Low Rheobase cells are excitatory
In order to investigate whether LR neurons were excitatory or
inhibitory, we next conducted whole-cell recordings coupled with
optogenetic activation of channelrhodopsin in CaMKII+ cells. CaMKII-Cre
x Ai32 mice (Jackson Laboratories 005359 and 024109 respectively,
crossed in house) were used for these experiments. In these mice, cells
containing the excitatory marker CaMKII express Cre, thus allowing for
expression of a cre-dependent channelrhodopsin (ChR2) exclusively in
CaMKII neurons (Figure 5A). We then used 1 ms light pulses in a 10 Hz
train to test ChR2 responses in the patched neurons. Of 20 LR cells
tested, 85% (17/20) directly responded to the optogenetic light pulse,
indicating that they were directly expressing ChR2 and thus were CaMKII
positive (Figure 5B&C). This suggested that they may be excitatory
neurons.