Lack of NMDA receptor subunit exchange alters Purkinje cell dendritic morphology in cerebellar slice cultures.

Early postnatal developmental changes in N-methyl-d-aspartate (NMDA) receptor (NR) subunits regulate cerebellar granule cell maturation and potentially Purkinje cell development. We therefore investigated Purkinje cell morphology in slice cultures from mice with genetic subunit exchange from NR2C to NR2B (NR2C-2B). NR2C-2B Purkinje cells after 12 days in vitro showed a significantly impaired dendritic arbour complexity with reduced branching density as compared to wild-type cells, a phenotype that was reversed by NMDA treatment. These data support the concept that in cerebellar slice cultures, Purkinje cell dendritic outgrowth is regulated by granule cell inputs.

Long-term NR2B expression in the cerebellum alters granule cell development and leads to NR2A down-regulation and motor deficits.

N-methyl-D-aspartate receptor (NMDAR) composition in granule cells changes characteristically during cerebellar development. To analyze the importance of NR2B replacement by NR2C and NR2A subunits until the end of the first month of age, we generated mice with lasting NR2B expression but deficiency for NR2C (NR2C-2B mice). Mutant phenotype was different from NR2C knock-out mice as loss of granule cells and morphological changes in NR2C/2B cerebellar architecture were already evident from the second postnatal week. Increased NR2B subunit levels led also to a gradual down-regulation of cerebellar NR2A levels, preceding the development of motor impairment in adult animals. Therefore, cerebellar NR2A is important for proper motor coordination and cannot be replaced by long-term expression of NR2B. Consequently, the physiological exchange of NMDA receptor subunits during cerebellar granule cell maturation is important for accurate postnatal development and function.

Combinatory chemical and biological approaches to investigate metal elements in agricultural runoff water.

As part of a project studying the interactions between farming practices, soil erosion processes, and fate of agricultural pollutants into runoff waters, we conducted a pilot study to investigate the relationship between metal contents and metallothionein-2A (MT-2A) as a bioindicator of metal exposure. Runoff water samples were collected between May and November 1999 at the point of outlet of an elementary watershed located in the Paris basin. Selected metals (Al, As, Cd, Cr, Cu, Pb, Hg, Ni, and Zn) were analyzed using conventional techniques. In parallel, human T cells were exposed to water samples for 6 and 18 h and then cell viability and MT-2A gene expression were measured. Results show that among the 10 water samples tested, Al and Zn predominate (highest values = 4.9 and 2.6 microM, respectively), while other metals were below the microM level. Five out of 10 samples induced MT-2A gene expression (30-80% increase at 18 h) as compared with the control. When comparing MT-2A induction profile with metals contents, no obvious correlation was found, suggesting that additional components or parameters are involved. Finally, there was an apparent inverse relationship between Ca concentration and MT-2A gene induction. Although still preliminary, in the absence of longer monitoring, this study shows that MT-2A gene expression is a useful tool to complement chemical analysis in assessing metal elements in water. These combinatory approaches will be pursued and integrated in an ongoing watershed field research project.