Abstracts

Galanin is a neuropeptide with both anticonvulsant and neuroprotective effects. In the hippocampus galanin acts through two receptor subtypes, GalR1 and GalR2. GalR1 knockout (KO) mice have been reported to exhibit spontaneous seizures, leading to the suggestion on the critical role of GalR1 in seizure regulation. We compared seizure susceptibility and neuronal injury in GalR1 KO mice in two models of status epilepticus (SE): induced by systemic kainic acid (KASE), and by LiCl-pilocarpine (LiPC-SE). Adult male C57Bl GalR1 KO mice, or their wild type (WT) littermates, were implanted with the recording electrode into the hippocampus. SE was induced by either i.p. injection of kainic acid (20 mg/kg), or of LiCl (3 meq/L, 1 ml/kg i.p.) followed by s.c. pilocarpine, 200, or 100 mg/kg. Seizure activity was acquired and analyzed using Harmonie software (Stellate systems). Neuronal injury was assessed using FluoroJade B and TUNEL staining in coronal brain sections from mice euthanized 3 days after SE induction. None of KO, or WT animals displayed spontaneous seizures during 1 week of observation and EEG recording prior to SE induction. No differences in seizure severity and duration were observed between KO and WT animals subjected to KASE. LiPC- SE was more severe in GalR1 KO animals, as compared to WT. Augmented severity of LiPC-SE was evident as higher mortality (40% vs. [lt]10% in WT); increased cumulative seizure time (3.5-5 hrs vs. 1-2.5 hrs) and a number of seizure episodes (215-310 vs. 50-95 in WT). KASE led to neuronal injury in neither GalR1 KO, nor WT animals, which was in line with previously reported enhanced resistance of hippocampal cells to kainic-acid- induced neuronal injury in C57Bl mice. Neuronal injury in GalR1 KO mice subjected to LiPC-SE was more severe in CA1 (75-90% vs. 35-55% in WT), but not CA3. In addition, KO animals showed cell injury to hilar interneurons (15-25%), which was never observed in WT. Administration of lower dose of pilocarpine to GalR1 KO (100 mg/kg) led to the development of SE comparable to the one observed after 200 mg/kg in WT. However, despite milder seizures, the severity and the pattern of neuronal injury was not different from those observed after 100 mg/kg. KO mice showed higher seizure severity and more profound and widespread injury after LIPC-SE, but not after KASE, suggesting specific interference of GalR1 with cholinergic, rather than with AMPA-kainate mechanisms. The fact that LiPC-SE of different severity (induced by two different doses of pilocarpine) led to similarly severe hippocampal injury suggests that galanin acting through GalR1 is neuroprotective aside from its anticonvulsant effects. The data are useful for understanding the endogenous brain mechanisms involved in seizure control and neuroprotection. (Supported by NIH grant NS 43409.)