Chronic stress and cytogenesis ablation disrupt hippocampal neuron connectivity, with fluoxetine restoring function with sex-specific effects

Hippocampal Adult-Born neurons (hABNs) play a critical role in maintaining brain homeostasis, exhibiting unique properties during their maturation. The absence of hABNs impacts surrounding neuronal networks, but the mechanisms are not fully understood. In this study, we examined how perturbations to adult hippocampal cytogenesis affect the neuronal inputs to adult-born and mature neurons in the dentate gyrus. In particular, we analyzed connectivity changes in GFAP-Tk transgenic rats with ablated neurogenesis, and in unpredictable Chronic Mild Stress (uCMS) rats with reduced neurogenesis, with a focus on sex-differences in stress-affected hABNs. Additionally, we evaluated the action of the antidepressant fluoxetine on brain connectivity. Using a virus-mediated retrograde tracing approach, we quantified synaptic inputs to mature neurons and hABNs. Our findings reveal significant impairments in both intra- and extra-hippocampal connectivity following disruptions in cytogenesis, providing new insights into hippocampal network dynamics in the context of cytogenetic impairment, depression, and therapeutic interventions.