Dept. of Neurobiology and Anatomy, Univ. of Texas Medical School, 6431 Fannin St., Houston, TX 77030, USA.
J Neurophysiol. 2011 Nov;106(5):2557-69. doi: 10.1152/jn.00550.2011. Epub 2011 Aug 3.
Serotonin (5-HT) has both direct and modulatory actions on central neurons contributing to behavioral arousal and cellular-synaptic plasticity in diverse species. In Hermissenda, 5-HT produces changes in intrinsic excitability of different types of identified interneurons in the circumesophageal nervous system. Using whole cell patch-clamp techniques we have examined membrane conductance changes produced by 5-HT that contribute to intrinsic excitability in two identified classes of interneurons, types I(i) and I(eA). Whole cell currents were examined before and after 5-HT application to the isolated nervous system. A 4-aminopyridine-sensitive transient outward K(+) current [I(K(A))], a tetraethylammonium-sensitive delayed rectifier K(+) current [I(K(V))], an inward rectifier K(+) current [I(K(IR))], and a hyperpolarization-activated current (I(h)) were characterized. 5-HT decreased the amplitude of I(K(A)) and I(K(V)) in both type I(i) and I(eA) interneurons. However, differences in 5-HT's effects on the activation-inactivation kinetics were observed in different types of interneurons. 5-HT produced a depolarizing shift in the activation curve of I(K(V)) and a hyperpolarizing shift in the inactivation curve of I(K(A)) in type I(i) interneurons. In contrast, 5-HT produced a depolarizing shift in the activation curve and a hyperpolarizing shift in the inactivation curve of both I(K(V)) and I(K(A)) in type I(eA) interneurons. In addition, 5-HT decreased the amplitude of I(K(IR)) in type I(i) interneurons and increased the amplitude of I(h) in type I(eA) interneurons. These results indicate that 5-HT-dependent changes in I(K(A)), I(K(V)), I(K(IR)), and I(h) contribute to multiple mechanisms that synergistically support modulation of increased intrinsic excitability associated with different functional classes of identified type I interneurons.
血清素（5-HT）对中枢神经元既有直接作用又有调节作用，有助于不同物种的行为觉醒和细胞突触可塑性。在海兔中，5-HT 会引起围食管神经系统中不同类型的已鉴定中间神经元的固有兴奋性发生变化。使用全细胞膜片钳技术，我们检查了 5-HT 引起的膜电导变化，这些变化有助于两种已鉴定的中间神经元类型 I(i)和 I(eA)的固有兴奋性。在将 5-HT 应用于分离的神经系统之前和之后，检查了全细胞电流。4-氨基吡啶敏感的瞬时外向 K(+)电流[I(K(A))]、四乙铵敏感的延迟整流 K(+)电流[I(K(V))]、内向整流 K(+)电流[I(K(IR))]和超极化激活电流（I(h)）进行了表征。5-HT 降低了 I(i)和 I(eA)两种中间神经元中 I(K(A))和 I(K(V))的幅度。然而，在不同类型的中间神经元中观察到 5-HT 对激活失活动力学的影响存在差异。5-HT 使 I(K(V))的激活曲线产生去极化偏移，并使 I(K(A))的失活曲线产生超极化偏移。相比之下，5-HT 使 I(K(V))和 I(K(A))的激活曲线产生去极化偏移，并使它们的失活曲线产生超极化偏移。此外，5-HT 降低了 I(i)中间神经元中 I(K(IR))的幅度，并增加了 I(eA)中间神经元中 I(h)的幅度。这些结果表明，5-HT 依赖性的 I(K(A))、I(K(V))、I(K(IR))和 I(h)变化有助于多种机制，这些机制协同支持与不同功能类型的已鉴定 I 型中间神经元相关的固有兴奋性增加的调节。
