Abstracts

Rationale: Alpha-2A adrenergic agonist guanfacine hydrochloride, it has been used in treatment of ADHD, can decrease the intracellular level of cyclic adenosine monophosphate (cAMP) resulting in closing HCN channels and pass through blood-brain barrier. In this study, we examined the effect of guanfacine hydrochloride on afterdischarges (ADs) induced by acute kindling of the rabbit hippocampus to reveal the contribution of HCN channel in epileptogenesis.Methods: We performed all experiments under appropriate conditions in accordance with the Declaration of Helsinki (revised version in 2000) and the Guide for Animal Experimentation at Soka University. Twenty-nine adult rabbits were used. Under deeply anesthesia and artificial respiration, four concentric bipolar electrodes were planted in the right and left hippocampus. After one to two hour recovery, we delivered kindling stimulations (1 msec, biphasic 50 Hz, 1 sec train) with 20 min interval through the electrode inserted in the right hippocampus under the same condition. EEG was recorded from both right and left hippocampus. Each EEG was digitalized with sampling frequency of 1 kHz by using Power Lab (Chart, ADInstrument). The kindling stimulations were performed at least 30 times unless alteration of frequency component of ADs shown in chronic kindling experiment (K. Tsuchiya et al. Epilepsy Res. 2011; 95:144-151). Spectral analysis on each AD was conducted by Igor software (WaveMetrics, Portland, OR, USA). In kindled condition, three doses (200 μM, 1 mM and 5 mM: 100 μl/1 min) of guanfacine hydrochloride or saline (100 μl/1 min) were administered directly to the right hippocampus.Results: The animals (n=26) that the stimulating electrode was histologically located in the stratum radiatum to lacunosum-moleculare of the hippocampal CA1 region were chosen for analysis. The 200 μM application suppressed bilateral AD occurrences at 34.1±32.4% (n=8; p>0.05 vs saline control). The 1 mM or 5 mM application prevented bilateral AD occurrences at 60.9±29.4% (n=8; p<0.01) or 73.3±33.5% (n=5; p<0.01), respectively. Consequently, 1mM and 5mM guanfacine hydrochloride significantly suppressed AD occurrence.Conclusions: Since guanfacine hydrochloride prevented AD occurrences in a dose dependent manner and raised AD threshold, guanfacine hydrochloride have a potential of a new AED. Additionally, it was suggested that intracellular cAMP level and HCN channel might regulate the AD occurrence.