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. 2016 Feb 3;89(3):645–657. doi: 10.1016/j.neuron.2016.01.008

Figure 4.

Figure 4

Nucleocortical Projection Imposes Unique Closed-Loop Circuit with Internal Feedback Properties

(A) Patch-clamp recording of an eYFP labeled MF rosette visualized by overlaying epifluorescence and DIC images.

(B) MF rosettes show current rectification, hyperpolarization sag (asterisk), and action potential firing (arrowhead) in response to steady-state current injections.

(C) Cell attached recording from a spontaneously firing nucleocortical MF.

(D) Repetitive current pulses drive MF rosette to fire robustly at 500 Hz with little adaptation in the action potential amplitudes.

(E) Optogenetic activation of a nucleocortical MF. The individual action potentials can be elicited with high temporal precision by a train of light pulses (1 ms 470 nm light at 30 Hz) in both cell attached and current-clamp modes.

(F) Nucleocortical MF (green) innervates granule cell dendrite (GrC, red, arrow).

(G) Whole cell recording of GrC-EPSC (left) and loose cell attached recording of GrC action potential firing (right) in response to 1 ms photo activation of NC-MF. We found a high success rate of inducing action potential firing in the GrC (81.7% ± 6.0% and n = 10).

(H) Nucleocortical MF (green) innervates Golgi cell dendrite (GoC, red, arrow).

(I) Whole cell recording of GoC-EPSC (left) and loose cell attached recording of GoC action potential firing (right) in response to 1 ms photo activation of NC-MF. We found a high success rate of inducing action potential firing in the GoC (83.8% ± 8.3% and n = 5).

(J) Experimental setup of identifying I/E ratio of PC responses. The GrC axon excites (+) the MLIs and PCs and the MLI in turn inhibits (−) the PCs. The ChR2 expressing nucleocortical MFs (green) are selectively activated by optogenetic stimulation, while a bundle of MFs with heterogeneous sites of origin (green and gray) are activated by electrical stimulation.

(K) Whole cell voltage clamp recordings of EPSC and IPSC elicited by optogenetic or electrical stimulation. The EPSC and IPSC components were isolated by clamping the PC at −75 mV and 0 mV, respectively. The higher IPSC to EPSC ratio (I/E ratio) from nucleocortical MFs circuits was found in PCs, compared with electrical stimulation (top). The optogenetic activation induces longer suppression of action potential firing compared with electrical stimulation (bottom). The data show mean ± SE.