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Long-lasting changes in the origin of spontaneous discharges from amygdala-kindled rats: piriform vs. perirhinal cortex in vitro

The origin of spontaneous field potentials in coronal slices of the amygdala-piriform-perirhinal area (A-P area) from amygdala-kindled and control rats was assessed. In Expt. 1, the field potentials initially originated in the perirhinal (PRh) cortex of control tissue while they originated in the piriform (Pir) cortex of amygdala-kindled tissue. In Expt. 2, this kindling-based change was observed in the A-P area ipsilateral but not contralateral to the kindled amygdala. In both experiments, subsequent exposure to perfusion medium containing 0 Mg2+ resulted in the genesis of strong discharges in both control and kindled tissues. After 2-3 h of such treatment, the origin of spontaneous discharges in control tissue changed from the PRh to the Pir area and persisted in a reduced form during reperfusion with medium containing Mg2+. This change in origin of the discharges in control tissue appeared similar to that seen in previously kindled tissue. In Expt. 3, during exposure to 0 Mg2+, the response of the basolateral amygdala (BLA) was compared with the Pir and PRh areas. Independent of the PRh discharge, the BLA discharge closely followed the Pir discharge both in time and morphology. These lasting changes in the ipsilateral A-P area in vitro must be related in vivo to the change which allows the kindled A-P area to participate in the triggering of generalized limbic-kindled convulsions.