In Diffusive Molecular Communication (DMC), information is transmitted by diffusing molecules. Synaptic signaling, as a natural implementation of this paradigm, encompasses functional components that, once understood, can facilitate the development of synthetic DMC systems. To unleash this potential, however, a thorough understanding of the synaptic communication channel based on biophysical principles is needed. Since synaptic transmission critically depends also on non-neural cells, such understanding requires the consideration of the so-called tripartite synapse. In this paper, we develop a comprehensive channel model of the tripartite synapse encompassing a three-dimensional, finite-size spatial model of the synaptic cleft, molecule uptake at the presynaptic neuron and at glial cells, reversible binding to individual receptors at the postsynaptic neuron, and spillover to the extrasynaptic space. Based on this model, we derive analytical time domain expressions for the channel impulse response (CIR) of the synaptic DMC system and for the number of molecules taken up at the presynaptic neuron and at glial cells, respectively. These expressions provide insight into the impact of macroscopic physical channel parameters on the decay rate of the CIR and the reuptake rate, and reveal fundamental limits for synaptic signal transmission induced by chemical reaction kinetics and the channel geometry. Adapted to realistic parameters, our model produces plausible results when compared to experimental and simulation studies and we provide results from particle-based computer simulations to further validate the analytical model. The proposed comprehensive channel model admits a wide range of synaptic configurations making it suitable for the investigation of many practically relevant questions, such as the impact of glial cell uptake and spillover on signal transmission in the tripartite synapse.

中文翻译：

---

DMC 的突触通道建模：三联突触中的神经递质摄取和溢出

在扩散分子通信 (DMC) 中，信息通过扩散分子传输。作为该范式的自然实现，突触信号包含功能组件，一旦理解，就可以促进合成 DMC 系统的开发。然而，为了释放这种潜力，需要彻底了解基于生物物理原理的突触通信通道。由于突触传递严重依赖于非神经细胞，因此这种理解需要考虑所谓的三方突触。在本文中，我们开发了三方突触的综合通道模型，包括突触间隙、突触前神经元和神经胶质细胞的分子摄取的三维、有限大小的空间模型，与突触后神经元的单个受体可逆结合，并溢出到突触外空间。基于该模型，我们分别推导出突触 DMC 系统的通道脉冲响应 (CIR) 和突触前神经元和神经胶质细胞吸收的分子数量的分析时域表达式。这些表达式提供了对宏观物理通道参数对 CIR 衰减率和再摄取率的影响的洞察，并揭示了由化学反应动力学和通道几何引起的突触信号传输的基本限制。适应现实参数，我们的模型与实验和模拟研究相比产生了合理的结果，我们提供了基于粒子的计算机模拟的结果以进一步验证分析模型。