AMYGDALA KINDLING MODIFIES EXTRACELLULAR OPIOID PEPTIDE CONTENT IN RAT HIPPOCAMPUS MEASURED BY MICRODIALYSIS

Opioid peptide release in the hippocampus was shown to be increased im mediately following amygdala kindling stimulation in freely moving rat s using microdialysis combined with a universal opioid peptide radioim munoassay (RIA). Extracellular opioid peptide levels were elevated (55 % above basal levels) within the first 10 min after electrical stimula tion-induced partial seizures in previously nonkindled animals. Fully kindled rats showed lower extracellular opioid peptide levels (40% red uction) during the interictal period [16 +/- 2.1 days (mean +/- SEM) a fter the last stage V seizure], in comparison with values obtained fro m the sham-kindled group under basal conditions. However, opioid pepti de release in fully kindled rats increased above 152% of interictal le vels within the first 20 min after onset of fully kindled seizures, at taining peak levels equal to that of the partial kindled group and ret urning to prestimulation conditions 40-60 min following the ictal even ts. The majority of the immunoreactive material recovered from the hip pocampus within the first 20 min following partial and generalized kin dled seizures coeluted with dynorphin-a (1-6), dynorphin-A (1-8), and Leu-enkephalin by HPLC/RIA analysis, It is proposed that the enhanced opioid peptide release in hippocampus induced by amygdala kindling sti mulation might be associated with either enhanced excitability or seiz ure suppression as seizure susceptibility fluctuates. The reduced inte rictal opioid peptide levels may also underlie some interictal behavio ral disturbances.