Ground state of the spin-1/2 Heisenberg antiferromagnet on an Archimedean 4-6-12 lattice

An investigation of the N\'eel Long Range Order (NLRO) in the ground state of antiferromagnetic Heisenberg spin system on the two-dimensional, uniform, bipartite lattice consisting of squares, hexagons and dodecagons is presented. Basing on the analysis of the order parameter and the long-distance correlation function the NLRO is shown to occur in this system. Exact diagonalization and variational (Resonating Valence Bond) methods are applied.Comment: 4 pages, 6 figure

Actions of Octocoral and Tobacco Cembranoids on Nicotinic Receptors

Nicotinic acetylcholine receptors (AChRs) are pentameric proteins that form agonist-gated cation channels through the plasma membrane. AChR agonists and antagonists are potential candidates for the treatment of neurodegenerative diseases. Cembranoids are naturally occurring diterpenoids that contain a 14-carbon ring. These diterpenoids interact with AChRs in complex ways: as irreversible inhibitors at the agonist sites, as noncompetitive inhibitors, or as positive modulators, but no cembranoid was ever shown to have agonistic activity on AChRs. The cembranoid eupalmerin acetate displays positive modulation of agonist-induced currents in the muscle-type AChR and in the related gamma-aminobutyric acid (GABA) type A receptor. Moreover, cembranoids display important biological effects, many of them mediated by nicotinic receptors. Cembranoids from tobacco are neuroprotective through a nicotinic anti-apoptotic mechanism preventing excitotoxic neuronal death which in part could result from anti-inflammatory properties of cembranoids. Moreover, tobacco cembranoids also have anti-inflammatory properties which could enhance their neuroprotective properties. Cembranoids from tobacco affect nicotine-related behavior: they increase the transient initial ataxia caused by first nicotine injection into naive rats and inhibit the expression of locomotor sensitization to repeated injections of nicotine. In addition, cembranoids are known to act as antitumor compounds. In conclusion, cembranoids provide a promising source of lead drugs for many clinical areas, including neuroprotection, smoking-cessation, and anti-cancer therapies

Kinin-B2 Receptor Mediated Neuroprotection after NMDA Excitotoxicity Is Reversed in the Presence of Kinin-B1 Receptor Agonists

Background: Kinins, with bradykinin and des-Arg 9-bradykinin being the most important ones, are pro-inflammatory peptides released after tissue injury including stroke. Although the actions of bradykinin are in general well characterized; it remains controversial whether the effects of bradykinin are beneficial or not. Kinin-B2 receptor activation participates in various physiological processes including hypotension, neurotransmission and neuronal differentiation. The bradykinin metabolite des-Arg 9-bradykinin as well as Lys-des-Arg 9-bradykinin activates the kinin-B1 receptor known to be expressed under inflammatory conditions. We have investigated the effects of kinin-B1 and B2 receptor activation on N-methyl-Daspartate (NMDA)-induced excitotoxicity measured as decreased capacity to produce synaptically evoked population spikes in the CA1 area of rat hippocampal slices. Principal Findings: Bradykinin at 10 nM and 1 mM concentrations triggered a neuroprotective cascade via kinin-B2 receptor activation which conferred protection against NMDA-induced excitotoxicity. Recovery of population spikes induced by 10 nM bradykinin was completely abolished when the peptide was co-applied with the selective kinin-B2 receptor antagonist HOE-140. Kinin-B2 receptor activation promoted survival of hippocampal neurons via phosphatidylinositol 3-kinase, while MEK/MAPK signaling was not involved in protection against NMDA-evoked excitotoxic effects. However, 100 nM Lys-des-Arg 9-bradykinin, a potent kinin-B1 receptor agonist, reversed bradykinin-induced population spik

Alien tree species as indicators of environmental transformation in Kampinoski National Park

