Low-frequency depression of synaptic responses recorded from rat visual cortex.
To characterize the low-frequency depression (LFD) of synaptic transmission in the visual cortex, we recorded field potentials and minimal excitatory postsynaptic potentials (EPSPs) from layer II/III following intracortical stimulation at various frequencies in cortical slices of rats. Field potentials were stable at 0.017 Hz, but showed an amplitude depression at 0.033-0.1 Hz at stimulus intensity of 1.5 times the threshold for induction of the postsynaptic component and at 0.1-0.2 Hz at intensity of 1.2 times the threshold. The LFD was input-specific and its magnitude correlated with the stimulus frequency. An interruption of stimulation for 15 min yielded a nearly complete recovery from LFD. Minimal EPSPs tested at 0.1-1.7 Hz often showed LFD with similar features. However, some inputs were stable or even facilitated during repeated stimulation. At 0.1 and 0.2 Hz, >50% of inputs were stable, whereas 10% and 25% were depressed, respectively. At 0.5 and 1.7 Hz, LFD was observed in >60% and 80% of inputs, respectively. The magnitude of LFD strongly varied across inputs. In 3 of the 41 inputs analyzed, LFD was so strong that these inputs became virtually silent. Occurrence of responses to the second pulse in the paired-pulse paradigm when the first response was absent and recovery of depressed EPSPs following stimulus interruption or shift to a lower frequency suggest that these synapses were presynaptically silent due to a lowered probability of transmitter release. Altogether, the results indicate that testing intervals of <10 or even < or =30 s cannot be regarded as completely neutral. At the single-cell level, frequency-dependent changes were strongly heterogeneous across different inputs. LFD and its spontaneous recovery may underlie the previously described "post-rest" potentiation, and should be taken into account when considering information processing in cortical networks.
Akaneya
Y
Y
CREST Program, Japan Science and Technology Corporation, Division of Neurophysiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita 565-0871, Japan.
Altinbaev
R Sh
RSh
Bayazitov
I T
IT
Kinoshita
S
S
Voronin
L L
LL
Tsumoto
T
T
D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D066298:In Vitro Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*