Morphological changes in pyramidal cells of mammalian neocortex associated with increased use

After long-term electrical stimulation of the brain, which presumably produced increased neuronal use, histological studies were made of neocortical neurons involved in transcallosal and extracallosal systems. Adult cats with implanted electrodes received 20 trains (2 sec each) of electrical stimulation to the suprasylvian gyrus daily for several weeks. In four cats, brain stimulation was paired with foreleg shock (trained), in two, it was not (untrained). Cortical tissues ipsilateral and contralateral to the stimulated side were prepared with a modified Golgi-Cox method. In cortex contralateral to the stimulated side, apical dendrites of layers II and III pyramidal cells had significantly more branchings in terminal regions, greater lengths, and terminated nearer the pia than they did on the stimulated side. There were also more spines on oblique, vertical, and terminal portions of apical dendrites. Increases in oblique and vertical spine counts appeared to be more related to training than to just brain stimulation. Qualitatively, apical dendritic terminals in contralateral cortex had fine branchings, filamentous bare twigs, especially long spines, convolutions with close packing of spines, acute angles of terminals reflecting from the pia, and a general appearance of increased density of apical dendrites near the pia. The observed changes in neuronal structure described in these experiments are interpreted as evidence that increased use of specific pathways to the cerebral cortex produces postsynaptic growth in some cortical neurons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22298/1/0000741.pd