The gustatory insular cortex (IC) is connected with not only the somatosensory cortex, but also the endopiriform nucleus (EPN). We have previously revealed that low-frequency electrical stimulation to the IC can elicit membrane potential oscillations at a frequency of 8-10 Hz in the somatosensory cortex of rat brain slices under bath-application of caffeine. Using the same procedure, we investigated whether the EPN has the ability to generate oscillations, and whether such oscillations emerge age-dependently. Electrical stimulations were delivered to the IC, and field potentials were recorded from the EPN. In the case of slices made from mature rats, stable field potential oscillations at 8-10 Hz were induced in the EPN after repetitive stimulations. Optical recordings revealed that signals traveled from the IC to the EPN by way of the claustrum. Generation of oscillations was N-methyl-d-aspartate (NMDA) receptor activity-dependent, since oscillatory phases disappeared following application of NMDA receptor antagonist. In slices from immature rats, however, oscillations were not induced. IC stimulation can thus age-dependently elicit membrane potential oscillations in the EPN, and the EPN oscillations were NMDA receptor activity-dependent. These findings suggest that developmental changes in properties of the EPN might contribute to development of information integration, including gustatory information.
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