Reach training selectively alters dendritic branching in subpopulations of layer II-III pyramids in rat motor-somatosensory forelimb cortex.

We have previously reported that training rats to reach for bits of cookies resulted in an increase in dendritic length and branching complexity in the apical branches of layer V pyramidal cells within the motor-sensory forelimb cortex. In this paper, we describe the effects of reach training upon the basilar branches of two subpopulations of pyramidal cells in layers II and III. The two subpopulations of pyramids are distinguishable by morphological characteristics and location within layers II and III. The basilar dendrites of one subtype, the forked apical pyramid, are selectively altered in size and complexity during reach training; whereas the other subtype, the single shaft apical cells, do not measurably change during training. Based upon these findings, we postulate that these cells may have different roles in governing the reaching behavior.