Multiple Sclerosis and COVID-19: Health and healthcare access, health information and consumer co-created strategies for future access at times of crisis.

BACKGROUND: Persons with multiple sclerosis (MS) need regular access to medical services for optimal health outcomes. During the COVID-19 crisis, evidence indicated some detrimental health changes in persons with MS. Maintaining access to healthcare providers and healthcare information may minimise detrimental health changes during times of crisis. In Australia, there is limited evidence of consultation with people who have chronic health conditions or disabilities regarding government decisions to restrict healthcare access and in the provision of health guidance during the COVID-19 crisis. Yet, there are good examples of government consultation with other minority populations in Australia, leading to beneficial outcomes. OBJECTIVE: To identify MS community members' (persons with MS carers, advocates, healthcare providers) concerns about the health and healthcare access of persons with MS, during the second year of the COVID-19 pandemic and to collaborate with consumers in the MS community to co-create strategies to improve future access and health information provision at times of crisis. METHOD: We undertook a consumer-co-created mixed-method study in the second year of the COVID-19 pandemic to identify healthcare access needs for MS. We presented results to our stakeholder group to identify support needs during crises. Persons with MS and care providers in the MS community completed an online survey and online interviews, and the stakeholder group participated in a stakeholder workshop. RESULTS: Forty-four people participated in surveys, 33 completed interviews, and seven stakeholders participated in the stakeholder workshops. Three themes were identified from the surveys and interviews: health concerns, accessing healthcare services and communication sources. Healthcare providers (76.9 % of persons with MS and 77.8 % of care providers) and websites specific to the pandemic (76.9 % of persons with MS and 83.3 % of care providers) were identified by most survey respondents as preferred information sources during the COVID-19 crisis. Consultation with stakeholders resulted in the co-creation of strategies directed at communication, health, and lifestyle, as well as policies and protocols to address the needs of the MS community during crises. CONCLUSION: We listened to persons with MS and care providers to identify strategies to support health-communication, -access, and -lifestyle during crises. Consumer-created strategies are directed at national and local health advocacy organisations and governments. They are relevant for the coordinated healthcare planning of persons with chronic health conditions and disabilities during crises, such as those experienced by persons with MS.

The impact of the Australian Black Summer Bushfires and the COVID-19 pandemic on wellbeing in persons with multiple sclerosis; preparation for future and ongoing crises.

PURPOSE: The Australian multiple sclerosis (MS) community experienced two recent major crises, widespread bushfires and the COVID 19 pandemic. We aimed to understand the needs of persons with MS during times of crisis. MATERIALS AND METHODS: A consumer-directed mixed-method study. We included an online survey, semi-structured interviews, and a workshop with persons with MS, carers, healthcare professionals, and disability advocates. Data were collected via: (1) 176 people completing online surveys to identify crisis concerns and communications, (2) 29 people completing online interviews on bushfire and pandemic impact, and (3) 13 people participating in a crises-priorities workshop. Descriptive data were calculated for survey response, and a general inductive analytical approach was taken with interview and workshop responses. RESULTS: The most significant concerns were bushfire smoke exposure and disease-modifying-medication and susceptibility to COVID-19 (66% and 63% mean concern score, respectively). Interviews indicated crises experiences from the bushfires, and the pandemic overlapped respective of changes in mood and symptom stability. For bushfires, a need for future preparations, and for the pandemic, the benefits of social restrictions, disclosing personal health information and increased care burden were important. CONCLUSIONS: Multiple crises challenged the MS community but offered lessons for healthcare in future crises. Continued progress in centralised crisis information, with considered use of telehealth and rural healthcare support, is needed.Implications for rehabilitationThe MS community showed high concerns for the effect of toxic smoke from the 2019/2020 Australian bushfires and, separately, for the disease-modifying-medication and susceptibility to COVID-19.The MS community placed priority on a crisis management plan for individuals.Reduced social activity due to restrictions was beneficial for MS symptom self-awareness and may help overall fatigue management.Healthcare system preparation must prepare to alleviate increased carer workload at times of crisis.

Exercise participation and promotion in the multiple sclerosis community; perspectives across varying socio-ecological levels.

