CO2 Stimulation Research Articles

A spatiotemporal comparison between olfactory and trigeminal event-related potentials

The present study compared the temporal and spatial aspects of human olfactory and trigeminal processing. A relatively selective trigeminal stimulus, CO2, and a relatively selective olfactory stimulus, H2S, were delivered with an olfactometer to young, healthy volunteers. The analysis was performed in a classical (5-electrode, main ERPs peaks) and modern approach (high topographical resolution, inverse solution, source localization). Results of microstate segmentation highlighted 5 maps that generally described the two processes at cerebral level. The trigeminal response differed from the olfactory response up to 300ms after stimulus onset. In this time range, source analysis pointed out that the olfactory stimulation involved olfactory related areas, while trigeminal stimulation involved noxious/somatosensory specific brain areas. Moreover, from 300ms on our data showed a similarity between the two processes. Statistical parametrical mapping of the differences between conditions suggested greater activation in a specific motor/sniffing network for the CO2 stimulation (probably related to a regulation of the potential noxious stimulus) and a greater activation of the ipsilateral primary olfactory cortex for H2S.

Sea anemones may thrive in a high CO2 world

Increased seawater pCO2 , and in turn 'ocean acidification' (OA), is predicted to profoundly impact marine ecosystem diversity and function this century. Much research has already focussed on calcifying reef-forming corals (Class: Anthozoa) that appear particularly susceptible to OA via reduced net calcification. However, here we show that OA-like conditions can simultaneously enhance the ecological success of non-calcifying anthozoans, which not only play key ecological and biogeochemical roles in present day benthic ecosystems but also represent a model organism should calcifying anthozoans exist as less calcified (soft-bodied) forms in future oceans. Increased growth (abundance and size) of the sea anemone (Anemonia viridis) population was observed along a natural CO2 gradient at Vulcano, Italy. Both gross photosynthesis (PG ) and respiration (R) increased with pCO2 indicating that the increased growth was, at least in part, fuelled by bottom up (CO2 stimulation) of metabolism. The increase of PG outweighed that of R and the genetic identity of the symbiotic microalgae (Symbiodinium spp.) remained unchanged (type A19) suggesting proximity to the vent site relieved CO2 limitation of the anemones' symbiotic microalgal population. Our observations of enhanced productivity with pCO2 , which are consistent with previous reports for some calcifying corals, convey an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater pCO2 . Understanding how CO2 -enhanced productivity of non- (and less-) calcifying anthozoans applies more widely to tropical ecosystems is a priority where such organisms can dominate benthic ecosystems, in particular following localized anthropogenic stress.

Probing for the influence of atmospheric CO2 and climate change on forest ecosystems across biomes

AbstractAimRising atmospheric CO 2 and climate warming have induced changes in tree growth and intrinsic water‐use efficiency (iWUE) world‐wide, but the long‐term impact of such changes on terrestrial productivity remains unknown. Based on a synthesis of the literature, here we investigate the net impact of recent atmospheric changes across forest biomes.LocationA range of sites covering major forest biomes.MethodsWe use dendrochronological and isotopic records to provide an integrated analysis of changes in growth and iWUE, evaluating the impacts of atmospheric changes in tree growth. In our analysis, positive relationships between changes in growth and iWUE reflect CO 2 stimulation, while neutral effects yield inflections in growth curves (plotted against iWUE), and negative relationships indicate the prevalence of stressors. To estimate net effects (since 1960) and compare responses across biomes, we use a response contrast (RC) index, based on the ratio between cumulative changes in growth and iWUE.ResultsIn 37 recently published case studies changes in iWUE were consistently positive, increasing by between 10 and 60%, but shifts in growth varied widely within and among forest biomes. Positive RC values were observed in high latitudes (> 40°N), while progressively lower (always negative) responses were observed toward lower latitudes. Growth rates declined between 15 and 55% in tropical forests. In subtropical sites growth declined by between 7 and 10%, while mixed responses occurred in other regions.Main conclusionsOver the past 50 years, tree growth decline has prevailed despite increasing atmospheric CO 2. The impact of atmospheric changes on forest productivity is latitude dependent (R 2 = 0.9, P < 0.05), but our results suggest that, globally, CO 2 stimulation of mature trees will not counteract emissions. In most surveyed case studies warming‐induced stress was evoked to explain growth decline, but other factors, such as nutrient limitation, could have overridden the potential benefits of rising CO 2 levels.

