Intracerebral microinjections of dermorphin: search for the epileptic induction thresholds

To test the different sensitivity of several central structures to the epileptogenic action of mu opiate agonists, intracerebral microinjections of the selective mu agonist dermorphin were delivered into different areas of the rat dorsal and ventral hippocampus, septum, amygdala, entorhinal cortex, thalamus, striatum and neocortex. The dose of dermorphin (up to 6 nmol) necessary to trigger electrical epileptic events in each of these regions was studied. Epileptic discharges were triggered only in the ventral hippocampus (CA1 and CA3 areas), amygdala and entorhinal cortex. The epileptic induction threshold was the lowest in the CA1 area of the ventral hippocampus. The results suggest that when a mu opiate agonist is injected intraventricularly, the epileptic activity originates in the ventral hippocampus.