Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, H4B 1R6, Canada.
Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montréal, Québec, H4B 1R6, Canada.
Cell Calcium. 2019 Jun;80:103-111. doi: 10.1016/j.ceca.2019.04.003. Epub 2019 Apr 10.
The entorhinal cortex plays an important role in temporal lobe processes including learning and memory, object recognition, and contextual information processing. The alteration of the strength of synaptic inputs to the lateral entorhinal cortex may therefore contribute substantially to sensory and mnemonic functions. The neuromodulatory transmitter dopamine exerts powerful effects on excitatory glutamatergic synaptic transmission in the entorhinal cortex. Interestingly, inputs from midbrain dopamine neurons appear to specifically target clusters of excitatory cells located in the superficial layers of the entorhinal cortex. We have previously demonstrated that dopamine facilitates synaptic transmission through the activation of D-like receptors. This facilitation of synaptic transmission is dependent on both activation of classical D-like-receptors, and upon activation of dopamine receptors linked to increases in phospholipase C, inositol triphosphate (IP), and intracellular calcium. In the present study we combined electrophysiological recordings of evoked excitatory postsynaptic currents with imaging of intracellular calcium using the fluorescent indicator fluo-4 to monitor calcium transients evoked by dopamine in electrophysiologically identified putative fan and pyramidal cells of the lateral entorhinal cortex. Bath application of dopamine (1 μM), or the phosphatidylinositol (PI)-linked D-like-receptor agonist SKF83959 (5 μM), induced reliable and reversible increases in fluo-4 fluorescence and excitatory postsynaptic currents in fan cells, but not in pyramidal cells. In contrast, application of the classical D-like-receptor agonist SKF38393 (10 μM) did not result in significant increases in fluorescence. Blocking release of calcium from internal stores by loading cells with the IP receptor blocker heparin (1 mM) or the ryanodine receptor blocker dantrolene (20 μM) abolished both the calcium transients and the facilitation of evoked synaptic currents induced by dopamine. Dopamine also induced calcium transients in fan cells when calcium was excluded from the extracellular medium, further indicating that the calcium transients are linked to release from internal stores. These results indicate that following D-like-receptor binding, dopamine selectively induces transient elevations in intracellular calcium via activation of IP and ryanodine receptors, and that these elevations are linked to the facilitation of synaptic responses in putative layer II entorhinal cortex fan cells.
内嗅皮层在包括学习和记忆、物体识别和上下文信息处理在内的颞叶过程中发挥着重要作用。因此，侧向内嗅皮层突触输入强度的改变可能对感觉和记忆功能有很大贡献。神经调质多巴胺对内嗅皮层的兴奋性谷氨酸能突触传递产生强大影响。有趣的是，中脑多巴胺神经元的输入似乎专门针对位于内嗅皮层浅层的兴奋性细胞簇。我们之前已经证明，多巴胺通过激活 D 样受体促进突触传递。这种突触传递的易化既依赖于经典 D 样受体的激活，也依赖于与 PLC、三磷酸肌醇 (IP) 和细胞内钙增加相关的多巴胺受体的激活。在本研究中，我们结合了外侧内嗅皮层电生理记录的诱发兴奋性突触后电流和使用荧光指示剂 fluo-4 进行的细胞内钙成像，以监测多巴胺在电生理鉴定的侧内嗅皮层潜在 fan 和锥体细胞中诱发的钙瞬变。多巴胺（1 μM）或磷脂酰肌醇 (PI) 连接的 D 样受体激动剂 SKF83959（5 μM）的浴应用诱导 fan 细胞中 fluo-4 荧光和兴奋性突触后电流的可靠和可逆增加，但不诱导锥体细胞增加。相比之下，经典 D 样受体激动剂 SKF38393（10 μM）的应用不会导致荧光显著增加。通过将 IP 受体阻断剂肝素 (1 mM) 或ryanodine 受体阻断剂 dantrolene (20 μM) 加载细胞来阻断细胞内钙库的钙释放，消除了多巴胺诱导的钙瞬变和诱发的突触电流的易化。当细胞外介质中排除钙时，多巴胺也会在 fan 细胞中诱导钙瞬变，进一步表明钙瞬变与细胞内储存的释放有关。这些结果表明，在 D 样受体结合后，多巴胺通过激活 IP 和 ryanodine 受体选择性地诱导细胞内钙的短暂升高，并且这些升高与潜在的 II 层内嗅皮层 fan 细胞中突触反应的易化有关。
