Abstracts

Rationale: Temporal lobe epilepsy is a common neurological disorder characterized by spontaneous seizures involving limbic structures in the temporal lobe. Patients with temporal lobe epilepsy are often refractory to surgery and antiepileptic drugs, thus warranting the use of alternative therapies like gene therapy. A growing body of research has showed that the endogenous neuropeptide somatostatin (SST) may play an active role in the attenuation of seizures as levels of SST change in a seizing animal and restoration of SST levels may provide neuroprotection against seizures. Methods: The efficacy of gene delivered SST was assessed in an animal model of limbic epilepsy by monitoring behavioral responses and EEG dynamics in three groups of rats. Group 1 comprised of adult male Sprague-Dawley rats with bilateral bipolar stainless steel electrodes implanted in the amygdala for electrical stimulation. This kindling paradigm continued until the rats were fully kindled (i.e. attained 3 consecutive grade 5 seizures on the Racine scale). Group 2 consisted of identically prepared animals, but with the addition of injections of 8-10 ul AAV5-SST into the dentate gyrus and CA1 of the hippocampi bilaterally prior to electrode implantation. Group 3 was composed of sham-injected rats identically prepared, with AAV5 expressing Green Fluorescent Protein (GFP) instead of SST. All animals were then sacrificed and perfused, and their brains dissected out. This tissue was stained via immunohistochemical techniques to detect the presence of somatostatin and GFP. Results: Animals across all groups were compared by evaluating the severity and duration of behavioral seizures as well as the number of stimulations required to elicit 3 consecutive grade 5 seizures. All group 1 rats (n=4) were fully kindled with 20 +/- 3 stimulations with 1109 seconds spent in afterdischarges, which are a hallmark of seizure activity as detected by EEG. 4 out of 5 animals in group 2 did not achieve a fully kindled state and visual histological analysis revealed a higher number of SST positive cells as compared to group 1 animals. Animals in group 3 (n=2) were fully kindled after 22 +/- 4 stimulations and 1213 seconds spent in afterdischarges. Conclusions: Somatostatin is an endogenous neuropeptide that may provide neuroprotection against epileptic seizures by antagonizing glutamatergic neurotransmission. Studies have shown that levels of certain neuropeptides decrease during seizures and thus increase the excitation to inhibition ratio. Injecting somatostatin in highly epileptogenic regions of the brain like the dentate gyrus and CA1 may modulate seizure threshold and protect against the development of seizures, as shown by our preliminary data and hence be an effective alternative treatment for refractory epilepsy.