Fig. 14.

Monosynaptic pretectal input onto preganglionic motoneurons. a An example of a very electron-dense, anterogradely labeled (star) pretectal terminal (At1D*) synapsing (arrowhead) on an unlabeled dendrite. b A retrogradely labeled (asterisk) preganglionic motoneuron dendrite is shown in cross section. Three terminal profiles lie adjacent to it. Two are unlabeled (At1 and At1D). A third, labeled profile is enclosed in a box and shown at higher magnification (d). It contains numerous clear spherical vesicles and a few dense-core vesicles (arrows), so it is classified at At1D. Another example with pre- and postsynaptic labeling is shown (c). The heavily labeled preganglionic motoneuron soma and proximal dendrite shown at low magnification (f) is contacted by an anterogradely labeled terminal. The boxed area containing this terminal is shown at higher magnification (e). Reaction product produces an electron-dense coat around the synaptic vesicles. This profile is classified as At1D. It makes asymmetric synaptic contacts (arrowheads) with both the dendritic shaft and a small spine. Scale bar in d = a, c