De novo gain-of-function mutations in Cav1.3 voltage-gated L-type calcium channels (CACNA1D gene) confer a high risk for neurodevelopmental and neuropsychiatric diseases. However, how these mutations affect neuronal function remains elusive. Previously, we demonstrated that the autism-associated A749G mutation induced an overall dendritic spine elongation in transfected mouse hippocampal neurons. This study aimed to investigate the influence of A749G Cav1.3 channels on the dendritic branching, spine density, and neuronal soma size in the brains of heterozygous (HET) A749G knock-in mice. To do so, we utilized a Golgi-Cox staining technique in saline-perfused brains of adult male mice and reconstructed neurons from different brain regions using the Neurolucida software. Our results showed that the proportion and density of stubby spines were significantly increased, while they were decreased for thin spines in CA1 hippocampal pyramidal neurons in mutant mice. Additionally, we demonstrated enhanced proximal dendritic branching as well as a reduction in cell soma area of CA1 hippocampal pyramidal neurons in HET compared to WT mice. In contrast, we found no significant differences in the morphology of medium spiny neurons in the dorsomedial striatum between mutant and control mouse brains. Currently, we also analyze morphological outcomes of the A749G mutation on other brain regions (dorsolateral striatum, hippocampal CA3 region), as well as investigate whether there are mutation-induced sex differences in neuronal morphology. To conclude, observed morphological changes can contribute to the neurodevelopmental phenotype and further confirm that CACNA1D should be considered as a high-risk gene for neurological disorders. Funding: FWF P35722, FWF P35087, DOC-30