Lundquist C T, Nässel D R
Department of Zoology, Stockholm University, Sweden.
J Neurobiol. 1997 Sep;33(3):297-315. doi: 10.1002/(sici)1097-4695(199709)33:3<297::aid-neu8>3.0.co;2-x.
Four tachykinin-related peptides, locustatachykinin 1-4 (LomTK 1-4) are distributed in interneurons throughout the central nervous system of the locust Locusta migratoria and may have important roles as neurotransmitters or neuromodulators. In search of the central actions of LomTKs, we analyzed the response of the efferent dorsal unpaired median (DUM) neurons in the locust metathoracic ganglion. Immunocytochemistry, using an antiserum against LomTK 1, combined with intracellular filling of efferent DUM neurons with Lucifer yellow, revealed that LomTK-immunoreactive fibers are in close proximity to dendritic arborizations of the DUM neurons. Hence, LomTKs may act on DUM neurons by releasing locally in the metathoracic ganglion. Intracellular recordings were made from somata of DUM neurons, and LomTKs were either bath-applied to an isolated metathoracic ganglion or pressure-ejected onto the DUM neuron soma. LomTK 1 at concentrations of 0.1 mM-0.1 microM caused a relatively slow, reversible depolarization with a subsequent increase in the frequency of action potential firing. Amino-terminally truncated forms of LomTK 1 were applied to DUM neurons. The heptapeptide [3-9]-LomTK 1 had a substantially reduced activity, and bioactivity was lost after further truncation. Spantide 1, an antagonist of mammalian tachykinin receptors, reversibly blocked the effect of LomTK 1. The effect of LomTK 1 was clearly reduced in the presence of GDP-beta-S, a stable analog of GDP that inactivates G-proteins. The action of LomTK 1 was potentiated by both IBMX and theophylline, two cyclic AMP (cAMP) phosphodiesterase inhibitors. The action of LomTK 1 was mimicked by pressure-ejecting 8-bromo-cAMP, a membrane permeable analog of cAMP, and by forskolin, an adenylate cyclase activator. Furthermore, cAMPS, a blocker of protein kinase A activity, reduced the effect of LomTK 1. These findings indicate that cAMP is involved in mediating DUM neuron depolarization.
四种速激肽相关肽，即飞蝗速激肽1 - 4（LomTK 1 - 4）分布于飞蝗（Locusta migratoria）中枢神经系统的中间神经元中，可能作为神经递质或神经调质发挥重要作用。为了探究LomTKs的中枢作用，我们分析了飞蝗后胸神经节中传出性背中无对神经元（DUM）的反应。利用抗LomTK 1抗血清进行免疫细胞化学，结合用荧光黄对传出性DUM神经元进行细胞内填充，结果显示LomTK免疫反应性纤维与DUM神经元的树突分支紧密相邻。因此，LomTKs可能通过在后胸神经节局部释放来作用于DUM神经元。从DUM神经元的胞体进行细胞内记录，将LomTKs浴加于分离的后胸神经节或压力喷射到DUM神经元胞体上。浓度为0.1 mM - 0.1 microM的LomTK 1引起相对缓慢、可逆的去极化，随后动作电位发放频率增加。将LomTK 1的氨基末端截短形式应用于DUM神经元。七肽[3 - 9]-LomTK 1的活性大幅降低，进一步截短后生物活性丧失。Spantide 1，一种哺乳动物速激肽受体拮抗剂，可逆地阻断LomTK 1的作用。在GDP-β-S（一种使G蛋白失活的GDP稳定类似物）存在的情况下，LomTK 1的作用明显减弱。LomTK 1的作用被两种环磷酸腺苷（cAMP）磷酸二酯酶抑制剂异丁基甲基黄嘌呤（IBMX）和茶碱增强。通过压力喷射8 - 溴 - cAMP（一种cAMP膜通透性类似物）和腺苷酸环化酶激活剂福斯可林可模拟LomTK 1的作用。此外，蛋白激酶A活性阻断剂cAMPS降低了LomTK 1的作用。这些发现表明cAMP参与介导DUM神经元去极化。
