Action of serotonin on the hyperpolarization-activated cation current (Ih) in rat CA1 hippocampal neurons

Eur J Neurosci. 1999 Sep;11(9):3093-100. doi: 10.1046/j.1460-9568.1999.00728.x.


We studied the effects of serotonin (5-HT) on hippocampal CA1 pyramidal neurons. In current-clamp mode, 5-HT induced a hyperpolarization and reduction of excitability due to the opening of inward rectifier K+ channels, followed by a late depolarization and partial restoration of excitability. These two components could be dissociated, as in the presence of BaCl2 to block K+ channels, 5-HT induced a depolarization accompanied by a reduction of membrane resistance, whereas in the presence of ZD 7288 [4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride], a selective blocker of the hyperpolarization-activated cation current (Ih), 5-HT only hyperpolarized neurons. We then studied the action of 5-HT on Ih in voltage-clamp conditions. 5-HT increased Ih at -90 mV by 29.1 +/- 2.9% and decreased the time constant of activation by 20.1 +/- 1.7% (n = 16), suggesting a shift in the voltage dependence of the current towards more positive potentials; however, the fully activated current measured at -140 mV also increased (by 14.1 +/- 1.7%, n = 14); this increase was blocked by ZD 7288, implying an effect of 5-HT on the maximal conductance of Ih. Both the shift of activation curve and the increase in maximal conductance were confirmed by data obtained with ramp protocols. Perfusion with the membrane-permeable analogue of cAMP, 8-bromoadenosine 3'5'-cyclic monophosphate (8-Br-cAMP), increased Ih both at -90 and -140 mV, although the changes induced were smaller than those due to 5-HT. Our data indicate that 5-HT modulates Ih by shifting its activation curve to more positive voltages and by increasing its maximal conductance, and that this action is likely to contribute to the 5-HT modulation of excitability of CA1 cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 8-Bromo Cyclic Adenosine Monophosphate / pharmacology
  • Animals
  • Electrophysiology
  • Hippocampus / cytology
  • Hippocampus / drug effects
  • Hippocampus / physiology*
  • In Vitro Techniques
  • Ion Channels / agonists
  • Ion Channels / drug effects
  • Ion Channels / physiology*
  • Male
  • Membrane Potentials / drug effects
  • Patch-Clamp Techniques
  • Potassium Channels / drug effects
  • Potassium Channels / physiology
  • Pyramidal Cells / cytology
  • Pyramidal Cells / drug effects
  • Pyramidal Cells / physiology*
  • Rats
  • Rats, Wistar
  • Second Messenger Systems / drug effects
  • Second Messenger Systems / physiology
  • Serotonin / pharmacology*


  • Ion Channels
  • Potassium Channels
  • 8-Bromo Cyclic Adenosine Monophosphate
  • Serotonin

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