Early molecular changes in the subfornical organ during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a commonly used animal model of multiple sclerosis that allows the investigation of early immune-neural interactions that may precede clinical symptoms. The subfornical organ (SFO), a sensory circumventricular structure devoid of a blood-brain barrier, is anatomically positioned to sense circulating inflammatory cues and may participate in central immune responses. To explore its role during the prodromal stage of EAE, rats were immunized with guinea pig spinal cord homogenate and examined at three stages: 7 days post-induction ("pre-onset" phase), 14 days post-induction ("peak" phase), and 21-25 days post-induction ("remission" phase). SFO changes were assessed using magnetic resonance imaging, immunofluorescence for ionized calcium binding adaptor molecule 1 (IBA1) and NACHT, LRR and PYD domains-containing protein 3 (NLRP3) or caspase-1, and serum enzyme-linked immunosorbent assay of interleukin (IL)-1β and IL-18. Pre-onset magnetic resonance imaging revealed no detectable structural changes, whereas serum IL-1β and IL-18 levels were elevated, accompanied by increased immunoreactivity of IBA1, NLRP3, and caspase-1 in the SFO. Because IBA1 can be expressed by both resident microglia and infiltrating peripheral myeloid cells under inflammatory conditions, the specific cellular sources of these changes remain unclear. During the peak phase, these molecular changes intensified and coincided with detectable T2 hyperintensity, and remission was associated with their partial resolution. These findings indicate that inflammation-related molecular alterations in the SFO precede structural or imaging abnormalities in EAE, suggesting that the SFO may serve as an early neuroimmune interface associated with inflammation-related alterations during EAE.