Prenatal development of neural excitation in rat thalamocortical projections studied by optical recording

Neuroscience. 2002;115(4):1231-46. doi: 10.1016/s0306-4522(02)00418-9.


To elucidate the formation of early thalamocortical synapses we recorded optical images with voltage-sensitive dyes from the cerebral cortex of prenatal rats by selective thalamic stimulation of thalamocortical slice preparations. At embryonic day (E) 17, thalamic stimulation elicited excitation that rapidly propagated through the internal capsule to the cortex. These responses lasted less than 15 ms, and were not affected by the application of glutamate receptor antagonists, suggesting that they might reflect presynaptic fiber responses. At E18, long-lasting (more than 300 ms) responses appeared in the internal capsule and in subplate. By E19, long-lasting responses increased in the cortical subplate. By E21, shortly before birth, the deep cortical layers were also activated in addition to the subplate. These long-lasting responses seen in the internal capsule and subplate were blocked by the antagonist perfusion, but the first spike-like responses still remained. The laminar location of the responses was confirmed in the same slices by Nissl staining and subplate cells were labeled by birthdating with bromodeoxyuridine at E13. Our results demonstrate that there is a few days delay between the arrival of thalamocortical axons at the subplate at E16 and the appearance of functional thalamocortical synaptic transmission at E19. Since thalamocortical connections are already functional within the subplate and in the deep cortical plate at embryonic ages, prenatal thalamocortical synaptic connections could influence cortical circuit formation before birth.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Action Potentials / physiology*
  • Animals
  • Cell Differentiation / drug effects
  • Cell Differentiation / physiology*
  • Electric Stimulation
  • Electronic Data Processing
  • Excitatory Amino Acid Antagonists / pharmacology
  • Female
  • Fetus
  • Glutamic Acid / metabolism
  • Male
  • Neural Pathways / cytology
  • Neural Pathways / embryology*
  • Neural Pathways / physiology
  • Presynaptic Terminals / drug effects
  • Presynaptic Terminals / physiology*
  • Presynaptic Terminals / ultrastructure
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Glutamate / drug effects
  • Receptors, Glutamate / metabolism
  • Somatosensory Cortex / cytology
  • Somatosensory Cortex / embryology*
  • Somatosensory Cortex / physiology
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology*
  • Ventral Thalamic Nuclei / cytology
  • Ventral Thalamic Nuclei / embryology*
  • Ventral Thalamic Nuclei / physiology


  • Excitatory Amino Acid Antagonists
  • Receptors, Glutamate
  • Glutamic Acid