Serotoninergic fine-tuning of the excitation-inhibition balance in rat visual cortical networks

Cereb Cortex. 2010 Feb;20(2):456-67. doi: 10.1093/cercor/bhp114. Epub 2009 Jun 11.


Fundamental brain functions depend on a balance between excitation (E) and inhibition (I) that is highly adjusted to a 20-80% set point in layer 5 pyramidal neurons (L5PNs) of rat visual cortex. Dysregulations of both the E-I balance and the serotonergic system in neocortical networks lead to serious neuronal diseases including depression, schizophrenia, and epilepsy. However, no link between the activation of neuronal 5-hydroxytryptamine receptors (5-HTRs) and the cortical E-I balance has yet been reported. Here we used a combination of patch-clamp recordings of composite stimulus-locked responses in L5PN following local electrical stimulations in either layer 2/3 or 6, simultaneous measurement of excitatory and inhibitory conductance dynamics, together with selective pharmacological targeting and single-cell reverse transcriptase-polymerase chain reaction. We show that cortical serotonin shifts the E-I balance in favor of more E and we reveal fine and differential modulations of the E-I balance between 5-HTR subtypes, in relation to whether layer 2/3 or 6 was stimulated and in concordance with the specific expression pattern of these subtypes in pyramidal cells and deep interneurons. This first evidence for the functional segregation of 5-HTR subtypes sheds new light on their coherent functioning in polysynaptic sensory circuits.

MeSH terms

  • Animals
  • Axons / metabolism*
  • Axons / ultrastructure
  • Electric Stimulation
  • Electrophysiology
  • Excitatory Postsynaptic Potentials / physiology*
  • Inhibitory Postsynaptic Potentials / physiology*
  • Interneurons / cytology
  • Interneurons / metabolism
  • Nerve Net / cytology
  • Nerve Net / metabolism*
  • Organ Culture Techniques
  • Patch-Clamp Techniques
  • Pyramidal Cells / cytology
  • Pyramidal Cells / metabolism
  • RNA, Messenger / analysis
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Wistar
  • Receptors, Serotonin / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Serotonin / metabolism*
  • Synaptic Transmission / physiology
  • Visual Cortex / cytology
  • Visual Cortex / metabolism*
  • Visual Perception / physiology


  • RNA, Messenger
  • Receptors, Serotonin
  • Serotonin