The morphology of identified neurons in the abdominal ganglion of Aplysia californica.

The morphology of identified neurons and of one multiaction interneuron (L10) of the abdominal ganglion of Aplysia has been studied using cobalt chloride, injected intracellularly. Cells with little synaptic input, R3-R14, had a relatively poorly developed dendritic tree, whereas the dendrite tree of cells L7 and L10, with extensive synaptic input, was highly complex. Cells L1-L6 and the RB cell cluster were found to have intermediate complexity of synaptic inputs and dendritic morphology. Within cell clusters, individual cells were often morphologically distinct. Identified cells have both invariant and variant axonal branches. Variant axons often project down other than their customary nerve trunks or are supernumerary. Three features of neuropil architecture were encountered. (1) When cells from the same cluster send their axons down the same nerve the axons often run in fascicles. (2) Although an identified cell's dendritic geometry varies from preparation to preparation, its dendrites always occupy approximately the same position in the neuropil. (3) The postsynaptic follower cells of L10 send their main axons through the axonal arborization of L10.