Abstract
BackgroundThe role of the piriform cortex (PC) in olfactory information processing remains largely unknown. The anterior part of the piriform cortex (APC) has been the focus of cortical-level studies of olfactory coding, and associative processes have attracted considerable attention as an important part in odor discrimination and olfactory information processing. Associational connections of pyramidal cells in the guinea pig APC were studied by direct visualization of axons stained and quantitatively analyzed by intracellular biocytin injection in vivo.ResultsThe observations illustrated that axon collaterals of the individual cells were widely and spatially distributed within the PC, and sometimes also showed a long associational projection to the olfactory bulb (OB). The data showed that long associational axons were both rostrally and caudally directed throughout the PC, and the intrinsic associational fibers of pyramidal cells in the APC are omnidirectional connections in the PC. Within the PC, associational axons typically followed rather linear trajectories and irregular bouton distributions. Quantitative data of the axon collaterals of two pyramidal cells in the APC showed that the average length of axonal collaterals was 101 mm, out of which 79 mm (78% of total length) were distributed in the PC. The average number of boutons was 8926 and 7101, respectively, with 79% of the total number of boutons being distributed in the PC. The percentage of the total area of the APC and the posterior piriform cortex occupied by the average distribution region of the axon collaterals of two superficial pyramidal (SP) cells was about 18 and 5%, respectively.ConclusionOur results demonstrate that omnidirectional connection of pyramidal cells in the APC provides a substrate for recurrent processes. These findings indicate that the axon collaterals of SP cells in the PC could make synaptic contacts with all granule cells in the OB. This study provides the morphological evidence for understanding the mechanisms of information processing and associative memory in the APC.
Highlights
The role of the piriform cortex (PC) in olfactory information processing remains largely unknown
superficial pyramidal (SP) cells have a pyramidal to ellipsoid soma. These cells exhibit a single apical dendrite whose branches extend to the superficial limit of the molecular layer, multiple basal dendrites, a high concentration of dendritic spines, and a deeply directed axon [6]
The total number of stained SP cells in the anterior part of the piriform cortex (APC) was fifteen; reconstructions and detailed analysis were performed on two of the cells that appeared to be representative of the population because of difficulties in serially reconstructing the extensively arborized axon collaterals that were 90-111 mm long
Summary
The role of the piriform cortex (PC) in olfactory information processing remains largely unknown. The piriform cortex (PC) has long been treated as the “primary” olfactory cortex because of the largest area Many differences in both axonal connections and the cytoarchitecture of different regions of the PC have been described [1, 4,5,6,7,8,9,10]. The PPC is situated posterior to the LOT and recognizable by a well-developed layer III, and the APCD is located dorsal to the LOT with a cytoarchitecture that is somewhat intermediate between that of the APCv and that of the PPC These differences in structure are believed to reflect differences in functional roles [10, 16]. The structure of the APC has led to the hypothesis that the PC functions as a distributed processing neural network and is critically involved in information processing and associative memory [17,18,19]
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