Characterization and anatomical distribution of selective long-term potentiation in the olfactory forebrain

High-frequency stimulation of the granule cell layer of the olfactory bulb (OB) has previously been shown to result in a form of long-term potentiation in the piriform cortex (PC) that is selective to late components of the potential evoked in the PC 58. This phenomenon was explored in male Long-Evans rats with chronically implanted electrodes by recording potentials evoked in the OB and in various sites in the ipsilateral and contralateral PC before and after repeated high-frequency stimulation of the OB. Recording at all sites exhibited a gradually developing potentiation that was selective to late components of the evoked potential. In the OB and ipsilateral PC this potentiation had an overt long-term component that lasted for days, and all sites exhibited a latent potentiation that enabled the reestablishment of substantial levels of potentiation by mild patterns of stimulation that had no effect in control animals. No potentiation of the population EPSP representing input from the lateral olfactory tract to the PC was seen. Available evidence concerning the neuronal elements activated by the stimulation and the neuronal events likely to underlie the potentiated components of the evoked potentials suggests that this potentiation may represent an enhancement of inhibitory interactions within the PC and between the PC and OB.