Intracortical excitation of spiny neurons in layer 4 of cat striate cortex in vitro.
Recordings were made from pairs of neurons in cat striate visual cortex in vitro to study the AMPA-channel-mediated components of intracortical excitatory synaptic connections between layer 4 spiny neurons and between layer 6 and layer 4 spiny neurons. Forty-six of the 72 cells recorded were identified morphologically. They consisted of spiny stellate and pyramidal cells in layer 4, and pyramidal cells in layer 6. Connections between layer 4 excitatory cells involve excitatory postsynaptic potentials (EPSPs) averaging 949 microV, with an average coefficient of variation of 0.21 (n = 30). The synapses operate at very high release probabilities (0.69-0.98). With repetitive stimulation these EPSPs show varying degrees of depression, largely mediated by presynaptic changes in release probability. Four pairs of layer 4 cells were reciprocally connected. The connections from layer 6 to layer 4 involve smaller, more variable EPSPs, with an average amplitude of 214 microV, and average coefficient of variation 0.72 (n = 7). These synapses operate at moderately high release probabilities (0.37-0.56). They show facilitation with repetitive stimulation, mediated largely by presynaptic changes in release probability. One excitatory connection from a layer 4 neuron to a layer 6 pyramidal cell was also detected. Thus, layer 4 spiny neurons receive effective excitation from two intracortical sources that have different synaptic dynamics and are likely to contribute significantly to the temporal properties of these cells in vivo.
Tarczy-Hornoch
K
K
University Laboratory of Physiology, Oxford, UK.
Martin
K A
KA
Stratford
K J
KJ
Jack
J J
JJ
D000818:Animals; D002415:Cats; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005829:Geniculate Bodies / Q000502:physiology; D017966:Pyramidal Cells / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*