| Research Abstract |
Voltage-gated ionic channel currents and GABAA receptor current in rat GnRH neurons were analyzed. Under deep anesthesia, brains were excised from adult GnRH-EGFP transgenic rats. After dissection, brains were enzymatically dispersed and the neurons were plated on coverslips and cultured overnight. Then the neurons were applied for perforated patch-clamp experiment. GnRH neurons, identified with EGFP-fluorescnce, exhibited the voltage-gated calcium currents, which were composed with L-, N-, P/Q-, R- and T-types. The R-type contributed 30% for total calcium current. L-, N-, P/Q- and T-type contributed 25, 20, 12 and 13%, respectively (Kato et al., 2006). This expression pattern differs from those of neonatal GnRH neurons but is similar to those from pubertal neurons. Therefore, expression pattern of voltage-gated calcium channels in rat GnRH neurons are developmentally regulated and completed around puberty. To study the roles of these calcium channels, we investigated the calcium-activ
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ated potassium currents. Rat GnRH neurons showed two types of calcium activated potassium currents. They were calcium- and voltage-activated potassium current (BK) and calcium-activated slow afterhyperpolarization current. The latter was specifically inhibited by SK channel blocker apamin. This slow afterhyperpolarization current is, therefore, carried through the SK channels. Furthermore, this current contributed for persistent firing evoked by strong depolarization (Kato et al., 2005, Japan Neuroscience Meeting ; Kato et al., 2006). Finally, we analyzed GABA action on rat GnRH neurons by means of calcium imaging method. GABA acted on the GABAA receptor and elevated intracellular calcium concentration in more than 50% of GnRH neurons isolated from adult rats. This GABA-induced response was abolished by the removal of extracellular calcium and by blocking the chloride transporter NKCC1. Therefore, GABA depolarizes rat GnRH neurons by acting GABAA receptor, thereby activating the voltage-gated calcium channels (Tanaka et al. 2006, International Congress of Neuroendocrinology; Watanabe et al., 2006 in preparation). Less
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