Giant Aplysia neuron R2 has distal dendrites: evidence for protein sorting and a second spike initiation site

Abstract

Because of its anatomy, the neuron R2 of Aplysia has been used to study how proteins are distributed to their appropriate destinations within the cell. The R2 cell body resides in the abdominal ganglion, while its axons terminate on glands in the skin. Using intracellular injection of HRP and intraxonal recordings, we found that R2 has a dendritic (receptive) arborization in the pleural ganglion. The structure of these dendrites was examined after injecting the soma with 3H-L-fucose, thereby labeling glycoproteins that are transported to all regions of the cell. Light- and electron-microscope autoradiography show that the openings to the dendrites are not on the periphery, but are suspended inside the axon by glial cell infoldings. All of the organelles seen in the axon are found in the dendrites, including 2 types of vesicles. Neither the axon nor the dendrites contain ribosomes. Thus, R2 has 3 functionally distinct regions--cell body, dendrites, presynaptic terminals--that are separated from each other by at least 4 cm. This implies that pre- and postsynaptic proteins made in the cell body are transported along the axon to the pleural ganglion, where they are sorted. To investigate this idea, we exposed the abdominal ganglion to 35S-methionine to label R2–s proteins. Analyses by SDS-PAGE of the rapidly transported labeled proteins from R2 consistently showed a 78 kDa band that accumulated in the pleural ganglion and did not move into the peripheral nerves. This then is a putative dendritic constituent.

Do different neurons age differently? Direct genome-wide analysis of aging in single identified cholinergic neurons

“…These motoneurons control mucus release from body surfaces (Rayport et al, 1983 ; Ambron et al, 1988 ). We have cloned choline acetyltransferase ChAT from Aplysia (AY163563, Table 1 ) and confirmed its specific expression in these cells (not shown).…”

Subcellular Analysis of d-Aspartate

“…R2 is an identified giant cholinergic neuron (Figure ) localized on the right dorsolateral margin of the abdominal ganglion of Aplysia; it has a major process that extends all the way to the pleural ganglion and other distal regions. − Figure C is a photomicrograph of an R2 neuronal soma separated from its neurite. The neurite was further divided into two sections, and each section was derivatized and analyzed separately.…”