DEVELOPMENTAL REGULATION OF VOLTAGE-GATED K-CELLS( CHANNEL AND GABA(A) RECEPTOR EXPRESSION IN BERGMANN GLIAL)

Bergmann glial cells are closely associated with neurons: during devel opment they provide guiding structures for migrating granule cells and in the adult cerebellum they display intimate interactions with Purki nje cells. In this study, we have addressed the question of whether su ch changes in neuronal-glial interactions during development are accom panied by variations in the membrane properties of Bergmann glial cell s. We used a mouse cerebellum slice preparation to study membrane curr ents of the Bergmann glial cells at various stages of development in s itu using the patch-clamp technique. The distinct morphology of Bergma nn glial cells was revealed by Lucifer yellow injections during record ing. While Bergmann glial cells in mice of postnatal day 20 (P20) to P 30 have thick processes with arborized, irregularly shaped leaf-like a ppendages, the processes of cells from younger mice (P5-P7) are thinne r and smoother. This morphological maturation is accompanied by a vari ation in voltage-gated currents. In cells from P5 to P7, delayed outwa rd- and inward-rectifying K+ currents were recorded, while older Bergm ann glial cells were characterized by, large, voltage- and time-indepe ndent K+ currents. In addition, application of GABA induces two effect s, a rapid activation of a Cl- conductance and a longer-lasting decrea se in the (resting) K+ conductance. Both effects were mediated by benz odiazepine-insensitive GABA, receptors. Responses in cells of P5-P7 mi ce were large as compared to the small or even undetectable responses in P20-P30 cells. These GABA(A) receptors were characterized immunohis tochemically in mice and rat brain sections with five subunit-specific antibodies. Bergmann glial cells exhibit a distinct but transient imm unoreactivity for the GABA(A) receptor alpha 2-, alpha 3-, and delta-s ubunits. Staining is maximal between P7 and P10 and decreases graduall y thereafter. In contrast, antibodies to the alpha 1- and beta 2,3-sub units fail to decorate Bergmann glial cells, although they yield a pro minent staining of both the Purkinje cells and the granule cells. Thes e changes in the Bergmann glial cell membrane properties and GABA, rec eptor expression suggest a transition between functional states during development of the Bergmann glial cells.