The goal of this study was to characterize the effects of corticotrophin-releasing factor (CRF) on rat paraventricular nucleus (PVN) putative parvocellular neurons using whole-cell patch-clamp recordings and single-cell reverse transcription-multiplex polymerase chain reaction (single-cell RT-mPCR) techniques. Under current-clamp, CRF (10 nM to 600 nM) increased the neuronal basal firing rate and depolarized neurons in a dose-dependent manner. CRF-induced depolarization was unaffected by co-perfusion with tetrodotoxin (TTX), 6-cyano-7-nitroquinoxaline-2 3-dione (CNQX), and bicuculline but was completely inhibited by ZD7288. Under voltage-clamp, 300 nM CRF significantly increased the hyperpolarization-activated cation current (I_H) in a voltage-dependent manner, shifted the I_H conductance-voltage relationship (V_1/2) towards depolarization by approximately 7.8 mV, and enhanced the I_H kinetics without changing the slope constant (k). Extracellular application of ZD7288 completely blocked I_H and the CRF-induced increase in I_H. Further, CRF-induced effects were completely blocked by extracellular application of 1 µM -helical CRF-(9-14) (-hCRF), a non-selective CRF receptor antagonist, but were not affected by extracellular application of antisauvagine-30, a selective CRF-receptor 2 antagonist. Single-cell RT-mPCR analysis showed that these neurons co-expressed CRF receptor 1 mRNA and CRF receptor 2 mRNA. Furthermore, CRF-sensitive neurons co-expressed HCN1 channel mRNA, HCN2 channel mRNA, and HCN3 channel mRNA but not HCN4 channel mRNA. These results suggest that CRF modulates the subpopulation of PVN parvocellular neuronal function by CRF-receptor 1-mediated potentiation of HCN ion channel activity.