Adenosine pre- and postsynaptic modulation of glutamate-dependent calcium activity in hypothalamic neurons.
Adenosine pre- and postsynaptic modulation of glutamate-dependent calcium activity in hypothalamic neurons.
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DOI：
10.1152/jn.1995.74.5.2150
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发表时间：
1995-11
影响因子：
2.5
通讯作者：
K. Obrietan;A. Belousov;H. Heller;A. N. van den Pol
中科院分区：
文献类型：
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作者：
K. Obrietan;A. Belousov;H. Heller;A. N. van den Pol
1. 据报道，在下丘脑中，腺苷影响温度调节、睡眠稳态和内分泌分泌。腺苷对下丘脑神经元的影响尚未在细胞水平上进行研究。在谷氨酸受体拮抗剂d -2-氨基-5-磷酸戊酸酯和6-氰基-7-硝基喹啉-2,3-二酮存在的情况下，腺苷（5 nM-30微米）对细胞内Ca2+或电活性没有影响；因此，在没有谷氨酸受体阻断的情况下，我们使用fura-2 Ca2+数字成像和全细胞膜片钳电生理检查了腺苷在调节培养下丘脑神经元（n bbb1700）中谷氨酸活性的作用。2. 当谷氨酸受体未被阻断时，腺苷（1-30微米）和选择性腺苷A1受体激动剂n6 -环戊基腺苷（CPA； 5纳米-1微米）引起细胞内Ca2+和电活动的大量减少，表明谷氨酸神经传递对腺苷的作用至关重要。神经元Ca2+水平可逆地降低CPA (50 nM)，最大降低90%，这些作用被A1受体拮抗剂8-环戊基-1,3-二丙基黄嘌呤（DPCPX）共同抑制。3. 未成熟神经元在突触发生前的Ca2+水平不受腺苷的影响。腺苷A1受体激活在体外8 ~ 73天抑制谷氨酸介导的神经元Ca2+活性。4. 腺苷（1或10微米）引起膜电位的超极化和内源性释放谷氨酸引起的大突触后电位的减少。低浓度的CPA （5 nM）降低了谷氨酸介导的神经元同步Ca2+瞬态的频率和突触后电位的频率。5. 为了比较腺苷对下丘脑神经元和其他大脑区域细胞的相对影响，我们分析了CPA对海马和皮质培养中谷氨酸介导的Ca2+的影响。CPA （50 nM）可逆地抑制下丘脑神经元中谷氨酸介导的Ca2+升高35%，而海马神经元为54%，皮质神经元为46%。6. 如果它确实发挥功能作用，腺苷应该由下丘脑细胞释放。在一些神经元中，腺苷A1受体拮抗剂环戊基茶碱或dcpx引起细胞内Ca2+的增加，这表明腺苷是由下丘脑细胞分泌的，强直性地抑制谷氨酸增强的神经元Ca2+。7. 为了确定腺苷是否能发挥突触后作用，我们在河豚毒素存在的情况下将其与谷氨酸激动剂共同应用。在下丘脑神经元亚群中，腺苷和CPA抑制（占总神经元的18%）或增强（占总神经元的6%）对谷氨酸、n -甲基- d -天冬氨酸和海钠酸盐的反应，分别为bb0或= 20%。8. 与在神经元中发现的适度作用相反，下丘脑星形胶质细胞对谷氨酸或代谢性谷氨酸受体激动剂(+/-)-反式-1-氨基-1,3-环戊二羧酸的反应被腺苷（平均+225%）和CPA强烈增强。9. 总之，这些发现表明腺苷在调节下丘脑谷氨酸神经传递中发挥主要的突触前作用和次要的突触后作用，在那里它可以在阻断大部分谷氨酸诱导的Ca2+上升中发挥重要作用。在没有谷氨酸传递的情况下，腺苷对神经元细胞内Ca2+或电活动的影响相对较小。
1. Within the hypothalamus, adenosine has been reported to influence temperature regulation, sleep homeostasis, and endocrine secretions. The effects of adenosine on hypothalamic neurons have not been studied at the cellular level. Adenosine (5 nM-30 microM) showed no influence on intracellular Ca2+ or electrical activity in the presence of glutamate receptor antagonists D-2-amino-5-phosphonovalerate and 6-cyano-7-nitroquinoxaline-2,3-dione; consequently, we examined the role of adenosine in modulating the activity of glutamate in cultured hypothalamic neurons (n > 1,700) with fura-2 Ca2+ digital imaging and whole cell patch-clamp electrophysiology in the absence of glutamate receptor block. 2. When glutamate receptors were not blocked, adenosine (1-30 microM) and the selective adenosine A1 receptor agonist N6-cyclopentyl adenosine (CPA; 5 nM-1 microM) caused a large reduction in intracellular Ca2+ and electrical activity, suggesting that glutamate neurotransmission was critical for an effect of adenosine to be detected. Neuronal Ca2+ levels were reversibly depressed by CPA (50 nM), with a maximum depression of 90%, and these effects were blocked by coadministration of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). 3. Ca2+ levels in immature neurons before the time of synaptogenesis were not affected by adenosine. Adenosine A1 receptor activation suppressed glutamate-mediated Ca2+ activity in neurons in vitro 8 to 73 days. 4. Adenosine (1 or 10 microM) caused a hyperpolarization of membrane potential and a reduction of large postsynaptic potentials arising from endogenously released glutamate. The administration of low concentrations of CPA (5 nM) decreased the frequency of glutamate-mediated, neuronally synchronized Ca2+ transients and the frequency of postsynaptic potentials. 5. To compare the relative effects of adenosine on hypothalamic neurons with cells from other brain regions, we assayed the effects of CPA on glutamate-mediated Ca2+ in hippocampal and cortical cultures. CPA (50 nM) reversibly depressed glutamate-mediated Ca2+ rises in hypothalamic neurons by 35%, compared with 54% in hippocampal neurons and 46% in cortical neurons. 6. If it does play a functional role, adenosine should be released by hypothalamic cells. In some neurons the adenosine A1 receptor antagonists cyclopentyltheophylline or DPCPX caused an increase in intracellular Ca2+, suggesting that adenosine was secreted by hypothalamic cells, tonically depressing glutamate-enhanced neuronal Ca2+. 7. To determine whether adenosine could exert a postsynaptic effect, we coapplied it with glutamate agonists in the presence of tetrodotoxin. Within subpopulations of hypothalamic neurons, adenosine and CPA either inhibited (18% of total neurons) or potentiated (6% of total neurons) responses to glutamate, N-methyl-D-aspartate, and kainate by > or = 20%. 8. In contrast to the modest effects found in neurons, responses of hypothalamic astrocytes to the application of glutamate or the metabotropic glutamate receptor agonist (+/-)-trans-1-amino-1,3-cyclopentanedicarboxylic acid were strongly potentiated by adenosine (mean +225%) and CPA. 9. Together, these findings suggest that adenosine exerts a major presynaptic effect and a minor postsynaptic effect in the modulation of glutamate neurotransmission in the hypothalamus, where it can play a significant role in blocking a large part of the glutamate-induced Ca2+ rise. In the absence of glutamate transmission, adenosine has relatively little effect on either neuronal intracellular Ca2+ or electrical activity.