Sustained increase of methylguanidine in rats after amygdala or hippocampal kindling

Methylguanidine (MG) and guanidinoacetic acid (GAA) are known to be endogenous convulsants in the mammalian brain. We have reported previously that MG and GAA concentrations were significantly elevated bilaterally in the amygdala (AM) 7 and 28 days after completion of AM kindling. In the present study, we investigated regional changes in MG and GAA in (1) AM-kindled rat brain 3 months after completion of kindling and (2) hippocampal (HIPP)-kindled rat brain 7 and 28 days after completion of kindling, using high-performance liquid chromatography. MG was increased significantly in the kindled AM 3 months after completion of AM kindling (76%, P < 0.05). Significant increases in MG levels were also found 7 and 28 days after completion of HIPP kindling (124%, P < 0.025 and 110%, P < 0.05, respectively) in the left AM, ipsilateral to the kindled site. GAA increased significantly (93%, P < 0.025) only in the left AM, ipsilateral to the kindled site, 7 days after completion of HIPP kindling. These results, together with our previous data, indicate that long-lasting increases of MG occur in the AM regardless of kindled foci, and may be important in producing neuronal hyperexcitability in kindled epileptogenesis.