PURPOSE: We undertook a qualitative study that explored exercise participation and exercise promotion in the multiple sclerosis (MS) community who live in regional or remote areas of Australia. By simultaneously gathering views from persons with MS, carers, healthcare providers and healthcare managers we aimed to gather unique perspectives which represented views from across socio-ecological levels of MS healthcare. METHODS: We used interpretive description methodology, and conducted semi-structured interviews or focus groups with people with MS (n = 28), carers (n = 8), healthcare providers (n = 12) and managers/supervisors of MS healthcare systems (n = 16). Data were analysed using thematic analysis. RESULTS: We identified three themes with 10 subthemes. The first theme was "Factors associated with exercise engagement" for the people with MS, from individual, interpersonal, organisational and community/public policy perspectives. The second theme was "Factors influencing the MS community's promotion of exercise" focusing on carers, healthcare providers and healthcare systems. The third theme was "Motivators to increase exercise promotion" which should be delivered by the MS community across varying socio-ecological levels of healthcare to encourage exercise participation. CONCLUSION: We identified new evidence on the factors which influence the MS community's promotion of exercise and we now better understand that training on exercise should be provided to the wider MS community, and exercise services should be considered locally and perhaps delivered via teleheath.IMPLICATIONS FOR REHABILITATIONCohesive healthcare campaigns, and clinical guidelines based on empirical evidence should be established for symptom management in MS with a focus on the role of exercise.Symptom management strategies should consider the whole MS community, including patients, carers, healthcare professional and healthcare co-ordinators.Internal factors (e.g., emotion and motivation) and broader factors (e.g., funding and location) must be considered when designing exercise interventions in persons with MS.

A comparison of song-lyric and prose self-instruction procedures for increasing novel skills in children.

We compared the effects of the effects of self-instructions in the form of prose or song lyrics in the acquisition of gross motor tasks in 4 third-grade children. We taught participants 4 pairs of gross motor tasks, with one task in each pair taught with prose self-instructions and the other taught with song lyric self-instructions. Both self-instruction procedures were effective for teaching tasks; however, acquisition was quicker with song lyric self-instruction for 4 task pairs, acquisition was quicker with prose self-instruction for 3 task pairs; and similar for 1 task pair. Participants were then able to select their preferred method of self-instruction for a novel, applied skill. Two participants selected song-lyric self-instructions and 2 participants selected prose self-instructions.

The Effects of Contingent Caregiver Imitation of Infant Vocalizations: a Comparison of Multiple Caregivers.

The present study replicated and extended the Pelaez et al. (Journal of Applied Behavior Analysis 44:33-40, 2011) study, which examined the reinforcing effects of mothers' contingent imitation of their infants' vocalizations. Three infants aged 7-12 months who could vocalize sounds but not words participated with two caregivers for each infant (i.e., triads). During the intervention phase, the caregivers were asked to immediately imitate all vocalizations emitted by the child for a 3-min period. During the yoked control phase, the caregivers listened to an audio recording from the preceding condition and provided vocalizations non-contingently on the infants' responses. The procedures yielded different results across participants; one infant emitted a higher frequency of vocalizations during the contingent imitation phases over the control phases, and the other two infants showed higher rates of responding during the control phases. However, all infants emitted more imitative return vocalizations during contingent reinforcement conditions compared with the yoked control condition.

Direct biophotolithographic method for generating substrates with multiple overlapping biomolecular patterns and gradients.

We describe an approach to generate multicomponent surface-immobilized patterns and gradients on the basis of the photochemically controlled covalent coupling of solution-phase biomolecules to benzophenone-modified substrates. Gradients were simply achieved by continuously varying the exposure to nondamaging UV light across the surface with the gradient profile controlled by biomolecule concentration and the spatial and temporal illumination of the surface. Sequential exposure of the same surface in the presence of different biomolecules resulted in overlapping patterns and gradients of proteins and carbohydrates. Finally, we preliminarily demonstrate that the resulting surfaces are suitable for generating model substrates to probe cell-substrate interactions.

An adjusting-dose procedure for assessing the reinforcing effects of nitrous oxide with humans.

