Intracerebroventricular administration of histidine reduces kainic acid-induced convulsive seizures in mice.

Kainic acid (KA)-induced seizures and other experimental models of epilepsy have been proven to be instrumental in identifying novel targets that could be responsible for human icto- and epileptogenesis. We have previously shown that the ablation of pharmacoresistant voltage-gated Ca channels with Ca2.3 as central ion-conducting pore (R-type Ca channel) reduces the sensitivity towards KA-induced epilepsy in mice. In vivo, Ca2.3 channels are thought to be under tight allosteric control by endogenous loosely bound trace metal cations (Zn and Cu) that suppress channel gating via a high-affinity trace metal-binding site. Metal dyshomeostasis in the brain, which is a common feature of (KA-induced) seizures, could therefore alter the normal function of Ca2.3 channels and may shift hippocampal and neocortical signaling towards hyperexcitation. To investigate the role of loosely bound metal ions for KA-induced hyperexcitation in vivo, we examined the effects of manipulating brain trace metal homeostasis in mice. To this end, we developed a murine system for intracerebroventricular administration of trace metal ions and/or histidine (His), which can bind Zn and Cu and is involved in their transendothelial transport at the blood-brain barrier. Unexpectedly, our preliminary findings indicate that application of His alone but not in the presence of Zn has substantial beneficial effects on the outcome of KA-induced epilepsy in mice. As such, our results emphasize previous findings on the complex, two-sided role of loosely bound metal ions with regard to neuronal excitation and degeneration under pathophysiological conditions.