Tamaki Takagi

Intracellular calcium concentration during pentylenetetrazol-induced bursting activity in snail neurons

To clarify the role of intracellular free calcium in the provocation of bursting activity, the intracellular calcium concentration was measured using calcium-sensitive microelectrodes during pentylenetetrazol (PTZ)-induced bursting activity in snail neurons. In the PTZ-sensitive neurons of the snail, Euhadra peliomphala, the intracellular calcium concentration was higher than that in the normal state during PTZ-induced bursting activity, but lower than that which induced the calcium-activated potassium conductance elevation. By application of 50 microM calcium ionophore, A23187, a slight increase in intracellular calcium concentration with a slight depolarization occurred. Then a greater increase of intracellular calcium concentration with bursting activity was observed. By application of 100 microM A23187, a rapid and intense increase of intracellular calcium concentration with hyperpolarization was observed. These findings suggest that, for the provocation of bursting activity, sustained elevation of the intracellular calcium concentration, higher than that in the normal state but lower than that which evokes calcium-activated potassium conductance elevation, is required.

Characteristics of primary cultured neurons from embryonic mutant El mouse cerebral cortex

To elucidate the differences between neurons of epileptogenic animals and those of normal animals, cellular characteristics of neurons of mutant strain El mice which are highly susceptible to seizures were investigated using immunocytochemical techniques. In neurons of 3-day primary cultures, the control ddY mouse neurons showed dividing stages in about 0.2% of neurofilament (NF)-positive neurons, whereas no dividing neurons were observed among the NF-positive El mouse neurons. In 7-day cultures, localization of GD3 ganglioside in the proliferating control ddY mouse neurons was observed, but there was no GD3 ganglioside in the mutant El mouse neuron. The content of GD3 ganglioside detected by high-performance thin-layer chromatography of El mouse cultured cells was ca. 1/4 of that of ddy mice. These findings suggest that neurons of the El mouse are differentiated earlier than those of the control ddY mouse.

Pentylenetetrazole-induced changes of the single potassium channel in primary cultured cerebral cortical neurons

To elucidate the behavior of the single ionic channels of cerebral cortical neurons during bursting activity, the effects of pentylenetetrazole (PTZ) on a single potassium channel of primary cultured cerebral cortical neurons from mice were examined. All of the examined 10-day-old primary cultured neurons of the cerebral cortex showed clear bursting activity after extracellular application of PTZ using whole-cell patch-clamp recording. Less than half of the examined single potassium channels, both outward and inward, of the 2- and 3-day-old as well as 6-10-day-old primary cultured cerebral cortical neurons showed the bursting-type open-close state by application of PTZ. The PTZ-sensitive single potassium channels were found in the voltage-dependent as well as calcium-activated channels.

Direct current potential changes of the vagal nuclear area induced by trigeminal stimulation

To elucidate the mechanism of the Reilly syndrome (irritation syndrome), direct current (DC) potential changes in the medulla oblongata were investigated. Ipsilateral and contralateral trigeminal stimulation induced a DC potential shift above the vagal nuclear area in the medulla. Maxillary and mandibular nerve stimulation showed a summation effect. Continuous stimulation of the tooth pulp cavity by croton oil induced a progressively developed DC shift. DC potential change by trigeminal stimulation was accompanied by the same process of elevation of extracellular potassium concentration. These findings suggest that trigeminal stimulation increases the excitability of vagal nuclear neurons and consequently provokes the Reilly syndrome.

Cellular Physiology of Epileptogenic Phenomena

Epilepsy is one of the most frequently occurring nervous diseases. One out of 200 persons suffers from epilepsy. Nevertheless, there is still no definite radical therapy against epilepsy. Actual therapy against epilepsy is merely the expectation of a spontaneous cure by long-term inhibition of convulsions that facilitate the next convulsions using so-called anticonvulsant drugs, even when patients are tortured with side effects. To achieve a reasonable radical therapy, it is dispensable to elucidate the process of intracellular change of normal regular firing neurons into seizure-evoking neurons; and the differences between neurons manifesting bursting activity and those showing normal regular firing. We have hitherto investigated the intracellular events during bursting activity in a single neuron. I would like to talk about our experiments on such cellular mechanisms of epileptogenic phenomena, especially intracellular events during seizure activity. I will also describe anticonvulsant effects of a herbal mixture,. TJ-960, which shows a different mechanism of action from pure chemical anticonvulsants; and finally I will give some hints for future therapy against epilepsy.

Mechanism of Phenytoin Action at the Cellular Level

The mechanism of phenytoin (PHT) action has been studied extensively by various investigators. Most of their conclusions can be summarized by 1) inhibition of the sodium channel in the excitable membrane, 2) inhibition of the calcium action related to neuronal excitation and 3) inhibition of cellular phosphorylation. They are all based on the inhibitory action on excitability of the normally functioning neurons.I* The mechanism of action of PHT has seldom been studied with respect to intracellular events. We described our experiments at the cellular level, and discuss the mechanism of PHT action.