Multivariate modeling of cognitive-motor stimulation on neurovascular coupling: transcranial Doppler used to characterize myogenic and metabolic influences

Neural activation induces changes in cerebral blood flow velocity (CBFV) with separate contributions from resistance-area product (V(RAP)) and critical closing pressure (V(CrCP)). We modeled the dependence of V(RAP) and V(CrCP) on arterial blood pressure (ABP), end-tidal CO(2) (EtCO(2)), and cognitive stimulation to test the hypothesis that V(RAP) reflects myogenic activity while V(CrCP) reflects metabolic pathways. In 14 healthy subjects, CBFV was measured with transcranial Doppler ultrasound, ABP with the Finapres device and EtCO(2) with infrared capnography. Two different paradigms (word or puzzle) were repeated 10 times (30 s on-off), and the corresponding square-wave signal was used, together with ABP and EtCO(2), as inputs to autoregressive-moving average (ARMA) models, which allowed identification of the separate contributions of the three inputs to either V(RAP) or V(CrCP). For both paradigms, the contribution of ABP was mainly manifested through V(RAP) (P < 0.005 for word; P < 0.004 for puzzle), while stimulation mainly contributed to V(CrCP) (P < 0.002 for word; P < 0.033, for puzzle). The contribution of EtCO(2) was relatively small (<10%) with greater contribution to V(CrCP) (P < 0.01 for puzzle; not significant for word). Separate step responses were also obtained for each of the three inputs. ARMA modeling of V(RAP) and V(CrCP) allows the separation of the effects of cerebral autoregulation and CO(2) reactivity from the main effects of cognitive-motor stimulation and have the potential to improve the diagnostic value of neurovascular coupling testing in physiological and clinical studies.

Feedback from plant species change amplifies CO2 enhancement of grassland productivity

Dynamic global vegetation models simulate feedbacks of vegetation change on ecosystem processes, but direct, experimental evidence for feedbacks that result from atmospheric CO2 enrichment is rare. We hypothesized that feedbacks from species change would amplify the initial CO2 stimulation of aboveground net primary productivity (ANPP) of tallgrass prairie communities. Communities of perennial forb and C4 grass species were grown for 5years along a field CO2 gradient (250-500μLL(-1) ) in central Texas USA on each of three soil types, including upland and lowland clay soils and a sandy soil. CO2 enrichment increased community ANPP by 0-117% among years and soils and increased the contribution of the tallgrass species Sorghastrum nutans (Indian grass) to community ANPP on each of the three soil types. CO2 -induced changes in ANPP and Sorghastrum abundance were linked. The slope of ANPP-CO2 regressions increased between initial and final years on the two clay soils because of a positive feedback from the increase in Sorghastrum fraction. This feedback accounted for 30-60% of the CO2 -mediated increase in ANPP on the upland and lowland clay soils during the final 3years and 1year of the experiment, respectively. By contrast, species change had little influence on the ANPP-CO2 response on the sandy soil, possibly because Sorghastrum increased largely at the expense of a functionally similar C4 grass species. By favoring a mesic C4 tall grass, CO2 enrichment approximately doubled the initial enhancement of community ANPP on two clay soils. The CO2 -stimulation of grassland productivity may be significantly underestimated if feedbacks from plant community change are not considered.

