O3 concentrations. No O3 exposure patterns were found on a west-to-east or south-to-north basis; however, the area known for lower O3 exposures within a smaller subsection of the study area showed consistently lower O3 exposures. Preliminary results regarding relationships of symptom responses within O3-sensitive bioindicators are also presented with black cherry (Prunus serotina, Ehrh.) and common milkweed (Asclepias syriaca, L.) showing clear evidence of increasing injury with increasing O3 exposures. Due to the extremely dry conditions encountered in north-central Pennsylvania during the 1999 growing season, O3-induced symptoms were sporadic and quite delayed until late-season rains during the latter portion of the observation period.

Inverse agonist actions of typical and atypical antipsychotic drugs at the human 5-hydroxytryptamine(2C) receptor.

Atypical antipsychotic drugs, which are distinguished from typical antipsychotic drugs by a lower incidence of extra-pyramidal side effects and less propensity to elevate serum prolactin levels (e.g., clozapine, olanzapine, risperidone, quetiapine, ziprasidone), have become the most widely used treatments for schizophrenia, although their precise mechanism of action remains controversial. It has been suggested that this group of atypical antipsychotic drugs is characterized by preferentially high affinities for 5-hydroxytryptamine (5-HT)2A serotonin receptors and relatively low affinities for D2-dopamine receptors. It has recently been proposed that these atypical antipsychotic drugs may also be distinguished from typical antipsychotic drugs (e.g., haloperidol, fluphenazine, chlorpromazine, and so on) by inverse agonist actions at the 5-HT2C-INI RNA edited isoform of the human 5-HT2C receptor transiently expressed in COS-7 cells. We have examined the relationship among 5-HT2C inverse agonist potency, efficacy, and atypical antipsychotic drug status in HEK-293 cells of a large number of typical and atypical antipsychotic drugs using human embryonic kidney (HEK)-293 cells stably transfected with the h5-HT2C-INI receptor. Inverse agonist actions at h5-HT2C-INI receptors were measured for both typical and atypical antipsychotic drugs. Thus, some typical antipsychotic drugs (chlorpromazine, mesoridazine, fluphenazine, and loxapine) were efficient inverse agonists, whereas several clinically effective atypical antipsychotic drugs (remoxapride, quetiapine, sulpiride, melperone, amperozide) were not. Additionally, several drugs without significant antipsychotic actions (M100907, ketanserin, mianserin, ritanserin, and amitriptyline) were potent inverse agonists at the 5-HT2C-INI isoform expressed in HEK-293 cells. Taken together, these results demonstrate that both typical and atypical antipsychotic drugs may exhibit inverse agonist effects at the 5-HT2C-INI isoform of the human 5-HT2C receptor and that no relationship exists between inverse agonist actions and atypicality.

Synthesis of potent and selective dopamine D(4) antagonists as candidate radioligands.

A series of dopamine D(4) antagonists was synthesized and evaluated as potential candidates for development as positron emission tomography (PET) radioligands. All new compounds display high affinity and selectivity for the D(4) receptors and compounds 5b, 5d, and 5e were identified as candidates for radioligand development.

Exploring the relationship between binding modes of 9-(aminomethyl)-9,10-dihydroanthracene and cyproheptadine analogues at the 5-HT2A serotonin receptor.

Comparison of the serotonin 5-HT2A receptor affinities of a parallel series of structural analogues of the novel ligand 9-aminomethyl-9,10-dihydroanthracene (AMDA) and a structurally similar prototypical tricyclic amine cyproheptadine suggests that the two agents bind to the receptor in different fashions. Examination of ligand-receptor model complexes supports the experimental data and suggests a potential origin for the differences in binding modes.

Influence of chain length and N-alkylation on the selective serotonin receptor ligand 9-(aminomethyl)-9,10-dihydroanthracene.

Comparison of the serotonin 5-HT2A receptor affinities of chain lengthened and N-alkylated analogues of the novel ligand 9-aminomethyl-9,10-dihydroanthracene (AMDA) and a structurally similar prototypical tricyclic amine imipramine suggests that the two agents bind to the receptor in different fashions. The demonstration that AMDA is highly selective for serotonin receptors (5-HT2A, K = 20nM; 5-HT2C, Ki=43nM) versus the dopamine D2 receptor (Ki>10,000nM), as well as the serotonin and norepinephrine transporters (Ki>10,000nM) further suggests that AMDA and the nonselective ligand imipramine interact with these target macromolecules in different ways.

N1-(Benzenesulfonyl)tryptamines as novel 5-HT6 antagonists.

