TY - JOUR T1 - Postnatal Development of the Hyperpolarization-Activated Excitatory Current <em>I</em><sub>h</sub> in Mouse Hippocampal Pyramidal Neurons JF - The Journal of Neuroscience JO - J. Neurosci. SP - 8992 LP - 9004 DO - 10.1523/JNEUROSCI.22-20-08992.2002 VL - 22 IS - 20 AU - Dmitry V. Vasilyev AU - Michael E. Barish Y1 - 2002/10/15 UR - http://www.jneurosci.org/content/22/20/8992.abstract N2 - The hyperpolarization-activated excitatory currentIh shapes rhythmic firing and other components of excitability in differentiating neurons, and may thus influence activity-dependent CNS development. We therefore studied developmental changes in Ih and underlying hyperpolarization-activated cyclic nucleotide-gated (HCN) channel subunits in pyramidal neurons of neonatal mouse hippocampus using electrophysiological and immunofluorescence approaches.Ih conductance (at −80 mV) tripled in CA3 neurons and quintupled in CA1 neurons between postnatal day 1 (P1) and P20; parallel changes in membrane area resulted in current density maxima at P5 in CA3 and P10 in CA1. Concurrently,Ih activation times fell sevenfold in CA3 and 10-fold in CA1. A computational model indicates that a decrease inIh activation time will increase the rhythmic firing rate. Two mechanisms contributed to more rapidIh activation at P20 in CA3 and CA1 neurons: a fall in the intrinsic time constants of two kinetic components, τfast and τslow, to 35–40% (at −90 mV) of their P1 values, and a preferential increase in fast component amplitude and contribution to Ih(from ∼35% to ∼74% of total). HCN1, HCN2, and HCN4 immunoreactivities showed independent temporal and spatial developmental patterns. HCN1 immunoreactivity was low at P1 and P5 and increased by P20. HCN2 immunoreactivity was detected at P1 and increased steadily up to P20. HCN4 immunoreactivity was initially low and showed a small increase by P20. We suggest that developmental increases in Ih amplitude and activation rate reflect changes in the number and underlying structure ofIh channels, and thatIh maturation may shape rhythmic activity important for hippocampal circuit maturation. ER -