Growth cone calcium elevation by GABA

Abstract

Cytoplasmic calcium plays a key role in neurite growth. In contrast to previous work suggesting that gamma aminobutyrate's (GABA) role in regulating growth cone calcium is primarily to antagonize the effects of glutamate, we report that GABA can act in an excitatory manner on developing hypothalamic neurites, independently raising calcium in growing neurites and their growth cones. Time-lapse digital video and confocal laser microscopy with the calcium-sensitive dyes fluo-3 and fura-2 were used to study the influence of GABA on neurite calcium levels. GABA (10 microM) evoked a calcium rise in both bicarbonate- and Hepes-based buffers. The calcium rise was greatly reduced after chloride transport was blocked. GABA raised calcium by stimulating the cell body, resulting in an increase in calcium throughout the neuronal cell body and dendritic arbor. GABA also acted locally, stimulating a neuritic calcium rise only in a single dendrite or growth cone. In some neurites and growth cones during early development, GABA generated a greater calcium rise than did glutamate. Bicuculline, a GABAA receptor antagonist, reduced calcium levels in neurites of young synaptically coupled neurons, indicating that ongoing synaptic release of GABA raised neuritic calcium. These data suggest that during early development, GABA may play a significant role in regulating process growth and modulating the formation of early connections in the hypothalamus. Our data support the hypothesis that GABA receptors are functionally active and may play a calcium regulating role similar to that of glutamate in neuronal development. This is particularly true in early development, as later in development GABA's role becomes more inhibitory, and glutamate plays the primary excitatory role.

Seizure Sensitivity Is Ameliorated by Targeted Expression of K+–Cl− Cotransporter Function in the Mushroom Body of the Drosophila Brain

“…One possibility is that the plasticity of these brain regions reflects the type of excitatory GABAergic signaling normally observed during early neuronal development (Ben-Ari et al 2007). Excitatory GABAergic signaling has been observed in the adult hippocampus, where rhythmic firing is believed to promote neuronal plasticity (Obrietan and van den Pol 1996;Ge et al 2006), but may also make this structure particularly susceptible to epileptic seizures.…”

GABA Activity Mediating Cytosolic Ca2+Rises in Developing Neurons Is Modulated by cAMP-Dependent Signal Transduction

“…In addition, DNA synthesis in cortical neural progenitor cells can be blocked by specifically inhibiting GABA A receptor activity (LoTurco et al, 1995). GABA can increase Ca 2ϩ levels in neurites and growth cones (Obrietan and van den Pol, 1996a), which may alter growth cone motility and the rate of neurite extension. In addition, GABA-mediated Ca 2ϩ influx in growth cones leads to an increase in GAP43 and MARCKS protein phosphorylation (Fukura et al, 1996).…”

“…The cAMP signal transduction pathway has been implicated in a variety of developmentally regulated processes, including cell cycle regulation (Grieco et al, 1996), neural migration (Behar et al, 1995), and gene induction (Zhang et al, 1993). Additionally, many neurotransmitters and neuropeptides that affect neural physiology through the regulation of adenylyl cyclase activity, including neuropeptide Y (NPY), dopamine, glutamate, and serotonin, are expressed in early development and could serve to modulate the Ca 2ϩ -elevating actions of GABA (Rajaofetra, 1989;Belin et al, 1991;Marti et al, 1992;van den Pol et al, , 1996aLieb et al, 1996). Based on these findings, we studied the modulation of GABAergic Ca 2ϩ elevating activity by the cAMP-mediated signal transduction pathway.…”

“…Other GABA-mediated actions during neural development include altering neurite outgrowth (Barbin et al, 1993), triggering chemokinesis (Behar et al, 1994), inducing GABA receptor expression (Meier et al, 1984), and regulating neural phenotype (Marty et al, 1996). We have recently reported that GABA triggers localized Ca 2ϩ increases in developing neurites and growth cones (Obrietan and van den Pol, 1996a), suggesting a possible Ca 2ϩ -dependent role for GABA in altering the directionality of growth cone motility and the rate of neurite outgrowth. Based on these reports and the findings in our paper, during early development the activation of neurotransmitter receptors (such as NPY, glutamate, dopamine, serotonin, melatonin, and acetylcholine) coupled to the cAMP signal transduction pathway could substantially alter GABA-related Ca 2ϩ rises.…”

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

“…GABA release from axonal growth cones of embryonic mouse hypothalamic neurons has also been detected electrically (Gao and van den Pol, 2000), and exogenously applied GABA has been shown to elevate Ca 2ϩ c in these growth cones via bicucullineand furosemide-sensitive mechanisms (Obrietan and van den Pol, 1996). Bicuculline also decreased ambient Ca 2ϩ c levels in hypothalamic neurons, which had been cultured for 6 d. This was attributed to blockade of synaptically released GABA acting at GABA A receptors.…”