Dendritic and axonal organization of mitral and tufted cells in the rat olfactory bulb

Abstract

The output cells of the main olfactory bulb, the mitral and tufted cells, can be categorized into subclasses on the basis of their intrabulbar dendritic and axonal characteristics. Their form was studied in rats following labeling by iontophoretic injection of horseradish peroxidase into the external plexiform layer (EPL). The fact that these extracellular injections labeled small numbers of neurons permitted reconstruction of individual cells. The injection depth within the EPL determined the type of cells labeled. Secondary dendrites of each cell type lay in one of three partially overlapping zones in the EPL. The deepest zone contained the secondary dendrites of one group of mitral cells (Type I), which had the deepest and longest dendrites of the output cells. An intermediate zone of the EPL contained the secondary dendrites of middle tufted and a second class of mitral cells (Type II). The superficial zone, adjacent to the glomerular layer, contained the relatively short, asymmetric dendritic fields of external tufted cells. The few labeled internal tufted cells had secondary dendrites in either the intermediate or deep zones. Every cell type, except the Type I mitral cells, had axon collaterals in the internal plexiform and upper granule cell layers. No cell types had axons re-entering the EPL. These results for output cells combined with our previous observations on granule cells point to a functional sublaminar organization of the EPL that has not previously been proposed.

Neonatal and Adult Neurogenesis Provide Two Distinct Populations of Newborn Neurons to the Mouse Olfactory Bulb

“…Indeed, GABAergic interneurons positioned at different depths within the GCL might have distinct neuronal targets, because the length of their proximal dendritic tree remains constant (Orona et al, 1983). In line with this, superficial and deep GCs differ with regards to the distribution of their dendritic tree (Orona et al, 1983) and their synaptic inputs (Orona et al, 1984;Kishi et al, 1984;. For instance, our previous electrophysiological recordings have shown that newborn neurons, the cell body of which resides close to the mitral cell layer, were clearly distinguished from deeper ones with a cell body closer to the core of the OB .…”

Properties of external plexiform layer interneurons in mouse olfactory bulb slices

“…Properties of EPL tufted cells have previously been studied by others (Schneider and Scott, 1983;Ezeh et al, 1993;Christie et al, 2001;Belluzzi et al, 2004). The tufted cells were identified by their glomerular tufts, lateral dendrites, and depth within the EPL (Orona et al, 1984;Ezeh et al, 1993). The major axis of the tufted cell bodies ranged from 12 to 18 m (mean 13.8Ϯ1.7 m, nϭ4).…”

Differences in Glomerular-Layer-Mediated Feedforward Inhibition onto Mitral and Tufted Cells Lead to Distinct Modes of Intensity Coding

“…Mitral cells (MCs) and tufted cells (TCs), the two principal types of neurons of the olfactory bulb, have been thought to play identical roles in odor coding despite clear anatomical differences (Mori et al, 1983;Orona et al, 1984;Igarashi et al, 2012). Recently, however, multiple studies have identified functional differences between MCs and TCs that suggest that the olfactory system segregates olfactory information into parallel pathways, much like other sensory systems (Fukunaga et al, 2012;Igarashi et al, 2012).…”