GNB1 encephalopathy (GNB1-E) is a rare neurodevelopmental disorder caused by pathogenic variants in the gene encoding the G protein subunit Gβ1. Clinically, GNB1-E is associated with motor dysfunction, epilepsy and learning disability. Prior research implicated altered Gβ1 in disrupting activation of GIRK (G-protein-coupled inwardly rectifying potassium) channels, leading to dysregulated neuronal excitability and seizures. The upstream regulators of Gβ1 and the downstream cellular and circuit consequences of GIRK dysfunction, particularly at dendrites and synapses, remained incompletely characterized.
The study used mice carrying the deleterious p.I80T mutation in Gnb1 in the heterozygous state (Gnb1I80T/+). Mice of both sexes expressing this allele displayed features consistent with GNB1-E, including developmental delay, decreased locomotion and increased anxiety. These behavioral readouts served to validate the model as relevant to the human disorder.
Investigators combined histological analysis with whole-cell patch-clamp electrophysiology and targeted pharmacology in ex vivo brain slices to assess hippocampal neuron structure, synaptic function and dendritic excitability. The described assays focused on hippocampal circuits because of their relevance to seizure generation and learning-related plasticity. Pharmacological manipulation included use of a specific GIRK activator, ML297, to probe causal relationships between GIRK function and dendritic physiology.
Histology revealed that hippocampal neurons from heterozygous Gnb1I80T/+ mice exhibited simplified dendritic morphologies relative to controls. The reported morphological phenotype indicates altered neuronal structural development or maintenance in the context of the p.I80T mutation, which may influence integrative properties of dendrites and synaptic connectivity.
Electrophysiological recordings demonstrated decreased synaptic inhibition mediated by metabotropic GABAB receptors in hippocampal neurons from mutant mice. Because GABAB receptor signaling is a canonical upstream activator of GIRK channels, reduced GABAB-mediated inhibition is consistent with impaired GIRK channel function downstream of altered Gβ1. The findings connect mutation-driven Gβ1 perturbation to a loss of inhibitory control at the synaptic level.
A principal functional consequence observed in Gnb1I80T/+ hippocampal neurons was increased dendritic excitability. Following synaptic afferent stimulation, mutant neurons generated dendritic calcium spikes of longer duration compared with controls. Dendritic calcium spikes are important drivers of burst firing and synaptic plasticity, so their prolongation represents a mechanistic route by which GIRK dysfunction may increase seizure susceptibility and alter learning-related circuit plasticity.
The prolonged dendritic calcium spike phenotype in mutant slices was reversed by application of ML297, a specific activator of GIRK channels. This pharmacological rescue supports a causal role for GIRK loss of function in producing increased dendritic excitability and indicates that channel activation can normalize a key cellular abnormality observed in the model.
Because dendritic calcium spikes influence burst firing patterns and induce forms of synaptic plasticity, their dysregulation in Gnb1I80T/+ mice provides a plausible mechanism linking GIRK dysfunction to both seizure propensity and cognitive deficits observed in GNB1-E. The ML297 rescue suggests that therapeutically targeting dendritic excitability by restoring GIRK channel activity may mitigate cellular-level abnormalities relevant to seizures and learning. The study therefore identifies dendritic excitability as a potential therapeutic axis in this genetic encephalopathy.
This report is a preprint and has not undergone peer review. The source describes experiments in ex vivo hippocampal slices and demonstrates short-term pharmacological reversal of a dendritic physiology phenotype; details about in vivo efficacy, long-term outcomes, behavioral rescue, dose–response, safety, or translational readiness were not reported in the source. Additional work will be required to define whether GIRK activation can ameliorate seizures or cognitive deficits in vivo and to assess potential therapeutic windows and risks.