Excess CO2 supply inhibits mixotrophic growth of Chlorella protothecoides and Nannochloropsis salina

Mixotrophy can be exploited to support algal growth over night or in dark-zones of a photobioreactor. In order to achieve the maximal productivity, however, it is fundamental also to provide CO2 in excess to maximize photosynthetic activity and phototropic biomass production. The aim of this paper is to verify the possibility of exploiting mixotrophy in combination with excess CO2. Two species with high biomass productivity were selected, Nannochloropsis salina and Chlorella protothecoides. Different organic substrates available at industrial scale were tested, and glycerol chosen for its ability to support growth of both species. In mixotrophic conditions, excess CO2 stimulated photosynthesis but blocked the metabolization of the organic substrate, thus canceling the advantages of mixotrophy. By cultivating microalgae under day–night cycle, organic substrate supported growth during the night, but only if CO2 supply was not provided. This represents thus a possible method to reconcile CO2 stimulation of photosynthesis with mixotrophy.

Plant−Soil Distribution of Potentially Toxic Elements in Response to Elevated Atmospheric CO2

The distribution of contaminant elements within ecosystems is an environmental concern because of these elements' potential toxicity to animals and plants and their ability to hinder microbial ecosystem services. As with nutrients, contaminants are cycled within and through ecosystems. Elevated atmospheric CO2 generally increases plant productivity and alters nutrient element cycling, but whether CO2 causes similar effects on the cycling of contaminant elements is unknown. Here we show that 11 years of experimental CO2 enrichment in a sandy soil with low organic matter content causes plants to accumulate contaminants in plant biomass, with declines in the extractable contaminant element pools in surface soils. These results indicate that CO2 alters the distribution of contaminant elements in ecosystems, with plant element accumulation and declining soil availability both likely explained by the CO2 stimulation of plant biomass. Our results highlight the interdependence of element cycles and the importance of taking a broad view of the periodic table when the effects of global environmental change on ecosystem biogeochemistry are considered.

Species‐specific tree growth responses to 9 years of CO2 enrichment at the alpine treeline

Summary 1. Using experimental atmospheric CO2 enrichment, we tested for tree growth stimulation at the high‐elevation treeline, where there is overwhelming evidence that low temperature inhibits growth despite an adequate carbon supply. We exposed Larix decidua (European larch) and Pinus mugo ssp. uncinata (mountain pine) to 9 years of free‐air CO2 enrichment (FACE) in an in situ experiment at treeline in the Swiss Alps (2180 m a.s.l.). 2. Accounting for pre‐treatment vigour of individual trees, tree ring increments throughout the experimental period were larger in Larix growing under elevated CO2 but not in Pinus. The magnitude of the CO2 response in Larix ring width varied over time, with a significant stimulation occurring in treatment years 3–7 (marginal in year 6). 3. After 9 years of treatment, leaf canopy cover, stem basal area and total new shoot production were overall greater in Larix trees growing under elevated CO2, whereas Pinus showed no such cumulative growth response. The Larix ring width response in years 3–7 could have caused the cumulative CO2 effect on tree size even if no further stimulation occurred, so it remains unclear if responsiveness was sustained over the longer term. 4. Larix ring width was stimulated more by elevated CO2 in years with relatively high spring temperatures and an early snowmelt date, suggesting that temperatures were less limiting in these years and greater benefit was gained from extra carbon assimilated under elevated CO2. The magnitude of CO2 stimulation was also larger after relatively high temperatures and high solar radiation in the preceding growing season, perhaps reflecting gains due to larger carbon reserves. 5. Synthesis. Contrasting above‐ground growth responses of two treeline tree species to elevated CO2 concentrations suggest that Larix will have a competitive advantage over less responsive species, such as co‐occurring Pinus, under future CO2 concentrations. Stimulation of Larix growth might be especially pronounced in a future warmer climate.

