Cell type-specific rearrangement of perisomatic inhibition in the valproate mouse model of autism

Abstract

Autism spectrum disorder (ASD) involves disrupted excitatory/inhibitory balance in brain circuits, with interneuron dysfunction implicated across cortical networks. Perisomatic inhibition by parvalbumin-containing (PV) and cholecystokinin-expressing (CCK) basket cells critically regulates principal neuron activity, yet their specific alterations in ASD remain unclear. We investigated cell type-specific changes in perisomatic inhibition within the amygdala using the valproic acid (VPA) mouse model of autism. Pregnant mice received VPA or saline at embryonic day 12.5. Male offspring underwent behavioral testing to assess autistic phenotypes. Following behavioral analysis, immunocytochemical techniques were used to quantify neuronal density, PV-expressing interneuron density, and perisomatic terminal densities of both PV and type 1 cannabinoid receptor (CB1)-expressing CCK basket cells in the lateral and basal amygdala nuclei. Single-cell analysis using Kv2.1 immunostaining quantified perisomatic inputs on individual principal neurons. Optogenetic stimulation combined with patch-clamp recordings validated PV interneuron output changes. Statistical comparisons used Mann-Whitney U tests and two-sample t-tests. VPA-treated mice exhibited autism-like behaviors including reduced ultrasound vocalizations, increased tactile sensitivity, and impaired social interaction and social novelty preferences. Immunocytochemical analysis revealed increased overall neuronal density but decreased PV-expressing interneuron density in the basal amygdala. CB1 + terminal density increased proportionally with neuronal density, while PV+ terminal density failed to compensate, resulting in 16% reduction in perisomatic PV+ inputs per principal neuron. Optogenetic experiments confirmed the decrease in PV interneuron-mediated inhibition independent from PV expression level, with significantly reduced recruitable terminals onto principal neurons, while presynaptic release properties remained unchanged. Prenatal VPA exposure causes selective reduction in PV basket cell-mediated perisomatic inhibition while preserving CCK basket cell terminals, demonstrating cell type-specific vulnerability. This imbalance likely contributes to amygdala hyperexcitability underlying social and emotional symptoms in ASD, suggesting that targeting specific interneuron subtypes rather than broad GABAergic enhancement may offer more effective therapeutic strategies.