Despite continued abuse, there is a paucity of empirical investigations on inhalants as reinforcers. The present study attempted to derive a method for studying the reinforcing effects of nitrous oxide (N2O) with human participants. An adjusting-dose procedure was employed to assess choice allocation for inhalation periods of varying doses of N2O. After experiencing the experimental parameters in forced-choice trials, participants made choices between a fixed dose of 0% N2O (i.e., 100% O2) and an adjusting dose of N2O (0-50% N2O in O2). The adjusting dose titrated as a function of the participant's choices. Conditions were run to stability and systematically replicated within-subject. Stable choice allocation served as both the chief dependent variable and an indication of the optimal reinforcing dose of N2O for that participant. Consistent with previous research on N2O, there was between-subject variability in the reinforcing effects of N2O; however, stable within-subject choice allocation was observed for 6 out of 8 participants. This method of assessing drug choice in humans allows for the testing of multiple doses within-subject, which is imperative, given that the reinforcing effects of drugs are known to vary across subjects and as a function of dose.

Choice of nitrous oxide and its subjective effects in light and moderate drinkers.

BACKGROUND: Alcohol-drinking status has been shown to modulate the reinforcing and subjective effects of a number of drugs. We have previously published two studies on the modulating effects of alcohol-drinking status on choice for, and subjective effects of, nitrous oxide, but the results were equivocal. Using a methodology different from our previous studies, we sought to determine in a more definitive fashion the degree to which the choice of nitrous oxide and its subjective effects were modulated by drinking status. METHODS: Four concentrations of nitrous oxide (0, 20, 30, and 40%) were administered to 16 moderate drinkers (MDs) and 16 light drinkers (LDs) across four 3.5-h sessions. During experimental sessions, subjects first completed two 10-min sampling trials in which one of the nitrous oxide concentrations and placebo (100% oxygen) were inhaled. Subjective and psychomotor tests were given 5min into each sampling trial. During the subsequent choice period, subjects were allowed to choose what they wanted to inhale (drug, placebo, or "drug-free air") on nine contiguous 5-min choice trials. RESULTS: Choice of nitrous oxide was modulated by drinking status: MDs but not LDs chose nitrous oxide significantly more times than placebo, and MDs also chose nitrous oxide significantly more times than did LDs. At each active nitrous oxide concentration, MDs reported more abuse liability-related subjective effects, especially at the 20% and 30% concentrations. CONCLUSIONS: The results of the present study provide more conclusive evidence that choice as well as subjective effects of nitrous oxide is modulated by alcohol-drinking status.

Choice of sevoflurane and its subjective and psychomotor effects in light and moderate drinkers.

BACKGROUND: Sevoflurane, an inhalant of the volatile anesthetic class, has neurobiological and behavioral effects in common with abused inhalants and ethanol. We sought to determine if choice for subanesthetic doses of sevoflurane, and its subjective and psychomotor effects, would differ as a function of alcohol-drinking status in healthy volunteers. METHODS: The effects of four concentrations of sevoflurane (0, 0.2, 0.4, 0.8% sevoflurane in oxygen) were studied in 16 light drinkers and 16 moderate drinkers. During each of four sessions, subjects sampled a concentration of sevoflurane and 100% O(2) (placebo) for 10 min each. Subjective and psychomotor testing commenced 5 min into each sampling trial. Later, within the session, subjects chose nine times, once every 5 min, among sevoflurane (e.g., "Agent A"), placebo (e.g., "Agent B," 100% O(2)), or neither (and were administered 100% O(2), identified as "drug-free air"). RESULTS: Choice for sevoflurane at the 0.4% concentration was significantly higher in the moderate drinkers than in the light drinkers. A number of subjective effects reported during inhalation of sevoflurane were markedly lower in the moderate-drinking group than in the light-drinking group. However, psychomotor impairment induced by sevoflurane was similar in magnitude in both groups. CONCLUSIONS: Alcohol-drinking status affected sevoflurane choice. The results are consistent with several studies comparing light and heavier drinkers, using other drugs. Although both drinking groups were similarly impaired by sevoflurane, the moderate drinkers reported less of a subjective response than light drinkers, suggestive of cross-tolerance.

Patterning of coronary arteries in wildtype and connexin43 knockout mice.

