Expression of the
opioid peptides dynorphin and
enkephalin is altered within the first 24 h after acutely induced
seizures in certain experimental models of
epilepsy. Using in situ hybridization, we examined the expression of
prodynorphin and
preproenkephalin messenger RNA acutely following induction of kindling with recurrent
seizures and in two models of chronic
temporal lobe epilepsy: (i) rats fully kindled with rapidly recurring hippocampal
seizures; and (ii) rats surviving after self-sustaining limbic
status epilepticus induced with focal electrical stimulation of the hippocampus. In naive animals, a ventral-dorsal gradient was identified in the expression of both
prodynorphin and
preproenkephalin messenger RNA in the dentate gyrus and expression of
prodynorphin message was demonstrated for the first time in the ventral portion of cornu Ammonis regio superior. After stimulation producing rapidly recurring hippocampal
seizures, acute decreases in
prodynorphin messenger RNA were seen in the dentate gyrus and cornu Ammonis regio superior at 24 h after the last seizure. In contrast, increases in
preproenkephalin messenger RNA expression were seen acutely in the dentate gyrus, with a decrease seen in the entorhinal cortex. The change in
prodynorphin message expression in cornu Ammonis regio superior persisted in kindled animals that were studied after one month seizure-free period. There were no changes in
preproenkephalin message in kindled animals studied after the one month seizure-free interval. No statistically significant changes were found for either
prodynorphin or
preproenkephalin message in the post-self-sustaining limbic
status epilepticus group at one month following induced
seizures. Acute changes in
peptide expression may contribute to increased excitation in the dentate gyrus during induction of kindling, while the chronic change identified in cornu Ammonis regio superior may contribute directly to persistently increased excitability in this region.