Abstract
By optical imaging of intrinsic signals, we have demonstrated a possible code for odor concentration in the anterior piriform cortex (PC). Lower concentrations activated the rostral region of the dorsal part of the anterior PC, whereas higher ones elicited caudally spreading activation, suggesting an important role of a rostro-caudal gradient in odor sensitivity among cortical neurons. These imaging results have also been confirmed with unit recordings, which indicated a rostro-caudal gradient in odor sensitivity among cortical neurons. In this study, we used optical imaging of voltage-sensitive dye signals to study spatiotemporal spread of signal propagation in the endopiriform nucleus (EPN), one of the main output targets from PC, using the horizontal slice preparations including both EPN and PC. Electrical stimulation of EPN evoked an excitation that propagated slowly (about 150-200 mm/s) to both the rostral and caudal directions from the stimulation site in EPN. On the other hand, stimulation of layer I in PC induced signal propagation from PC to EPN. Excitation in EPN, then, propagated slowly (160-250 mm/s) from rostral to caudal, but the rostral propagation was weak. These findings suggest that a rostro-caudal slow propagation in EPN is involved in further processing of information from the anterior PC, which may be associated with odor concentration. [J Physiol Sci. 2008;58 Suppl:S166]
