Effects Of Carnosine On Pentylenetetrazol-induced Seizures And Fast Electrical Amygdala Kindling

Epilepsy is a serious chronic neurological disease, which is characterized by recurrent abnormal discharge of cerebral neurons and transient disfunction of brain. The clinical symptoms include a variety of abnormities in motor, sense, conscious state, vegetative nervous and psychology. According to WHO, 50 million persons worldwide, and 8 million in China have suffered from the diseases. The exact pathogenesis of epilepsy remains largely unclear. Excessive excitability, over-synchronized discharges and the imbalance between excitation and inhibition of cerebral neurons may contribute to seizures. With the currently available antiepileptic drugs, the disease in about 80% patients who have no serious injuries in the brain, especially those with less frequency of seizures and normal interictal EEGs, are well controlled. By contrast, about 20% epileptic patients can't get effective therapies using those drugs. This epilepsy is called drug-resistance or intractable epilepsy. Moreover, long application of those antiepileptic drugs often results in some adverse responses in psychological, neurological, splanchnic and skin system. Thus, developing new safe and effective antiepileptic drugs is urgently expected.Histamine, a biogenic amine, is an important neurotransmitter or neuromodulator in the mammalian central nervous system. Brain histaminergic system seems to be involved in various physiological and behavioral functions including sleep-wake cycles, appetite control, neuroendocrine, learning and memory through its specific receptors. The studies from others and our laboratory have alsoreported that brain histamine may be involved in the epileptogenesis and regulate seizure susceptibility as an endogenous anticonvulsant substance. Recently, our group further found that increasing brain histamine levels (e.g. i.p. injection of histidine; i.c.v. injection of histamine or H₃ receptor antagonist clobenpropit) markedly delays pentylenetetrazol-induced seizure development, while knock out of histamine H₁ receptor or histidine decarboxylase genes accelerates pentylenetetrazol-induced seizure development in mice. These evidences indicate that histaminergic system exerts an antiepileptic effect in the brain. Moreover, it is proposed that certain histaminergic drags may be used as new anticonvulsants in clinic in future.Carnosine (β-alanyl-1-histidine) is a naturally occurring dipeptide, it serves as a reservoir for histidine, which is a precursor of histamine, and can easily enter the central nervous system from the periphery. It has many putative roles such as anti-inflammatory agent, free radical scavenger, and protein glycosylation inhibitor. Our recent studies have showed that it can significantly inhibit amygdaloid kindled seizures in rats, and it simultaneously induces a significant increase in carnosine, histidine and histamine levels in the amygdala. The mechanisms of the protective effect of carnosine may involve at least two different (direct and indirect) pathways: pathway I, directly acting at histamine H₁-receptors and provoking a histamine-like response; pathway II, indirectly activating histamine Hi-receptors after metabolic transformation into histamine. In the present study, we used both histidine decarboxylase-deficient (HDC-KO) and wild-type (WT) mice to further elucidate the possible role of carnosine in pentylenetetrazol (PTZ)-induced seizures, which is an animal model of human absence epilepsy and myoclonic, generalized tonic-clonic seizures. We also derived a fast electrical amygdala kindling model in WT mice to test the effects of carnosine. We expect to elucidate the relations between carnosine and epilepsy in the two different epilepsy models. It has been found that carnosine can protect against PTZ-induced seizures and its action is mainly through the carnosine-histidine-histamine metabolic pathway. Additionally, in the fast electrical amygdala kindling model, carnosine inhibit the seizure grades and induced a significant enhance of postictal seizure protection in WT mice. In conclusion, ourstudy provides more evidences that carnosine has a significant anticonvulsant effect on seizures in mice, we develops the knowledge about the relations between carnosine and epilepsy, provides necessary theories for the development of histaminergic antiepileptic drugs, especially the medical use of carnosine in future.1. Mechanism of carnosine on PTZ-induced seizures in miceIn the present study, we used both histidine decarboxylase-deficient (HDC-KO) mice and wild-type (WT) mice to elucidate the possible role of carnosine in pentylenetetrazol (PTZ)-induced seizures, In the acute PTZ challenge study, PTZ (75 mg/kg) was injected intraperitoneally (i.p.) to induce seizures. Carnosine (200, 500 or 1000 mg/kg, i.p.) significantly decreased seizure stage, and prolonged the latency for myoclonic jerks in WT mice in a dose-dependent manner. The effects of carnosine (500 mg/kg) were time-dependent and reached a peak at 1 h. However, it had no significant effect on HDC-KO mice. Carnosine (500 mg/kg) also significantly elevated the thresholds in WT mice but not HDC-KO mice following intravenous (tail vein) administration of PTZ. We also found that α-fluoromethylhistidine substantially reversed the protective effects of carnosine in WT mice. In addition, carnosine pretreatment reduced the cortical EEG activity induced by PTZ (75 mg/kg, i.p.). These results indicate that carnosine can protect against PTZ-induced seizures and its action is mainly through the carnosine—histidine-histamine metabolic pathway. This suggests that carnosine may be an endogenous anticonvulsant factor in the brain and may be used as a new antiepileptic drug in the future.2. The effect of carnosine on fast electrical amygdala kindling in miceTo test the effect of carnosine in fast electrical amygdala kindling in mice, we derived a fast electrical amygdala kindling model (40 stimulations, 5 min intervals). We found that an injection of carnosine (500 mg/kg) significantly decreased seizure stage, afterdischarge duration, generalized seizure, and induced a significant enhance of postictal seizure protection in WT mice. The study suggests that carnosine can protect against the fast electrical amygdala kindling. It may be an endogenous anticonvulsant factor in the brain and could be used as a new antiepileptic drug in the future.