The organisation of dendritic bundles in the prelimbic cortex (area 32) of the rat.

Using an antibody against microtubule associated protein 2 (MAP-2; a specific marker for neuronal dendrites), this paper reports the structural organisation of pyramidal cell apical dendrites in the rat prelimbic (PL) cortex. In the coronal plane, MAP-2-immunoreactive apical dendrites of pyramidal neurons in layers 5, 3 and 2 were found bundled together as they ascended radially through the cortex. These bundles of dendrites dispersed in upper layer 2 to form apical dendritic tufts in layer 1. In tangential cross-section, the immunolabelled bundles were organised into a latticework of discrete clusters of differentially sized profiles. At the boundary between layers 3 and 5, clusters were composed of 26 +/- 8 dendritic profiles (group mean value +/- S.D., five animals), whereas clusters in layer 2 contained 55 +/- 15 profiles. The number of clusters per unit surface area was not significantly different throughout layers 5, 3 and 2 (760 +/- 75 per mm2) with the average centre-to-centre intercluster distance in these layers being 44.2 +/- 4.9 microns. The data indicate that apical dendritic bundles are a feature of the radial organisation of PL cortex. These structural subunits may subserve specific integrative functions in the PL area of the rat medial prefrontal cortex.