On Convergence and Threshold Properties of Discrete Lotka-Volterra Population Protocols

In this work we focus on a natural class of population protocols whose dynamics are modelled by the discrete version of Lotka-Volterra equations. In such protocols, when an agent $a$ of type (species) $i$ interacts with an agent $b$ of type (species) $j$ with $a$ as the initiator, then $b$'s type becomes $i$ with probability $P\_{ij}$. In such an interaction, we think of $a$ as the predator, $b$ as the prey, and the type of the prey is either converted to that of the predator or stays as is. Such protocols capture the dynamics of some opinion spreading models and generalize the well-known Rock-Paper-Scissors discrete dynamics. We consider the pairwise interactions among agents that are scheduled uniformly at random. We start by considering the convergence time and show that any Lotka-Volterra-type protocol on an $n$-agent population converges to some absorbing state in time polynomial in $n$, w.h.p., when any pair of agents is allowed to interact. By contrast, when the interaction graph is a star, even the Rock-Paper-Scissors protocol requires exponential time to converge. We then study threshold effects exhibited by Lotka-Volterra-type protocols with 3 and more species under interactions between any pair of agents. We start by presenting a simple 4-type protocol in which the probability difference of reaching the two possible absorbing states is strongly amplified by the ratio of the initial populations of the two other types, which are transient, but "control" convergence. We then prove that the Rock-Paper-Scissors protocol reaches each of its three possible absorbing states with almost equal probability, starting from any configuration satisfying some sub-linear lower bound on the initial size of each species. That is, Rock-Paper-Scissors is a realization of a "coin-flip consensus" in a distributed system. Some of our techniques may be of independent value

Long-term impact of the COVID-19 pandemic on the quality of life of people with dementia and their family carers

\ua9 The Author(s) 2024. Published by Oxford University Press on behalf of the British Geriatrics Society. INTRODUCTION: Few studies have longitudinally mapped quality of life (QoL) trajectories of newly diagnosed people with dementia and their carers, particularly during coronavirus disease-2019 (COVID-19). METHODS: In a UK cohort study, 261 newly diagnosed people with dementia and 206 family carers were assessed prior to the pandemic (July 2019-March 2020), followed up after the first lockdown (July-October 2020) and then again a year and 2 years later. Latent growth curve modelling examined the level and change of QoL over the four time-points using dementia-specific QoL measures (DEMQOL and C-DEMQOL). RESULTS: Despite variations in individual change scores, our results suggest that generally people with dementia maintained their QoL during the pandemic and experienced some increase towards the end of the period. This contrasted with carers who reported a general deterioration in their QoL over the same period. \u27Confidence in future\u27 and \u27Feeling supported\u27 were the only carer QoL subscales to show some recovery post-pandemic. DISCUSSION: It is positive that even during a period of global disruption, decline in QoL is not inevitable following the onset of dementia. However, it is of concern that carer QoL declined during this same period even after COVID-19 restrictions had been lifted. Carers play an invaluable role in the lives of people with dementia and wider society, and our findings suggest that, post-pandemic, they may require greater support to maintain their QoL

Increased 5-HT3-mediated signalling in pelvic afferent neurons from mice deficient in P2X2 and/or P2X3 receptor subunits

Extracellular ATP and 5-hydroxytryptamine (5-HT) are both involved in visceral sensory pathways by interacting with P2X and 5-HT3 receptors, respectively. We have investigated the changes in P2X and 5-HT3-mediated signalling in pelvic afferent neurons in mice deficient in P2X2 and/or P2X3 subunits by whole-cell recording of L6–S2 dorsal root ganglion (DRG) neurons and by multi-unit recording of pelvic afferents of the colorectum. In wildtype DRG neurons, ATP evoked transient, sustained or mixed (biphasic) inward currents. Transient currents were absent in P2X3−/− neurons, whereas sustained currents were absent in P2X2−/− DRG neurons. Neither transient nor sustained currents were observed following application of ATP or α,β-methylene ATP (α,β-meATP) in P2X2/P2X3Dbl−/− DRG neurons. 5-HT was found to induce a fast inward current in 63% of DRG neurons from wildtype mice, which was blocked by tropisetron, a 5-HT3 receptor antagonist. The percentage of DRG neurons responding to 5-HT was significantly increased in P2X 2−/−, P2X3−/− and P2X2/P2X3Dbl−/− mice, and the amplitude of 5-HT response was significantly increased in P2X2/P2X3Dbl−/− mice. The pelvic afferent response to colorectal distension was attenuated in P2X2/P2X3Dbl−/− mice, but the response to serosal application of 5-HT was enhanced. Furthermore, tropisetron resulted in a greater reduction in pelvic afferent responses to colorectal distension in the P2X2/P2X3Dbl−/− preparations. These data suggest that P2X receptors containing the P2X2 and/or P2X3 subunits mediate purinergic activation of colorectal afferents and that 5-HT signalling in pelvic afferent neurons is up-regulated in mice lacking P2X2 or P2X3 receptor genes. This effect is more pronounced when both subunits are absent

Gut contents, digestive half-lives and feeding state prediction in the soil predatory mite Pergamasus longicornis (Mesostigmata: Parasitidae)

