Glutamate controls vessel-associated migration of GABA interneurons from the pial migratory route via NMDA receptors and endothelial protease activation.

During cortex development, fine interactions between pyramidal cells and migrating GABA neurons are required to orchestrate correct positioning of interneurons, but cellular and molecular mechanisms are not yet clearly understood. Functional and age-specific expression of NMDA receptors by neonate endothelial cells suggests a vascular contribution to the trophic role of glutamate during cortical development. Associating functional and loss-of-function approaches, we found that glutamate stimulates activity of the endothelial proteases MMP-9 and t-PA along the pial migratory route (PMR) and radial cortical microvessels. Activation of MMP-9 was NMDAR-dependent and abrogated in t-PA-/- mice. Time-lapse recordings revealed that glutamate stimulated migration of GABA interneurons along vessels through an NMDAR-dependent mechanism. In Gad67-GFP mice, t-PA invalidation and in vivo administration of an MMP inhibitor impaired positioning of GABA interneurons in superficial cortical layers, whereas Grin1 endothelial invalidation resulted in a strong reduction of the thickness of the pial migratory route, a marked decrease of the glutamate-induced MMP-9-like activity along the PMR and a depopulation of interneurons in superficial cortical layers. This study supports that glutamate controls the vessel-associated migration of GABA interneurons by regulating the activity of endothelial proteases. This effect requires endothelial NMDAR and is t-PA-dependent. These neurodevelopmental data reinforce the debate regarding safety of molecules with NMDA-antagonist properties administered to preterm and term neonates.

In utero alcohol exposure exacerbates endothelial protease activity from pial microvessels and impairs GABA interneuron positioning.

In utero alcohol exposure can induce severe neurodevelopmental disabilities leading to long-term behavioral deficits. Because alcohol induces brain defects, many studies have focused on nervous cells. However, recent reports have shown that alcohol markedly affects cortical angiogenesis in both animal models and infants with fetal alcohol spectrum disorder (FASD). In addition, the vascular system is known to contribute to controlling gamma-aminobutyric acid (GABA)ergic interneuron migration in the developing neocortex. Thus, alcohol-induced vascular dysfunction may contribute to the neurodevelopmental defects in FASD. The present study aimed at investigating the effects of alcohol on endothelial activity of pial microvessels. Ex vivo experiments on cortical slices from mouse neonates revealed that in endothelial cells from pial microvessels acute alcohol exposure inhibits both glutamate-induced calcium mobilization and activities of matrix metalloproteinase-9 (MMP-9) and tissue plasminogen activator (tPA). The inhibitory effect of alcohol on glutamate-induced MMP-9 activity was abrogated in tPA-knockout and Grin1flox/VeCadcre mice suggesting that alcohol interacts through the endothelial NMDAR/tPA/MMP-9 vascular pathway. Contrasting with the effects from acute alcohol exposure, in mouse neonates exposed to alcohol in utero during the last gestational week, glutamate exacerbated both calcium mobilization and endothelial protease activities from pial microvessels. This alcohol-induced vascular dysfunction was associated with strong overexpression of the N-methyl-d-aspartate receptor subunit GluN1 and mispositioning of the Gad67-GFP interneurons that normally populate the superficial cortical layers. By comparing several human control fetuses with a fetus chronically exposed to alcohol revealed that alcohol exposure led to mispositioning of the calretinin-positive interneurons, whose density was decreased in the superficial cortical layers II-III and increased in deepest layers. This study provides the first mechanistic and functional evidence that alcohol impairs glutamate-regulated activity of pial microvessels. Endothelial dysfunction is characterized by altered metalloproteinase activity and interneuron mispositioning, which was also observed in a fetus with fetal alcohol syndrome. These data suggest that alcohol-induced endothelial dysfunction may contribute in ectopic cortical GABAergic interneurons, that has previously been described in infants with FASD.