Heat transfer and flow regimes in quasi-static magnetoconvection with a vertical magnetic field

Numerical simulations of quasi-static magnetoconvection with a vertical magnetic field are carried out up to a Chandrasekhar number of Q = 108 over a broad range of Rayleigh numbers Ra. Three magnetoconvection regimes are identified: two of the regimes are magnetically constrained in the sense that a leading-order balance exists between the Lorentz and buoyancy forces, whereas the third regime is characterized by unbalanced dynamics that is similar to non-magnetic convection. Each regime is distinguished by flow morphology, momentum and heat equation balances, and heat transport behaviour. One of the magnetically constrained regimes appears to represent an ‘ultimate’ magnetoconvection regime in the dual limit of asymptotically large buoyancy forcing and magnetic field strength; this regime is characterized by an interconnected network of anisotropic, spatially localized fluid columns aligned with the direction of the imposed magnetic field that remain quasi-laminar despite having large flow speeds. As for non-magnetic convection, heat transport is controlled primarily by the thermal boundary layer. Empirically, the scaling of the heat transport and flow speeds with Ra appear to be independent of the thermal Prandtl number within the magnetically constrained, high-Q regimes

Metabotropic action of postsynaptic kainate receptors triggers hippocampal long-term potentiation

Long-term potentiation (LTP) in the rat hippocampus is the most extensively studied cellular model for learning and memory. Induction of classical LTP involves an NMDA receptor- and calcium-dependent increase in functional synaptic AMPA receptors mediated by enhanced recycling of internalized AMPA receptors back to the postsynaptic membrane. Here we report a novel, physiologically relevant NMDA receptor-independent mechanism that drives increased AMPA receptor recycling and LTP. This pathway requires the metabotropic action of kainate receptors and activation of G-protein, protein kinase C and phospholipase C. Like classical LTP, kainate receptor-dependent LTP recruits recycling endosomes to spines, enhances synaptic recycling of AMPA receptors to increase their surface expression and elicits structural changes in spines, including increased growth and maturation. These data reveal a new and previously unsuspected role for postsynaptic kainate receptors in the induction of functional and structural plasticity in the hippocampus

Analyses of the spatiotemporal expression and subcellular localization of liprin-alpha proteins

The members of the Liprin-alpha protein family, Liprin-alpha 1-4, are scaffolding proteins that play important roles in the regulation of synapse assembly and maturation, vesicular trafficking, and cell motility. Recent evidence suggests that despite their high degree of homology, the four isoforms can be differentially regulated and fulfill diverging functions. However, to date their precise regional and subcellular distribution has remained elusive. Here, we examine the spatiotemporal expression patterns of Liprins-alpha in the rodent by using in situ hybridization, immunoblotting, and immunochemistry of primary cells as well as brain and retina sections. We show that Liprin-alpha 1-4 mRNA and protein are widely expressed throughout the developing and adult central nervous system, with Liprin-alpha 2 and -alpha 3 being the major Liprin-alpha isoforms in the brain. Our data show that the four Liprin-alpha proteins differ in their regional distribution, in particular in the hippocampus, the cerebellum, and the olfactory bulb. Liprin-alpha 1 exhibits a unique spatiotemporal expression pattern as its levels decrease during synaptogenesis, and it is the only Liprin-alpha with substantial non-neuronal expression. Immunocytochemistry of cultured primary neurons with pre- and postsynaptic marker proteins shows all four Liprins-alpha to be present at synapses and nonsynaptic sites to varying degrees. Together, these results show that neurons in different brain regions express a distinct complement of Liprin-alpha proteins. J. Comp. Neurol. 519:3019-3039, 2011. (C) 2011 Wiley-Liss, Inc