A proposed role for the Ca ion in the chemotactic response of Physarum polycephalum

Bibliography: pages 107-111.Durham, in a review published in 1974, presented the following hypotheses concerning the factors that control amoeboid movement: (1) actin and myosin are present in all cells that exhibit amoeboid movement and, changes in the internal [Ca⁺⁺] regulate contraction, (2) filaments of actin and myosin form an intimate association with the surface membrane and depending on the local [Ca⁺⁺] , the filaments can cause the membrane to relax or become rigid, (3) Ca⁺⁺ fluxes across the external membrane (viz. efflux and influx) regulate the state of contraction in the proposed actinomyosin-surface membrane network and, (4) such Ca++ fluxes operating across the membrane manifest themselves (especially with slime mould plasmodia) as waves of adhesion running across the undersurface of a cell and aid in movement. A working hypothesis, that encompasses the ideas of Durham, is that Ca⁺⁺ entry and efflux across the external membrane control such cellular processes as extension of pseudopodia, exocytosis, endocytosis and the direction of movement (chemotactic response) of amoeboid cells. In the specific case of slime mould plasmodia, which best exemplify all of Durham's hypotheses, the simplest hypothesis to explain the control of chemotaxis is that attractants (sugars, food; organisms) cause a Ca⁺⁺ efflux across the membrane and a subsequent movement forward. Repellents would act in a reverse manner by causing Ca⁺⁺ entry. This hypothesis also allows for the existence of a Ca⁺⁺-accumulating organelle. This organelle might replace or act in concert with the proposed Ca⁺⁺ fluxes across the external membrane. The investigations reported in this thesis were devised to examine experimentally this hypothesis

Defining the contribution of dorsal vagal complex astrocytes to the regulation of food intake

Food intake is controlled by the coordinated action of numerous brain regions but a complete understanding of the process remains elusive. The nucleus of the solitary tract (NTS), located in the brainstem dorsal vagal complex (DVC) is the first site for integration of visceral synaptic and hormonal cues that act to inhibit food intake. NTS neurons receive synaptic input from sensory neurons of the vagus nerve that relay signals of gastrointestinal stretch and nutrient content. In response to these signals of ingestion, NTS neurons signal to higher brain centres in the hypothalamus and midbrain to inhibit hunger and promote meal termination. A role for astrocytes in brain circuits controlling food intake has begun to be identified. Hypothalamic astrocyte signalling has been implicated in regulating energy homeostasis. Despite a wealth of evidence showing astrocytes in the NTS/DVC are involved in synaptic integration of vagal signals and control of autonomic physiology, the potential role of these cells in feeding control has not been investigated. We hypothesised that NTS astrocytes, and those in the wider DVC, would be responsive to increases in food intake and, in turn, their activation would act in concert with NTS neurons to drive a corresponding suppression of food intake. To investigate this prospect we used dietary manipulation, immunohistochemistry, selective chemogenetic manipulation of DVC astrocytes, behavioural assays and electrophysiology in mice. The key findings of these studies show that in response to acute nutrient excess and gastric distention NTS astrocytes increase their expression of the cytoskeletal glial fibrillary acidic protein and adopt a more ramified morphology, indicative of activation. We also show that selective activation of Gq-proteincoupled receptor signalling in DVC astrocytes suppresses nocturnal food intake and refeeding after a fast. These studies provide evidence that astrocytes may be integrators and effectors of satiety signals and appropriate feeding responses in the DVC

The Role of TASK Two-Pore-Domain Potassium Channels in General Anaesthesia

TASK channels, members of the two-pore-domain potassium channel family, contribute towards the resting membrane potential and have been implicated in the mechanism of general anaesthesia. Previous work from our group with a TASK-3 channel knockout (T3KO) mouse showed a reduction in halothane sensitivity using a loss of righting reflex (LORR) assay, and absence of the theta brain oscillation induced in wild type (WT) mice by halothane anaesthesia. Two further strains of knockout mice, the TASK-1 knockout (T1KO) and the double knockout (DKO: TASK-1 and -3 channels), were compared with WT using the LORR assay, cortical electroencephalogram recording in response to halothane and during sleep. The mechanistic basis for the diminished theta oscillation in T3KO mice was investigated by recording in CA1 pyramidal cells of the hippocampus. The LORR assay revealed a decrease in halothane sensitivity in T1KO but not DKO compared with WT. The T1KO strain had a theta oscillation induced by exposure to halothane similar to that of WT mice, whereas that observed in the DKO was intermediate between WT and T3KO. T1KO differed from other strains in that the distribution of sleep and wake periods was uniform across the diurnal cycle. The resting membrane potential did not differ between strains during control or halothane exposure. During control there was no strain difference in action potential (AP). Halothane altered AP shape in WT but not the T3KO strain. WT had a greater ability to sustain AP firing than T3KO during halothane. These data show that T1KO mice have decreased anaesthetic sensitivity and altered sleep structure compared with WT, indicating a role for this channel in anaesthetic sensitivity and sleep. The similar resting membrane potential and lack of response to halothane in the T3KO makes pyramidal cells an unlikely source of the theta ablation observed

Прикладна фізика : українсько-російсько-англійський тлумачний словник. У 4 т. Т. 2. З – Н

Словник охоплює близько 30 тис. термінів з прикладної фізики і дотичних до неї галузей знань та їх тлумачення трьома мовами (українською, російською та англійською). Багато термінів і визначень, наведених у словнику, якими послуговуються у відповідній галузі знань, досі не входили до жодного зі спеціалізованих словників. Словник призначений для викладачів, науковців, інженерів, аспірантів, студентів вищих навчальних закладів, перекладачів з природничих і технічних дисциплін