The effect of increased genioglossus activity and end-expiratory lung volume on pharyngeal collapse

Increasing either genioglossus muscle activity (GG) or end-expiratory lung volume (EELV) improves airway patency but not sufficiently for adequate treatment of obstructive sleep apnea (OSA) in most patients. The mechanisms by which these variables alter airway collapsibility likely differ, with increased GG causing airway dilation, whereas increased EELV may stiffen the airway walls through caudal traction. We sought to determine whether the airway stabilizing effect of GG activation is enhanced when EELV is increased. To investigate this aim, 15 continuous positive airway pressure (CPAP)-treated OSA patients were instrumented with an epiglottic catheter, intramuscular GG-EMG electrodes, magnetometers, and a nasal mask/pneumotachograph. Subjects slept supine in a sealed, head-out plastic chamber in which the extra-thoracic pressure could be lowered (to raise EELV) while on nasal CPAP with a variable deadspace to allow CO(2) stimulation (and GG activation). The pharyngeal critical closing pressure (P(CRIT)) was measured by sudden reduction of CPAP for three to five breaths each minute during non-rapid eye movement (NREM) sleep in 4 conditions: a) baseline, b) 500 ml increased EELV, c) 50% increased GG, and d) conditions b and c combined. P(CRIT) was found to be reduced from 2.2 + or - 0.7 cmH(2)O at baseline to -1.0 + or - 0.5 with increased EELV, 0.6 + or - 0.7 with increased GG and -1.6 + or - 0.7 when both variables were raised (P < 0.001). The slope of the P(CRIT) curves remained unchanged in all conditions (P = 0.05). However, the CPAP level at which flow limitation developed was lower in both increased EELV conditions (P = 0.001). These findings indicate that while both increased GG and EELV improve airway collapsibility, the combination of both variables has little additional effect over increasing EELV alone.

Transient responses to increasing CO2 and climate change in an unfertilized grass–clover sward

Mechanisms controlling transient responses to elevated CO2 concentration and climate change in an unfertilized grassland on the Swiss Plateau were examined in light of simulations with PROGRASS, a process-based model of grass-clover interactions. Daily weather for a series of tran- sient climate scenarios spanning the 21st century were developed for the study site with the help of the LARS-WG weather generator. Changes in the length of dry and wet spells, temperature, precip- itation and solar radiation defining the scenarios were obtained from regional climate simulations carried out in the framework of the PRUDENCE project. Compared to 1961-1990, the latter indicated that for 2071-2100 there would be a noticeable increase in temperature (roughly 3°C in winter and 5°C in summer), a significant drop in summer precipitation (of the order of -30%) and a nearly 2-fold increase in the length of dry spells. Assuming that clover is less drought-tolerant than grass, we examined whether clover abundance would decrease as a consequence of increasing heat and water stress, or be promoted on account of CO2 stimulation. Results indicated that: (1) at our site, climate change alone did not curtail biological N2 fixation to the point as to alter the composition of the sward but nevertheless entailed a decrease in grassland productivity; (2) increasing CO2 clearly promoted clover growth (via feedbacks on nitrogen acquisition) and grassland productivity; and (3) even with CO2 stimulation, the additional N input from symbiotic N2 fixation was not sufficient to substantially improve the mineral N status of the system and promote grass competitiveness.

Simulation and evaluation of terrestrial ecosystem NPP with M-SDGVM over continental China

