Table 2.
Dendritic, axonal, and glial invaginating projections: major ones mentioned in this review, classified by animal groups
| Animal group | Dendritic projection (“Synapse/ Neuronal Invaginating Projections in the Simplest Animals”, “Spine/ Dendrite-Derived Invaginating Projections” sections) |
Axonal projection (“Synapse/Neuronal Invaginating Projections in the Simplest Animals”, “Presynaptic Terminal/Axon- Derived Invaginating Projections” sections) |
Glial projection (“Synapse/Neuronal Invaginating Projections in the Simplest Animals”, “Glia-Derived Invaginating Projections” sections) |
|---|---|---|---|
| Porifera (sponges) |
Possibly (spine-like process on neuron-like cell into another cell) |
Possibly (terminal-like process on neuron-like cell into another cell) |
|
| Cnidaria (jellyfish) |
Spine into terminal Nematocyte process into axon |
Axon into nematocyte | |
| Platyhelminthes (flatworms) |
Presumptive postsynaptic process into terminal |
Terminal into presumptive postsynaptic process |
Trophospongium [also trophic prolongations of parenchymal cells (not glia)] |
| Nematoda | Amphid microvilli into sheath cell | ||
| Annelida | Trophospongium | ||
| Mollusca (snails, squid, octopi, chitons) |
Spines and tunnel fibers into terminal Spinules into chiton sensory hair supporting cell |
Axon–axon spinules Axon–axon projections associated with the squid eye |
Trophospongium |
| Crustacea (crayfish) |
Trophospongium | ||
| Arachnida (scorpion) |
Between two nerve fibers or a nerve fiber and a terminal in the cardiac ganglion |
||
| Insecta | Axon–axon projections associated with fly, bee, butterfly eyes Invaginating axon terminals in larval NMJ |
Trophospongium Capitate projections (fly eye) Gnarls (fly eye) |
|
| Fish | Lamprey-presumptive postsynaptic invaginations into terminal Fish retinal spinules |
PSIs in synapses with electrical organ of torpedo ray Spinule of presynaptic membrane into postsynaptic process in electromotor n. of gymnotid fish |
|
| Amphibia (frogs) |
Filopodia into terminals | PSIs in NMJ | Filopodia into terminals Schwann cell processes at frog NMJ |
| Reptiles (lizard) | Spinule of presynaptic membrane into postsynaptic process in oculomotor nucleus |
||
| Birds | Axon spinules in Purkinje dendrites | ||
| Mammals (mouse, rat, cat, primate, etc.) |
Spines, filopodia, and spinules into terminals (including regular and giant mossy terminals) |
PSIs on the sides of synaptic terminals PSI-like projections of GABAergic terminals into the postsynaptic neuron Axon spinules in Purkinje dendrites Spinules in dendritic processes at mossy fibers Invaginating terminals into spines |
Oligodendrocyte processes into spinal motor axons Schwann cell processes into spinal ganglion neurons |