Synaptic transmission and plasticity in an active cortical network.
BACKGROUND
The cerebral cortex is permanently active during both awake and sleep states. This ongoing cortical activity has an impact on synaptic transmission and short-term plasticity. An activity pattern generated by the cortical network is a slow rhythmic activity that alternates up (active) and down (silent) states, a pattern occurring during slow wave sleep, anesthesia and even in vitro. Here we have studied 1) how network activity affects short term synaptic plasticity and, 2) how synaptic transmission varies in up versus down states.


RESULTS
Intracellular recordings obtained from cortex in vitro and in vivo were used to record synaptic potentials, while presynaptic activation was achieved either with electrical or natural stimulation. Repetitive activation of layer 4 to layer 2/3 synaptic connections from ferret visual cortex slices displayed synaptic augmentation that was larger and longer lasting in active than in silent slices. Paired-pulse facilitation was also significantly larger in an active network and it persisted for longer intervals (up to 200 ms) than in silent slices. Intracortical synaptic potentials occurring during up states in vitro increased their amplitude while paired-pulse facilitation disappeared. Both intracortical and thalamocortical synaptic potentials were also significantly larger in up than in down states in the cat visual cortex in vivo. These enhanced synaptic potentials did not further facilitate when pairs of stimuli were given, thus paired-pulse facilitation during up states in vivo was virtually absent. Visually induced synaptic responses displayed larger amplitudes when occurring during up versus down states. This was further tested in rat barrel cortex, where a sensory activated synaptic potential was also larger in up states.


CONCLUSIONS
These results imply that synaptic transmission in an active cortical network is more secure and efficient due to larger amplitude of synaptic potentials and lesser short term plasticity.
Instituto de Neurociencias de Alicante, Universidad Miguel Hernandez-CSIC, San Juan de Alicante, Spain.
Ramon
R
Reig
Maria V
MV
Sanchez-Vives
D000758:Anesthesia; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D002415:Cats / Q000502:physiology*; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D005289:Ferrets / Q000502:physiology*; D008297:Male; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D009473:Neuronal Plasticity / Q000502:physiology*; D009949:Orientation; D012890:Sleep / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D013788:Thalamus / Q000187:drug effects / Q000502:physiology; D014673:Vecuronium Bromide / Q000494:pharmacology; D014793:Visual Cortex / Q000187:drug effects / Q000502:physiology*
D009467:Neuromuscular Depolarizing Agents; D014673:Vecuronium Bromide