• Proceedings of the Korean Biophysical Society Conference
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• 2001.06a
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• pp.53-53
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• 2001

When repolarization of neuronal action potential does not decline monotonically but interrupted by additional depolarization, this prolonged depolarization phase is referred to afterdepolarization(ADP). ADP is considered to playa crucial role in the modulation of neuronal excitability, since it contributes to burst firing. We studied the ionic mechanisms underlying ADP in the soma of dentate granule cells, using rat hippocampal slice (300${\mu}{\textrm}{m}$ in thickness) prepared from 3- to 3-week-old SD rats.(omitted)

• Progress in Medical Physics
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• v.18 no.2
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• pp.73-80
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• 2007

Fruitful findings have been produced from five out of sixty cells which were obtained from each 63 individual Aplisia caught at the Jeju coast. Spiking patterns of three out of five cells, such as relaxation oscillator, bursting within a short time of the inter-burst interval, chaotic bursting, period doubling sequences, bursting with long trains of action potentials separated by short silent periods, regular repeated beating or elliptic bursting, and silent states had been changed in order as the temperature was lowered to $10^{\circ}C\;from\;32^{\circ}C$. In the intervals of every about 40 minutes repeated ups and downs of temperature produced similar firing patterns at the allowable temperature ranges. The other two cells showed difference from these. The amplitudes of the action potentials of the two cells will not be highly decreased in 24 hours. Average spike frequencies, the inter-burst interval, peak to peak spike amplitude of action potentials, minimum potential values are compared and analyzed by using the computer programme. The spike frequencies according to temperature show the distribution of bell type, with maximal spike frequencies at intermediate temperatures and minimal ones at either end. The most common pattern consist of high spike frequency during failing and low one during rising temperatures.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.3
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• pp.143-147
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• 2002

Granule cells in dentate gyrus of hippocampus relay information from entorhinal cortex via perforant fiber to pyramidal cells in CA3 region. Their electrical activities are known to be closely associated with seizure activity as well as memory acquisition. Since action potential is a stereotypic phenomena which is based on all-or-none principle of $Na^+$ current, the neuronal firing pattern is mostly dependent on afterpotentials which follows the stereotypic $Na^+$ spike. Granule cells in dentate gyrus show afterdepolarization (ADP), while interneurons in dentate gyrus have afterhyperpolarizaton. In the present study, we investigated the ionic mechanism of afterdepolarization in hippocampal dentate granule cell. Action potential of dentate granule cells showed afterdepolarization, which was characterized by a sharp notch followed by a depolarizing hump starting at about $-49.04{\pm}1.69\;mV\;(n=43,\;mean{\pm}SD)$ and lasting $3{\sim}7$ ms. Increase of extracellular $Ca^{2+}$ from 2 mM to 10 mM significantly enhanced the ADP both in amplitude and in duration. A $K^+$ channel blocker, 4-aminopyridine (4-AP, 2 mM), enhanced the ADP and often induced burst firings. These effects of 10 mM $Ca^{2+}$ and 4-AP were additive. On the contrary, the ADP was significantly suppressed by removal of external $Ca^{2+},$ even in the presence of 4-AP (2 mM). A $Na^+$ channel blocker, TTX (100 nM), did not affect the ADP. From these results, it is concluded that the extracellular $Ca^{2+}$ influx contributes to the generation of ADP in granule cells.