Mid- and hind-gut lumenal changes are described in the free-living predatory soil mite Pergamasus longicornis (Berlese) from a time series of histological sections scored during and after feeding on fly larval prey. Three distinct types of tangible material are found in the lumen. Bayesian estimation of the change points in the states of the gut lumenal contents over time is made using a time-homogenous first order Markov model. Exponential processes within the gut exhibit ’stiff’ dynamics. A lumen is present throughout the midgut from 5 min after the start of feeding as the gut rapidly expands. It peaks at about 21.5 h - 1.5 days and persists post-feeding (even when the gut is contracted) up until fasting/starvation commences 10 days post start of feeding. The disappearance of the lumen commences 144 h after the start of feeding. Complete disappearance of the gut lumen make take 5-9 weeks from feeding commencing. Clear watery prey material arrives up to 10 min from the start of feeding - driving gut lumen expansion. Intracellular digestion triggered by maximum gut expansion is indicated. Detectable granular prey material appears in the lumen during the concentrative phase of coxal droplet production and, despite a noticeable collapse around 12 h, lasts in part for 52.5 h. Posterior midgut regions differ slightly from anterior regions in their main prey food dynamics being somewhat faster in processing yet being slightly delayed. Posterior regions are confirmed as Last-In-Last-Out depots, anterior regions confirmed as First-In-First-Out conveyor belt processes. Evidence for differential lability of prey fractions is found. A scheme of granular imbibed prey material being first initially rapidly absorbed (t andfrac12; = 23 min), and also being quickly partly converted to globular material extra-corporeally/extracellularly (t andfrac12; = 36 min) - which then rapidly disappears (t andfrac12; =1.1 h, from a peak around 4 h) is presented. This is then followed by slow intracellular digestion (t andfrac12; = 6.9 h) of the resultant resistant prey residue matching the slow rate of appearance of opaque pre-excretory egestive refractive grains (overall t andfrac12; = 4.5 days). The latter confirmed latent ’catabolic fraction’ (along with Malpighian tubule produced guanine crystals) drives rectal vesicle expansion as ’faeces’ during the later phases of gut emptying/contraction. Catabolic half-lives are of the order of 6.3-7.8 h. Membraneous material is only present in the lumen of the gut in starving mites. No obvious peritrophic membrane was observed. The total feeding cycle time may be slightly over 52.5 h. Full clearance in the gut system of a single meal including egestive and excretory products may take up to 3 weeks. Independent corroborative photographs are included and with posterior predictive densities confirm the physiological sequence of:- ingestion/digestion; egestion; excretion; defecation; together with their timings. Visually dark midguts almost certainly indicate egestive refractive grains (?xanthine) production. Nomograms to diagnose the feeding state of P.longicornis in field samples are presented and show that the timing of these 4 phases in the wild could be inferred by scoring 10-12 mites out of a sample of 20. Suggestions to critically confirm or refute the conclusions are included

Real-time detection of serotonin release from enterochromaffin cells of the guinea pig ileum

Serotonin (5-hydroxytryptamine; 5-HT) containing enterochromaffin (EC) cells may detect chemical or mechanical stimuli in the intestinal lumen and respond with release of 5-HT. The aim of this study was to use real-time electrochemical detection methods to detect release of 5-HT from small numbers of EC cells. In guinea-pig ileum, basal release of 5-HT from the unstimulated, unparalyzed intestine was composed of individual release events (8.4 ± 1.8 events, 0.33 ± 0.06 Hz) of different amplitudes but with similar kinetics. Local compression of the mucosa with the electrode evoked peak 5-HT release of 12.3 ± 2.8 μmol L−1 with a sustained release of 3.0 ± 0.7 μmol L−1. Brief application of acetylcholine (ACh) or carbachol elicited a transient peak (5.7 ± 1.3 μmol L−1 occurring at 35 ± 18 s, n = 9) followed by cyclic release of 5-HT (9.7 ± 2.2 events, 0.40 ± 0.13 Hz, n = 6). This study shows that the release of 5-HT occurs rapidly as individual events from a small number of cells and can reach very high concentrations locally

Genetic reassortment amoung recently circulating human influenza A and B viruses

Evolution of influenza viruses involves both the gradual accumulation of mutations and genetic reassortment, due to the segmented nature of the RNA genome. Co-circulation of H1N1 and H3N2 viruses since 1977 provided the opportunity for reassortment between the subtypes. Although various reassortant viruses have circulated to limited extents, not until 2002 did H1N2 viruses, deriving an H1 from H1N1 viruses and seven genes from contemporary H3N2 viruses, become established worldwide. Following the re-emergence of B/Victoria/2/87-lineage viruses during 2001 2002, reassortants possessing a B/Victoria-lineage HA and B/Yamagata-lineage NA became the predominant B viruses circulating since the latter part of 2002. As well as demonstrating the role of reassortment in antigenic and genetic variation, these events provide further evidence of the limited divergence in the functional characteristics of HA and NA of distinct subtypes or lineages during the evolution of human influenza viruses. (C) 2003 Elsevier B.V. All rights reserved.</p

Genetic reassortment amoung recently circulating human influenza A and B viruses

Evolution of influenza viruses involves both the gradual accumulation of mutations and genetic reassortment, due to the segmented nature of the RNA genome. Co-circulation of H1N1 and H3N2 viruses since 1977 provided the opportunity for reassortment between the subtypes. Although various reassortant viruses have circulated to limited extents, not until 2002 did H1N2 viruses, deriving an H1 from H1N1 viruses and seven genes from contemporary H3N2 viruses, become established worldwide. Following the re-emergence of B/Victoria/2/87-lineage viruses during 2001 2002, reassortants possessing a B/Victoria-lineage HA and B/Yamagata-lineage NA became the predominant B viruses circulating since the latter part of 2002. As well as demonstrating the role of reassortment in antigenic and genetic variation, these events provide further evidence of the limited divergence in the functional characteristics of HA and NA of distinct subtypes or lineages during the evolution of human influenza viruses. (C) 2003 Elsevier B.V. All rights reserved.</p