Występowanie obcych gatunków drzew jest wskaźnikiem stopnia antropogenicznych przemian szaty roślinnej. Liczba obcych taksonów drzew (40) stwierdzonych w stanie dzikim na terenie Kampinoskiego Parku Narodowego i otuliny przewyższa liczbę rodzimych (33). Blisko połowa stwierdzonych obcych gatunków drzew (18) występuje licznie lub masowo. Za inwazyjne uznano 4 gatunki: czeremchę amerykańską Padus serotina (Ehrh.) Borkh., klon jesionolistny Acer negundo L., dąb czerwony Quercus rubra L., robinię akacjową Robinia pseudoacacia L. W aktualnym planie urządzania lasu obce gatunki drzew (12) występujące w drzewostanie, podszycie lub podroście zostały stwierdzone w 13% wydzieleń, zajmujących łącznie powierzchnię 5 tys. ha (19% powierzchni leśnej). Do najliczniejszych należą wymienione wyżej gatunki inwazyjne oraz sosna Banksa Pinus banksiana Lamb. i sosna smołowa Pinus rigida Mill. Tak liczne występowanie obcych gatunków drzew w Kampinoskim Parku Narodowym świadczy o znacznych przekształceniach antropogenicznych przyrody i jest przejawem degeneracji fitocenoz leśnych.Anthropogenic transformation of vegetation cover is indicated by the presence of alien tree species. It is estimated that within Kampinoski National Park the number of alien tree taxons (40) found in the wild is by far greater than nativ ones (33). Nearly half (18) of mentioned above alien species can be found growing in large or even great numbers. Out of the lot, four species are regarded as invasive: Padus serotina (Ehrh.) Borkh., Acer negundo L., Quercus rubra L., Robinia pseudoacacia L. Present forest taxation confirms that 12 alien tree species in stand and shrub layer can be found in 13% of forest unts, covering 5 000 ha which is 19% of the whole forest territory. The most numerous of them are invasive species mentioned above as well as Pinus banksiana Lamb. and Pinus rigida Mill

Changes of the herb layer species richness within Scots pine forest of the dune belts in the Kampinos National Park (central Poland) at the beginning of XXI century

Scots pine forest are of the main economic importance to the forest management in lowland Europe. Large areas of spontaneous pine forest, including old−growths, are located on two vast dune belts of the Kampinos National Park (central Poland). These forests grow on oligotrophic sandy soils with deep groundwater level. This makes the area unique to study long−term changes in this type of pine forest communities. The aim of the work was to assess the changes in the species composition and richness of undergrowth of Scots pine forests at the beginning of the XXI century. The study was conducted on 10 permanent and 53 semi−permanent plots located within stands of Peucedano−Pinetum and Querco−Pinetum associations on both dune belts of Kampinos National Park. The fieldworks were performed in 2001 and 2002, and repeated in 2015 and 2018. Based on Ward’s cluster analysis we described five local forms of plant communities. Seven species groups were distinguished and changes in their richness assessed using one sample Wilcoxon test. Each species group included species characteristic and/or differentiating for a given set of syntaxonomical units. The results confirmed the hypothesis of gradual decrease of the total species richness. The median of species richness change was –0.308 species per year and was statistically significant. The changes were bigger within the local forms of the Querco−Pinetum association in comparison to Peucedano−Pinetum. The decrease was connected especially with dry grassland and heathland species (characteristic for syntaxons of Koelerio−Corynephoretea and Nardo−Callunetea classes) as well as with coniferous forest generalist species (characteristic for syntaxons of Vaccinio−Piceetea and Cladonio−Vaccinietalia). The results suggest that the two main processes shaping the species composition at the beginning of XXI century within pine forest located on the dune belts of Kampinos National Park may be identified as (i) fluctuation, and (ii) simplification, manifested by species richness decrease. This is probably connected with forest regeneration after past human use and disturbance

γ-Aminobutyric acid type a receptor inhibition triggers a nicotinic neuroprotective mechanism

Nicotinic acetylcholine receptor (nAChR)-mediated neuroprotection has been implicated in the treatment of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases and hypoxic ischemic events as well as other diseases hallmarked by excitotoxic and apoptotic neuronal death. Several modalities of nicotinic neuroprotection have been reported. However, although this process generally involves α4β2 and α7 subtypes, the underlying mechanisms are largely unknown. Interestingly, both activation and inhibition of α7 nAChRs have been reported to be neuroprotective. We have shown that inhibition of α7 nAChRs protects the function of acute hippocampal slices against excitotoxicity in an α4β2-dependent manner. Neuroprotection was assessed as the prevention of the N-methyl-D-aspartate-dependent loss of the area of population spikes (PSs) in the CA1 area of acute hippocampal slices. Our results support a model in which α7 AChRs control the release of γ-aminobutyric acid (GABA). Blocking either α7 or GABA(A) receptors reduces the inhibitory tone on cholinergic terminals, thereby promoting α4β2 activation, which in turn mediates neuroprotection. These results shed light on how α7 nAChR inhibition can be neuroprotective through a mechanism mediated by activation of α4β2 nAChRs