Li De-Pei, Chen Shao-Rui, Pan Hui-Lin
Department of Anesthesiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
J Neurophysiol. 2002 Nov;88(5):2664-74. doi: 10.1152/jn.00540.2002.
Nitric oxide (NO) in the paraventricular nucleus (PVN) is involved in the regulation of the excitability of PVN neurons. However, the effect of NO on the inhibitory GABAergic and excitatory glutamatergic inputs to spinally projecting PVN neurons has not been studied specifically. In the present study, we determined the role of the inhibitory GABAergic and excitatory glutamatergic inputs in the inhibitory action of NO on spinally projecting PVN neurons. Spinally projecting PVN neurons were retrogradely labeled by a fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocasbocyane (DiI), injected into the spinal cord of rats. Whole cell voltage- and current-clamp recordings were performed on DiI-labeled PVN neurons in the hypothalamic slice. The spontaneous miniature inhibitory postsynaptic currents (mIPSCs) recorded in DiI-labeled neurons were abolished by 20 microM bicuculline, whereas the miniature excitatory postsynaptic currents (mEPSCs) were eliminated by 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione. Bath application of an NO donor, 100 microM S-nitroso-N-acetyl-penicillamine (SNAP), or the NO precursor, 100 microM L-arginine, both significantly increased the frequency of mIPSCs of DiI-labeled PVN neurons, without altering the amplitude and the decay time constant of mIPSCs. The effect of SNAP and L-arginine on the frequency of mIPSCs was eliminated by an NO scavenger, 2-(4-carboxypheny)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, and an NO synthase inhibitor, 1-(2-trifluoromethylphenyl) imidazole, respectively. Neither SNAP nor L-arginine significantly altered the frequency and the amplitude of mEPSCs. Under current-clamp conditions, 100 microM SNAP or 100 microM L-arginine significantly decreased the discharge rate of the DiI-labeled PVN neurons, without significantly affecting the resting membrane potential. On the other hand, 20 microM bicuculline significantly increased the impulse activity of PVN neurons. In the presence of bicuculline, SNAP or L-arginine both failed to inhibit the firing activity of PVN neurons. This electrophysiological study provides substantial new evidence that NO suppresses the activity of spinally projecting PVN neurons through potentiation of the GABAergic synaptic input.
室旁核（PVN）中的一氧化氮（NO）参与调节PVN神经元的兴奋性。然而，NO对投射至脊髓的PVN神经元的抑制性γ-氨基丁酸能（GABAergic）和兴奋性谷氨酸能输入的影响尚未得到专门研究。在本研究中，我们确定了抑制性GABA能和兴奋性谷氨酸能输入在NO对投射至脊髓的PVN神经元的抑制作用中的作用。将荧光染料1,1'-二油酰基-3,3,3',3'-四甲基吲哚羰花青（DiI）注入大鼠脊髓，逆行标记投射至脊髓的PVN神经元。对下丘脑切片中DiI标记的PVN神经元进行全细胞电压钳和电流钳记录。20微摩尔荷包牡丹碱可消除DiI标记神经元中记录到的自发性微小抑制性突触后电流（mIPSCs），而20微摩尔6-氰基-7-硝基喹喔啉-2,3-二酮可消除微小兴奋性突触后电流（mEPSCs）。浴用NO供体100微摩尔S-亚硝基-N-乙酰青霉胺（SNAP）或NO前体100微摩尔L-精氨酸，均显著增加DiI标记的PVN神经元mIPSCs的频率，而不改变mIPSCs的幅度和衰减时间常数。NO清除剂2-（4-羧基苯基）-4,4,5,5-四甲基咪唑啉-1-氧基-3-氧化物和NO合酶抑制剂1-（2-三氟甲基苯基）咪唑分别消除了SNAP和L精氨酸对mIPSCs频率的影响。SNAP和L-精氨酸均未显著改变mEPSCs的频率和幅度。在电流钳条件下，100微摩尔SNAP或100微摩尔L-精氨酸显著降低DiI标记的PVN神经元的放电率，而不显著影响静息膜电位。另一方面，20微摩尔荷包牡丹碱显著增加PVN神经元的冲动活动。在存在荷包牡丹碱的情况下，SNAP或L-精氨酸均未能抑制PVN神经元的放电活动。这项电生理研究提供了大量新证据，表明NO通过增强GABA能突触输入来抑制投射至脊髓的PVN神经元的活动。
