Axon Branching and Synaptic Bouton Phenotypes in GABAergic Nonpyramidal Cell Subtypes

Abstract

GABAergic nonpyramidal cells, cortical interneurons, consist of heterogeneous subtypes differing in their axonal field and target selectivity. It remains to be investigated how the diverse innervation patterns are generated and how these spatially complicated, but synaptically specific wirings are achieved. Here, we asked whether a particular cell type obeys a specific branching and bouton arrangement principle or differs from others only in average morphometric values of the morphological template common to nonpyramidal cells. For this purpose, we subclassified nonpyramidal cells within each physiological class by quantitative parameters of somata, dendrites, and axons and characterized axon branching and bouton distribution patterns quantitatively. Each subtype showed a characteristic set of vertical and horizontal bouton spreads around the somata. Each parameter, such as branching angles, internode or interbouton intervals, followed its own characteristic distribution pattern irrespective of subtypes, suggesting that nonpyramidal cells have the common mechanism for formation of the axon branching pattern and bouton arrangement. Fitting of internode and interbouton interval distributions to the exponential indicated their apparent random occurrence. Decay constants of the fitted exponentials varied among nonpyramidal cells, but each subtype expressed a particular set of interbouton and internode interval averages. The distinctive combination of innervation field shape and local axon phenotypes suggests a marked functional difference in the laminar and columnar integration properties of different GABAergic subtypes, as well as the subtype-specific density of inhibited targets.

Specialized Cortical Subnetworks Differentially Connect Frontal Cortex to Parahippocampal Areas

“…They were then postfixed in 1% OsO 4 in PB containing 7% glucose, dehydrated, and flat embedded on glass slides in Epon. After all the procedures, the tissues shrink to approximately 90% in length (Karube et al, 2004). The shrinkage was not corrected in the analysis.…”

Recurrent Connection Patterns of Corticostriatal Pyramidal Cells in Frontal Cortex

“…After all of the procedures, the tissue shrank to ϳ90% in length (Karube et al, 2004). The shrinkage was not corrected in the analysis.…”

Chandelier Cells Control Excessive Cortical Excitation: Characteristics of Whisker-Evoked Synaptic Responses of Layer 2/3 Nonpyramidal and Pyramidal Neurons

“…Cortical inhibitory interneurons have been classified into many subtypes on the basis of their morphological, anatomical, biochemical, intrinsic, and synaptic properties (Kawaguchi, 1995;Cauli et al, 2000;Gupta et al, 2000;Karube et al, 2004). Accumulating in vitro and in vitro studies on inhibitory interneurons in the neocortex (Agmon and Connors, 1992;Reyes et al, 1998;Larkum et al, 1999;Beierlein et al, 2000;Galarreta and Hestrin, 2001;Porter et al, 2001;Tamas et al, 2003), as well as those in the hippocampus (Buhl et al, 1994;Miles et al, 1996;Parra et al, 1998;Klausberger et al, 2003) and thalamus (Curro Dossi et al, 1992; Zhu and Lo, 1998;Cox and Sherman, 2000;Zhu and Heggelund, 2001;Perreault et al, 2003), have now provided compelling evidence that diverse classes of interneurons can generate various forms of inhibitions important for distinct information processes; however, how distinct types of interneurons receive and integrate sensory inputs and how they are functionally different are poorly understood.…”