Abnormal patterning of coronary arteries (CAs) is a clinically significant problem, and as yet, few animal models have been systematically investigated for coronary patterning defects. Here we characterized coronary artery (CA) insertion and branching patterns of the proximal coronary stems in the hearts of wildtype and heterozygous connexin43 knockout (Cx43alpha1 KO) mice. This study entailed the use of high-resolution micro CT imaging for three-dimensional coronary reconstructions. MicroCT of 17 wildtype mice showed a remarkably consistent pattern of CA deployment in the normal mouse heart. Two main CA stems are inserted from the left and right into the aorta. The right coronary artery then branches immediately into the right main and the septal-conal branch, while the left coronary artery branches further distally into the circumflex and the anterior descending CA. This patterning of CA anatomy was confirmed by histology, and by using a vascular smooth muscle or endothelial cell specific lacZ reporter gene to delineate the CAs. A parallel analysis of 25 heterozygous Cx43alpha1 KO mouse hearts showed 22 had defects in patterning of the CAs. They exhibited a wide variation in CA anatomy, including abnormal origin and course of the main CA stems, multiple accessories, and dual septal-conal branches. Overall, these studies show loss of one Cx43alpha1 allele (haploinsufficiency) leads to a high incidence of coronary patterning defects. These findings suggest CA patterning is sensitive to Cx43alpha1 gene dosage.

Within-subject comparison of the subjective and psychomotor effects of a gaseous anesthetic and two volatile anesthetics in healthy volunteers.

Inhalant abuse is a serious public health problem throughout the world. The present study compared the states of intoxication produced by three inhaled anesthetics that represent two of the three major classes of abused inhalants, as classified by [Balster, R.L., 1998. Neural basis of inhalant abuse. Drug Alcohol Depend 51, 207-214.]. Isoflurane and sevoflurane represent the class of volatile substances, and nitrous oxide (N2O) comprises a class of its own. Fourteen healthy volunteers inhaled the vehicle (100% O2) and two concentrations each of isoflurane (0.1 and 0.2%), sevoflurane (0.2 and 0.4%), and N2O (15 and 30%) for 40 min each, across seven separate sessions. Drug concentrations were chosen to produce similar ratings of drug effect strength and similar impairment on a psychomotor test, the digit-symbol substitution test (DSST). Ratings of drug effect strength and performance on the DSST were similar across drugs; however, the volatile anesthetics produced greater sedation and greater impairment on three other psychomotor tests than N2O, whereas N2O produced a greater magnitude of putatively pleasant and psychedelic-like subjective effects. These results are consistent with the drugs' putative receptor mechanisms of action and confirm Balster's classification of the volatile anesthetics into a class distinct from N2O.

Connexin43 deficiency causes dysregulation of coronary vasculogenesis.

The connexin43 knockout (Cx43alpha1 KO) mouse dies at birth from outflow obstruction associated with infundibular pouches. To elucidate the origin of the infundibular pouches, we used microarray analysis to investigate gene expression changes in the pouch tissue. We found elevated expression of many genes encoding markers for vascular smooth muscle (VSM), endothelial cells, and fibroblasts, cell types that are epicardially derived and essential for coronary vasculogenesis. This was accompanied by increased expression of VEGF and genes in the TGFbeta and VEGF/Notch/Eph cell-signaling pathways known to regulate vasculogenesis/angiogenesis. Using immunohistochemistry and a VSM lacZ reporter gene, we confirmed an abundance of ectopic VSM and endothelial cells in the infundibular pouch and in some regions of the right ventricle forming secondary pouches. This was associated with distinct thinning of the compact myocardium. TUNEL labeling showed increased apoptosis in the pouch tissue, in agreement with the finding of altered expression of many apoptotic genes. Defects in vascular remodeling were indicated by a marked reduction in the branching complexity of the distal coronary arteries. In the near term KO mouse, we also observed a profusion of large coronary vascular plexuses subepicardially. This was associated with elevated epicardial expression of VEGF and abnormal epicardial cell morphology. Together, these observations indicate that dysregulated coronary vasculogenesis plays a pivotal role in formation of the infundibular pouches and suggests an essential role for Cx43alpha1 gap junctions in coronary vasculogenesis and vascular remodeling.

Rapid high resolution three dimensional reconstruction of embryos with episcopic fluorescence image capture.

