GABA stimulates chemotaxis and chemokinesis of embryonic cortical neurons via calcium-dependent mechanisms

Abstract

During rat cortical development, when neurons migrate from the ventricular zone to the cortical plate, GABA localizes within the target destinations of migratory neurons. At this time, cells in germinal zones and along migratory pathways express GABA receptor subunit transcripts, implying that in vivo, GABA may be a chemoattractant. We used an in vitro strategy to study putative chemotropic effects of GABA on embryonic rat cortical cells. GABA stimulated neuronal migration in vitro at embryonic day 15 (E15). From E16 onward, two concentration ranges (fM and microM) induced motility. Femtomolar GABA primarily stimulated chemotaxis (migration along a chemical gradient), whereas micromolar GABA predominantly initiated chemokinesis (increased random movement). These effects were mimicked by structural analogs of GABA with relative specificity at GABAA (muscimol), GABAB (R-baclofen), and GABAC (trans- or cis-4-aminocrotonic acid) receptors. Antagonists of GABAB (saclofen) and GABAC (picrotoxin) receptors partially inhibited responses to both femto- and micromolar GABA; however, only responses to femtomolar GABA were partially blocked by bicuculline, a well established antagonist of GABA at GABAA receptors. Hence, chemotactic responses to femtomolar GABA seem to involve all three classes of GABA receptor proteins, whereas chemokinetic responses to micromolar GABA involve GABAB and GABAC receptor proteins. GABA-induced motility was blocked by loading the cells with the Ca(2+)-chelating molecule bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid, suggesting that intracellular Ca2+ mediates GABA-induced cell movement. Optical recordings of cells loaded with Ca2+ indicator dye revealed that both femto- and micromolar GABA evoked increases in intracellular Ca2+. Thus, GABA-stimulated increases in intracellular Ca2+ may mediate both chemotactic and chemokinetic responses in embryonic cortical cells.

γ-Amino Butyric Acid Type B Receptors Stimulate Neutrophil Chemotaxis during Ischemia-Reperfusion

“…In neutrophils, disassembly of the microtubule network has been shown to induce development of polarity, a key feature required for chemokinesis and chemotaxis (24). Recent studies have suggested a role for the GABA B R in directed migration of embryonic cortical neuron, and motility of spinal neuroblasts, thus supporting the concept that these receptors can guide directed migration or growth (25). The present study shows that GABA B R selectively induces neutrophil chemotaxis via an Akt-dependent mechanism because pretreatment with LY294003 or simultaneous addition of CGP52432 inhibited baclofen-stimulated neutrophil chemotaxis.…”

The role of ATP signaling in the migration of intermediate neuronal progenitors to the neocortical subventricular zone

“…Our hypothesis was based on the previous findings that Ca 2ϩ signaling influences the mitosis of neuronal progenitors and their nuclear interkinetic translocation in the embryonic retina (21), and that [Ca 2ϩ ] fluctuations also affect cellular migration in cerebellar granular cells (22)(23)(24), cultured neuronal progenitors (25), and postmitotic cortical neurons (26). Spontaneous Ca 2ϩ transients or Ca 2ϩ waves are visible in both the VZ and SVZ and increase in intensity during corticogenesis (27,28), suggesting their involvement in neuronal proliferation and migration.…”

GABA Expression Dominates Neuronal Lineage Progression in the Embryonic Rat Neocortex and Facilitates Neurite Outgrowth via GABAAAutoreceptor/Cl−Channels

“…Baclofen did not produce detectable changes in either membrane potential or Ca 2ϩ c (data not shown), implying either that the function of GABA B receptor/ Ca 2ϩ channels might have been compromised during acute cell preparation or that the activation of these receptors nominally contributes to membrane potential or Ca 2ϩ c at this stage of cortical neuron development. Relatively modest contributions of GABA B receptor/Ca 2ϩ channels to Ca 2ϩ c levels were indeed shown in cell cultures of migrating and differentiating cortical neurons after recovery from dissociation (see Behar et al, 1996) (see Fig. 9B).…”

“…Functional GABA B receptors have been shown previously to mediate cortical neuronal migration from the VZ/SVZ to the CP/SP in rat neocortex over E17-E19 (Behar et al, 1996(Behar et al, , 1998(Behar et al, , 2000.…”

“…GABA added to cortical slice preparations differentially modulates neural cell proliferation in the VZ and SVZ (LoTurco et al, 1995;Haydar et al, 2000). In vitro, GABA also acts like a chemoattractant and directs the migration of postmitotic neurons from the VZ/SVZ to the CP/SP via GABA B receptors (Behar et al, 1996(Behar et al, , 1998(Behar et al, , 2000. In addition, GABA can both stimulate random motility in CP/SP neurons via GABA B receptor-coupled Ca 2ϩ signals and attenuate their own movement via GABA A receptor/Cl Ϫ channels, as neurons become arranged into primitive layers (Behar et al, 1998).…”