Time-course of hypothalamic-pituitary-adrenal axis activity and inflammation in juvenile rat brain after cranial...

Area of Science:

• Neuroscience
• Endocrinology
• Radiation Biology

Background:

• Cranial irradiation (CI) in juvenile rodents impacts hypothalamic-pituitary-adrenal (HPA) axis stability and induces inflammation.
• The precise role of central nervous system (CNS) inflammation as a mediator of the HPA axis response to CI remains unclear.

Purpose of the Study:

• To investigate the hypothesis that inflammatory reactions within the CNS mediate the HPA axis response to cranial irradiation in juvenile rats.
• To analyze the temporal dynamics of serum corticosterone, IL-1β, and TNF-α levels post-CI.
• To examine the expression and localization of glucocorticoid receptor (GR) and nuclear factor kappaB (NFκB) in the hippocampus.

Main Methods:

• Juvenile rats were exposed to cranial irradiation (CI).
• Time-course analysis of serum corticosterone, hypothalamic IL-1β, and TNF-α levels.
• Assessment of hippocampal protein and gene expression for GR and NFκB using Western blot and RT-PCR.
• Immunohistochemistry to evaluate NFκB nuclear translocation.

Main Results:

• CI rapidly induced both GR and NFκB mRNA and protein in the hippocampus within 1 hour.
• NFκB protein levels increased for 2 hours, shifting the NFκB/GR ratio in favor of NFκB.
• Hypothalamic IL-1β levels increased, peaking at 2-4 hours post-CI, while serum cytokines remained undetectable.
• Enhanced hypothalamic IL-1β correlated with NFκB nuclear translocation and decreased NFκB mRNA in the hippocampus at 6 hours.
• Serum corticosterone levels and hippocampal GR nuclear translocation increased at 6 hours post-CI.

Conclusions:

• Acute cranial irradiation elicits a rapid inflammatory response within the CNS, characterized by increased IL-1β and altered NFκB/GR dynamics in the hippocampus.
• Central inflammation appears to be a key mediator of the HPA axis activation following CI.
• The observed HPA axis activation and GR changes may represent a compensatory mechanism to manage the inflammatory response, potentially protecting the organism.