Figure 5. LR cells directly respond to ChR2 in CaMKII-Cre x Ai32 mice, indicating expression of CaMKII in this cell type. A. Schematic showing the experimental set-up. Top panel, Mouse indicating the genetic cross of CaMKII-Cre (Jackson Laboratories, 005359) and Ai32 (Jackson Laboratories, 024109) on a C57Bl6 background (crossed in house). Bottom panel, Schematic of the experimental set up. 10 Hz LED pulses were delivered to layers 2 and 3 of the RSG while the responses of whole-cell patched neurons were recorded. B. Representative responses of LR cell to the 10 Hz opto LED pulses. Left traces show all 10 opto LED pulses (1ms each) over the span of one second and the patched LR cell spiking one to two times in response to each 1ms LED pulse. Right trace is a zoomed in view of the first LED pulse and respective spike from the LR cell. The neuron response to the light almost instantaneously, indicating a direct response by ChR2. C. Bar graph representing the percentage of LR cells tested that directly expressed ChR2 (85%, 17/20).
We then confirmed the excitatory nature of LR cells using paired recordings of layer 2/3 RSG neurons. Although connections were rare, when LR cells were connected to neighboring cells, they led to excitatory post-synaptic potentials (EPSPs) in their paired FS cell (Figure 6D). This is the first demonstration that LR cells in RSG are indeed excitatory neurons.