N-Benzenesulfonyl-5-methoxy-N,N-dimethyltryptamine (BS/5-OMe DMT; 5) was shown to bind at human 5-HT6 serotonin receptors with high affinity (Ki = 2.3 nM) relative to serotonin (Ki = 78 nM). Structural variation failed to result in significantly enhanced affinity. BS/5-OMe DMT acts as an antagonist of 5-HT-stimulated adenylate cyclase (pA2 = 8.88 nM) and may represent the first member of a novel class of 5-HT6 antagonists.

A highly conserved aspartic acid (Asp-155) anchors the terminal amine moiety of tryptamines and is involved in membrane targeting of the 5-HT(2A) serotonin receptor but does not participate in activation via a "salt-bridge disruption" mechanism.

Discovering the molecular and atomic mechanism(s) by which G-protein-coupled receptors (GPCRs) are activated by agonists remains an elusive goal. Recently, studies examining two representative GPCRs (rhodopsin and alpha(1b)-adrenergic receptors) have suggested that the disruption of a putative "salt-bridge" between highly conserved residues in transmembrane (TM) helix III, involving aspartate or glutamate, and helix VII, involving a basic residue, results in receptor activation. We have tested whether this is a general mechanism for GPCR activation by constructing a model of the 5-hydroxytryptamine (5-HT)(2A) receptor and characterizing several mutations at the homologous residues (Asp-155 and Asn-363) of the 5-HT(2A) serotonin receptor. All of the mutants (D155A, D155N, D155E, D155Q, and S363A) resulted in receptors with reduced basal activity; in no case was evidence for constitutive activity revealed. Structure-function studies with tryptamine analogs and various Asp-155 mutants demonstrated that Asp-155 interacts with the terminal, and not indole, amine moiety of 5-HT(2A) agonists. Interestingly, the D155E mutation interfered with the membrane targeting of the 5-HT(2A) receptor, and an inverse relationship was discovered when comparing receptor activation and targeting for a series of Asp-155 mutants. This represents the first known instance in which a charged residue located in a putative TM helix alters the membrane targeting of a GPCR. Thus, for 5-HT(2A) receptors, the TMIII aspartic acid (Asp-155) is involved in anchoring the terminal amine moiety of indole agonists and in membrane targeting and not in receptor activation by salt-bridge disruption.

2-Substituted tryptamines: agents with selectivity for 5-HT(6) serotonin receptors.

Several 2-alkyl-5-methoxytryptamine analogues were designed and prepared as potential 5-HT(6) serotonin agonists. It was found that 5-HT(6) receptors accommodate small alkyl substituents at the indole 2-position and that the resulting compounds can bind with affinities comparable to that of serotonin. In particular, 2-ethyl-5-methoxy-N, N-dimethyltryptamine (8) binds with high affinity at human 5-HT(6) receptors (K(i) = 16 nM) relative to 5-HT (K(i) = 75 nM) and was a full agonist, at least as potent (8: K(act) = 3.6 nM) as serotonin (K(act) = 5.0 nM), in activating adenylate cyclase. Compound 8 displays modest affinity for several other populations of 5-HT receptors, notably h5-HT(1A) (K(i) = 170 nM), h5-HT(1D) (K(i) = 290 nM), and h5-HT(7) (K(i) = 300 nM) receptors, but is otherwise quite selective. Compound 8 represents the first and most selective 5-HT(6) agonist reported to date. Replacing the 2-ethyl substituent with a phenyl group results in a compound that retains 5-HT(6) receptor affinity (i.e., 10: K(i) = 20 nM) but lacks agonist character. 2-Substituted tryptamines, then, might allow entry to a novel class of 5-HT(6) agonists and antagonists.

Evidence for possible involvement of 5-HT(2B) receptors in the cardiac valvulopathy associated with fenfluramine and other serotonergic medications.

BACKGROUND: Serotonergic medications with various mechanisms of action are used to treat psychiatric disorders and are being investigated as treatments for drug dependence. The occurrence of fenfluramine-associated valvular heart disease (VHD) has raised concerns that other serotonergic medications might also increase the risk of developing VHD. We hypothesized that fenfluramine or its metabolite norfenfluramine and other medications known to produce VHD have preferentially high affinities for a particular serotonin receptor subtype capable of stimulating mitogenesis. METHODS AND RESULTS: Medications known or suspected to cause VHD (positive controls) and medications not associated with VHD (negative controls) were screened for activity at 11 cloned serotonin receptor subtypes by use of ligand-binding methods and functional assays. The positive control drugs were (+/-)-fenfluramine; (+)-fenfluramine; (-)-fenfluramine; its metabolites (+/-)-norfenfluramine, (+)-norfenfluramine, and (-)-norfenfluramine; ergotamine; and methysergide and its metabolite methylergonovine. The negative control drugs were phentermine, fluoxetine, its metabolite norfluoxetine, and trazodone and its active metabolite m-chlorophenylpiperazine. (+/-)-, (+)-, and (-)-Norfenfluramine, ergotamine, and methylergonovine all had preferentially high affinities for the cloned human serotonin 5-HT(2B) receptor and were partial to full agonists at the 5-HT(2B) receptor. CONCLUSIONS: Our data imply that activation of 5-HT(2B) receptors is necessary to produce VHD and that serotonergic medications that do not activate 5-HT(2B) receptors are unlikely to produce VHD. We suggest that all clinically available medications with serotonergic activity and their active metabolites be screened for agonist activity at 5-HT(2B) receptors and that clinicians should consider suspending their use of medications with significant activity at 5-HT(2B) receptors.

