A Rare Second Year - Lake Ice Cover in the Canadian High Arctic

Colour Lake, Axel Heiberg Island, N.W.T. (79 25 N; 90 45 W), remained largely ice covered from autumn 1985 to summer 1987. This is a relatively rare event. Observations and measurements of the thickness and specific conductance of the lake ice cover were made at the end of the 1986 summer and again in the following spring. The residual ice cover (second-year ice with first-year ice beneath it) was significantly thicker and had a lower specific conductance than first-year ice formed in marginal leads (moat) that had been ice free in 1986. The first-year ice that grew beneath the residual ice cover had the lowest specific conductance. Distribution of snow on the lake was affected by the roughness of the second-year ice (as compared to the smoother moat ice) and differences in elevation between second-year (high) and moat ice.Key words: High Arctic, specific conductance, residual ice cover, snow distributionMots clés: Extrême-Arctique, conductivité spécifique, couverture de glace résiduelle, répartition de la neig

Role of Ectonucleotidases in the Synapse Formation During Brain Development: Physiological and Pathological Implications

Extracellular adenine nucleotides and nucleosides, such as ATP and adenosine, are among the most recently identified and least investigated diffusible signaling factors that contribute to the structural and functional remodeling of the brain, both during embryonic and postnatal development. Their levels in the extracellular milieu are tightly controlled by various ectonucleotidases: ectonucleotide pyrophosphatase/phosphodiesterases (E-NPP), alkaline phosphatases (AP), ectonucleoside triphosphate diphosphohydrolases (E-NTPDases) and ecto-5'-nucleotidase (eN). During central nervous system development and in adulthood all ectonucleotidases have diverse expression pattern, cell specific localization and function. Formation, maturation, and refinement of synaptic contacts are influenced by neurotransmitters and neuromodulators, and control of extracellular adenine nucleotide levels by ectonucleotidases are important for understanding the role of purinergic signaling in developing tissues and potential targets in developmental disorders such as autism