CRHR2 Activation by Urocortins Regulates Splenic Microbiota-Immune-brain Axis in a Single Prolonged Stress Model of Post-Traumatic Stress in Male Rats

Post-traumatic stress disorder (PTSD) is associated with dysfunction of the hypothalamo-pituitary-adrenocortical (HPA) axis, accompanied by alterations in immune function, microbiota composition, and brain regions, including the hippocampus. CRHR2 receptor agonists, urocortin 2 (UCN2) and urocortin 3 (UCN3), regulate stress-related neuroendocrine activity. The present study aimed to investigate how a single intranasal administration of UCN2 or UCN3 modulates bacterial composition and inflammatory activity in the spleen/isolated splenocytes and alters the expression of neuroinflammatory and neurogenic markers in the dorsal (dHipp) and ventral hippocampus (vHipp) in male rats exposed to single prolonged stress (SPS) model of PTSD.SPS increased Enterobacteriaceae 16S rRNA levels and slightly reduced Lactobacillus abundance, while both urocortins prevented these effects. In the spleen, SPS suppressed expression of immune cell function markers, whereas UCN3 mitigated these effects. In isolated splenocytes stimulated ex vivo with lipopolysaccharide, UCN2 and UCN3 restored the reduced mRNA expression of proinflammatory markers, including IL-1β, IL-12p40, NOS, and CD69. Alterations in inflammatory markers correlated with Enterobacteriaceae and Lactobacillus. In the brain, SPS-induced changes were observed primarily in the vHipp, where expression of neuroinflammatory markers, including Iba1, TREM2, and CX3CR1, were decreased and restored by urocortin treatment. Conversely, SPS increased DCX mRNA levels, whereas UCN2 and UCN3 reduced them. Neuroinflammatory markers in the vHipp correlated with splenic microbiota and inflammatory markers.Overall, these findings suggest that CRHR2 stimulation by intranasal UCN2/UCN3 administration prevents PTSD-induced alterations through interconnected effects on splenic microbiota composition, peripheral immune responses, and hippocampal synaptic plasticity and neuroinflammatory markers.