9-(Aminomethyl)-9,10-dihydroanthracene is a novel and unlikely 5-HT2A receptor antagonist.

Structural elaboration of phenylethylamine to 9-(aminomethyl)-9,10-dihydroanthracene (AMDA) produces an agent with high affinity (Ki = 9.5-21 nM) at 5-HT2A receptors. It was shown that AMDA acts as a 5-HT2A receptor antagonist. The structure and molecular geometry of AMDA are not consistent with existing pharmacophore models for 5-HT2A receptor antagonist activity. Thus, AMDA may be a structurally novel parent of a new class of 5-HT2A receptor antagonists that binds to the receptor in a unique fashion that is distinct from the binding topology of existing 5-HT2A receptor antagonists.

Foliar response of black cherry (Prunus serotina) clones to ambient ozone exposure in central Pennsylvania.

During late summer of 1996 and 1997 we examined ozone-induced foliar injury in a plantation of 111 black cherry trees (ramets) comprising 15 clones originating from wild ortets growing in the Allegheny National Forest, Pennsylvania, and the Monongahela National Forest, West Virginia. The experimental plantation was a clonal seed orchard in Centre County, Pennsylvania, started in 1971 using ortet buds grafted onto seedling rootstocks of mixed origin. Clones differed significantly in severity of foliar injury symptoms (F=31.83, p<0.001). One clone (R-12) had significantly more foliar injury with >50% leaf area affected than other clones during both years. In contrast, clone R-14, which is from the same area in northcentral Pennsylvania as R-12, exhibited significantly less injury (LAA<6%). Although ambient O(3) concentrations were similar in both years, foliar injury was significantly greater (15.7%) in 1996 than in 1997 (9.9%). This is probably explained by lower stomatal conductance in 1997 caused by drier and hotter weather patterns in June and July of that year. Despite very different weather patterns and overall levels of injury in 1996 and 1997, mean clonal injury was significantly correlated between both years of assessment (r=0.92, p<0.001). Within tree crowns, foliage in lower and inner crown positions was significantly more injured than foliage in upper and exterior crown positions. There was no evidence of geographically based population differences in sensitivity to foliar O(3) injury. On the contrary, results demonstrate that wild genotypes of proximal geographic origin may differ greatly in sensitivity.

Observations of ozone-induced foliar injury on black cherry (Prunus serotina, var. capuli) within the Desierto de Los Leones National Park, Mexico City.

A survey for ozone-induced foliar injury of black cherry was conducted in mid-June 1995 within the Desierto de Los Leones National Park located southwest of Mexico City. Evaluations of the upper and lower tree crowns of 18 trees revealed evidence of significant upper surface stipple, leaf reddening and premature senescence on 72% of the trees. A general survey of an additional 169 trees disclosed that 41% exhibited similar symptoms. A gradient of increasing symptoms with increasing elevation was also evident. For the most part, asymptomatic trees were observed to be situated within well-shaded coves at the lower elevations with very few symptomatic trees present in these areas.

Light environment alters ozone uptake per net photosynthetic rate in black cherry trees.

Foliar ozone uptake rates of different-sized black cherry (Prunus serotina Ehrh.) trees were compared within a deciduous forest and adjacent openings in north-central Pennsylvania during one growing season. Study trees included open-grown seedlings and saplings, forest understory seedlings and saplings, and sunlit and shaded portions of mature canopy tree crowns. Instantaneous ozone uptake rates were highest in high-light environments primarily because of higher stomatal conductances. Low ozone uptake rates of seedlings and saplings in the forest understory could be attributed partially to lower average ambient ozone concentrations compared to the canopy and open environments. Among the tree size and light combinations tested, ozone uptake rates were highest in open-grown seedlings and lowest in forest-grown seedlings. Despite lower ozone uptake rates of foliage in shaded environments, ozone uptake per net photosynthesis of foliage in shaded environments was significantly higher than that of foliage in sunlit environments because of weaker coupling between net photosynthesis and stomatal conductance in shaded environments. The potential for greater ozone injury in shaded environments as a result of greater ozone uptake per net photosynthesis is consistent with previous reports of greater ozone injury in shaded foliage than in sunlit foliage.