Altered projection-specific synaptic remodeling and its modification by oxytocin in an idiopathic autism marmoset model

communications biology Article https://doi.org/10.1038/s42003-024-06345-9 Altered projection-specific synaptic remodeling and its modification by oxytocin in an idiopathic autism marmoset model Check for updates 1 1 1 1 1 1234567890():,; 1234567890():,; Jun Noguchi , Satoshi Watanabe , Tomofumi Oga , Risa Isoda , Keiko Nakagaki , Kazuhisa Sakai1, Kayo Sumida2, Kohei Hoshino3, Koichi Saito2, Izuru Miyawaki3, Eriko Sugano 4, Hiroshi Tomita 4, Hiroaki Mizukami5, Akiya Watakabe6, Tetsuo Yamamori6,7,8 & Noritaka Ichinohe 1 Alterations in the experience-dependent and autonomous elaboration of neural circuits are assumed to underlie autism spectrum disorder (ASD), though it is unclear what synaptic traits are responsible. Here, utilizing a valproic acid–induced ASD marmoset model, which shares common molecular features with idiopathic ASD, we investigate changes in the structural dynamics of tuft dendrites of upper-layer pyramidal neurons and adjacent axons in the dorsomedial prefrontal cortex through two-photon microscopy. In model marmosets, dendritic spine turnover is upregulated, and spines are generated in clusters and survived more often than in control marmosets. Presynaptic boutons in local axons, but not in commissural long-range axons, demonstrate hyperdynamic turnover in model marmosets, suggesting alterations in projection-specific plasticity. Intriguingly, nasal oxytocin administration attenuates clustered spine emergence in model marmosets. Enhanced clustered spine generation, possibly unique to certain presynaptic partners, may be associated with ASD and be a potential therapeutic target. Autism spectrum disorder (ASD) is a developmental disorder characterized by impairments in social communication, social interaction, and stereotyped behaviors1,2. Individuals with ASD often have learning disabilities and have difficulty learning to recognize verbal or non-verbal social information3. Proper refinement of neural networks during learning is achieved by coordinated synaptic remodeling, which may be altered in ASD. Dendritic spines, which are postsynaptic protrusions that receive most excitatory inputs4–6, have been observed longitudinally using two-photon microscopy in mouse models of ASD. This has made it possible to explore the spatiotemporal characteristics of synaptic remodeling in ASD. Morphological analysis of dendrites with in vivo two-photon microscopy has shown that accelerated spine generation and elimination in the motor and primary sensory cortices is a consistent phenotype in numerous ASD mouse models (BTBR, 15q11–13 duplication, Neuroligin mutant, FMR1 knockout, MeCP2 duplication, etc.)7–10. Clustered generation of postsynaptic dendritic spines, in which new spines form in close proximity to one another, plays a critical role in learning and memory11–17. Training increases clustered spine generation, which has been found to be correlated with learning performance in corresponding brain regions10,18. Neuronal modeling studies have suggested that enhanced clustered spine generation increases memory discrimination and the storage capacity of neuronal networks17,18. Excessively clustered spines may contribute to the development of ASD symptoms, but little is known about their involvement in this condition. On the other hand, it has been reported that diversity of excitatory synapses includes several synapse types or subtypes defined by molecular and other characteristics, and that certain circuits or connectome networks prefer particular types of synapses19. Changes in gene expression in ASD may alter the plasticity of specific cortical projections, which may in turn perturb the formation of neural circuits adapted to learning. 1 Department of Ultrastructural Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira, Japan. 2Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., Osaka, Japan. 3Preclinical Research Laboratories, Sumitomo Pharma Co., Ltd., Osaka, Japan. 4Laboratory of Visual Neuroscience, Graduate Course in Biological Sciences, Iwate University, Morioka, Japan. 5Division of Genetic Therapeutics, Jichi Medical University, Shimotsuke, Japan. 6Laboratory for Molecular Analysis of Higher Brain Function, Center for Brain Science, RIKEN, Wako, Japan. 7Present address: Laboratory for Haptic Perception and Cognitive Physiology, Center for Brain Science, RIKEN, Wako, Japan. 8Present address: Department of Marmoset Biology and Medicine, e-mail: ; CIEM, Kawasaki, Japan. Communications Biology | (2024)7:642 1 https://doi.org/10.1038/s42003-024-06345-9 However, projection-specific variations of synapse remodeling in ASD have not been explored. The common marmoset (Callithrix jacchus), a small New World monkey, has attracted considerable attention due to its rich repertoire of social behaviors, a well-developed prefrontal cortex (PFC) that supports high-level social ability, and gene expression networks that are similar to those in humans20. In fact, marmosets are more similar to humans than rodents in terms of their synaptic proteome21. We previously developed a valproic acid (VPA)–induced ASD model in the common marmoset22. VPA is an antiepileptic drug and also functions as a histone deacetylase inhibitor that may epigenetically increase the risk of ASD in humans by suppressing histone deacetylases in the fetal brain. Despite the fact that VPA administration was the sole environmental factor contributing to the development of ASD in this model, and there were no genetic variations, it was sufficient to induce gene expression changes in juvenile marmosets that were more typical of human idiopathic ASD than those in monogenetic ASD rodent models22. The characteristics of VPA-exposed marmosets suggest that these ASD models may be useful for bridging rodent ASD studies and human ASD. A notable portion of individuals with ASD persists in experiencing a range of challenges such as anxiety or depression in their daily lives into adulthood23,24. It is critical to understand ASD pathophysiology in adult ASD model animals and explore treatments. In this study, we investigated the temporal remodeling of neural circuits using in vivo two-photon longitudinal imaging in VPA-exposed adult marmosets. We analyzed synaptic dynamics at 3-day intervals in the apical tuft dendrites of pyramidal neurons in the primate-specific dorsomedial PFC (dmPFC). The dmPFC is involved in social cognition and habit formation, and was found to exhibit less activity in nonverbal information–biased judgment in ASD individuals25. We also observed the axonal boutons of local and longdistance cortical callosal connections labeled with fluorescent proteins of different colors to investigate whether circuit-specific synaptic remodeling was altered in the ASD model animal. Our study revealed that in VPAexposed marmosets, turnover of postsynaptic dendritic spines was upregulated, and spines were actively generated in clusters but (...truncated)