cAMP-dependent protein kinase mediates activity-regulated synaptic targeting of NMDA receptors.

Chronic activity blockade increases synaptic levels of NMDA receptor immunoreactivity in hippocampal neurons. We show here that blockade-induced synaptic NMDA receptors are functional and mediate enhanced excitotoxicity in response to synaptically released glutamate. Activity blockade increased the cell surface association of NMDA receptors. Blockade-induced synaptic targeting of NMDA receptors did not require protein synthesis but required phosphorylation and specifically cAMP-dependent protein kinase (PKA). Furthermore, activation of PKA was sufficient to induce synaptic targeting of NMDA receptors regardless of receptor activity status. These results implicate PKA activity downstream of receptor blockade as a mediator of enhanced synaptic transport or stabilization of NMDA receptors. Synaptic clustering of NR1-green fluorescent protein was observed in living neurons in response to NMDA receptor and cAMP phosphodiesterase antagonists and occurred gradually over the course of a day. This pathway represents a cellular mechanism for synaptic homeostasis and is likely to function in metaplasticity, long-term regulation of the ability of a synapse to undergo potentiation or depression.

Use of the lichen Rhizoplaca melanophthalma as a biomonitor in relation to phosphate refineries near Pocatello, Idaho.

Phosphate refineries are point sources for atmospheric Cr, Cd, Zn and P. Concentrations of these and other elements were determined in the lichen Rhizoplaca melanophthalma (Ram.) Leuck. and Poelt in relation to distance and direction from phosphate refineries northwest of Pocatello, Idaho. Elemental concentrations in lichens collected were measured using a multi-element Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Linear regression analysis revealed that concentrations of Cd, Cr, Zn, and P were negatively correlated with distance from the refineries. The concentrations of the elements Cd, Zn, Ca, Mn, B, and Pb were significantly different among four transects in different directions from the pollution source. Analysis of covariance indicated significant differences in concentrations of Cd, Cr, Zn, P, Cu, Ca, Mg, and K in lichens as a function of distance and direction from the pollution source. These results indicate that this lichen species may be used to determine deposition patterns of air pollutants in semi-arid environments.

Event-by-event analysis of proton-induced nuclear multifragmentation: determination of the phase transition universality class in a system with extreme finite-size constraints.

A percolation model of nuclear fragmentation is used to interpret 10.2 GeV/c p+197Au multifragmentation data. Emphasis is put on finding signatures of a continuous nuclear matter phase transition in finite nuclear systems. Based on model calculations, corrections accounting for physical constraints of the fragment detection and sequential decay processes are derived. Strong circumstantial evidence for a continuous phase transition is found, and the values of two critical exponents, sigma = 0.5+/-0.1 and tau = 2.35+/-0.05, are extracted from the data. A critical temperature of T(c) = 8.3+/-0.2 MeV is found.