Quantitative analysis of axon collaterals of single neurons in layer IIa of the piriform cortex of the guinea pig

Abstract

To study the various types of neurons in layer IIa in the piriform cortex (PC) and the spatial distribution of their axons, axon collaterals of three neurons in layer IIa were labeled and quantitatively analyzed by intracellular injection of biocytin in the guinea pig. Individual neurons have highly distributed axon collaterals, which display a little tendency toward patchy concentrations inside as well as outside the PC. One semilunar cell in the posterior PC had 54-mm-long axon collaterals and 4,200 boutons, out of which 2,100 (49% of the total number of boutons) were distributed in the PC. One semilunar-pyramidal transitional cell in the posterior PC had 256-mm-long axon collaterals and 23,000 boutons, out of which 16,100 (70% of the total number of boutons) and 4,000 (18% of the total number of boutons) were respectively distributed in all layers and in layer Ia of the PC. One multipolar cell in the posterior PC had 188-mm-long axon collaterals and 18,000 boutons, out of which 13,700 (78% of the total number of boutons) were distributed in the PC. Our results revealed that the connection patterns of individual cells in layer IIa have most of the features required for an associative neural network, which may function as a content-addressable memory for the association of odor stimuli.

Optophysiological analysis of associational circuits in the olfactory cortex

“…A final intriguing point is that there is a distinct lack of functional projections from pPC to aPC. This is consistent with anatomical evidence based on reconstructions of axon collaterals of individual pPC neurons, as well as bulk tracer labeling (Datiche et al, 1996; Johnson et al, 2000; Chen et al, 2003; ul Quraish et al, 2004; Yang et al, 2004). …”

Neural Coding by Two Classes of Principal Cells in the Mouse Piriform Cortex

“…1 A, left) and SL cells (Fig. 1 A, right) are morphologically distinctive but are embedded in similar circuits in the piriform cortex Yang et al, 2004). Both receive monosynaptic input from the olfactory bulb via the lateral olfactory tract (LOT), which forms excitatory synapses on the distal apical dendrites in layer Ia (see Fig.…”

“…Is it possible that SL cells, with their regularspiking APs and distinctive LOT input, are a kind of GABAergic interneuron? This seems unlikely, because they express the glutamate-synthesizing enzyme PAG (phosphate-activated glutaminase) (Kaneko and Mizuno, 1988) but not the GABAsynthesizing enzyme GAD (glutamate decarboxylase) (Ekstrand et al, 2001), and their axonal projections are wide-ranging, typical of excitatory principal neurons (Neville and Haberly, 2004;Yang et al, 2004).…”

Complementary Sensory and Associative Microcircuitry in Primary Olfactory Cortex

“…At the extreme, pyramidal cells deep in layer II (L2Ps) have been morphologically (Haberly, 1983), biophysically Bekkers, 2006, 2011), and functionally (Suzuki and Bekkers, 2011) distinguished from semilunar cells (L2Ss) that are located more superficially. In contrast to this apparent dichotomy, a graded morphological transition from semilunar cells to superficial pyramidal cells in layer II has been described, yielding semilunar-pyramidal transition cells (Yang et al, 2004). Superficial pyramidal cells in layer II are gradually replaced by layer III pyramidal cells (L3Ps) constituting the main population of principal neurons in superficial layer III.…”

“…Different principal cell types in the aPC were distinguished based on characteristic biophysical properties (Suzuki and Bekkers, 2006), vertical position, and morphology (Haberly, 1983;Yang et al, 2004), although the latter was only taken into account when probing the excitability of cells after laser stimulation. We analyzed excitatory cells distributed over the whole vertical axis of layer II.…”