MAP2 expression and neuritic outgrowth and branching are coregulated through region-specific neuro-astroglial interactions.

Embryonic neurons from the rat striatum and mesencephalon were plated on mesencephalic or striatal astrocytes in 4 possible combinations. It was found that specific traits are expressed by the neurons when they are grown on homotopic astrocytes (neurons and astrocytes from the same region). These traits are the following: 1. The number of cells stained with an antibody raised against the microtubule-associated protein 2 (MAP2) is higher in homotopic than in heterotopic cocultures. This is true for both mesencephalic and striatal neurons. 2. In homotopic conditions, there is an increase in the number of cells having more primary neurites and branching points. This effect is observed for both neuronal populations but is more pronounced in mesencephalic neurons. 3. The intensity of MAP2 staining was correlated with the branching ability of the neurons. First, on comparing MAP2-positive and MAP2-negative cells, it was found that, in any combination (homotopic and heterotopic cocultures), the number of primary neurites and branching points was much higher in MAP2-positive cells. In fact, almost no branching activity was found in MAP2-negative neurons. Second, within the MAP2-positive neuronal population, the higher number of branching points observed under homotopic neuro-astroglial conditions was mostly due to the neuritic compartment, which was strongly and homogeneously stained with the anti-MAP2 antibody. These observations strongly suggest that the astrocytic environment regulates the synthesis and/or intracellular distribution of MAP2, as well as the morphology of the neurons, and that this regulation is region specific.