Functional implications of atypical action potential generation in the (patho)physiological brain: from developmental...

Atypical action potentials (aAPs) are fast depolarizing electrical spikes recorded from the cell body, with a smaller amplitude. Despite varying in the generating mechanisms, aAPs have been reported in various brain cell types, including neurons, oligodendrocyte precursor cells (OPCs), and glioma cells. In this mini-review, we summarize the mechanisms and physiological functions of aAPs and outline their contributions to neurological diseases, particularly in glioma pathology. aAPs have been observed in mature brains, arising from mechanisms such as ectopic depolarizations and gap junction coupling, thereby supporting synaptic integration and network synchrony. It is also a signature of immature neurons in development. Subsets of NG2⁺ OPCs and immature oligodendrocyte-lineage cells exhibit state-, region-dependent excitability, ranging from subthreshold depolarizations to AP-like events, with potential roles in neuron-glial communication, ischemic vulnerability, and myelination. Accumulating human studies have demonstrated that glioma cells generate aAPs, while until recently their molecular profile was characterized by patch-seq. In IDH-mutant glioma, aAP cells exhibit a mixed GABAergic and OPC signature. At the leading edge (LE) of IDH-wild-type gliomas, aAPs are present in both adjacent non-tumor cells and glioblastoma cells (GBCs) across diverse GBC states, yet exhibit reduced proliferation and increased inflammatory signaling. In conclusion, aAPs are a recurrent but context-dependent electrophysiological feature observed in subsets of glioma cells, and may indicate an active role in network integration and active release. Dissecting the differential roles of aAP and no-aAP GBCs through targeted manipulations informed by transcriptomic results may reveal crucial mechanisms underlying multifaceted tumor-neuron crosstalk in glioma progression.