Can a generalized kindling seizure induce a reward state?

Abstract

The postictal behavioral depression (PBD), characterized by behavioral immobility and unresponsiveness to environmental stimuli, observed after a stage 5 kindling seizure is opioid dependent. Morphine injection prolongs while naloxone and naltrexone (opioid antagonists) reduce or eliminate PBD. Opioids have clear rewarding actions that can be easily detected by place preference conditioning (PPC). In the present study, we evaluated if the opioid release after a stage 5 kindling seizure that produces PBD could induce PPC. Male rats were kindled in the medial preoptic area (MPOA), the amygdala (AMG) or insular cortex (IC). After kindling was established their initial preference in a three-compartment chamber was determined. During conditioning, subjects received a standard kindling stimuli that evoked a stage 5 seizure. At the end of the after discharge and during the PBD the animals were placed in the non-preferred chamber for 30 min. On alternate days they were placed without stimulation in the preferred chamber. At the end of conditioning the kindled groups showed a clear change of preference. This change of preference was completely blocked by injection of naloxone. These results suggest that opioid release after a stage 5 kindling seizure can induce a positive affect of sufficient intensity and duration to induce conditioning.