Using the regional terrestrial Net Primary Production (NPP) from different observations and models over China, we validated the NPP simulations and explored the relationship between NPP and climate variation at interannual and decadal scales in the Modified Sheffield Dynamic Global Vegetation Model (M-SDGVM) during 1981–2000. M-SDGVM shows agreement with the NPP data from 743 sites under the Global Primary Production Data Initiative (GPPDI). The spatial and the zonal averaged NPP of M-SDGVM agree well with different historic datasets and are closest to the IGBP NPP. Compared to the 1980s, NPP in the 1990s increases in most of China with a high degree of spatial heterogeneity. The multi-year mean NPP of forest types is reasonably modeled (above 500 g C m−2 yr−1) while that of C3 path of photosynthesis (C3) grasslands is underestimated. The NPP of 7 M-SDGVM main plant functional types (PFTs) increases and the increment of the broad-leaved deciduous forest is the most obvious (5.05 g C m−2 yr−1). During the studied period, the annual NPP of M-SDGVM over China increases, with significant fluctuations, at an average rate of 0.0164 Gt C yr−1. Regulated by annual temperature and precipitation, the interannual variation of the total NPP shows more significant correlation with temperature (relativity and probability are R= 0.61, P = 0.00403) than precipitation (R = 0.40, P = 0.08352). CO2 fertilization may play a key role in the increase of terrestrial ecosystem NPP over continental China, and CO2 stimulation increases with CO2 concentrations, and also with the climate variability of the 1980s and 1990s.

Influence of elevated CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentrations on cell division and nitrogen fixation rates in the bloom-forming cyanobacterium &amp;lt;i&amp;gt;Nodularia spumigena&amp;lt;/i&amp;gt;

Abstract. The surface ocean absorbs large quantities of the CO2 emitted to the atmosphere from human activities. As this CO2 dissolves in seawater, it reacts to form carbonic acid. While this phenomenon, called ocean acidification, has been found to adversely affect many calcifying organisms, some photosynthetic organisms appear to benefit from increasing [CO2]. Among these is the cyanobacterium Trichodesmium, a predominant diazotroph (nitrogen-fixing) in large parts of the oligotrophic oceans, which responded with increased carbon and nitrogen fixation at elevated pCO2. With the mechanism underlying this CO2 stimulation still unknown, the question arises whether this is a common response of diazotrophic cyanobacteria. In this study we therefore investigate the physiological response of Nodularia spumigena, a heterocystous bloom-forming diazotroph of the Baltic Sea, to CO2-induced changes in seawater carbonate chemistry. N. spumigena reacted to seawater acidification/carbonation with reduced cell division rates and nitrogen fixation rates, accompanied by significant changes in carbon and phosphorus quota and elemental composition of the formed biomass. Possible explanations for the contrasting physiological responses of Nodularia compared to Trichodesmium may be found in the different ecological strategies of non-heterocystous (Trichodesmium) and heterocystous (Nodularia) cyanobacteria.

Developmental neurotoxicity impairs ventilatory control: insight from an amphibian model

Neurotoxins (nicotine, ethanol) elicit deficits in neuroventilation by impairing responses to CO2. This may explain why these toxins are risk factors for SIDS. We recorded neuroventilation from tadpole hindbrains before and during CO2 stimulation. Recordings were made during acute toxin exposure of hindbrains from naïve animals or following chronic toxin exposure of intact animals. Acute nicotine exposure decreased baseline neuroventilation in some tadpole stages but did not alter CO2 responses. Acute ethanol exposure depressed baseline neuroventilation but did not alter CO2 responses. Chronic exposure (nicotine or ethanol) abolished CO2 responses. These data indicate that chronic and acute toxin exposures differentially impair the neuroventilation. To determine the potential for recovery, tadpoles were returned to control conditions following chronic toxin exposure. Impairment by chronic nicotine disappeared over a 3 wk recovery period, but impairment by chronic ethanol persisted despite 6 wk recovery. Chronic ethanol causes a persistent developmental deficit in the neuroventilatory CO2 response, whereas chronic nicotine produces transient impairment. To determine whether neurogenesis underlies recovery, we exposed recovering tadpoles to BrDU. BrDU labeling unique to nicotine‐recovery animals could indicate regeneration of neurons critical to the CO2 response.

