Toshitaka Morishima

GABA imaging in brain slices using immobilized enzyme-linked photoanalysis

GABA plays an important role in inhibitory neurotransmission. In the developing brain, GABA also acts as a paracrine chemical mediator. To evaluate the ambient GABA gradients in the brain, an enzyme-linked imaging system that consisted of GABase and NADP(+) was developed. In rat cerebellar slices, GABA release was observed in the layers containing GABAergic neurons. In telencephalic slices from embryonic GAD67-GFP knock-in mice, ambient GABA levels were high in the ganglionic eminence, where GABA cells are generated, but missing in homozygotes. This study indicates that this method will be useful to study the topography and dynamics of ambient GABA concentrations.

Accumulation of GABAergic Neurons, Causing a Focal Ambient GABA Gradient, and Downregulation of KCC2 Are Induced During Microgyrus Formation in a Mouse Model of Polymicrogyria

Although focal cortical malformations are considered neuronal migration disorders, their formation mechanisms remain unknown. We addressed how the γ-aminobutyric acid (GABA)ergic system affects the GABAergic and glutamatergic neuronal migration underlying such malformations. A focal freeze-lesion (FFL) of the postnatal day zero (P0) glutamic acid decarboxylase–green fluorescent protein knock-in mouse neocortex produced a 3- or 4-layered microgyrus at P7. GABAergic interneurons accumulated around the necrosis including the superficial region during microgyrus formation at P4, whereas E17.5-born, Cux1-positive pyramidal neurons outlined the GABAergic neurons and were absent from the superficial layer, forming cell-dense areas in layer 2 of the P7 microgyrus. GABA imaging showed that an extracellular GABA level temporally increased in the GABAergic neuron-positive area, including the necrotic center, at P4. The expression of the Cl– transporter KCC2 was downregulated in the microgyrus-forming GABAergic and E17.5-born glutamatergic neurons at P4; these cells may need a high intracellular Cl– concentration to induce depolarizing GABA effects. Bicuculline decreased the frequency of spontaneous Ca2+ oscillations in these microgyrus-forming cells. Thus, neonatal FFL causes specific neuronal accumulation, preceded by an increase in ambient GABA during microgyrus formation. This GABA increase induces GABAA receptor-mediated Ca2+ oscillation in KCC2-downregulated microgyrus-forming cells, as seen in migrating cells during early neocortical development.

Proliferation of cerebellar granule cell precursors is promoted by GABA released from Bergmann glial cells

found that the SNr GABAergic neurons respond to dopamine under blockade of glutamateand GABA-mediated fast transmissions in slice. However, these SNr neurons did not respond to dopamine in acutely dissociated conditions in most cases (46 out of 48), suggesting complex sites of action of the dendritically released dopamine. Here we show that dopamine can induce gliotransmitter release from astrocytes by multiple techniques including calcium imaging, a cell-sensor method, and high performance liquid chromatography. Based on the results, we discuss our hypothesis that dopamine regulates GABAergic SNr neuron activity through gliotransmitter release from astrocytes.

Non-neuronal GABA release in external granular layer and transient VGAT distribution

P1-b18 Non-neuronal GABA release in external granular layer and transient VGAT distribution Kengo Okochi1, Mariko Tanaka1, Shoichiro Hirano1, Toshitaka Morishima1, Yasuo Kawaguchi2, Yuchio Yanagawa3, Naohiro Hozumi4, Sachiko Yoshida1 1 Department of Material Science, Toyohashi University of Technology, Toyohashi, Japan; 2 National Institute for Physiological Sciences, Okazaki, Japan; 3 Gunma University, Maebashi, Japan; 4 Aichi Institute of Technology, Toyota, Japan