ChR2- mCherry expression in cholinergic MS/DBB projection neurons and light-induced IPSCs in CA1 pyramidal cells.

<p>A) Tissue section through the MS/DBB showing ChR2-mCherry, immunostaining for ChAT, and the merged image. B) Section of the hippocampus showing ChR2-mCherry expression in axons. sr = <i>s. radiatum</i>; sp = <i>s. pyramidale</i>; so = <i>s. oriens</i>. C) Schematic drawing of the recording arrangement. D1) Continuous recording from a CA1 pyramidal cell in a ChR2-expressing slice. Repeated 10-s trains of 5-ms blue light flashes repeated at 2-min intervals (squares) elicited bursts of L-IPSCs (downward deflections). A single light pulse (downward triangle) had no obvious effect. The small upward deflections (truncated in the illustration) are capacitive transients produced by conductance pulses given to the cell. D2) Two trials (1 and 3 in D1) in the absence of iGluR antagonists were aligned at the time of the light train and overlapped. D3) Two trials (4 and 5 in D1) in the presence of iGluR antagonists, 5 µM NBQX plus 5 µM CGP37849, were aligned and overlapped. An expanded portion of the trace (below) reveals the occurrence of rhythmic L-IPSCs after the end of the light train. (The traces in D2 and D3 are shown at a larger amplitude scale than in D1, and the largest IPSCs are cut off.) The autocorrelation function (D4, left) and power spectrum (D4, right) illustrate the regularity (peak frequency ∼3 Hz) of L-IPSC activity from this cell.