Effects of short inter-stimulus intervals on olfactory and trigeminal event-related potentials

Conclusion: Chemosensory event-related potentials (CSERPs) were identified in all measurements using the 20 s and the 10 s inter-stimulus interval (ISI) protocol, reducing the recording time to 75% or 57% compared with the standard protocol. A possible explanation for the rising CSERP amplitudes by shortening the ISI in CO2 stimulation is due to a phenomenon known as trigeminal sensitization during repeated stimulation. Objectives: CSERPs are influenced by the ISI. The aim of this study was to evaluate the changes in CSERPs by decreasing the ISI from 30 s to 20 s or 10 s, respectively. Subjects and methods: Ten normosmic healthy subjects participated this study. Phenyl ethyl alcohol (PEA), hydrogen sulphide (H2S) and carbon dioxide (CO2) were used in CSERP measurements with different ISI protocols (30 s (standard), 20 s and 10 s). Amplitudes and latencies of ISI protocols were submitted to ANOVA for repeated measurements and t tests for paired samples. Results: The amplitudes of CSERPs with PEA and H2S stimuli were decreasing with shortening the ISI significantly. In contrast, the highest amplitudes of trigeminal CSERPs were recorded with the 10 s ISI protocol with CO2. The ANOVA revealed a significantly different effect of shortening the ISI on CSERPs on the right and the left side.

Systemic vs. Central Administration of Common Hypnotics Reveals Opposing Effects on Genioglossus Muscle Activity in Rats

To determine if systemic administration of selected sedative-hypnotics that modulate the function of the y-amino-butyric acid-A (GABAA) receptor can: (i) delay arousal thereby allowing genioglossus (GG) activity to increase more in response to respiratory stimulation during sleep, (ii) also cause the robust increase in GG activity during undisturbed sleep recently observed with barbiturates. We also determined effects on GG activity with local application to the hypoglossal motor nucleus (HMN). Sleep-wake states, GG and diaphragm activities were recorded in freely-behaving rats after systemic administration of lorazepam (0.5 mg/kg and 1 mg/kg, n = 9 and 5 mg/kg, n = 7), zolpidem (5 mg/kg and 10 mg/kg, n = 6) and the antihistamine diphenhydramine (20 mg/kg, n = 9). Rats were also exposed to ramp increases in inspired CO2 in NREM sleep. The effects of lorazepam and zolpidem applied directly to the HMN were also determined in 37 anesthetized rats. Lorazepam, zolpidem and diphenhydramine all increased arousal threshold, consistent with their sedative action. GG activity before arousal in response to hypercapnia was increased with lorazepam and zolpidem only, an effect mainly due to increased baseline activity before CO2 stimulation. Lorazepam and zolpidem applied directly to the HMN, however, decreased GG activity. Lorazepam and zolpidem have an inhibitory effect on GG activity via local effects at the HMN. Following systemic administration, however, this inhibitory effect can be outweighed both by a delay in arousal (allowing greater CO2-mediated respiratory stimulation in sleep) and excitatory influences on baseline GG activity via mechanisms operating outside the HMN.

Biomass responses to intraspecific competition differ between wild species and CO2

Aims How growth of wild and crop species responds to global environmental perturbations has both ecological and agricultural significance in a changing world. The primary aim of this synthesis was to quantitatively assess the interactive effects of intraspecific competition and elevated CO2 on biomass production in herbaceous species. Methods Using meta-analytical techniques, we synthesized data from publications before 2006 that reported biomass responses to elevated CO2 in 321 herbaceous species grown in isolation or in competition with con-specific individuals. Important findings Intraspecific competition differentially modified biomass responses to elevated CO2 in wild and crop species. For example, competition reduced CO2 stimulation of total biomass (WT) from 27 to 23% in wild species, but by a much greater magnitude, i.e., from 43 to 32% in crops. Competition had no effect on responses of either above(WAG) or below-ground (WBG) biomass to elevated CO2 in wild species, but significantly diminished CO2 enhancement of WAG, although not of WBG, in crops. Considerable variations were found among functional groups in the modification of growth responses to elevated CO2 by intraspecific competition, which exerted greater depression on CO2 enhancement in C3 than in C4 species and in non-legumes than in legumes. Elevated CO2 affected leaf and stem growth of individually grown C3 graminoids and forbs similarly, but increased leaf growth only in C4 graminoids and stem growth only in C4 forbs. Results from this synthesis demonstrated that intraspecific competition differentially affected growth responses to elevated CO2 in wild and crop species. The wild–crop species differences will have important implications for understanding primary production by herbaceous species in both natural and agricultural ecosystems in the future when atmospheric CO2 is significantly higher than the current level.

