On October 17th, the Journal of Neuroscience published an ION finding entitled “Activity-dependent development of callosal projections in the somatosensory cortex”. This work was conducted primarily by graduate students Chun-Lei Wang and Lei Zhang in Dr. Ding’s laboratory, with collaborations from Dr. Xiong and Dr. Duan’s laboratories at ION.

The callosum corpus, the largest commissural system in the brain, is responsible for the communication between two hemispheres. However, the mechanism that regulates their growth to the contralatereal cortex is not well understood. Utilizing in utero electroporation to label layer II/III pyramidal cells in the somatosensory cortex on one hemisphere, Wang and colleagues revealed a region- and layer-specific callosal projection in the contralateral somatosensory cortex, and found that their development is dependent on both electrical activity and synaptic transmission. Prenatal suppression of neuronal excitation was achieved via overexpression of the inward rectifying potassium channel, Kir 2.1. This manipulation resulted in abnormal callosal projections with many axons extending beyond layers II-III to terminate in layer I and also a great reduction of the axons at the border between the primary and secondary somatosensory cortices. Blocking synaptic transmission via misexpression of a tetanus toxin light chain (TeNT-LC) led to a more pronounced reduction in the projections to the border region, and an eventual disappearance of callosal projections over the entire somatosensory cortex.

These results reveal the critical roles of neural activity in wiring the neuronal circuitry between the two brain hemispheres. Furthermore, this study also identifies an in vivo model system in which axonal development can be clearly visualized and molecularly manipulated using in utero electroporation of cerebral cortical neurons.