Gap junctional coupling of molecular layer interneurons enables transient NMDA driven synchronization

Molecular layer interneurons (MLIs) play a crucial role in modulating the output of the cerebellar cortex through their inhibition of Purkinje cells. MLIs also inhibit other MLIs synaptically and are coupled electrically through gap junctions. While synchronization of MLIs has been observed, comprehensive understanding of the role of gap junctional coupling in shaping MLI network activity is lacking. Dendro-dendritic gap junctional coupling in MLIs involves propagation of signals to and from the dendritic gap junction location which can lead to neural synchronization. However, how this is regulated by the intrinsic electrical properties of MLIs, including dendritic properties, is poorly understood. In this study, we apply conductance-based computational modelling to examine the effect of dendritic filtering on gap junctional coupling in pairs of ball-and-stick MLI models, demonstrating that gap junctional properties, rather than the active dendritic properties of MLIs, primarily dictate gap junction-driven synchronization. By systematically reducing the ball-and-stick model to a one-compartment MLI model, we additionally investigate the role of MLI gap junctional coupling in mediating MLI network synchrony. Our results reveal that transient AMPA input drives brief network-wide synchronization, whereas NMDA-mediated elevated firing enables gap junction-dependent oscillatory synchronization that is further enhanced by MLI-MLI inhibition in a positive feedback loop, producing pronounced peaks of network coactivity resembling sensory-evoked MLI activity observed in vivo. These findings provide important insights into network dynamics of MLIs and how gap junctions shape their activity, with broader implications for other neural networks that rely on gap junctional coupling.