Hwang L L, Dun N J
Department of Anatomy and Neurobiology, Medical College of Ohio, Toledo 43614, USA.
J Neurophysiol. 1998 Sep;80(3):1033-41. doi: 10.1152/jn.1998.80.3.1033.
Whole cell patch recordings were made from rostral ventrolateral medullar (RVLM) neurons of brain-stem slices from 8- to 12-day-old rats. By superfusion or pressure ejection to RVLM neurons, 5-hydroxytryptamine (5-HT) elicited three types of membrane potential changes: a slow hyperpolarization (5-HTH), a slow depolarization (5-HTD) and a biphasic response, which persisted in a tetrodotoxin (TTX, 0.3 microM)-containing solution. 5-HTH were accompanied by a decrease of input resistance in the majority of responsive neurons. Hyperpolarization reduced and depolarization increased the 5-HTH; the mean reversal potential was -92.3 mV in 3.1 mM and shifted to -69.3 mV in 7 mM [K+]o. Barium (Ba2+, 0.1 mM) but not tetraethylammonium (TEA, 10 mM) suppressed 5-HTH. The 5-HT1A receptor agonist (+/-)-8-hydroxy-dipropylamino-tetralin (8-OH-DPAT; 5-50 microM) hyperpolarized RVLM neurons. The 5-HT1A antagonist pindobind-5-HT1A (PBD; 1-3 microM) and the 5-HT2/5-HT1 receptor antagonist spiperone (1-10 microM) suppressed 5-HTH and the hyperpolarizing phase of biphasic responses; the 5-HT2 receptor antagonist ketanserin (3 microM) was without significant effect. 5-HTD were associated with an increase or no apparent change of input resistance in RVLM neurons. Hyperpolarization of the membrane decreased or caused no apparent change in 5-HTD. 5-HTD were reduced in an elevated [K+]o (7.0 mM) solution and > 60% in a low Na+ (26 mM) solution and were not significantly changed in a low Cl- (6.7 mM) or Ca(2+)-free/high Mg2+ (10.9 mM) solution. The 5-HT2 receptor agonist alpha-methyl-5-HT (50 microM) depolarized RVLM neurons, and the 5-HT2 antagonist ketanserin (1-10 microM) attenuated the 5-HTD and the depolarizing phase of biphasic responses, whereas the 5-HT1A receptor antagonist PBD (2 microM) was without effect. Inclusion of the hydrolysis resistant guanine nucleotide GDP-beta-S in patch solution significantly reduced the 5-HTH as well as the 5-HTD. The present study shows that, in the immature rat RVLM neurons, 5-HT causes a slow hyperpolarization and depolarization probably by interacting with 5-HT1A and 5-HT2 receptors, which are G-proteins coupled. 5-HTH may involve an increase of an inwardly rectifying K+ conductance, and 5-HTD appear to be caused by a decrease of K+ conductance and/or increase of nonselective cation conductance.
采用全细胞膜片钳记录技术，对8至12日龄大鼠脑干切片的延髓头端腹外侧区（RVLM）神经元进行记录。通过向RVLM神经元 superfusate 或压力喷射5-羟色胺（5-HT），可引起三种类型的膜电位变化：缓慢超极化（5-HTH）、缓慢去极化（5-HTD）和双相反应，这些反应在含有河豚毒素（TTX，0.3 microM）的溶液中持续存在。大多数反应性神经元的5-HTH伴随着输入电阻的降低。超极化降低而去极化增加5-HTH；在3.1 mM [K+]o中平均反转电位为-92.3 mV，在7 mM [K+]o中移至-69.3 mV。钡（Ba2+，0.1 mM）而非四乙铵（TEA，10 mM）抑制5-HTH。5-HT1A受体激动剂（+/-）-8-羟基-二丙基氨基-四氢萘（8-OH-DPAT；5-50 microM）使RVLM神经元超极化。5-HT1A拮抗剂pindobind-5-HT1A（PBD；1-3 microM）和5-HT2/5-HT1受体拮抗剂螺哌隆（1-10 microM）抑制5-HTH和双相反应的超极化相；5-HT2受体拮抗剂酮色林（3 microM）无显著作用。5-HTD与RVLM神经元输入电阻的增加或无明显变化相关。膜超极化降低或未引起5-HTD的明显变化。在升高的[K+]o（7.0 mM）溶液中5-HTD降低，在低Na+（26 mM）溶液中降低>60%，在低Cl-（6.7 mM）或无Ca(2+)/高Mg2+（10.9 mM）溶液中无显著变化。5-HT2受体激动剂α-甲基-5-HT（50 microM）使RVLM神经元去极化，5-HT2拮抗剂酮色林（1-10 microM）减弱5-HTD和双相反应的去极化相，而5-HT1A受体拮抗剂PBD（2 microM）无作用。在膜片钳溶液中加入抗水解鸟嘌呤核苷酸GDP-β-S可显著降低5-HTH以及5-HTD。本研究表明，在未成熟大鼠RVLM神经元中，5-HT可能通过与G蛋白偶联的5-HT1A和5-HT2受体相互作用引起缓慢超极化和去极化。5-HTH可能涉及内向整流K+电导的增加，而5-HTD似乎是由K+电导的降低和/或非选择性阳离子电导的增加引起的。
