Activation of a heterologously expressed octopamine receptor coupled only to adenylyl cyclase produces all the features of presynaptic facilitation in Aplysia sensory neurons

Short-term behavioral sensitization of the gill-withdrawal reflex after tail stimuli in Aplysia leads to an enhancement of the connections between sensory and motor neurons of this reflex. Both behavioral sensitization and enhancement of the connection between sensory and motor neurons are importantly mediated by serotonin. Serotonin activates two types of receptors in the sensory neurons, one of which is coupled to the cAMP/protein kinase A (PKA) pathway and the other to the inositol triphosphate/protein kinase C (PKC) pathway. Here we describe a genetic approach to assessing the isolated contribution of the PKA pathway to short-term facilitation. We have cloned from Aplysia an octopamine receptor gene, Ap oa1, that couples selectively to the cAMP/PKA pathway. We have ectopically expressed this receptor in Aplysia sensory neurons of the pleural ganglia, where it is not normally expressed. Activation of this receptor by octopamine stimulates all four presynaptic events involved in short-term synaptic facilitation that are normally produced by serotonin: (i) membrane depolarization; (ii) increased membrane excitability; (iii) increased spike duration; and (iv) presynaptic facilitation. These results indicate that the cAMP/PKA pathway alone is sufficient to produce all the features of presynaptic facilitation.

Allosteric modulation of Ca2+ channels by G proteins, voltage-dependent facilitation, protein kinase C, and Cavβ subunits

N-type and P/Q-type Ca2+ channels are inhibited by neurotransmitters acting through G protein-coupled receptors in a membrane-delimited pathway involving Gβγ subunits. Inhibition is caused by a shift from an easily activated “willing” (W) state to a more-difficult-to-activate “reluctant” (R) state. This inhibition can be reversed by strong depolarization, resulting in prepulse facilitation, or by protein kinase C (PKC) phosphorylation. Comparison of regulation of N-type Ca2+ channels containing Cav2.2a α1 subunits and P/Q-type Ca2+ channels containing Cav2.1 α1 subunits revealed substantial differences. In the absence of G protein modulation, Cav2.1 channels containing Cavβ subunits were tonically in the W state, whereas Cav2.1 channels without β subunits and Cav2.2a channels with β subunits were tonically in the R state. Both Cav2.1 and Cav2.2a channels could be shifted back toward the W state by strong depolarization or PKC phosphorylation. Our results show that the R state and its modulation by prepulse facilitation, PKC phosphorylation, and Cavβ subunits are intrinsic properties of the Ca2+ channel itself in the absence of G protein modulation. A common allosteric model of G protein modulation of Ca2+-channel activity incorporating an intrinsic equilibrium between the W and R states of the α1 subunits and modulation of that equilibrium by G proteins, Cavβ subunits, membrane depolarization, and phosphorylation by PKC accommodates our findings. Such regulation will modulate transmission at synapses that use N-type and P/Q-type Ca2+ channels to initiate neurotransmitter release.

Subthreshold facilitation and suppression in primary visual cortex revealed by intrinsic signal imaging.

Neurons in primary visual cortex (area 17) respond vigorously to oriented stimuli within their receptive fields; however, stimuli presented outside the suprathreshold receptive field can also influence their responses. Here we describe a fundamental feature of the spatial interaction between suprathreshold center and subthreshold surround. By optical imaging of intrinsic signals in area 17 in response to a stimulus border, we show that a given stimulus generates activity primarily in iso-orientation domains, which extend for several millimeters across the cortical surface in a manner consistent with the architecture of long-range horizontal connections in area 17. By mapping the receptive fields of single neurons and imaging responses from the same cortex to stimuli that include or exclude the aggregate suprathreshold receptive field, we show that intrinsic signals strongly reveal the subthreshold surround contribution. Optical imaging and single-unit recording both demonstrate that the relative contrast of center and surround stimuli regulates whether surround interactions are facilitative or suppressive: the same surround stimulus facilitates responses when center contrast is low, but suppresses responses when center contrast is high. Such spatial interactions in area 17 are ideally suited to contribute to phenomena commonly regarded as part of "higher-level" visual processing, such as perceptual "popout" and "filling-in."

Community attributes determine facilitation potential in a semi-arid steppe

Studies on positive plant–plant relations have traditionally focused on pair-wise interactions. Conversely, the interaction with other co-occurring species has scarcely been addressed, despite the fact that the entire community may affect plant performance. We used woody vegetation patches as models to evaluate community facilitation in semi-arid steppes. We characterized biotic and physical attributes of 53 woody patches (patch size, litter accumulation, canopy density, vegetation cover, species number and identity, and phylogenetic distance), and soil fertility (organic C and total N), and evaluated their relative importance for the performance of seedlings of Pistacia lentiscus, a keystone woody species in western Mediterranean steppes. Seedlings were planted underneath the patches, and on their northern and southern edges. Woody patches positively affected seedling survival but not seedling growth. Soil fertility was higher underneath the patches than elsewhere. Physical and biotic attributes of woody patches affected seedling survival, but these effects depended on microsite conditions. The composition of the community of small shrubs and perennial grasses growing underneath the patches controlled seedling performance. An increase in Stipa tenacissima and a decrease in Brachypodium retusum increased the probability of survival. The cover of these species and other small shrubs, litter depth and community phylogenetic distance, were also related to seedling survival. Seedlings planted on the northern edge of the patches were mostly affected by attributes of the biotic community. These traits were of lesser importance in seedlings planted underneath and in the southern edge of patches, suggesting that constraints to seedling establishment differed within the patches. Our study highlights the importance of taking into consideration community attributes over pair-wise interactions when evaluating the outcome of ecological interactions in multi-specific communities, as they have profound implications in the composition, function and management of semi-arid steppes.