One of the overarching goals in developmental biology is the elucidation of mechanisms that elaborate form and function. To this end, an accurate morphological description of embryonic development is essential. However, visualizing dynamic changes in the three-dimensional (3D) structure of the developing embryo has been a "holy grail" in the field of developmental biology. The fundamental difficulties that have hindered all efforts in 3D reconstruction using two-dimensional (2D) image stacks revolve around the seemingly intractable problems of section registration and distortion. A remarkably simple solution has come about with the development of a new technique referred to as episcopic fluorescence image capture (EFIC). With EFIC imaging, tissue autofluorescence is used to image the block face prior to cutting each section. The 2D resolution obtained is close to that achieved by histology, and such 2D image stacks can be readily reconstructed in 3D. The 3D models generated provide fine structural details with resolution unmatched by 3D reconstructions obtained with any other imaging modalities. Given the perfect registration of EFIC image stacks, another important capability provided by EFIC is digital resectioning in any plane. This provides complete flexibility in the selection of optimal virtual sectioning planes for viewing different features in a specimen, and is invaluable for analyzing dynamic changes in tissue structure in the developing embryo. The capabilities provided by EFIC for rapid high resolution 3D reconstruction together with digital resectioning make this an unparalleled tool for characterizing morphogenetic events in the developing embryo. Although our review is focused on using EFIC for studying embryonic development, it is important to note that there is no intrinsic limitation on the size of the specimen that can be analyzed by EFIC imaging. Overall, EFIC should serve as an important imaging technique that will complement other 3D imaging modalities such as MRI and optical tomography. Given the feasibility of generating EFIC image stacks using cryoembedded or polyethylene glycol (PEG)-embedded specimens, there is the possibility that EFIC may be combined with 3D RNA or protein expression profiling. Together, such studies may help further elucidate the relationship between form and function.

Reinforcing and subjective effects of the volatile anesthetic, sevoflurane.

Sevoflurane is a volatile anesthetic that is chemically similar to volatile substances of abuse and can be safely administered to humans in laboratory research. In this study, the reinforcing and subjective effects of five concentrations of sevoflurane (0, 0.2, 0.4, 0.6, 0.8% sevoflurane in O2) were studied in 20 non-drug-abusers. During each of five sessions, subjects sampled a concentration of sevoflurane and 100% O2 (placebo) for 10 min each. Later, within the session, they chose nine times, once every 5 min, among sevoflurane (e.g. "Agent A"), placebo (e.g. "Agent B"), or neither (and were administered 100% O2, identified as "drug-free air"). Although "neither" was selected most frequently, mean preference ratios (sevoflurane choices/[sevoflurane choices+placebo choices]) and total sevoflurane choice peaked at the 0.4% concentration. Choice patterns varied across subjects, with some subjects never choosing sevoflurane and other subjects showing monotonic increasing or bitonic concentration-choice functions. Concentration-related increases in subjective effects were observed, including effects that are putatively associated with abuse liability. Ratings of drug liking and of wanting to inhale the drug again were positively correlated with sevoflurane choice. This study shows that sevoflurane can function as a reinforcer and produce abuse liability-related subjective effects in some healthy volunteers.

Assessing subjective and psychomotor effects of the herbal medication valerian in healthy volunteers.

Valerian is the common name given to the genus Valeriana, an odiferous, herbaceous perennial plant widely distributed in the temperate regions of Asia, Europe, and North America. It is among the most widely used herbal medicines in the world. Numerous clinical studies have demonstrated valerian's ability to improve sleep; however, to the best of our knowledge, no study has systematically assessed subjective and psychomotor/cognitive effects of valerian in young healthy adults across a range of doses. In the present study, we sought to determine whether valerian extract (Valeriana officinalis) altered mood and/or impaired psychomotor/cognitive performance in young healthy volunteers. We examined the effects of valerian extract (600, 1200, and 1800 mg) and 10 mg diazepam (positive control) compared to placebo in 10 young healthy volunteers. Dependent measures included subjective and psychomotor variables. The valerian extract had no significant effects on any of the dependent measures. Diazepam, though, produced subjective effects as measured by four different rating scales, and impaired psychomotor/cognitive performance. The data suggest that acute administration of valerian does not have mood-altering or psychomotor/cognitive effects in young healthy volunteers.

Bitonic dose-response functions for reinforcing and self-reported effects of nitrous oxide in humans.

