Chromatophore Activity during Natural Pattern Expression by the Squid Sepioteuthis lessoniana: Contributions of Miniature Oscillation

Squid can rapidly change the chromatic patterns on their body. The patterns are created by the expansion and retraction of chromatophores. The chromatophore consists of a central pigment-containing cell surrounded by radial muscles that are controlled by motor neurons located in the central nervous system (CNS). In this study we used semi-intact squid (Sepioteuthis lessoniana) displaying centrally controlled natural patterns to analyze spatial and temporal activities of chromatophores located on the dorsal mantle skin. We found that chromatophores oscillated with miniature expansions/retractions at various frequencies, even when the chromatic patterns appear macroscopically stable. The frequencies of this miniature oscillation differed between “feature” and “background” areas of chromatic patterns. Higher frequencies occurred in feature areas, whereas lower frequencies were detected in background areas. We also observed synchronization of the oscillation during chromatic pattern expression. The expansion size of chromatophores oscillating at high frequency correlated with the number of synchronized chromatophores but not the oscillation frequency. Miniature oscillations were not observed in denervated chromatophores. These results suggest that miniature oscillations of chromatophores are driven by motor neuronal activities in the CNS and that frequency and synchrony of this oscillation determine the chromatic pattern and the expansion size, respectively

Gravito-electromagnetic analogies

We reexamine and further develop different gravito-electromagnetic (GEM) analogies found in the literature, and clarify the connection between them. Special emphasis is placed in two exact physical analogies: the analogy based on inertial fields from the so-called "1+3 formalism", and the analogy based on tidal tensors. Both are reformulated, extended and generalized. We write in both formalisms the Maxwell and the full exact Einstein field equations with sources, plus the algebraic Bianchi identities, which are cast as the source-free equations for the gravitational field. New results within each approach are unveiled. The well known analogy between linearized gravity and electromagnetism in Lorentz frames is obtained as a limiting case of the exact ones. The formal analogies between the Maxwell and Weyl tensors are also discussed, and, together with insight from the other approaches, used to physically interpret gravitational radiation. The precise conditions under which a similarity between gravity and electromagnetism occurs are discussed, and we conclude by summarizing the main outcome of each approach.Comment: 60 pages, 2 figures. Improved version (compared to v2) with some re-write, notation improvements and a new figure that match the published version; expanded compared to the published version to include Secs. 2.3 and

The P2X1 receptor and platelet function

Extracellular nucleotides are ubiquitous signalling molecules, acting via the P2 class of surface receptors. Platelets express three P2 receptor subtypes, ADP-dependent P2Y1 and P2Y12 G-protein-coupled receptors and the ATP-gated P2X1 non-selective cation channel. Platelet P2X1 receptors can generate significant increases in intracellular Ca2+, leading to shape change, movement of secretory granules and low levels of αIIbβ3 integrin activation. P2X1 can also synergise with several other receptors to amplify signalling and functional events in the platelet. In particular, activation of P2X1 receptors by ATP released from dense granules amplifies the aggregation responses to low levels of the major agonists, collagen and thrombin. In vivo studies using transgenic murine models show that P2X1 receptors amplify localised thrombosis following damage of small arteries and arterioles and also contribute to thromboembolism induced by intravenous co-injection of collagen and adrenaline. In vitro, under flow conditions, P2X1 receptors contribute more to aggregate formation on collagen-coated surfaces as the shear rate is increased, which may explain their greater contribution to localised thrombosis in arterioles compared to venules within in vivo models. Since shear increases substantially near sites of stenosis, anti-P2X1 therapy represents a potential means of reducing thrombotic events at atherosclerotic plaques