Protein tyrosine kinase inhibitors modify kainic acid-induced epileptiform activity and mossy fiber sprouting but do not protect against limbic cell death

Intrahippocampal administration of kainic acid (KA) induces synaptic release of neurotrophins, mainly brain-derived neurotrophic factor, which contributes to the acute neuronal excitation produced by the toxin. Two protein tyrosine kinase inhibitors, herbimycin A and K252a, were administered intracerebroventricularly, in a single dose, to attenuate neurotrophin signaling during the acute effects of KA, and their role in epileptogenesis was evaluated in adult, male Wistar rats weighing 250-300 g. The latency for the first Racine stage V seizure was 90 ± 8 min in saline controls (N = 4) which increased to 369 ± 71 and 322 ± 63 min in animals receiving herbimycin A (1.74 nmol, N = 4) and K252a (10 pmol, N = 4), respectively. Behavioral alterations were accompanied by diminished duration of EEG paroxysms in herbimycin A- and K252a-treated animals. Notwithstanding the reduction in seizure severity, cell death (60-90 percent of cell loss in KA-treated animals) in limbic regions was unchanged by herbimycin A and K252a. However, aberrant mossy fiber sprouting was significantly reduced in the ipsilateral dorsal hippocampus of K252a-treated animals. In this model of temporal lobe epilepsy, both protein kinase inhibitors diminished the acute epileptic activity triggered by KA and the ensuing morphological alterations in the dentate gyrus without diminishing cell loss. Our current data indicating that K252a, but not herbimycin, has an influence over KA-induced mossy fiber sprouting further suggest that protein tyrosine kinase receptors are not the only factors which control this plasticity. Further experiments are necessary to elucidate the exact signaling systems associated with this K252a effect.

Activation of JNK and p38 in rat hippocampus after kainic acid induced seizure

Kainic acid, an analogue of glutamate, causes limbic seizures and induces cell death in the rat brain. We examined the activation of MAPK family kinases; ERKs, JNKs and p38 kinase in rat hippocampus after KA treatment. Activation of all three kinases were observed at 30 min after the treatment, but, in contrary to ERK phosphorylation, which lasted up to 3 h, the phosphorylation of JNK and p38 returned to the basal level by 2 h. The phosphorylation of' upstream kinases for the MAPK family was distinct. The phosphorylation of MEK1 clearly increased at 30 min but diminished rapidly thereafter. The phosphorylation of MKK6 was also increased but reached peak at 2 h after KA treatment. However, the phosphorylation of other upstream kinases, SEK1 and MKK3, gradually decreased to 3 h after KA treatment. These results indicate that the KA activates all of the three MAPK family kinases with different time patterns and suggest the possibility that MKK3 and MKK6, and SEK1 may not be the upstream kinases for p38 and JNK in rat hippocampus.

Development of self-sustaining limbic status epilepticus by continuous ventral hippocampal stimulation followed by low dose pilocarpine in rats.

Sequential treatment of rats with low doses of lithium and pilocarpine, a high dose of pilocarpine, or continuous hippocampal stimulation [CHS] (9 epochs, 10 min each) is reported to result in status epilepticus (SE). We report a novel method to establish SE based on continuous ventral hippocampal stimulation (5 epochs) followed by low dose pilocarpine (40 mg/kg) challenge. Motor limbic seizures occured in all the control rats. The latency to spike activity was 15 +/- 1 min after pilocarpine administration. Ventral hippocampal [VHc] and cortical EEG recordings were used to monitor the protective effect of diazepam (5 mg/kg). Except phenobarbital, all the three drugs completely prevented all the phases of seizure activity. Initiation of spikes was significantly prolonged by phenobarbital pretreatment. Further study on the characteristics of these convulsions offers a unique possibility for the recognition of brain regions, pathways, and neurotransmitters engaged in the spread of seizures in this model.

Effects of maprotiline, nomifensine and Trazodone on gamma amino butyric acid turnover in the limbic system

The effects of chronic treatment with 3 antidepressant drugs: Maprotilline, Nomifensine and Trazodone on the turnover rate of gamma amino butyric acid were studied in 4 rat brain areas related to the limbic system. Trazodone markedly increased the Gamma amino butyric acid level in the hypothalamus and hippocampus but lowered its level in the amygdala and olfactory tubercle. Nomifesine increased its level in the hypothalamus and hippocampus and markedly decreased it in the olfactory tubercle. Maprotilline on the other hand consistently lowered its level in all 4 areas. These results indicate the involvement of gamma amino butyric acid in the mechanism of action of antidepressant drugs. Its possible role in modulating other neurotransmltters and production of antidepressant manifestations are discussed

Effects of maprotiline, nomifensine, and trazodone on monoamine turnover in the limbic system

The effects of 14-day treatment of three antidepressant drugs [maprotiline, nomifensine, and trazodone] was studied on the turnover of norepinephrine, dopamine and serotonin in 4 limbic areas of rat brain hypothalamus, hippocampus, amygdala and olfactory tubercle. The monoamine metabolites accumulated in those brain areas were analyzed by HPLC method. The 3 drugs produced significant increase in the level of norepinephrine metabolite [MHPC] in the hypothalamus and hippocampus, nomifensine increased its level also in the olfactory tubercle. In the amygdala, maprotiline significantly decreased while the two other drugs slightly increased the MHPG level on the Dopamine metabolite [HVA]. Nomifensine significantly increased its level in the hippocampus, hypothalamus and the olfactory tubercle and trazodone produced the highest increase in the amygdala. On serotonin metabolite [5-HIAA] trazodone produced marked increase of its level in the hypothalamus, hippocampus and amygdala and maprotiline markedly increased its level in the amygdala. The results indicated that the primary action of maprotiline is to enhance norepinephrine turnover, while nomifensine markedly increased turnover of both norepinephrine and dopamine and trazodone markedly increased turnover of serotonin and norepinephrine