The reinforcing and self-reported effects of nitrous oxide (10%, 30%, and 50% N(2)O in O(2)) were examined in 13 humans. During each of three sessions, subjects sampled one dose of N(2)O and 100% O(2) (placebo) for 10 min each, separated by 30-min recovery periods. The agents were identified by letter code, and later in the session, subjects chose nine times, once every 5 min, among N(2)O (e.g., "Agent A"), placebo (e.g., "Agent B"), or "neither" (also 100% O(2), identified as "drug-free air"). Self-reported and psychomotor effects were measured at various times. Dose-response functions varied across subjects and included bitonic, monotonic increasing, monotonic decreasing, U-shaped, and flat dose-response functions for reinforcing and/or self-reported effects. For subjects who showed bitonic reinforcing effects, the descending limb of the dose-response function could not be attributed to behavioral impairment. This study replicates previous studies showing dose-dependent effects of N(2)O, as well as between-subject variability in N(2)O effects. Bitonic dose-response functions for some subjects extend the generality of the phenomenon of bitonicity of drug effects to N(2)O effects in humans.

Seaweeds in cold seas: evolution and carbon acquisition.

Much evidence suggests that life originated in hydrothermal habitats, and for much of the time since the origin of cyanobacteria (at least 2.5 Ga ago) and of eukaryotic algae (at least 2.1 Ga ago) the average sea surface and land surface temperatures were higher than they are today. However, there have been at least four significant glacial episodes prior to the Pleistocene glaciations. Two of these (approx. 2.1 and 0.7 Ga ago) may have involved a 'Snowball Earth' with a very great impact on the algae (sensu lato) of the time (cyanobacteria, Chlorophyta and Rhodophyta) and especially those that were adapted to warm habitats. By contrast, it is possible that heterokont, dinophyte and haptophyte phototrophs only evolved after the Carboniferous-Permian ice age (approx. 250 Ma ago) and so did not encounter low (

Analysis of the reinforcing and subjective effects of different doses of nitrous oxide using a free-choice procedure.

The reinforcing and subjective effects of five doses of nitrous oxide (0, 10, 20, 30, 40% N(2)O in O(2)) were studied in 20 non-drug-abusers using a free-choice procedure. During each of five sessions, subjects sampled a dose of N(2)O and 100% O(2) (placebo) for 10 min each. Later they chose nine times, once every 5 min, among N(2)O (e.g. 'Agent A'), placebo (e.g. 'Agent B'), or a no-drug option. Mean preference ratios (N(2)O choices/[N(2)O choices+placebo choices]) and total N(2)O choice increased with increasing N(2)O dose. Individual preference ratios suggested that at least one active dose of N(2)O functioned as a reinforcer in 80% of subjects, and the doses that functioned as reinforcers varied across subjects. N(2)O choice was positively correlated with end-of-session and post-session ratings of N(2)O liking and of wanting to inhale N(2)O again, but not with ratings of those effects during sampling. Placebo was chosen significantly less than the no-drug option, even though both were 100% O(2). More robust reinforcing effects of N(2)O were observed in this subject population than in previous studies. Choice data emphasize the importance of examining a range of doses, and of examining those effects within-subject, when assessing reinforcing effects of drugs. Inclusion of the no-drug option eliminated the 'forced' choice of placebo, making preference ratios easier to interpret than in previous, forced-choice procedures. Reinforcing effects were more correlated with subjective effects assessed after the session than with subjective effects obtained while subjects were under the influence of the drug.

Mechanistic interpretation of carbon isotope discrimination by marine macroalgae and seagrasses.

The literature, and previously unpublished data from the authors' laboratories, shows that the δ13C of organic matter in marine macroalgae and seagrasses collected from the natural environment ranges from -3 to -35‰. While some marine macroalgae have δ13C values ranging over more than 10‰ within the thallus of an individual (some brown macroalgae), in other cases the range within a species collected over a very wide geographical range is only 5‰ (e.g. the red alga Plocamium cartilagineum which has values between -30 and -35‰). The organisms with very negative δ13C (lower than -30‰) are mainly subtidal red algae, with some intertidal red algae and a few green algae; those with very positive δ13C values (higher than -10‰) are mainly green macroalgae and seagrasses, with some red and brown macroalgae. The δ13C value correlates primarily with taxonomy and secondarily with ecology. None of the organisms with δ13C values lower than -30‰ have pyrenoids. Previous work showed a good correlation between δ13C values lower than -30‰ and the lack of CO2 concentrating mechanisms for several species of marine red algae. The extent to which the low δ13C values are confined to organisms with diffusive CO2 entry is discussed. Diffusive CO2 entry could also occur in organisms with higher δ13C values if diffusive conductance was relatively low. The photosynthesis of organisms with δ13C values more positive than -10‰ (i.e. more positive than the δ13C of CO2 in seawater) must involve HCO3- use.