Stella N, Magistretti P J
Laboratoire de Recherche Neurologique, Institut de Physiologie et Service de Neurologie du CHUV, Faculté de Médecine, Université de Lausanne, 7 rue du Bugnon, 1005 Lausanne, Switzerland.
J Biol Chem. 1996 Sep 27;271(39):23705-10. doi: 10.1074/jbc.271.39.23705.
Glutamatergic neurotransmission is associated with release of arachidonic acid (AA) from membrane phospholipids of both neurons and astrocytes. Since free AA has been shown to enhance glutamate-mediated synaptic transmission, it can be postulated that glutamate release and AA formation constitute a positive feed-back mechanism for sustained excitatory neurotransmission. In the present study, we examined whether the glutamate-evoked release of AA could be modulated by peptides. Using mouse cortical neurons in primary cultures, we show that the release of AA evoked by glutamate is potentiated by vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide (PACAP). This effect is mediated through the activation of PACAP I receptors. However, several arguments show that this potentiating mechanism does not involve the cAMP/PKA pathway. 1) Increasing intracellular cAMP by either cholera toxin, forskolin, or 8-Br-cAMP treatments does not affect the glutamate-evoked release of AA; 2) potentiation of the glutamate response by PACAP is not prevented by the PKA inhibitor 8-Br-Rp-cAMPS. Also, an involvement of the phospholipase C protein kinase C pathways is unlikely since inhibitors of both phospholipase C (i.e. U-73122) and protein kinase C (i.e. Ro 31-8220) do not affect the potentiation of the glutamate response by PACAP. These observations indicate an effect mediated by PACAP I receptors, which does not involve the second messenger pathways classically associated with activation of this type of receptors. Furthermore, results indicate that this potentiating mechanism mediated by PACAP I receptor acts at a level downstream of the glutamate receptor-mediated calcium influx.
谷氨酸能神经传递与花生四烯酸（AA）从神经元和星形胶质细胞的膜磷脂中释放有关。由于游离AA已被证明可增强谷氨酸介导的突触传递，因此可以推测谷氨酸释放和AA形成构成了持续兴奋性神经传递的正反馈机制。在本研究中，我们研究了谷氨酸诱发的AA释放是否可被肽调节。使用原代培养的小鼠皮层神经元，我们发现血管活性肠肽和垂体腺苷酸环化酶激活多肽（PACAP）可增强谷氨酸诱发的AA释放。这种作用是通过激活PACAP I受体介导的。然而，一些证据表明这种增强机制不涉及cAMP/PKA途径。1）用霍乱毒素、福斯可林或8-溴-cAMP处理增加细胞内cAMP不会影响谷氨酸诱发的AA释放；2）PKA抑制剂8-溴-Rp-cAMPS不能阻止PACAP对谷氨酸反应的增强作用。此外，磷脂酶C/蛋白激酶C途径参与的可能性不大，因为磷脂酶C抑制剂（即U-73122）和蛋白激酶C抑制剂（即Ro 31-8220）均不影响PACAP对谷氨酸反应的增强作用。这些观察结果表明PACAP I受体介导了一种作用，该作用不涉及与这类受体激活经典相关的第二信使途径。此外，结果表明由PACAP I受体介导的这种增强机制作用于谷氨酸受体介导的钙内流的下游水平。
