Changes in Prefrontal Axons May Disrupt the Network in Autism

TLDR

Neural communication in autism is disrupted by mechanisms that remain unclear. The study investigates whether axonal alterations underlie disrupted neural communication in autism. The authors examined single axons and their ultrastructure in postmortem white matter beneath the ACC, OFC, and LPFC to assess region‑specific axonal changes linked to autism. The study found that in autism, ACC axons were reduced in size with overexpression of growth‑associated protein 43 and excess thin axons, OFC axons had thinner myelin, while LPFC axons were unchanged, yet the altered white matter in ACC and OFC disrupted connectivity among prefrontal regions, potentially explaining attentional, repetitive, and social deficits and pointing to therapeutic targets.

Abstract

Neural communication is disrupted in autism by unknown mechanisms. Here, we examined whether in autism there are changes in axons, which are the conduit for neural communication. We investigated single axons and their ultrastructure in the white matter of postmortem human brain tissue below the anterior cingulate cortex (ACC), orbitofrontal cortex (OFC), and lateral prefrontal cortex (LPFC), which are associated with attention, social interactions, and emotions, and have been consistently implicated in the pathology of autism. Area-specific changes below ACC (area 32) included a decrease in the largest axons that communicate over long distances. In addition, below ACC there was overexpression of the growth-associated protein 43 kDa accompanied by excessive number of thin axons that link neighboring areas. In OFC (area 11), axons had decreased myelin thickness. Axon features below LPFC (area 46) appeared to be unaffected, but the altered white matter composition below ACC and OFC changed the relationships among all prefrontal areas examined, and could indirectly affect LPFC function. These findings provide a mechanism for disconnection of long-distance pathways, excessive connections between neighboring areas, and inefficiency in pathways for emotions, and may help explain why individuals with autism do not adequately shift attention, engage in repetitive behavior, and avoid social interactions. These changes below specific prefrontal areas appear to be linked through a cascade of developmental events affecting axon growth and guidance, and suggest targeting the associated signaling pathways for therapeutic interventions in autism.