Figure 5.

Putative Chorda Tympani Nerve Synaptic Sites. Contacts between the chorda tympani (CT) nerve (red in panel A and magenta panels B–F) and an rNTS-PBN projection neuron dendrite (green) can be visualized with high-magnification confocal microscopy (same neuron as in Figure 4). (A) Lower magnification reveals the location of the apposition on the dendritic tree (dashed box represents the area of interest for the other panels). This contact occurs after the first branch point on the proximal dendritic tree. (B) The dendritic segment and surrounding afferent label are visualized in a 3-dimensional rendering and rotated to reveal the overlapping fluorophores. The overlapping region of the two fluorophores can be seen as a yellow band at the contact zone. Note that there is also a contact visible between a chorda tympani and glossopharyngeal axon (blue). Interestingly, axo-axonal innervation has been noted for both nerves in past EM studies, but the post-synaptic identity has remained undetermined (Whitehead, 1986; May et al., 2007). (C–F) Other examples of 3-D renderings of CT putative synaptic sites (white arrows) onto ascending projection neuron dendrites display the same characteristic yellow contact band. Touching processes without displaying fluorophore overlap (black arrows) were not considered to be putative synaptic sites, as due to fluorescent spread the processes were likely separated by at least 150 nm (the resolution of the images). Note that in C–F, IX processes were removed to aid in visualization of CT putative synaptic sites. In panels B–F red channels were pseudocolored magenta to aid in visualization. Scale in A = 10 μm, Scale in B–F = 3 μm. R = Rostral, L = Lateral.