Excitatory inputs to layer V pyramidal cells of rat primary visual cortex revealed by acetylcholine activation.
Cells in layers II-III or VI were activated by microdrop application of acetylcholine (ACh), while monitoring the intracellular response of layer V pyramidal cells. This enabled the tracing of functional connections between the cells of layers II-III or VI with those of layer V. ACh activation of layer II-III or VI cells resulted in a small depolarization of these cells, accompanied by a burst of excitatory postsynaptic potentials (EPSPs) from layer V pyramidal cells. These effects of ACh were blocked by tetrodotoxin (TTX), suggesting the involvement of action potentials in their production. The input resistance of layer V pyramidal cells during and after the EPSP burst was not significantly different from control values, further suggesting an indirect effect of ACh on layer V pyramidal cells. Isolation of the supragranular layer, by horizontal cutting, did not prevent the EPSP burst evoked by ACh application to the lower layer VI, suggesting a direct input from layer VI to layer V pyramidal cells. ACh applied near pyramidal cells in layers II-III, V or VI caused transient hyperpolarization associated with a decrease in input resistance followed by a large depolarization, an increase in input resistance, and action potential discharges. The ACh-mediated hyperpolarization and the train of action potentials of layer II-III pyramidal cells were blocked by TTX. Thus the ACh-activated cells in layers II-III and VI make an excitatory synaptic contact with layer V pyramidal cells, producing the EPSP burst observed in layer V.
Kenan-Vaknin
G
G
Neurobiology Department, Weizmann Institute of Science, Rehovot, Israel.
Malach
R
R
Segal
M
M
D000109:Acetylcholine / Q000502:physiology*; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D005071:Evoked Potentials / Q000502:physiology*; D066298:In Vitro Techniques; D009434:Neural Pathways / Q000502:physiology; D051381:Rats; D014793:Visual Cortex / Q000166:cytology / Q000502:physiology*
D000109:Acetylcholine