Facilitation Among Saproxylic Insects Inhabiting Tree Hollows in a Mediterranean Forest: The Case of Cetonids (Coleoptera: Cetoniidae) and Syrphids (Diptera: Syrphidae)

Tree hollows offer an ideal niche for saproxylic insects in mature Mediterranean forests, where Diptera and Coleoptera are the richest groups. Co-occurrence is frequently observed among many species of both groups in these microhabitats, and some of these species have been considered to facilitate the presence of other species by acting as ecosystem engineers. One of the systems that is found in Mediterranean tree hollows is formed by cetonid (Coleoptera: Cetoniidae) and syrphid (Diptera: Syrphidae) larvae. Here, cetonid larvae feed on wood and litter and produce a substrate that is easier to decompose. To assess the possible role of these larvae as facilitating agents for the saproxylic guild, we studied whether the presence of saprophagous Syrphidae inside tree hollows is associated with the activity of cetonid larvae. Furthermore, in laboratory conditions, we tested whether cetonid larvae activity can improve the development and fitness of the saprophagous syrphid species. Our results show that “cetonid activity” was the variable that best explained the presence of saprophagous syrphid species in natural conditions. Myathropa florea (L., 1758) was one of the species most influenced by this activity. The laboratory experiment gave similar results, demonstrating that an enriched substrate with Cetonia aurataeformis Curti, 1913 larval feces improves syrphid larval growth rate and fitness of adults (measured as longer wing length) of M. florea.

Experience facilitation process e o posicionamento estratégico de unidades hoteleiras

A indústria hoteleira é hoje reconhecida como uma indústria global, com produtores e consumidores espalhados por todo o mundo. Um dos grandes desafios dos nossos dias passa por maximizar a satisfação do seu consumidor e simultaneamente garantir um crescimento exponencial da procura face à concorrência. O EFP (Experience Facilitation Process) tem levantado novos desafios na gestão do turismo e da hotelaria, associado aos novos processos de gestão de negócios turísticos e à emergência de novos produtos e atributos valorizados pelos turistas. O presente estudo visa compreender até que ponto os hotéis facilitam a experiência turística e o usufruto dos seus hóspedes, maximizando a sua satisfação. Pretende-se, neste contexto, perceber se o posicionamento estratégico preconizado pelo sector coloca o enfase no elemento mais importante de uma organização, o cliente. Para o efeito, é proposto um modelo em que a EFP (Experience Facilitation Process) influencia a recomendação do hotel. O EFP é por sua vez explicado pela easiness in performance, pela tecnologia adotada, pela qualidade de F&B e pelas facilidades. O modelo foi empiricamente testado através da aplicação de uma amostra de 299 questionários recolhidos online. Tendo o modelo conceptual sido testado a partir dum modelo de equações estruturais, por recurso ao AMOS 21. Os resultados indicam que a perceção de experiência facilitada se traduz em indicadores tangíveis tais como a easiness in performance e a tecnologia. A facilitação da experiência determina a recomendação, ainda que esta recomendação seja modesta. As implicações teóricas e de gestão foram discutidas mostrando que a facilitação da experiência é um processo determinante para a satisfação dos turistas. Estes resultados empíricos, ainda que não generalizáveis, revelam a complexidade do serviço hoteleiro ao mesmo tempo que emprestam à análise do posicionamento competitivo uma nova perspetiva.

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Mode of access: Internet.

Training and facilitation handbook /

"OPM-NPC-06."

Does interhemispheric competition mediate motion-induced blindness? A transcranial magnetic stimulation study

Motion-induced blindness (MIB) is a phenomenon, perhaps related to perceptual rivalry, where stationary targets disappear and reappear in a cyclic mode when viewed against a background (mask) of coherent, apparent 3-D motion. Since MIB has recently been shown to share similar temporal properties with binocular rivalry, we probed the appearance-disappearance cycle of MIB using unilateral, single-pulse transcranial magnetic stimulation (TMS)-a manipulation that has previously been shown to influence binocular rivalry. Effects were seen for both hemispheres when the timing of TMS was determined prospectively on the basis of a given subject's appearance-disappearance cycle, so that it occurred on average around 300 ms before the time of perceptual switch. Magnetic stimulation of either hemisphere shortened the time to switch from appearance to disappearance and vice versa. However, TMS of left posterior parietal cortex more selectively shortened the disappearance time of the targets if delivered in phase with the disappearance cycle, but lengthened it if TMS was delivered in the appearance phase after the perceptual switch. Opposite effects were seen in the right hemisphere, although less marked than the left-hemisphere effects. As well as sharing temporal characteristics with binocular rivalry, MIB therefore seems to share a similar underlying mechanism of interhemispheric modulation. Interhemispheric switching may thus provide a common temporal framework for uniting the diverse, multilevel phenomena of perceptual rivalry.