Food restriction and hyperactivity differentially shape microglial Iba1 immunoreactivity across feeding-, cognitive-, and reward-related circuits in the activity-based anorexia model

: Anorexia nervosa (AN) is characterized by marked metabolic, behavioral, and neurobiological alterations. Although neuroinflammation and microglial activation have been suggested to contribute to its pathophysiology, preclinical evidence remains inconsistent and appears to depend on the experimental conditions and brain regions examined. Here, we asked whether the two core components of the activity-based anorexia (ABA) paradigm, food restriction and voluntary hyperactivity, are associated with distinct regional patterns of Iba1 immunoreactivity across neural circuits involved in energy balance, cognition, and reward, and whether these alterations relate to the behavioral and metabolic severity of the model. Using the ABA rat model, we quantified the percentage of Iba1-positive area in the prefrontal cortex, dorsal and ventral hippocampus, anterior cingulate cortex, nucleus accumbens, caudate putamen, amygdala, and the arcuate and paraventricular nuclei of the hypothalamus. ABA animals displayed an overall reduction in Iba1 immunoreactivity, with significant decreases in the hippocampus and paraventricular nucleus. Conversely, food restriction alone increased Iba1 coverage in the arcuate nucleus, whereas voluntary physical activity selectively enhanced Iba1 immunoreactivity in reward-related areas, particularly the nucleus accumbens. These findings indicate that starvation and hyperactivity induce distinct, region-specific changes in Iba1 immunoreactive coverage, potentially reflecting alterations in microglial responses that may differentially affect hypothalamic, cognitive, and reward-related circuits implicated in AN pathophysiology.