8-NITRO-CGMP REGULATES THE PERSISTENCE AND DIRECTIONALITY OF CEREBELLAR SYNAPTIC PLASTICITY

Synaptic plasticity is considered a cellular basis of learning and memory, and many signaling molecules have been implicated in its regulation. However, despite the persistent nature of memory, the molecular mechanisms underlying the long-term maintenance of synaptic plasticity remain poorly understood.
Long-term depression (LTD) at the parallel fiber (PF)–Purkinje cell (PC) synapse in the cerebellum is regarded as a cellular substrate for cerebellum-dependent motor learning, including optokinetic responses. Previous studies have shown that calcium signaling, inositol trisphosphate (IP₃), and the nitric oxide (NO)–cGMP–protein kinase G (PKG) pathway contribute to PF-LTD induction; however, these mechanisms alone cannot fully explain the long-term persistence of LTD.
8-Nitro-cGMP is a recently identified signaling molecule generated by the simultaneous production of NO and reactive oxygen species (ROS) in the presence of GTP. Unlike cGMP, 8-nitro-cGMP is resistant to phosphodiesterase-mediated degradation and exerts sustained effects on target proteins via S-guanylation, leading to prolonged PKG activation. We therefore hypothesized that 8-nitro-cGMP contributes to LTD maintenance by substituting for cGMP in LTD-related signaling.
Using acute cerebellar slices from mice, we found that inhibition of 8-nitro-cGMP or blockade of ROS-producing enzymes significantly suppressed PF-LTD. Imaging analyses further revealed enzyme-dependent ROS production following LTD-inducing stimulation. Moreover, while PF stimulation alone induced long-term potentiation (LTP), combined stimulation with PC depolarization induced LTD. Under these conditions, 8-nitro-cGMP suppressed LTP-related signaling, enabling stable LTD induction.
These findings indicate that ROS, previously considered mainly detrimental, act as physiological messengers via 8-nitro-cGMP to regulate both the persistence and directionality of synaptic plasticity.