Lateralisation of intranasal trigeminal chemosensory event-related potentials

To determine whether or not chemosensory event-related brain potentials (CSERP) elicited by nociceptive unilateral intranasal (CO2) trigeminal stimulation are lateralized and, if they are, whether this hemispheric lateralization is related to the side of the stimulated nostril. Nine healthy right-handed subjects participated to the study. CSERPs were recorded after left or right monorhinal CO2 stimulation. Latency and baseline-to-peak amplitude of each CSERP component were compared across stimulation conditions (left and right nostril), scalp locations (lower-frontal, frontal, mid-temporal, central, posterior-temporal, parietal) and hemispheres (left or right), using a three-factor analysis of variance (ANOVA) for repeated measures. Intranasal trigeminal CO2 stimulation elicited a large N400-P550 complex. This complex was preceded by an earlier N300 component. Whatever the stimulated nostril, N300, N400 and P550 amplitudes were significantly higher on the right as compared to the left hemisphere, at lower-frontal recording sites. The side of chemosensory stimulation (left or right nostril) did not significantly affect CSERP components. This study showed that in healthy right-handed volunteers with normal olfactory ability, intranasal chemosensory trigeminal stimulation may elicit a series of event-related brain potentials, which all display a significant right-hemisphere predominance, irrespective of the stimulated nostril. The observed lateralization was maximal at lower-frontal recording sites.

Process-based estimates of terrestrial ecosystem isoprene emissions: incorporating the effects of a direct CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;-isoprene interaction

Abstract. In recent years evidence has emerged that the amount of isoprene emitted from a leaf is affected by the CO2 growth environment. Many – though not all – laboratory experiments indicate that emissions increase significantly at below-ambient CO2 concentrations and decrease when concentrations are raised to above-ambient. A small number of process-based leaf isoprene emission models can reproduce this CO2 stimulation and inhibition. These models are briefly reviewed, and their performance in standard conditions compared with each other and to an empirical algorithm. One of the models was judged particularly useful for incorporation into a dynamic vegetation model framework, LPJ-GUESS, yielding a tool that allows the interactive effects of climate and increasing CO2 concentration on vegetation distribution, productivity, and leaf and ecosystem isoprene emissions to be explored. The coupled vegetation dynamics-isoprene model is described and used here in a mode particularly suited for the ecosystem scale, but it can be employed at the global level as well. Annual and/or daily isoprene emissions simulated by the model were evaluated against flux measurements (or model estimates that had previously been evaluated with flux data) from a wide range of environments, and agreement between modelled and simulated values was generally good. By using a dynamic vegetation model, effects of canopy composition, disturbance history, or trends in CO2 concentration can be assessed. We show here for five model test sites that the suggested CO2-inhibition of leaf-isoprene metabolism can be large enough to offset increases in emissions due to CO2-stimulation of vegetation productivity and leaf area growth. When effects of climate change are considered atop the effects of atmospheric composition the interactions between the relevant processes will become even more complex. The CO2-isoprene inhibition may have the potential to significantly dampen the expected steep increase of ecosystem isoprene emission in a future, warmer atmosphere with higher CO2 levels; this effect raises important questions for projections of future atmospheric chemistry, and its connection to the terrestrial vegetation and carbon cycle.

