Figure 9.

Functional synaptic output of small axonless neurons. A, Lentivirus-ChR2-YFP injection and recording protocol. B, A YFP-expressing small axonless neuron (left) was recorded in current-clamp and submitted either to somatic depolarization via the patch-clamp pipette (middle) or blue light (right). Note the similar firing pattern in the two conditions. C, A cell in the vicinity of a YFP-expressing small axonless neuron was recorded first in current-clamp to obtain its firing pattern (left) and subsequently in voltage clamp while applying brief pulses of blue light (middle). Five superimposed postsynaptic currents in response to blue light are shown (average in red). Postsynaptic currents were abolished by application of GABAzine 10 μm (right, 5 traces and average), proving their GABAergic nature. D, Construct design for the GFP-IRES-tWGA/DsRed retroviral vector. E, E′, Transsynaptic labeling with WGA indicating synaptic connectivity. E, Confocal image of a GFP-positive small axonless (green) neuron 21 d after retrovirus injection in the SVZ at P4 showing WGA/RFP expression (red) in the soma. The boxed area is expanded on the right, including DAPI nuclear staining (blue) and orthogonal views showing colocalization of GFP and tWGA/DsRed. E′, Same as in E, 40 d after retrovirus injection. Clusters of tWGA/DsRed (red) are visible in the infected cell and also in the cell soma of neighboring cells, indicating transsynaptic transport. Right panels are magnifications of the boxed areas in E′, with DAPI nuclear staining (blue) and orthogonal views. Scale bars: E (overview and enlarged area, respectively), 20 and 10 μm. nuc., Nucleus; cyt, cytoplasm.