Receptor-activated calcium signals in tangentially migrating cortical cells.

Recent studies have shown that the two main types of cortical neurons, pyramidal and nonpyramidal, have different origins and use different migratory routes--radial and tangential respectively. The role of neurotransmitters in radial migration is well known; however, there are no data about their effect on intracellular calcium--[Ca(2+)](i)--in tangentially migrating cells. We have performed ratiometric and confocal calcium imaging of 1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine labelled tangentially migrating neurons in the intermediate zone cells of fetal rat coronal slices. Superfusion with N-methyl-D-aspartic acid (NMDA) leads to an increase in [Ca(2+)](i), which is blocked by the antagonist APV or the presence of Mg(2+) in the medium. Kainate produced an increase in [Ca(2+)](i) that could be blocked by the non-NMDA antagonist CNQX. Muscimol, an agonist of GABAa-receptors, produced a transitory increase in [Ca(2+)](i) that was blocked by the specific antagonist bicuculline or the presence of tetrodotoxin in the medium. We conclude that tangentially migrating cells display consistent [Ca(2+)](i) changes in response to agonists of NMDA, non-NMDA and GABAa receptors, suggesting that these cells are quite mature and homogeneous. The endogenous activation of these receptors may have either a direct effect on tangential migration or modulate the response of migrating cells to external cues.