Transient expression of thyrotropin releasing hormone peptide and mRNA in the rat hippocampus following global cerebral ischemia/reperfusion injury

Introduction The role of extra-hypothalamic thyrotropin-releasing hormone (TRH) has been investigated by pharmacological studies using TRH or its analogues and found to produce a wide array of effects in the central nervous system. Methods Immunofluorescence, In situ labeling of DNA (TUNEL), in situ hybridization chain reaction and quantitative real-time polymerase chain reaction were used in this study. Results We found that the granular cells of the dentate gyrus expressed transiently a significant amount of TRH-like immunoreactivity and TRH mRNA during the 6-24 h period following global cerebral ischemia/reperfusion injury. TUNEL showed that apoptosis of neurons in the CA1 region occurred from 48 h and almost disappeared at 7 days. TRH administration 30 min before or 24 h after the injury could partially inhibit neuronal loss, and improve the survival of neurons in the CA1 region. Conclusion These data suggest that endogenous TRH expressed transiently in the dentate gyrus of the hippocampus may play an important role in the survival of neurons during the early stage of ischemia/reperfusion injury and that delayed application of TRH still produced neuroprotection. This delayed application of TRH has a promising therapeutic significance for clinical situations.