Structural variation and interactions among astrocytes of the rostral migratory stream and olfactory bulb: II. Golgi and electron microscopic study of the adult rat

- Amphomorphic cells of the rostral migratory stream have neuron-astrocyte phenotype.
- Amphomorphic cell corresponds to the B1-cell.
- Processes of amphomorphic cell bear spatial distribution.
- Processes of adjacent amphomorphic cells structure gap junctions.
- Amphomorphic- and A1-cells receive synaptic inputs.

Cytological characteristics of a cell sharing structure of both an astrocyte and a neuron, previously termed amphomorphic cell (AC), were defined here in adult rat rostral migratory stream (RMS). The AC perikaryon corresponds to that of the B1 cell of the adult mouse subventricular zone (SVZ)-RMS. The AC and its processes are confined to the RMS. Each AC originates four sets of processes that overlap with those from its homologues and adjacent neural and stromal elements. ACs interact between them via reciprocal sets of processes: those directed caudally bear spheroidal vesicles (SVP) and form gap junctions with pleomorphic vesicles (PVs) associated with the anterior set from the adjacent AC. Large asymmetric synapses, a set of them arising from the anterior olfactory nucleus, converge on each SV. The interlacing processes of the AC, together with a set of perikaryal out-growths form the glial cuff surrounding migrating neuroblasts described earlier. Small asymmetrical and symmetrical synapses terminate in subsets of differentiated A-cells, termed here A1, in the bulbar part of the RMS. Both AC- and A1-cells form electrical synapses between them and with their homologues. The strategic, wide-spread distribution between the neuropil and blood vessels of the AC, its processes, and migrating neuroblasts, suggests that the AC might mediate between both endogenous inductors and neurotransmitters, influencing the adult-born neurons it had previously originated.

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