SERT knock‐out mice have altered control of breathing and thermoregulation

Serotonin (5HT) transport protein (SERT) knock-out (KO) mice have increased anxiety-like behaviors and decreased aggression associated with absent brainstem SERT, increased 5HT synthesis and extracellular levels, decreased 5HT1A receptors and decreased 5HT neuron firing rates (Kim et al., Neuropharm 2005). This pattern of neurochemical abnormalities is similar to that recently described in the brainstem of Sudden Infant Death Syndrome (SIDS) cases, namely, increased numbers of 5HT neurons, decreased 5HT1A binding and decreased SERT per 5HT neuron (Paterson et al., JAMA 2006). Here we evaluate ventilatory and thermoregulatory physiology in adult SERT KO mice of both genders during wakefulness. Ventilation was measured in un-instrumented control and SERT-KO mice using whole body plethysmography. While breathing air, male KO mice breathed faster and tended to hypoventilate while female KO mice breathed like controls. With 5% CO2 stimulation, male KO mice had a 39–46% decrease in their response compared to control males or KO females. With 10% O2 stimulation, the VE/VO2 responses of KO mice of both genders were decreased compared to controls. To test thermoregulation we placed individually housed mice into a cold room (4°C) for 120 min. Females had a ~3.0°C drop in body temperature while males and controls had a 0.9 and 1.4°C drop, respectively. Awake, adult SERT-KO mice have gender specific abnormalities in the control of breathing (males) and in the regulation of body temperature in the cold (females) and both genders have altered responses to hypoxia. Such abnormalities could contribute to a lessening of physiological regulatory system function and provide possible insight into mechanisms involved in SIDS as many SIDS cases exhibit anatomical abnormalities in the brainstem 5HT system as well as a genetic association with SERT allele distribution. (Support By: NIH HL 28066, NICHD 36379).

Respiratory Responses to CO2 Stimulation in Hypercapnic Patients with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea can be associated with daytime chronic hypercapnia in some patients, but the prevalence of the phenomenon is highly variable in the published literature. The most often it is found in patients with coexisting COPD. There is also an evidence of persisting hypercapnia in OSA patients without other respiratory disease. In previous studies lung function impairment, obesity, gender, severity of OSAS have been considered to contribute to daytime hypercapnia. Several studies demonstrated that the defect in control of breathing can play a role in the development of chronic hypercapnia in patients with OSAS. The aim of the study was to estimate respiratory responses to hypercapnic stimulation in patients with OSAS and chronic daytime hypercapnia. Material consisted of 38 patients with OSAS and chronic hypercapnia (COPD was present in 24–group B, “pure” OSA in 14–group A) and 40 normocapnic OSA patients (group C). Lung function testing, blood gases and chemical control of breathing tests were performed in all of them before initiating therapy with nCPAP. Diagnosis of OSAS was stated with standard polisomnography and AHI was similar in mentioned groups. Results: Respiratory responses to hypercapnic stimulation were signifi cantly lower in hypercapnic patients (A 10.6 ± 4.6; B 9.5 ± 5.6) in opposition to normocapnics (C 23.3 ± 14.0 l/min/kPa). In all studied patients PaCO2 level signifi cantly correlated with respiratory responses to hypercapnic stimulation (r= −0.61), lung function indices (VC r = −0.69 and FEV1 r = −0.71), mean SaO2 during sleep (r = −0.68), and BMI (r = 0.49), but not with the factors like age, AHI or minimal SaO2 during sleep. Analysis with multiple regression revealed that hypercapnic drive, mean SaO2 during sleep, FEV1 and BMI were the best predictors of hypercapnia in studied group, being responsible for 72% of the total variance in PaCO2 in our OSA patients (R2 = 0.72; p &lt; 0.0001). Conclusion: predisposition to daytime hypercapnia in our OSA patients was related to dimished chemosensitivity to CO2, mean desaturation during sleep, the severity of obesity and impairment of lung function mainly due to coexisting COPD.