Voltage-sensitive dye imaging demonstrates an enhancing effect of corticotropin-releasing hormone on neuronal activity propagation through the hippocampal formation

Corticotropin-releasing hormone (CRH) is thought to play an important role in the pathophysiology of stress-related psychiatric disorders, such as major depressive disorder (MDD) and post-traumatic stress disorder (PTSD). However, knowledge about the actions of CRH at the neuronal network level is only scarce. Here, we examined whether CRH affects neuronal activity propagation through the hippocampal formation (HF), a brain region which is likely to be involved in MDD and PTSD. For this purpose, we applied voltage-sensitive dye imaging (VSDI) to specifically cut hippocampal brain slices obtained from adult mice. This approach allowed us to investigate evoked neuronal activity propagation through the HF with micrometer spatial and millisecond temporal resolution. Application of CRH (50 nM) to slices increased neuronal activity propagation from the dentate gyrus (DG) to the CA1 subfield. This effect of CRH was caused by amplification of neuronal excitation on its passage through the HF and absent in mice lacking the CRH receptor type 1 (CRHR1). In conclusion, our study presents a VSDI assay for the investigation of neuronal activity propagation through the HF and demonstrates that CRH, via CRHR1, enhances this activity propagation. This effect of CRH might contribute to alterations of memory formation seen in MDD and PTSD. Moreover, it could influence hippocampal regulation of hypothalamic-pituitary-adrenal axis (HPA-axis) activity.