Mitral cells display a variety of spiking patterns, ranging from bursting to regular spiking, when observed in olfactory bulb slices (Angelo et al., 2011; Yu et al., 2015). The expression of Hyperpolarization-activated cationic current (Ih) is highly diverse among mitral cells (Angelo et al., 2011; Angelo et al., 2012). Previous studies conducted in vitro have indicated that the expression of Ih in mitral cells is associated with a regular spiking pattern and increased intrinsic excitability (Angelo et al., 2011; Burton et al., 2014) but do not provide any mechanistic explanation. Therefore, the precise role of Ih in mitral cell spiking remains unknown and has not been examined in vivo. To investigate this question, we conducted both in vitro and in vivo recordings of mitral cells using patch clamp on OB slices and sharp electrode intracellular recordings in young adult rats (P42-P70). Our results showed a similar distribution of Ih expression in both our in vivo and in vitro recordings. Furthermore, we discovered a positive correlation between Ih and spike afterhyperpolarization (AHP) in both in vitro and in vivo recordings. Therefore, the magnitude of Ih predicts the intra-burst spiking frequency of mitral cells recorded in vitro. However, the blockade of Ih by ZD7288 did not affect spike AHP charge. Consequently, although Ih seems to be a reliable predictor of mitral cell firing properties, the underlying mechanisms responsible for this phenomenon remain unclear. Experiments: We used both in vivo intracellular recordings and in vitro patch clamp recordings in order to investigate the potential effect of Ih on mitral cells firing.