Repetitive and compulsive behavior after Early-Life-Pain in mice

Abstract Pain in early life may affect cortical development and risk of chronic pain. We developed an optogenetic Cre/loxP mouse model of "early-life-pain" (ELP) using mice with transgenic expression of channelrhodopsin-2 (ChR2) under control of the Advillin ( Avil ) promoter, which drives expression of ChR2 in peripheral somatosensory neurons. Avil-ChR2 (Cre+) and ChR2-flfl control mice were exposed to blue light in a chamber once daily from P1-P5 together with their Cre-negative mother. ELP caused cortical hyperexcitability at P8-9 as assessed via multi-electrode array recordings that coincided with reduced expression of synaptic genes (RNAseq) including Grin2b , neurexins, piccolo and voltage gated calcium and sodium channels, suggesting activity-dependent synaptic pruning. Young adult (8-16 wks) Avil-ChR2 mice presented with nociceptive hypersensitivity upon heat or mechanical stimulation, which did not resolve up until one year of age. The persistent "pain" phenotype was reflected by capsaicin hypersensitivity in primary sensory neurons of aged mice (1 year) as assessed by calcium imaging. Adult Avil-ChR2 mice behaved like controls in maze tests of anxiety, social interaction and spatial memory but IntelliCage behavioral studies revealed repetitive nosepokes and corner visits and compulsive lickings. Compulsiveness at the behavioral level was associated with a reduction of sphingomyelin species in brain and plasma lipidomic studies pointing to alterations of sphingolipid metabolisms, which have been previously described in the context of addiction and psychiatric diseases. Hence, ELP may predispose to chronic pain and compulsive psychopathology.