Tonic activation of GLUK5 kainate receptors decreases neuroblast migration in whole-mounts of the subventricular zone.

In the postnatal subventricular zone (SVZ), neuroblasts migrate in chains along the lateral ventricle towards the olfactory bulb. AMPA/kainate receptors as well as metabotropic glutamate receptors subtype 5 (mGluR5) are expressed in SVZ cells. However, the cells expressing these receptors and the function of these receptors remain unexplored. We thus examined whether SVZ neuroblasts express mGluR5 and Ca(2+)-permeable kainate receptors in mouse slices. Doublecortin (DCX)-immunopositive cells (i.e. neuroblasts) immunostained positive for mGluR5 and GLU(K5-7)-containing kainate receptors. RT-PCR from approximately 10 GFP-fluorescent cell aspirates obtained in acute slices from transgenic mice expressing green fluorescent protein (GFP) under the DCX promoter showed mGluR5 and GLU(K5) receptor mRNA in SVZ neuroblasts. Patch-clamp data suggest that approximately 60% of neuroblasts express functional GLU(K5)-containing receptors. Activation of mGluR5 and GLU(K5)-containing receptors induced Ca(2+) increases in 50% and 60% of SVZ neuroblasts, respectively, while most neuroblasts displayed GABA(A)-mediated Ca(2+) responses. To examine the effects of these receptors on the speed of neuroblast migration, we developed a whole-mount preparation of the entire lateral ventricle from postnatal day (P) 20-25 DCX-GFP mice. The GABA(A) receptor (GABA(A)R) antagonist bicuculline increased the speed of neuroblast migration by 27%, as previously reported in acute slices. While the mGluR5 antagonist MPEP did not affect the speed of neuroblast migration, the homomeric and heteromeric GLU(K5) receptor antagonists, NS3763 and UB302, respectively, increased the migration speed by 38%. These data show that although both GLU(K5) receptor and mGluR5 activations increase Ca(2+) in neuroblasts, only GLU(K5) receptors tonically reduce the speed of neuroblast migration along the lateral ventricle.