Differences in the cellular distributions of two microtubule-associated proteins, MAP1 and MAP2, in rat brain.

The distribution of microtubule-associated proteins (MAPs) 1 and 2 in rat brain was studied using monoclonal antibodies. Immunochemical staining showed that both MAP1 and MAP2 are present only in neurons and both are highly concentrated in dendrites compared to axons. Otherwise, they differed in distribution in various ways. MAP1 was present at low levels in axons, whereas MAP2 was never detectable in axons with either of two different fixation methods used. In the cerebellum the two MAPs differed in relative concentration in various classes on neurons. Thus, anti-MAP1 staining was strong in Purkinje cells but very faint in granule cells, whereas anti-MAP2 staining was strong in both. There were also distributional differences within the same cell. Thus, in Purkinje cells, anti-MAP1 staining is strong in the cell body, initial axon segment and throughout the dendritic tree, but anti-MAP2 staining is present only in dendrites beyond the initial proximal portion. These results suggest that microtubules with different molecular compositions are present in the cerebellum where they are distributed differently between cells as well as within the same cell.