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.