Fig. 12.

Subcellular distribution of GABA and a model of GABAergic-signaling pathways in a differentiating CP/SP neuron. CP/SP neurons were cultured for 24 hr in Neurobasal/B27 and then fixed in PF and processed for immunoelectron microscopy using colloidal gold-conjugated anti-GABA antibody followed by silver enhancement (see Materials and Methods for details). GABA immunoreaction (black particles) is nonuniformly distributed throughout the cytoplasm of the cell body with clusters evident in subplasmalemmal spaces. Similar distribution of GABA immunoreaction and the absence of transmitter-containing vesicles are observed in the growth cones of these neurons. Superimposed on the image of the cell body is a model summarizing the different components identified in this study, which compose the autocrine GABAergic circuit mediating the early phase of neurite outgrowth. GLUT,l-glutamate; Ca²⁺_L, voltage-dependent L-type Ca²⁺ channel.